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  ATTACK

  OF

  FORTIFIED PLACES.

  INCLUDING

  SIEGE-WORKS, MINING, AND
  DEMOLITIONS.

  PREPARED FOR THE USE OF THE

  _CADETS OF THE UNITED STATES
  MILITARY ACADEMY_.

  BY

  JAMES MERCUR,

  _Professor of Civil and Military Engineering at the United States
  Military Academy, West Point, N. Y._

  _FIRST EDITION._
  FIRST THOUSAND.

  NEW YORK
  JOHN WILEY & SONS,
  53 EAST TENTH STREET.
  1894.




  COPYRIGHT, 1894,
  BY
  JAMES MERCUR,
  West Point, N. Y.

  _Right of Translation Reserved._




PREFACE.


In this work an attempt has been made to give in outline the best
modern methods of attack upon a fortified position by assault,
surprise, blockade, or siege; and also the detailed constructions of
those types of trenches, batteries, magazines, etc., etc., which seem
best suited to resist the fire of modern cannon, and to afford cover to
a besieging force.

It is not supposed that these types will be exactly copied in all
cases of actual practice, but that a wise discretion will be used in
modifying or combining them when necessary or desirable.

The constructions given are standard types, which have grown up by
combining the suggestions and the experience of the military engineers
of all civilized nations.

In selecting them I have drawn freely upon the textbooks of the schools
of military engineering at Chatham, Fontainebleau, Vienna, and Berlin,
as well as upon that of the late Professor Mahan, and the manuals of
Duane and Ernst.

The standard work of Gumpertz and Lebrun is frequently referred to
in “Military Mining”; and I am also under obligations to General H.
L. Abbot, Corps of Engineers, for the use of his unpublished notes
on the experimental mines at Willett’s Point, and the result of his
experiments upon the mining effects of shells charged with different
explosives.

  J. M.

  WEST POINT, N. Y.,
  October, 1894.




INTRODUCTION.


Modern wars have been marked by sharp aggressive campaigns and great
battles in the open field, with few close and long-continued sieges.

The subject of siege-works has therefore attracted less popular
attention than was formerly devoted to it.

Fort Wagner, Vicksburg, Petersburg, Strasburg, Belfort, Paris, Plevna,
and Géok Tépé have shown, however, that at their respective dates
regular siege and mining operations were necessary to reduce either
permanent or field fortifications, if well equipped and defended.

The volume of fire delivered by the small arms and machine guns now in
use has made an open assault upon a well-supplied and well-defended
parapet, under ordinary circumstances, a hopeless undertaking, and has
necessitated more deliberate methods of attack.

The increased accuracy and penetration of modern cannon have rendered
obsolete many of the older methods of making regular approaches.

The newer constructions described herein, while giving greater
protection to the attack, are in general slower in their advance than
those previously used. This seems, however, to be an unavoidable evil,
which is mitigated only by taking advantage of every opportunity for
rapid advance offered by the errors of the defence.

It is not to be inferred that light field works and lines will in the
general case require for their attack a system of regular approaches;
but trenches and saps may be necessary for placing a battery or parapet
in a commanding position or one favorable for enfilade, or for giving a
covered approach over an exposed ridge; and their frequent employment
may be expected on future fields.

The destructive effect of grenades and Coehorn shells charged with
high explosives will doubtless in many cases check or stop the advance
of saps and trenches, and necessitate the use of blinded approaches
or mining-galleries in stubbornly contested sieges. The successful
application of mines at Géok Tépé will doubtless lead to their future
employment under similar circumstances. In the close attack upon a
shielded casemate or disappearing turret their use seems a necessity,
and when these defences are founded on rock or massive concrete
foundations, tunnelling operations by drilling and blasting will
be required. When practicable they will be expedited by the use of
power-drills driven by electricity.

It seems hardly necessary to add, that in sapping and mining
operations, as in all other branches of military engineering, all new
and improved inventions and methods which are applicable to the work on
hand will be used, as a matter of course.

The thickness of cover given in the text is based upon the penetrations
of the hostile projectiles.

For ready reference the maximum penetrations obtained in experimental
firing up to this date (1894) are given herewith, viz.:

Service bullets, copper or German-silver jacket, of 6.5 to 8 mm.
calibre, initial velocity from 2000 to 2550 f. s.:

                         At Muzzle.   100 yds.  900 yds.  2000 yds.  2730 yds.
                           Inches.    Inches.    Inches.   Inches.    Inches.
  Pine wood               30 to 50   31 to 35   10 to 14                4.4
  Seasoned oak wood        4 to  8                          1.18
  Untamped clay           60 to 78
  Light sand                  8       At 500 yds   17 inches.

                                     330 yds.  440 yds.   880 yds.   2000 yds.
                                     Inches.   Inches.    Inches.     Inches.
  Sand and earth             36         33       20          14          4
  Steel and iron plate  0.31 to 0.38   0.28     0.24
  Brick masonry            4½
  Ice                       63

Special steel-coated bullets, cal. 0.26 and 0.30:

  Pine wood                55
  Oak wood, seasoned    16 to 24
  Beech wood            23 to 30
  Sand                     14

Special steel-coated bullets, cal. 0.236, vel. 2600 f. s.

  Pine wood              62

French authorities give a muzzle penetration of 12 mm. = 0´´.473 in
iron plates for the Lebel bullet. No published experiments confirm this.

But few experiments seem to have been made to determine the penetration
of the projectile of field and siege guns into earth, and the published
data are very meagre and unsatisfactory.

The German Engineer’s Handbook (Pionier Taschenbuch, 1892) prescribes
the following thicknesses of parapets for cover against small-arm and
cannon fire, viz.:

  ----------------------------+------------+------------+------------+------------
                              |            |Shrapnel and|            |
            Material.         | Small Arm. | Splinters. |Field-guns. |Siege-guns.
  ----------------------------+------------+------------+------------+------------
  Earth, sandy                |    30"     | 20" to 40" |   16½'     |    23'
  Turf and marshy earth       |    60"     |            |            |
  Wood                        | 34" to 40" |            |            |
  Brick masonry               |    15"     |            |            |
  Brick masonry, single shot  |            |            |    3' 4"   |
  Two steel plates each 0.32" |   0.64"    |            |            |
  Packed snow                 |    6'      |            |     26'    |
  Sheaves of grain            |   16½'     |            |            |
  ----------------------------+------------+------------+------------+------------

English authorities report craters of 21 feet length and 8 feet depth
blown out from an earth parapet by a single 200-lb. 8-in. howitzer
shell. They also state that the projectile of the pneumatic dynamite
gun has penetrated 40 feet of earth.

Owing to the rapid development of ordnance the current scientific and
military periodicals are in general the only source from which the
latest results in penetration, etc., can be obtained.




CONTENTS.

ATTACK OF FORTIFIED PLACES.


                                                                  PAGE
  INTRODUCTION.                                                      v

  CHAPTER I.

  THE ATTACK WITHOUT THE USE OF REGULAR APPROACHES.

  ARTICLE

   1. Blockade,                                                      1

   2. Surprise,                                                      2

   3. Defence against Surprise,                                      4

   4. Assault,                                                       4

   5. Dispositions for an Assault,                                   5

   6. Defence against an Assault,                                    7

   7. Bombardment,                                                   8

   8. Defence against a Bombardment,                                10


  CHAPTER II.

  SIEGE OR ATTACK BY REGULAR APPROACHES, PRELIMINARY CONSTRUCTIONS,
  DEFINITIONS, ETC.

   9. Siege, Progress of,                                           12

  10. Tools and Appliances,                                         13


  CHAPTER III.

  TRENCHES, APPROACHES, PARALLELS, SAPS, SPLINTER-PROOFS AND PASSAGE
  OF THE DITCH.

  11. Trenches,                                                     15

  12. Parallels,                                                    15

  13. Approaches,                                                   16

  TRACING AND CONSTRUCTING PARALLELS AND APPROACHES.

  14. Tracing Parallels,                                            17

  15. Tracing Approaches,                                           18

  16. Posting Working Parties,                                      18

  EXECUTION OF PARALLELS AND APPROACHES.

  17. Simple Trench and Flying Sap,                                 20

  18. Construction by Simple Trench,                                20

  19. Construction by Flying Sap,                                   22

  SPLINTER-PROOF COVER.

  20. Splinter-proofs,                                              23

  21. Bomb-proofs,                                                  25

  SAPPING.

  22. Definitions, etc.,                                            27

  23. Full Sap,                                                     28

  24. Organization and Duties of Detachment,                        28

  25. Driving the Sap,                                              28

  26. Breaking out a Sap from a Parallel,                           30

  27. Circular Place of Arms,                                       31

  28. Shallow Sap,                                                  31

  29. Overground Approaches,                                        31

  30. Double Sap,                                                   32

  31. Execution of the Double Sap,                                  32

  32. Changing Direction of the Double Sap,                         33

  33. Breaking out a Double Sap from a Parallel,                    33

  34. Traversed Sap,                                                33

  35. Traverse by Blinded Sap,                                      35

  36. Crowning the Covered Way,                                     35

  37. Trench Cavalier,                                              36

  38. Former Methods of Sapping,                                    36

  39. Passage of the Ditch,                                         37

  40. A Wet Ditch without Current,                                  38

  41. A Wet Ditch with Current,                                     40


  CHAPTER IV.

  BATTERIES, OBSERVATORIES, AND MAGAZINES.

  42. Batteries Defined, etc.,                                      42

  43. General Requirements of Siege-batteries,                      42

  44. Construction of Batteries for Field-guns,                     43

  45. Batteries for Siege-guns and Howitzers, Elevated
          and Sunken,--General Considerations,                      44

  46. Screens,                                                      45

  47. Exposed Sunken Battery,                                       46

  48. Tracing the Battery,                                          47

  49. Constructing the Central Passage and Splinter-proof,          48

  50. Constructing the Battery,                                     49

  51. Alternative Construction,                                     50

  52. Splinter-proofs (additional),                                 50

  53. Sunken Battery in a Parallel,                                 51

  54. Battery behind Crest of a Hill,                               53

  55. Batteries on Sloping Ground,                                  53

  56. Embrasures,                                                   53

  57. Observatories,                                                54

  58. Drainage,                                                     55

  59. Mortar-batteries,                                             55

  60. Magazines,                                                    57

  61. Cover for Magazines,                                          58

  62. Location of Magazines,                                        58

  63. Construction of a Magazine subject to Direct Fire only,       60

  64. Manner of Executing the Work,                                 61

  65. Mined Magazines,                                              61

  66. Elevated Magazines,                                           62

  67. Precautions against Dampness,                                 63


  CHAPTER V.

  SIEGE OPERATIONS.

  68. The Attack--Successive Steps,                                 64

  69. The First Period,                                             65

  70. The Investment,                                               65

  71. Bringing Up and Posting the Besieging Force,                  67

  72. Fortifying the Camps, Parks, etc.,                            68

  73. Distance of the Line of Investment from the Works,            70

  74. Strength and Composition of the Besieging Force,              70

  75. The Point of Attack,                                          73

  76. First Artillery Position,                                     75

  77. Opening Fire,                                                 76

  78. Plan of Attack,                                               78

   79. The First Parallel,                                          78

   80. Opening the Parallel,                                        80

   81. The Second Artillery Position,                               81

   82. Counter-batteries,                                           82

   83. Enfilading-batteries,                                        82

   84. Breaching-batteries,                                         83

   85. Batteries of Rifled Mortars and of Howitzers
       for Vertical Fire,                                           83

   86. Opening and Conduct of Fire from Second Artillery
       Position,                                                    83

   87. Musketry Fire,                                               84

   88. The Advance from the First Parallel,                         84

   89. The Second Parallel,                                         85

   90. The Third Period,                                            86

   91. Capture and Crowning of the Covered Way,                     87

   92. Breaching the Scarps and Counter-scarps,                     88

   93. Capture and Crowning of the Breach,                          89

   94. The Attack by Sap,                                           91

   95. Additional Operations Necessary in the Attack of
       an Intrenched Camp,                                          91

   96. Occupation of a Conquered Place,                             93

   97. Vauban’s Maxims,                                             94

   98. Journal of the Attack,                                       97

CHAPTER VI.

THE DEFENCE.

   99. Preliminary Considerations,                                  98

  100. Garrison,                                                    99

  101. Armament,                                                   100

  102. Ammunition, Provisions and Supplies,                        101

  103. Sanitation and Hygiene,                                     101

  104. Preparations for Defence,                                   101

  105. Defence during the First Period,                            103

  106. Opening of Artillery Fire by the Defence,                   104

  107. Defence during the Bombardment and Assault,                 105

  108. Defence during the Second Period of the Siege,              106

  109. Defence during the Third Period of the Siege,               107

  110. The Capitulation,                                           109

  111. Journal of the Defence,                                     110

CHAPTER VII.

PARKS, DEPOTS, SHELTERS AND HUTS, KITCHENS, OVENS, SINKS, LATRINES,
WATER-SUPPLY, ETC.

ARTICLE PAGE

  112. Parks and Depots,                                           111

  113. Shelters and Huts,                                          113

  114. Kitchens and Ovens,                                         114

  115. Latrines, Sinks, etc.,                                      115

  116. Water-supply,                                               116

_PART II._

MILITARY MINING.

CHAPTER I.

NOMENCLATURE AND THEORY.

ARTICLE PAGE

   1. Definitions,                                                 119

   2. Theory of Explosion,                                         120

   3. Form and Volume of Crater,                                   121

   4. Relation between Volume of Crater and Charge,                122

   4. Miner’s Rule,                                                122

   5. Charge for One Cubic Yard,                                   123

   6. Rule for Common Mines in Ordinary Earth,                     124

   7. Overcharged and Undercharged Mines,                          125

   7. Deduction of Formula for Charge,                             125

   8. Relation between Charges of Common and Over- or
       Undercharged Mines,                                         127

   8. Charge to Produce a Camouflet,                               128

   9. Radius of Rupture,                                           128

  10. Theoretical Value of Radius of Rupture,                      129

  11. Values Adopted by English Authorities,                       131

  12. Theoretical Value Too Small,                                 131

  13. High Explosives,                                             131

  14. Experimental Determinations,                                 131

  15. Choice of Explosives,                                        132

  16. Probable Advantage of High Explosives for
       Overcharged Mines,                                          133

  17. Relative Advantages and Disadvantages of Gunpowder
       and High Explosives,                                        134

CHAPTER II.

PRACTICAL OPERATIONS AND DETAILS.

  18. Tools and Appliances, Description of,                        136

GALLERIES AND SHAFTS.

  19. Dimensions of Galleries and Shafts,                          138

  20, 21. Shaft and Gallery Linings,                               139

  22. Shaft and Gallery Frames,                                    140

  23. Dimensions of Pieces of Frames, etc.,                        141

  24. Relative Advantages of Cases and Frames,                     141

  25-28. Sinking Shaft by Frames and Sheeting,                     141

  29. Precautions Needed,                                          144

  30. Partly-lined Shafts,                                         145

  31. Driving a Gallery with Frames and Sheeting,                  145

  32. Use of False Frame,                                          146

  33. Use of Shield,                                               147

  34. Inclined Galleries,                                          147

  35. Position of Frames,                                          148

  36. Partly-lined Galleries,                                      148

  37-39. Change of Direction of Galleries with Frames
        and Sheeting,                                              148

  38. Change of Slope, of Galleries,                               149

  40, 41. Returns,                                                 150

  42, 43. Maps and Drawings,                                       151

  44, 45. Sinking a Shaft with Cases,                              152

  46-48. Driving a Gallery with Cases,                             153

  49. Change of Direction of Galley Lined with Cases,              154

  50, 51. Change of Slope, 7 Galleries Lined with Cases,           155

  52. Shafts à la Boule,                                           156

  53-55. Blinded Galleries,                                        156

  56. Rate of Advance of Galleries,                                157

VENTILATION OF MINES.

  57. Sources of Deleterious Gases,                                158

  58. Ventilation by Forcing in Air,                               159

  59.      "      by Exhausting Air,159

  60.      "      by Assisting Natural Ventilation,                160

  61.      "      by Use of Masks, etc.,160

MINE-CHAMBERS.

  62. Form, Size, and Location of Chambers,                        160

LOADING AND FIRING MINES.

  63. Preparing the Charge,                                        161

  64. Distribution of Fuses in Charge,                             161

  65. Character and Construction of Fuses,                         163

  66-68. Electric Fuses,                                           163

  69. Placing the Fuses in the Charge,                             164

  70. The Fuzes in Frozen Dynamite,                                165

  71. Placing the Charge,                                          165

  72. Tamping Mines,                                               166

  73. Firing Mines,                                                166

CAMOUFLETS BY BORING.

  74. In Favorable Soil,                                           167

  75. In Stony Soil,                                               168

CHAPTER III.

ORGANIZATION AND TACTICS OF MINES.

  76. Organization of Mines,                                       169

  77. The Attack,                                                  169

  78.     The Lodgment, Galleries, Transverses,
            Listening-galleries, etc.,                             170

  79.     Avoid Exposing a Flank,                                  171

  80.     Use Overcharged Mines,                                   171

  81. The Defence,                                                 171

  82.     Conditions to be Fulfilled,                              171

  83.     System of Galleries Used,                                172

  84.     Use Undercharged Mines,                                  172

  85.     Shaft Mines,                                             172

MINE TACTICS.

  86. Tactics Derived from Results of Experience,                  172

  87. Todleben’s Rules,                                            173

  88. The Attack,                                                  173

  89. The Defence,                                                 174

  90. Advantage Lies with Besieger,                                176

BREACHING BY MINES.

  91. Preparation of Wall Location and Size of Charge,             176

  92. Galleries behind Counter-scarps,                             177

  93. Galleries through Scarp,                                     177

CHAPTER IV.

BLASTING AND DEMOLITIONS.

   94-97. Definitions; Tools and Appliances,                       178

   98. Tamping Blasts,                                             179

   99. Determining the Charge,                                     179

  100. Precautions,                                                180

DEMOLITIONS.

  101. Deliberate Demolitions,                                     180

  102. Hasty Demolitions,                                          181

  103. Houses and Magazines,                                       181

  104. Walls,                                                      181

  105. Stockades,                                                  182

  106. Bridges,                                                    182

  107. Tunnels, Canal-locks, etc.,                                 183

  108. Railroads,                                                  183

  109. Rolling-stock,                                              184

  110. Excess of Explosive to be Used,                             184




ATTACK OF FORTIFIED PLACES.




CHAPTER I.

THE ATTACK WITHOUT THE USE OF REGULAR APPROACHES.


=1.= A fortified position may be taken by _blockade_, _surprise_,
_assault_, _bombardment_, or _siege_.

A =blockade= consists in so surrounding a place and closing its
communications as to keep the garrison from receiving reinforcements,
provisions, and supplies sufficient to enable it to continue the
defence and to avoid starvation.

The object of the attacking force is, in general, to completely close
all communications between the garrison and the exterior; but this
is not always possible, nor is it necessary in all cases, since such
obstruction of communications as will reduce the incoming supplies
below the necessary expenditures of the garrison will ultimately
exhaust its stores.

An efficient blockade, continued long enough, will consequently reduce
any place.

Whether it is advisable to attempt to reduce a place by blockade will
depend upon the time which will probably be taken in its reduction,
the force required for surrounding it, and repelling sorties from
the interior or beating back a relieving army, and the expense in men
and materials of taking the work by other methods. Blockades are more
effective in reducing cities and towns than in taking places occupied
only by a military garrison, since the presence of a large number of
non-combatants in a place rapidly exhausts its store of provisions,
renders epidemics more likely to break out, and by the suffering and
misery resulting demoralizes the garrison, unnerves the commander, and
eventually causes its fall. This justifies the apparent harshness of
not allowing non-combatants to leave a beleaguered place.

The steps necessary for establishing the blockade are identical with
those taken for the investment in a regular siege and will be described
hereafter.

The capture of Paris in 1870-71 is one of the most recent and striking
examples of a blockade on a large scale.


SURPRISE.

=2.= A sudden and unexpected attack made upon a garrison
unprepared to receive it is called a =surprise=.

Formerly these were of not infrequent occurrence, but with modern means
of communication and methods of warfare they can hardly be looked for,
except in small affairs, where, through the weakness or exhaustion of a
garrison or the incapacity of its commander, the necessary and ordinary
precautions for their prevention are impracticable or are neglected;
or where they are brought about through treachery in the garrison, by
which the gates are opened to the attack.

Probably in the majority of cases attempts at surprise will be detected
and defeated; but as a success is usually valuable far in excess of the
losses suffered in its execution, promising opportunities for their
trial should not be neglected.

Surprises, when thought possible, are undertaken under the cover of
night, fog, or severe storms. The tactical disposition of the troops
is similar to that used in open assault, the columns being preceded by
ladder-parties for scaling walls, engineers for blowing down barriers,
etc., etc., according to the nature of the case, and followed by a
large reserve which is designed to hold any points captured by the
advancing columns. It is usually considered best to make simultaneous
attacks at several points, in order to confuse and divide the defence,
holding the main reserve nearest to the column which is expected to
succeed; but making provision also for promptly and fully supporting
any other party which may have forced an entrance into the work.
An entrance secured, consecutive points should be occupied and
held, preserving communication between them, and avoiding too great
dispersion of the troops, until a foothold is gained which can in all
probability be held against the defence. After this greater boldness
may be used in attacking important points within the place.

The complete capture of the work and its garrison cannot ordinarily be
expected, however, until daylight allows the systematic movement of the
attack throughout the place. In case of failure, any captured gate must
be held if possible until all the troops have retreated through it and
are covered by the reserves.


DEFENCE AGAINST SURPRISE.

=3.= The measures necessary to guard a fortified place against
surprise are of two classes. First, for its prevention, by use of all
the usual outposts and interior guards,--the organization and duties of
which need not be repeated here,--and of telegraphic and other signals
and communications with the surrounding country by which the approach
and movements of any attacking force may be made known before it comes
near the work.

Second, for its repulse, by so training and disciplining the garrison
that, upon the alarm being given, the parapets, batteries, etc.,
will be manned and all defensive measures will be taken before the
assaulting body can enter the work.

This will be accomplished by so thoroughly drilling the garrison in
its duties that each man will go at once to his proper station fully
equipped for his duties at any hour day or night, without confusion or
unnecessary excitement. The subsequent measures are the same as for
resisting any other assault.


ASSAULT.

=4.= By an =assault= is meant an open attack upon a position
by troops in line or column.

Formerly it was recommended to make assaults at early dawn, in order
to have the increasing daylight for securing the results of victory;
more recently night attacks have been more strongly advocated in order
to diminish the losses from the fire of the defence while making the
attack, and the still greater ones which follow a repulse when, the
fire of the supports and reserves of the attack being suspended for
fear of injuring the retreating troops, the defence pours upon the
latter the full close and deadly fire of all its arms. Whether the
advantages of a night attack more than counterbalance the dangers
resulting from the confusion due to darkness is, however, a question
not yet settled.

Open assaults upon fortified positions, well manned and armed, have,
since the introduction of firearms, been considered the most bloody,
uncertain, and frequently the most unjustifiable operations in war.
With the introduction of machine and rapid-fire guns and magazine
rifles it may be considered as an established fact that a well-defended
line cannot be carried by an assault in front until its fire is
overpowered or its ammunition exhausted.

This conclusion, which has been drawn from attacks on field-works, is
still more positive in regard to attack upon works of strong profile
protected by deep ditches and other obstacles.


DISPOSITIONS FOR AN ASSAULT.

=5.= When an assault is ordered the tactical dispositions must be
so made as to keep the fire of the defence down to its lowest possible
limit, until the assailant can close in with the bayonet.

With this end in view, batteries are established sweeping the lines;
the assaulting columns, well supplied with ammunition, are formed where
protected from fire; working parties are arranged and provided with
such tools and appliances as are necessary for removing or overcoming
obstacles; and all preparations are made for simultaneous action by
the entire force.

It is manifest that to silence the fire of the work the attack must
have a marked preponderance of artillery arranged both for enfilade
and front fire upon the front of attack and the collateral works; and
that the batteries must be established, the fire opened, and the guns
of the defence silenced before the assault is made; and that this fire
must continue until the assaulting troops are so near the work as to
necessitate its discontinuance to avoid injury to them.

The working parties--carrying axes, saws, crowbars, and similar tools
which are needed for removing the existing obstacles; explosives for
blowing down gates, barriers, etc.; fascines, gabions, hurdles, etc.,
for crossing ditches, covering trous de loup, and other purposes; and,
when necessary, ladders for escalade--move forward with the columns of
attack; the latter must be so handled that, when the artillery fire is
suspended, they can keep down the fire of the defence with rifle and
light machine-gun fire.

Under cover of this fire the obstacles must be removed by the working
parties, and the first assault made by the troops detailed for this
purpose. With these troops should be a certain number of artillerists
provided with lanyards, friction primers, etc., to serve any guns that
may be captured, turning them against the defence.

A party of engineers provided with high explosives for blowing down
gates, etc., should follow closely behind the advance in case of an
escalade; they should also be provided with appliances for blowing up
magazines, etc., when possible, in case of a repulse. The gates being
captured and opened, the mass of the assaulting troops enter by them
and complete the capture of the place.

In case of repulse the retreat of the advanced parties is covered, when
possible, by the infantry fire of the reserves, and that of the latter
by the artillery, as in the advance.


DEFENCE AGAINST AN ASSAULT.

=6.= Permanent works being designed to be secure against
assaults and surprise, their guns of position are protected as well
as circumstances admit against the hostile artillery and infantry
fire. During the cannonade preliminary to an assault a wise discretion
must be used as to how much ammunition may be profitably expended in
replying to it, and how great an exposure of the men to the artillery
fire is justifiable. As a rule but little reply is made from the work.

The machine and rapid-fire guns should be withdrawn from the parapets
and be protected under bomb-proofs until the relaxation of the hostile
fire due to the near approach of the assault allows them to be run out
and to open fire. The infantry of the garrison is similarly handled,
being held under cover until the proper moment, then manning the
parapet and pouring a close, rapid, and deadly fire upon the assault.

The fire of the fronts directly attacked, both machine-gun and
infantry, will be directed principally at the assaulting columns and
working parties, the collateral works and fronts will, in addition to
pouring a cross-fire upon the assaulting columns, direct a large part
of their machine-gun fire upon the supports and reserves, while the
more powerful guns will generally direct their fire upon the hostile
artillery.

The troops not needed for manning the parapets are held under cover in
a central position as a reserve, to strengthen the force at any part of
the parapet or to meet and drive out any body of the enemy penetrating
the work.

Should the attack be repulsed, the most rapid and destructive fire
from all arms is directed upon the retreating troops with a view to
inflicting the greatest possible losses; but a counter-attack is,
as a rule, not attempted. When made, however, it should be limited
to making an advance upon one or both flanks to a position giving a
more effective fire upon the retreating troops, and retiring from
this position to the cover of the work as soon as the main attack is
completely repulsed and before the advanced troops become compromised
by a close engagement with the enemy.


BOMBARDMENT.

=7.= By a =bombardment=, technically speaking, is meant
a more or less continuous shell-fire upon a place with a view to
destroying magazines, buildings, materials, and supplies of all
kinds, in addition to inflicting the greatest possible losses upon
the garrison and producing among the inhabitants a state of terror
and unrest, frequently extending to mutiny, and finally causing the
surrender of the place.

The term bombardment is also frequently applied to a cannonade opened
upon a place to silence its artillery prior to an assault or during a
siege.

A bombardment promises success when the place is small and not
well provided with bomb-proofs, when the garrison is weak or of
bad morale, when the inhabitants are numerous and not in sympathy
with the garrison, or when the commandant is weak. A well-built and
well-equipped modern fort can hardly be reduced by bombardment with any
reasonable expenditure of time and ammunition; although the successful
use of torpedo-shells charged with high explosives will probably render
untenable works not designed to resist their effects.

When it is designed to reduce a place by bombardment a complete
investment is, as a rule, necessary only to prevent the withdrawal of
the non-combatants (a severe measure, but one frequently adopted), or
to insure the capture of the garrison upon the fall of the place.

The disposition of the troops is made for the special object in view.
The infantry, cavalry, and field artillery complete the investment,
if made; or, when the place is not invested, are concentrated at such
points as may be necessary to protect the artillery from any sorties
from the place, and to meet and repel attacks from any relieving force.

The artillery of larger calibre used for the bombardment proper should
consist principally of rifled howitzers and mortars, which are easier
to transport and more suitable for high-angle fire. As it is not
intended to dismount or silence the guns of the place by direct or
enfilade fire, an artillery duel should be avoided.

The batteries should be located, so far as possible, in places screened
from the artillery of the defence by undulations of the ground, etc.;
or, if this is impossible, by artificial screens as a cover from sight,
and by trenches as a protection from fire.

Considerable latitude is allowed in selecting sites for batteries. For
convenience of supply and unity of command they should be collected in
groups, the batteries of the groups separated by at least 100 to 200
yards; and the groups should be located, so far as other considerations
allow, near the main lines of communication.

If these groups do not entirely surround the place, they should, when
practicable, extend at least half way around, so as to bring a reverse
fire on all covers.

The fire, once opened, should continue night and day. If a
conflagration breaks out, a sharp fire of shells should be directed
upon it and its vicinity to prevent its extinction. Special efforts
should be made to blow up magazines and destroy shops, storehouses,
docks, roads, bridges, or other communications useful to the
defence; but, so far as is practicable consistently with these, an
attempt should be made to avoid injury to public monuments, museums,
antiquities, and works of art.

Bombardments are sometimes commenced and continued for a longer or
shorter time without the expectation of reducing the place, but to
destroy some of the constructions above mentioned or to prevent the
completion or arming of a work which it is intended to attack by other
methods. A slow bombardment may also precede the active cannonade
which prepares for an assault, or the systematic artillery attack of a
regular siege.


DEFENCE AGAINST BOMBARDMENT.

=8.= The defence against bombardment is frequently, from
necessity, strictly passive, and consists in so disposing the troops
and materials as to protect them under bomb- and splinter-proofs,
repairing damages to the latter and to magazines and parapets as
occasion offers; saving the ammunition of the place by firing only such
shots as promise to pay for themselves by the effect produced; and
reserving all the strength of the place to meet the subsequent attack,
if made.

When circumstances admit, a more active defence may be made, by a
strong garrison, by well-conducted sorties which may capture and
destroy the hostile guns and batteries and defeat and drive off their
supports.

Sorties of this kind may sometimes be profitably made against the
flanks of the attacking force, or against isolated batteries, even when
a general attack cannot be made. Opportunities for their use should not
be neglected.




CHAPTER II.

SIEGE OR ATTACK BY REGULAR APPROACHES.


PRELIMINARY CONSIDERATIONS, DEFINITIONS, ETC.

=9.= By a regular siege is meant a systematic and more or less
deliberate attack upon a fortified place, in which the besieger aims
to invest the place and capture its fortifications in succession by
regular approaches, beginning with the most advanced and ending only
with the reduction of the innermost keep and the surrender of the
garrison.

The successive steps of a siege are usually the following:

The investment.

The artillery attack.

The construction of parallels and approaches.

Breaching by artillery or mines.

The final assault.

The introduction of modern breech-loading rifled guns, howitzers and
mortars, rapid-fire and machine guns, and magazine small arms has
brought with it the need of a higher grade of mechanical skill and
improved machinery for making the ordinary repairs. This imposes upon
both attack and defence the necessity for providing machine shops and
tools fitted for work of this kind, with the steam power required
to drive them. In connection with these, steam sawmills and other
simple wood-working machines should be provided, as well as all other
available labor-saving appliances which can be used to lighten the
labor of the troops.

Portable tools, such as picks, shovels, crowbars, rammers, axes,
hatchets, bill-hooks, gabion-knives, hammers, saws, carpenters',
joiners' and blacksmiths' tools, etc., etc., must be provided.

=10.= The principal =special tools and appliances= used are
the following, viz.: sap-forks, sand-bag forks, scrapers, sap-shields,
measuring-rods of various lengths, pocket compasses with attachments
for fastening them to measuring-rods, tracing-lanterns, dark and
ordinary lanterns, tracing tape or cord, tracing pickets or stakes,
fascines, gabions, hurdles, sand-bags, blindage and gallery frames and
sheeting, etc., etc.

The _sap-fork_ and _sand-bag fork_ (Pl. I, Figs. 1 and 2), about 4½ and
4 feet long, respectively, have steel heads with three and four prongs,
as shown in the figures, those of the sap-fork being sharp and those of
the sand-bag fork blunt.

They are used for handling and placing gabions, fascines, and sand-bags
in position when, without their use, the sappers' arms would be exposed
to fire.

The _scraper_ (Pl. I, Fig. 3) is a large hoe, of about the dimensions
given in the figure, used for levelling off the surface of parapets,
etc.

The _sap-shield_, introduced by the English (Pl. I, Figs. 4 and 6), is
a flat plate of mild steel 3 feet 6 inches by 1 foot 9 inches × ¼ inch,
with two handles on its back as shown. Total weight, about 80 lbs.

It may be used as shown in the figure, and sometimes by small parties
as a body-shield in such operations as blowing in gates, etc., etc.

_Measuring-rods_ of rectangular cross-section, straight and divided
into feet and inches, are needed for special purposes; but the ordinary
rods are cut from round brush wood and to the length required.

_Tracing-tape_ is usually a white tape, about 1½ inches wide, in
lengths of 150 feet, marked at equal intervals, usually 5 feet, by
short pieces of tape sewed to it. A loop of strong cord is fastened to
each end. For convenience in use it is ordinarily rolled into a ball.

_Tracing-pickets_ are about 18 inches long and one inch in diameter.
To make them visible in a dim light the bark is removed from them.
_Ordinary pickets_ are usually 3½ or 4 feet long, 1½ to 1¾ inches in
diameter, sharpened to a triangular point.

The _tracing-lantern_ (Pl. I, Fig. 5) is a dark lantern with a
reflector arranged to throw a light vertically downward.

The other tools, materials, and appliances above mentioned, not of the
ordinary commercial patterns, are described in Field Fortifications and
Military Mining, _q.v._




CHAPTER III.

TRENCHES, APPROACHES, PARALLELS, SAPS, SPLINTER PROOFS, AND PASSAGE OF
THE DITCH.


=11.= =Trenches.=--A _military trench_ consists of a ditch
and embankment affording cover from direct fire. Trenches are used for
_approaches_ (or _boyaux_), _parallels_, and _communications_ with
magazines, etc.

=12.= =Parallels= are trenches which take their name from
the fact that they usually are located on lines approximately parallel
to the general front of attack. In a regular siege at least three and
frequently a greater number of parallels are used. The exterior one,
which is first made, is known as the _first parallel_, the next one
as the _second parallel_, and so on. They are used to cover the part
of the besieging force known as “_the guard of the trenches_,” which
protects the men making the approaches, etc., and also as “places of
arms” for assembling troops for assault or for other purposes.

The trench of a parallel is usually 10 feet wide at the bottom and 4
feet deep, finished on the reverse with a slope and on the front with
two steps and a berm, with treads of 18 inches and rises of 15-18
inches (Pl. I, Figs. 7 to 13).

The parapet of the parallel should not be higher than 4 feet 6 inches.
Its upper surface, particularly in the second and third parallels,
should be made approximately plain with a scraper, and its interior
slope should be finished and if necessary revetted, so as to afford
a good infantry-fire. To allow the troops to move out to the front in
line, portions of the interior slope should be cut into steps of not
more than about 18 inches rise, and be revetted with fascines or other
materials (Pl. I, Figs. 12 and 13). These portions should be 25 or more
yards long and near the approaches. If a general assault is to be made,
the parallels must be similarly arranged for the necessary length of
front.

=13.= =Approaches= are trenches leading up toward the
fortification on the front of attack; they connect the parallels and
give protection to the besiegers in moving back and forth. To avoid
enfilading fire they usually run in zigzags (Pl. VIII, Figs. 80 and
81) across the capitals of the work, with branches seldom exceeding
100 yards in length at the first parallel, and growing continually
shorter as they approach the work. Each branch is so directed that
its prolongation will pass from 30 to 40 yards outside the most
advanced position within effective range held by the defence. At each
turning-point of the zigzag the more advanced branch is prolonged from
10 to 20 or more yards to the rear, to cover the angle of the approach.
These returns are also useful for storing trench material, etc.

After the return is completed the sharp angle in the trench is rounded
off to allow gun-carriages, etc., to make the turn.

Approaches are usually 4 feet deep, 9 to 12 feet wide at bottom, with
slopes in front and rear as steep as the earth will stand, and have a
rough parapet not less than 4½ feet high, separated from the trench
by a berm of 18 inches, or more if necessary (Pl. VIII, Fig. 82).
When drainage requires it, as it very frequently does, the bottom of
the trench is sloped from front to rear about 6 inches; a ditch cut
along the reverse slope, discharging into the drainage ditches of the
vicinity, or into drainage pits excavated in rear of and outside the
approaches. These may be lined with a gabion to prevent their sides
falling in.


TRACING AND CONSTRUCTING PARALLELS AND APPROACHES.

=14.= =Tracing Parallels.=--Parallels are located by engineer
officers after careful reconnoissance of the ground. Guiding points and
lines are marked so as to be readily found in the dusk, but so that
they cannot be seen by the defence. When completely screened from view
important points are marked by posting sappers at them.

When no other practicable method can be used, the directions are
determined by the use of a pocket compass fastened to a straight
measuring-rod.

Tracing is begun as soon as the approaching darkness will conceal
the parties from the defence, while close objects are still visible.
The length of parallel traced by each officer should not exceed that
occupied by one unit, usually a battalion, as a working party. (A
battalion of 500 men will occupy 800 yards).

The tracing party consists of one officer, one N. C. officer, and one
sapper to each 50 yards of parallel, with one or two extra men.

The officer is provided with a pocket compass and measuring-rod. The
N. C. officer has a tracing-lantern and a mallet with muffled head.
Each sapper carries a roll of tracing-tape, a tracing-picket, and a
six-foot measuring-rod. The officer stations the first sapper at the
initial point, and, taking one end of his tracing-tape, moves along the
line of the parallel, accompanied by the rest of the sappers; the first
sapper places his picket between his feet, and the N. C. officer drives
it into the ground far enough to make it secure. The sapper drops the
ball of tape on the ground and lets it run out through his hands until
nearly out, when he checks it, and when it is all out places the loop
over his picket and lies down to await the arrival of the working
party. The N. C. officer, as soon as he has driven the first picket,
follows on to the second, etc.

The officer, having run out the tape of the first sapper, halts the
second, takes the end of his tape, and proceeds as before until the
parallel is traced, and a sapper is left at each 50 yards of its
length. Each sapper is told the designation, by number and section, of
the point he occupies.

=15.= =Tracing Approaches.=--The approaches are traced in the
same manner as the parallels, but at each turning point of the zigzags
a picket is driven, around which the tape is carried. After tracing the
branch in front, the tape is cut at five yards in rear of the picket,
and the end carried out to the rear in prolongation of the branch in
front to indicate “the return,” which is then prolonged to the proper
length (from 10 to 20 yards) by a short piece of tracing-tape.


POSTING THE WORKING PARTIES.

=16.= The working parties are commanded by their own officers,
under the guidance of the engineers. They carry their arms and
ammunition. Each battalion (or other unit) is marched in column to the
depots, where the tools are laid out in lines, so that each man can
take up his pick and shovel when drawn up in front of them. But when
time does not allow of this arrangement, they are piled, the picks in
one pile, the shovels in another, and the men pass the piles in single
file to the right of the picks and the left of the shovels, each man
receiving a pick and shovel as he passes the pile. If gabions are to be
carried, they are distributed in a similar way. When two are carried,
the shovel is secured inside one and the pick inside the other, and the
gabions are then carried by the picket inserted for that purpose. When
one only is carried, the pick is usually secured inside it, the gabion
carried on the shoulder, and the shovel in the hand.

The working party, in column, provided with its tools, etc., is then
led by the engineer officer to the parallel, and forms on right (or
left) into line along it in single rank at five-foot intervals,
beginning at the initial point of each section.

The N. C. officer of engineers assists in this formation, and each
sapper points out to the men of the working party the five-foot
intervals marked upon the tracing-tape of his 50 yards, verifies their
positions along it, and subsequently superintends their work. Each man
when properly placed drives his pick into the ground at the left of
his task, places his shovel beside it, and lies down until the command
“Commence work” is given.

When gabions are used the working party is posted in a manner entirely
similar, except that the column is of necessity formed in single rank
when marching to the initial point. The men form on right (or left)
into line and place their gabions in front of the tape and touching
each other; each man then takes out his tools, places them behind the
gabions, lies down, and awaits the command to commence work. The sapper
sees that the gabions of his 50 yards are properly aligned and touch
each other throughout.

Both the sappers and working parties are divided into reliefs, usually
of eight hours. The sappers of the tracing parties superintend the
work of the first relief of the working party, but are relieved long
enough before them (½ hour to 1 hour) for the second relief to become
acquainted with the details of its sections before the second relief of
the working party arrives. A similar arrangement is made for the third
relief.


EXECUTION OF PARALLELS AND APPROACHES.

=17.= =Simple Trench.=--A trench made by excavating the earth
and forming a parapet without revetment of any kind is known as a
“_simple trench_,” or as “_simple trench-work_.”

_Flying sap_ or _flying trench-work_.--When, in order to obtain cover
more quickly, gabions are used to hold the earth first excavated,
and subsequently to serve as a revetment to the interior slope of
the parapet, the trench is known as a “_flying sap_” or “_flying
trench-work_.”

=18.= =Construction by Simple Trench.=--The first parallel
and the distant approaches are usually constructed by the use of the
simple trench, as follows, viz. (Pl. I, Figs. 9 and 10): The men
having been posted along the tracing-tape at five-foot intervals, as
previously described, and their positions verified by the engineer
officers, the command “Commence work” is given. Each man marks the left
and front of his task by a line dug with his pick, and, commencing at
the left of his task, at once excavates a trench 3 feet long, 1½ feet
deep, and 6½ feet wide, throwing the earth to the front, and making a
parapet 1½ feet high, leaving a berm of 1½ feet. Then, commencing at
1½ feet from the front of his trench, he deepens it to 4 feet, making
the parapet 3 feet high. When the task of a party is finished each man
cleans off his pick and shovel, places them at the rear of the trench,
and leaves them there for the use of the second relief.

By excavating in this way, partial cover while at work and a defensible
parapet are rapidly obtained, and, at the completion of the task, the
parapet admits of a strong defence, and affords cover sufficient to
allow the first relief to be withdrawn and the second to be posted
without exposure. Special care must be taken during the work to make
the men face toward the parapet while digging, in order to avoid
striking their neighbors with the pick when raising it for a blow.

The second relief widens the trench 4 feet; forms a bottom step 18
inches wide with such materials as are available; heightens the parapet
to 4½ feet, and throws the rest of the earth to the front to thicken it
(Pl. I, Fig. 8).

The third relief widens the trench 2½ feet at the bottom and slopes
off the reverse as steep as the earth will stand. The earth is used to
thicken the parapet, additional shovels and shovellers being provided
if found necessary.

The approaches (Pl. VIII, Fig. 82) are extended in a similar manner;
the tasks of the reliefs are marked on the sections.

Variations from these sections are made when rendered necessary by the
presence of rock or water in the soil (Pl. I, Fig. 11); when a wider
trench is required for a tramway or for free communication; or, in
special cases, when a narrower trench will answer the purpose and save
work. Should a specially heavy fire make additional cover necessary,
it may be obtained by deepening the ditch and thickening the parapet,
leaving its crest at the same height. The sections above given have
been found best for ordinary cases.

=19.= =Construction by Flying Sap.=--The construction of the
first parallel having indicated to the defence the front of attack,
further operations will usually be subject to a more destructive
small-arm and machine-gun fire. This will, as the siege advances,
render the losses experienced in constructing a simple trench too
extravagant, and a quicker method of obtaining cover must be used. This
method is found in the flying sap (Pl. I, Figs. 8 and 13), which is
executed as follows, viz.:

The men are posted and the gabions placed as previously described. The
engineer officer having marked the lines, the order “Commence work”
is given. Each man marks with his pick the front and left of his task
(which in this case is 4 × 6½ feet, leaving a berm of 1½ feet), and
proceeds at once to dig on its left, filling first the left gabion,
next the right, and then throwing the earth over and in front of the
gabions. Each gabion, when it is half filled, is tipped outward until
it has a slope of about 4 on 1. The filling is then completed.

As each man of the first relief occupies only 4 feet of front (2
gabions), his task is four-fifths as great as it is in executing the
simple trench.

The second and third reliefs have the same tasks as in the simple
trench. When the first relief finishes its task, every fifth workman
(indicated by the sapper of the section) retains his pick and shovel
and returns them to the depot when he marches past it.

The others leave their tools for the use of the second and third
reliefs. In good soil the gabions may be filled in from 7 to 15 minutes.

The English sap-shield is designed for use when the fire is so severe
that the flying sap with gabions becomes impracticable. Owing to its
weight (80 lbs.) a man can carry but one; hence a carrying party equal
to the working party assists in placing the shields and then retires.
This gives to each workman a task of 3½ × 6½ feet.

The shields are placed as shown in Pl. I, Fig. 6; the trench is
executed as previously described, the earth being thrown over and
beyond the shield. The shields are removed after the task of the first
relief is finished.

The sap-shield is designed to be used in special cases for covering the
head of a full sap (described further on), in which case it is placed
as shown on Pl. I, Fig. 4; and also as a body cover for a man moving
for a short distance in the face of a heavy fire, as is necessary at
times in sapping and mining operations. It has not yet stood the test
of service in a siege.


SPLINTER-PROOF COVER.

=20.= =Splinter-proofs= for the guards of the trenches,
for field-hospitals, latrines, etc., should be provided as soon as
possible after the parallels are finished. They may be placed in
the returns of the approaches, or in rear of the parallels, and be
connected with them by trenches. Pl. II, Figs. 14-16, show their
construction when in rear of the parallel and revetted with logs,
fascines, or sawn lumber. The trench is 9 feet wide by 4½ feet deep.
Its front edge should be 25 or 30 feet in rear of the reverse slope of
the parallel. This width of trench will allow 2 to 4 men per yard of
its length to work advantageously. They should finish it in 8 hours.

In digging the trench the earth is thrown out on both sides, leaving a
berm of about 1½ feet on each side to allow the woodwork to be properly
placed. When this is completed the earth in rear is thrown forward to
complete the cover, as shown in the plate.

Steps for egress and openings for light and ventilation may be placed
at intervals along the rear, and, when desirable, bunks may be built,
as shown in the figures.

When the splinter-proofs are built in the returns of the approaches,
the overhead cover may extend entirely across, steps and openings being
provided as in the previous case; or posts and longitudinal beams
may be set in the trench to hold up the rear end of the cross-beams,
leaving the rear of the splinter-proof open. Portions of this may be
closed, if desired, by leaning short posts or fascines against the
longitudinal beam and banking earth against them.

The splinter-proofs may generally be drained into the parallels or
approaches. When this cannot be done drainage-pits must be used.
Limited portions of the splinter-proofs may be protected against
leakage through the earth cover by first filling over the covering
beams with earth, packing it to a smooth surface with a gentle slope,
placing upon it raw hides, roofing felt or other waterproof material,
and then completing the cover by adding the necessary thickness of
earth, giving finally to its top surface a slope to carry off the rain.


BOMB-PROOFS.

=21.= When, in the close attack of the work, the besiegers are
subject to vertical fire from small mortars, better overhead cover must
be obtained by bomb-proofs, constructed by deepening the trench, using
stronger beams, and a greater thickness of earth. Twelve-inch timbers
laid touching each other, with spans of 5 feet and 5 feet of earth
cover, have been considered sufficient; but with the improvement of
high-angle fire and the use of high-explosive shells greater protection
will be needed in the future. Experimental data for fixing the amount
is not now available; an approximate thickness of earth cover may be
computed as indicated below.

The mining effect of dynamite in common earth is something less than
twice that of an equal weight of gunpowder. (See Military Mining, Arts.
13 and 14.)

An explosive enclosed in a strong case, however, expends a part of
the energy due to explosion in rupturing this case. The stronger the
explosive the less will be the percentage of the total energy required
for breaking the case, and the greater the percentage remaining for
performing other work. For this reason equal weights of high explosives
and of gunpowder enclosed in strong shells will not produce the same
relative effects in forming craters, &c., that they would if contained
in paper cases. The effect of the high explosive is relatively much
greater when contained in a strong shell. Experiments made at Fort
Hamilton, 1890-91, with 8-inch shells loaded with explosive gelatine,
showed this explosive to have between 4 and 5 times the effect of
gunpowder, while in paper cases the relative effects were as 1.7 to
1.0. (See Report of Board of Ordnance and Fortification, Ex. Doc. No.
12, 52d Congress, 1st Session, January 5th, 1892.)

Since the mining effects of the charges contained in shells are,
however, less than when packed in thin cases, the thickness of cover
determined by the use of the usual mining formulas should err on the
side of safety.

Knowing the charge contained in shells to be fired against a
bomb-proof, and their probable penetration, the formulas given in Arts.
7 to 12, Military Mining, may be used for finding equivalent common
mines and radii of rupture for dynamite and explosive gelatine by
substituting in them 1/17 for 1/10.

The values given in Art. 11 will probably be sufficiently accurate for
the radii of rupture. The cover given in the direction of the fire must
be greater than the sum of the penetration and the radius of rupture.

When the penetration is equal to or greater than twice the L. L. R. of
an equivalent common mine a camouflet will probably be formed, whose
radius of rupture, from the formulas, will be equal in all directions
and may be assumed as ⅕ of the L. L. R. of the equivalent common mine.

In this connection, see par. 61, p. 58.


SAPPING.

=22.= When the trenches have been carried so near the work that
the simple or flying trench cannot be used without undue loss, recourse
must be had to the _sap_.

A =sap= is a narrow trench (subsequently widened), which is
continually prolonged in the desired direction by digging away the
earth at its head and throwing it to the front and exposed flank as a
cover for the working party.

When the sap is subject to an oblique front-fire, exposing one flank
only, the parapet is constructed on that flank and at the head. This is
known as a _single_ or _full sap_. When both flanks and the head of the
sap are exposed to fire two full saps are driven parallel and very near
to each other, each with its parapet on the outer flank. The tongue of
earth left between them is removed to widen the narrow trenches, thus
making a single trench with a parapet on each side. This is called a
“_double sap_.”

The trench is sometimes deepened and given a splinter-proof roof or
cover. This is known as a “_blinded sap_.” A sap gaining ground to the
right and front is called a “_right-handed sap_;” its parapet is on its
left flank. A “_left-handed sap_” has its parapet on its right flank.

To expedite the work in sapping several reliefs should be employed, and
task-work should be adopted to induce the men to work rapidly.

In all sapping operations the use of the simple trench and flying sap
will be resumed when circumstances admit without involving too great
losses.

=23. The full sap= (Pl. II, Figs. 17-21) requires a detachment,
or “=brigade=,” of 1 non-commissioned officer and 8 men, provided
with the following tools, viz.:

  For No. 1, a miner’s pick, a miner’s shovel, a measuring-rod,
  4' 6", marked at 3', and a
  sand-bag fork.

  No. 2, a measuring-rod of 1' 6" and a shovel.

  No. 3, a pick, a shovel, and a measuring-rod 5'
  long, marked at 4' 6".

  No. 4, a shovel and a scraper with a handle 9'
  long.

For the rest of the detachment, a 6' measuring-rod, knee-caps for 4
men, 2 shovels and 1 pick (in reserve), and, when necessary, a crowbar,
axe, and bill-hook. From 100 to 150 sand-bags are supplied to each
detachment.

=24. Organization and Duties of the Detachment.=--The sappers are
numbered 1, 2, 3, and 4 in each rank; the front rank extends the sap
1 yard and is then relieved by the rear rank, and so alternately. The
sappers change places at each relief; those who serve as Nos. 1 and 2
during their first task becoming Nos. 3 and 4 during the second, and so
on throughout their tour.

If a detachment is reduced below 8 in number by casualties it
nevertheless keeps 4 men at work driving the sap, and reduces its
reserve until new men are supplied.

=25. Driving the Sap.=--The sap is driven as follows, viz.: Nos.
1 and 2 dig a ditch 4' 6" deep, 1' 6" wide at bottom, and 3' or more
at top; the berm side has a slope of 3/1, and the reverse is vertical,
or as nearly so as the earth will stand. They leave no berm, as they
need all the cover they can get. Nos. 3 and 4 widen this trench 2 feet
and form a berm of 1' 6" by digging away the foot of the parapet and
throwing the earth upon its top and exterior slope. The head of their
work is kept at 9' in rear of the head of the sap.

The side parapet made by Nos. 1 and 2 is about 2' 6" high and
bullet-proof (about 2' 6" to 3' thick) at 18 inches above the ground.
The head parapet is made up of about 60 sand-bags, from ½ to 2⅔ filled.
It joins the side parapet and extends across the head of the sap. It is
about 2' 6" high.

As the sap is driven forward the head parapet is advanced by throwing
the rear sand-bags over to the front by hand or by the use of the
sand-bag fork. In excavating the trench No. 1 kneels down, undermines,
and digs down enough earth to advance his trench about 9 inches. He
is replaced by No. 2, who shovels this earth upon the side parapet
toward the head of the sap. No. 1 then resumes his place and throws
the sand-bags at the head of the trench over the parapet until he
has uncovered about a foot in advance. He uses a sand-bag fork when
necessary. The trench is advanced 9 inches more in the same manner. No.
2, besides throwing out the earth dug by No. 1, trims up the slopes and
gives the trench its proper width and depth.

Nos. 1 and 2 change places when they have advanced the head of the sap
1' 6", and are relieved as before stated when 3 feet is gained.

Nos. 3 and 4 work together upon their task. In shovelling the earth
upon the parapet they throw it somewhat toward the front and regulate
its height with the scraper. The rate of advance is usually from 2 to 4
feet per hour.

_Widening the Sap._--The sap is widened by working parties, usually of
infantry, who work at about, but not less than, 25 feet in rear of the
head of the sap. In an approach their task is equal in volume to that
of the sappers, and can be finished in one relief. In a parallel when
steps are to be provided, a second relief makes the steps, drainage
ditches, drainage pits, etc.

_A change of direction_ in a full sap (Pl. II, Fig. 20) is made by
No. 1 turning in the new direction and working through the old side
parapet; No 2 throwing the earth over the old head parapet. The
sand-bags of the old are gradually removed and used for a new head
parapet, 20 or 30 additional sand-bags being ready for use if needed
before the others can be safely removed. Nos. 3 and 4 follow on as
before.

A _return_ can be driven back when desired by another detachment of
sappers. No head parapet will be needed, but the side parapet will be
kept a little in advance of the head of the sap.

=26.= =Breaking Out a Sap from a Parallel.=--The head parapet
of a sap is about 2' 6" high. The parapet of a parallel is about 4' 6"
high. A sap of the usual form driven through the parapet of a parallel
will expose the latter to fire through the opening formed. To reduce
the danger from this exposure, the sap is broken out at night, and to
cover the opening in the shortest time two or three men may creep over
the parapet of the parallel and cover themselves by rapidly digging
a hole, from which they may work back and join the sappers, who are
working outward. The sap being driven obliquely to the front, the
trench widened, and the parapet made full size (Pl. II, Fig. 21), the
opening will be covered; or a few men may in some cases construct in
front of the parallel a short section of flying sap, under cover of
which the full sap may be broken out (Pl. III, Fig. 28).

Preliminary preparations for breaking out should be made during the
day, but should be so conducted as not to indicate the selected point
to the enemy.

=27.= =Circular places of arms= (Pl. IX, Fig. 83) may be
formed in front of a parallel by breaking out two single saps from
points 80 to 100 yards apart and so directing them as to meet at 25 or
30 yards in front of the parallel. They may be used by the guards of
the trenches or as depots for trench material, etc.

=28.= =Shallow Sap.=--When the presence of water in the
soil or of rock near the surface prevents driving the full sap 4' 6"
deep, a shallow or modified sap (Pl. II, Figs. 22 and 23) may be used,
provided a trench 3' deep can be driven forward. In this case Nos. 1
and 2 must both work kneeling, and Nos. 3 and 4 must throw the earth
well to the front and keep the parapet as high as possible, leaving
the construction of the berm to the widening party, who will give
to the trench the necessary width, and will then obtain earth for
strengthening the parapet by deepening the trench when practicable and
widening it when necessary, making, however, no irregularities which
will injure it as a communication and no depressions which will collect
water. This sap advances about as rapidly as the full sap.

=29.= =Overground Approaches.=--When the water or rock
comes to the surface of the ground, approaches can, under favorable
circumstances, be driven for short distances by carrying forward earth
in sand-bags, forming with them head and side parapets, and moving
forward by continually building up the latter and advancing the former
as before described.

The expenditure of time, labor, and sand-bags is so great in driving
approaches in this way that the minimum height of parapet (possibly 5')
should be made with sand-bags. This may be subsequently heightened and
strengthened with earth brought forward in barrows or hand-carts and
thrown upon the top and exterior slope.

=30.= =Double Sap.=--(Pl. III, Figs. 24, 25, and 26).--The
double sap consists of two parallel single saps driven side by side,
the cutting lines of the berms, usually 10 feet apart, making the
bottom of the completed trench 7 feet wide. It is used when the
zigzags, to avoid enfilade, make such a slow advance as to be no longer
profitable, i.e., when the amount gained in advance does not exceed ⅓
the length driven. The double sap is directed toward the work, and is
exposed to an enfilading and also to a slant fire from both directions.
It must therefore have a parapet in front and on both flanks.

=31.= =Execution of the Double Sap.=--The double sap is
driven by two detachments, each organized and equipped exactly as for
a single sap, except that a greater number of sand-bags should be
supplied when practicable. The sappers work as in driving a single
sap, with the following modifications only: The Nos. 1 prolong their
head parapets until they meet, and in advancing their heads of sap
leave undisturbed the 4 feet of head parapet intervening between their
trenches, but, by continually throwing sand-bags or earth obliquely to
the front, keep the head parapet continuous and nearly straight.

This leaves between the trenches made by the Nos. 1 and 2 of the two
detachments a tongue of earth 4 feet thick, surmounted with a parapet
about 2' or 2' 6" high, which serves as a parados and protects these
sappers from reverse fire.

Nos. 3 and 4 of both detachments, in completing their tasks, remove
this tongue and pass forward the sand-bags forming its parapet for use
by Nos. 1 and 2; otherwise the tasks are as in driving a single sap.
When sufficient sand-bags are not available the middle part of the head
parapet must be made of loose earth, giving much less protection to
Nos. 1 and 2.

This sap, from its method of construction, is completed by the sappers
without the assistance of the infantry working parties. Its rate of
advance is about the same as that of the single sap.

=32.= =Changing Direction of a Double Sap.=--When a change of
direction is to be made No. 1 of the first detachment marks on the berm
the width of the top of the trench (10'), Nos. 1 and 2 of the wheeling
flank come around the tongue and the leading sappers of the two
detachments start their sap-heads in the new direction. Nos. 3 and 4 of
both detachments remove the tongue of earth and complete the parapets
of the original trench and then follow up their Nos. 1 and 2 as before.

=33.= =Breaking Out a Double Sap from a Parallel.=--A
double sap is broken out by methods entirely similar to those already
described for the single sap (Pl. III, Figs. 27 and 28). The figures
explain themselves.

=34.= =Traversed Sap.=--A sap may be traversed to protect
it against enfilade by frequent changes of direction, generally
rectangular (Pl. III, Figs. 29, 30, and 31), or by making hollow
traverses by blinding the sap at points separated by limited distances
(Pl. III, Figs. 32-35).

In traversing a double sap by change of direction, a single sap is
broken out to the right or left (or one in each direction) and pushed
forward to the desired length. From the flank of this the double sap
is again broken out and driven to the front until another traverse is
required. When the saps are driven to both right and left a double sap
is driven to the front from the extremity of each, and at the next
change of direction the single saps are driven towards each other until
they meet, and the double sap is driven in the prolongation of its
original direction. This forms what is called a _cube traverse_, and
gives additional room in the communications. The single sap is used in
making traverses, since by throwing all the earth on one side better
cover is given. When the sap is so far advanced that it becomes subject
to a reverse fire the double sap will have to be used in making the
traverses.

_Length of Traverses._--Traverses should extend at least 12 feet beyond
the trench in their rear, which will give them a length of from 25 to
30 feet on the berm. The salient angles of the sides of the trenches
should be rounded as much as practicable to allow the easy passage
of guns, and those of the parapets should, when necessary to screen
the trench, be held as nearly vertical as practicable by sand-bags.
Ramps leading to the surface of the ground may be made in rear of
the traverses when needed. For guns they are 8' wide, with slope not
greater than 1/4. The work in making traverses being considerable, they
should be spaced as far apart as practicable.

_Spacing Traverses._--In driving the sap to the front the low head
parapet of the sap will defilade a less length in the rear than would
the finished parapet of the traverse, which is from 2 to 3 feet higher.
The sap is, nevertheless, pushed forward to as great a length as will
be defiladed by the traverse when finished, the sappers meanwhile
passing the partly protected portion by stooping or creeping when
necessary.

=35.= =Traverse by Blinded Sap.=--In traversing a sap by
blinding a part of its length (Pl. III, Figs. 32-35) the sap is
first deepened 2 feet over this part; mine-cases, frames similar
to mining-frames, or regular blindage-frames (see Military Mining,
Arts. 53-55) are then put in position, the side slopes are held up
by sheeting, when necessary, and the top is covered with sheeting,
fascines, rails, or other material; earth is then thrown upon the top
to bring it up to the desired height for a traverse, which will usually
give at least 3 feet of earth covering. When a considerable thickness
of earth is to be used the frames must be made correspondingly strong.
For a clear opening, 6 feet at bottom, 8 feet at top, and 6' 6" high
the English engineers recommend frames at 3-foot intervals, with 6-inch
square posts, 2-inch thick sills, and 9 inch × 6 inch caps 12 feet
long. The end frames should be braced against outward thrust by 6" × 6"
struts.

These traverses are usually made at least 20 feet in length. They can
be used only when good drainage can be secured.

=36.= =Crowning the Covered Way= (Pl. IV., Fig. 36).--The
traversed sap is used for “_crowning the covered way_,” which consists
in constructing a battery or infantry parapet along the crest of the
covered way, from which a fire can be brought upon the ditch and the
scarp-wall of the work. To accomplish this the sap is run parallel to
the crest, with its nearer cutting line 18 or 20 feet from it. For an
infantry trench the traverses may be of the dimensions already given.

To cover a battery they should be about 33' long. It will generally be
necessary to use the double sap altogether in their construction, but
usually the earth excavated by Nos. 3 and 4 of both brigades will be
thrown on the parapet next the work, the parapet on the reverse side
formed by Nos. 1 and 2 affording sufficient cover for constructing
the sap and traverses. The parapet is prepared for infantry fire as
described for the parallels. The emplacements for guns, the service
magazines, etc., etc., are prepared and the embrasures are cut, or the
parapet prepared for the overbank carriages at the last moment, under
cover of the small-arm and machine-gun fire from the parallels and
places of arms, and the artillery fire from batteries, which do not
endanger the working parties.

=37.= =Trench Cavalier.=--In order to obtain a greater
plunge upon the covered way and ditch, short lengths of double sap are
sometimes run at right angles to the direction of the crests of the
covered way at about 30 yards outside its salient. The parapet on the
side of the sap towards the work is thrown forward and built up to the
desired height with gabions and sand-bags, and provided with steps and
sand-bag loopholes, giving a short length of parapet with considerable
command, firing directly along the covered way at short range.

This construction is called a _Trench cavalier_. It will be seldom, if
ever, used in the future.

=38.= =Former Methods of Sapping.=--Before the general
introduction of machine and rapid-fire guns and of small arms of
extreme accuracy and penetration saps were constructed by No. 1
sapper driving a trench 18" × 18", which was enlarged successively by
Nos. 2, 3, and 4. Cover for the sappers was obtained by the use of a
sap-roller (a large gabion, 7' 6" long and 4' in diameter, stuffed with
fascines and rods) as a movable head parapet, and the construction
of the side parapet was expedited by the use of gabions, sap-fagots,
etc. This method cannot be used against an enemy well equipped with
modern weapons. It is referred to only as a suggestion that a readily
improvised modification of it might be used to capture, with the least
possible loss, a party of rioters, criminals, or other badly-armed men
occupying an isolated house or other cover.


PASSAGE OF THE DITCH.

=39.= When breaches which are practicable are made in both
counter-scarp and scarp of a dry ditch an assault may sometimes be made
successfully; but when the scarp-wall is not breached, or when, for
other reasons, an assault from the crowning of the covered way is not
considered advisable, the ditch must be crossed and the breach, when
made, must be crowned by regular approaches. This is accomplished by
the use of a _sap_, _single_ or _double_, depending upon whether it is
exposed to fire upon one or both flanks. Owing to the plunging fire of
the defence it may be necessary to make the sap deeper than 4' 6", or
in some cases to _blind_ it for a part or the whole of its length. It
is generally impracticable to drive the sap down the slope of a breach
in the counter-scarp; therefore a _blinded descent_ (Military Mining,
pars. 53 and 54) is used. It is so directed that when the counter-scarp
is reached the floor of the gallery will be at the required depth below
the bottom of the ditch; i.e., at the depth fixed for the bottom of
the sap. When the small-arm fire of the defence is so severe as to
necessitate blinding the sap from the counter-scarp across the ditch,
it will usually be imperative to provide a _shield_, under cover of
which the sappers may start the blinded sap. This may be made of boards
covered with bullet-proof iron-plates, and of such width and length
that it may be carried through the gallery, thrust out into the ditch,
and then turned, placed in position, and blocked up at such angle and
to such height as may be wished, by men who move on their hands and
knees and support the shield on their backs. Under cover of this shield
the head parapet of the blinded sap may be thrown up and the sap then
driven in the usual way.

For method of breaching by mines, see Military Mining, pars. 91 and 92.

After breaching the scarp, if an assault is to be made, the
counter-scarp, for a length equal to or greater than the length of
the breach, should be blown down, to give the assaulting party access
to the breach. If the breach is to be crowned, and approaches are to
be driven against interior retrenchments, a gallery of descent should
be driven to the counter-scarp at one side of the breach before the
assault is made. From this a trench should be driven to the crowning of
the breach (usually by flying sap), by means of which communication is
maintained between the crowning of the breach and the exterior.

=40.= =A wet ditch without current= may be crossed by
building a causeway, upon one or each side of which a parapet is
constructed (Pl. IV., Figs. 37, 38, and 41).

The floor of the gallery of descent should strike the ditch at about
one foot above the level of the water. The counter-scarp wall having
been broken through, a shield similar to that described in the
preceding paragraph may be used to cover the sappers working at the
outlet of the gallery in the first stages of the succeeding work.
The causeway is built by throwing into the ditch short fascines or
brushwood mats, having bound up with them stones enough to sink them,
broken-stone gravel or other available material, until the causeway is
8 or 10 feet long, about one foot above the level of the water and wide
enough for the roadway and parapets. The head and side parapets are
then constructed with sand-bags, which are passed out under the shield
and piled at its head and sides. The causeway is continued by throwing
material over the head parapet, and the approach is driven forward
somewhat like a sap. So soon as the head and side parapets are made the
shield may be raised up and supported upon two or three cross-balks
resting upon the side parapets. It may then be progressively moved
forward and the approach in its rear be blinded by sappers working
under its protection. Unless the plunge of the fire upon the approach
is equal to or greater than 45° this shield will, however, when
vertical, cover a greater length of trench than when in a horizontal
position. It may, therefore, if desired, be turned into a vertical
position and be supported by a frame built for that purpose, which can
be moved forward as the approach advances (Pl. IV., Fig. 41).

When the head of the approach is subjected to the fire of
rifle-bullets only, it may be practicable to dispense with the head
parapet, replacing it with a bullet-proof screen covering the head of
the approach and with wings extending back and overlapping the side
parapets (Pl. IV., Fig. 40); the shield floating on a raft of light
logs, or other material which cannot be sunk by rifle fire. This shield
would, of course, be erected and launched under cover of the one
already referred to. To save sand-bags, etc., the interior slope of the
side parapets may be revetted with gabions about 4' 6" long, resting on
two short fascines and crowned with three others, giving a height of
about 6' 3". Upon these, when necessary, cross-beams are laid and the
blinding of the approach is finished with sand-bags thrown on top.

=41.= =A wet ditch with current=, or one in which the water
level may be varied by the defence, presents greater difficulties. The
method of crossing which seems most promising is by a causeway made
of materials which will allow the water to pass freely through it.
For this purpose it is usually recommended to use casks with their
heads knocked out, or strong gabions lashed to balks, so as to form
continuous tubes, which are loaded with stones and sunk with their
axes parallel to the counter-scarp by sappers working under cover
of a shield. When the top of the causeway is about a foot above the
high-water mark it is levelled off with fascines and the approach
driven forward as previously described. When available, iron or
terra-cotta pipes of large diameter may, perhaps, be advantageously
substituted for casks or gabions. Cormontaigne, at Philipsburg, in
1734, successfully used floating bridges of fascines with parapets of
gabions and fascines covered with raw hides. Two bridges were made.
They were 128 feet long, 48 feet wide, and 6 feet thick. The water
was about 15 feet deep. To construct and hold in place, in a strong
or varying current, a floating bridge of sufficient width and depth
to support, without sinking or capsizing, the parapets necessary
for protection against modern small arms and machine guns is a task
presenting such great difficulties that it will hardly be undertaken,
except as a last resort, and then with a very uncertain issue.

When, however, the fire of the work is nearly or entirely silenced, a
floating bridge of pontoons, casks, spars, or other materials, with a
slightly masked roadway, may furnish a sufficiently good crossing and
may be constructed with little difficulty and loss.[1]




CHAPTER IV.

BATTERIES, OBSERVATORIES, AND MAGAZINES.


=42.= =Batteries= in siege operations are for field-guns,
siege-guns, howitzers, and mortars.

When the gun-platform is on or above the level of the ground they
are known as “_elevated batteries_,” when it is below the surface as
“_sunken batteries_.”

When they are concealed from the view of the enemy by natural
or artificial screens they are called “_screened_” or “_masked
batteries_,” and when on sites which can be seen by the enemy “_exposed
batteries_.”


GENERAL REQUIREMENTS OF SIEGE BATTERIES.

=43.= 1st. A good _platform_ for and sufficient space to work each
gun. The platform must be suited to the gun used. The space required is
about 15 feet front by 20 to 25 feet depth.

2d. A _parapet_ which cannot be penetrated by the projectiles which
will be fired against it, and which is high enough to afford cover to
the gun and its detachment against curved fire. A thickness of 30 feet
of earth will usually be enough for the most exposed batteries. A less
thickness may be used when the conditions justify it. The height of the
interior crest above the terre-plein should not be less than 7½ feet
when this is attainable and may sometimes be greater.

3d. _Traverses._ Each gun is usually separated from the next by a
traverse, whose thickness when subject to enfilade fire is the same as
that of the parapet (30 feet); under other circumstances the thickness
may be reduced if deemed advisable, but should, when practicable, be
such that a shell bursting at any point within it will blow out at the
top or on one side only.

4th. _Bomb_ and _splinter proofs_ sufficient to cover the gun
detachment and reserves against vertical fire. The thickness of cover
for these is to be regulated according to the principles laid down in
par. 21.

5th. _Magazines_ which will hold at least 24 hours' supply of
ammunition, besides recesses near the guns for shells and a few
cartridges.

6th. Easy and direct _communications_ for bringing up the guns and
placing them in position; including tramways, ramps, etc., etc.

7th. _Look-outs_ or _observatories_ from which the effect of the fire
can be seen. These when possible will be placed in high sheltered
places well on the flanks of the battery and preferably in advance of
it. They may be connected with it by signals, telegraph, or telephone,
when necessary.

8th. _Screens._--Earthen screens should when possible be thrown up in
front of all exposed batteries.


CONSTRUCTION OF BATTERIES.

=44.= =Batteries for Field Guns.=--When the place is
invested, the field artillery is placed in positions considered most
advantageous for repelling attacks from the garrison upon the investing
force. _Gun-pits_ (described in “Field Fortifications”) are usually
made at once for cover for the guns and their detachments. When any of
these sites are occupied during the siege the gun-pits may be connected
and converted into a battery as indicated by Pl. IV, Figs. 42-45.

A similar construction may sometimes be used during the siege when the
artillery fire of the place is weakened, and it is desirable to place
a field battery in position for reaching some point in the work. As
a rule, however, batteries for field guns will during the siege be
constructed in the same way as are those for siege guns and howitzers.

=45.= =Batteries for Siege Guns and Howitzers.=--These may
be _screened_ or _exposed_, _sunken_, or _elevated_. As a rule each
battery has a magazine on each flank. The amount of powder necessary to
serve two guns for 24 hours (150 to 200 rounds per gun = 2500 to 6000
lbs.) is as much as it is advisable to have in one magazine, in order
to limit so far as possible the disastrous effects of an explosion. For
this reason the number of guns in a battery is usually restricted to
four. This number may be increased when necessary, or when howitzers
firing small charges render it unobjectionable.

=Elevated batteries= require much more labor for their
construction and for obtaining cover for the men and material than the
sunken batteries. They are therefore used only when the target has to
be seen and the gun has to be raised for this purpose, or when owing
to the presence of rock or water in the soil, or the liability of the
site to be flooded it is impracticable to sink the platforms below
the surface. As a rule they can be constructed only when covered by a
screen either natural or artificial, and then with earth carried in
wheelbarrows, sand-bags, etc., etc.

=Sunken Batteries.=--When constructed under cover of a screen the
depth of the terre-plein of a sunken battery may be limited by the
presence of rock or water in the soil, the character of the guns and
carriages, and the time available for the work. In a hasty construction
the depth of the terre-plein is usually limited to from 3 to 4 feet,
which can be dug out in a short time. When more time is available the
gun platforms may be put at 5 to 6 feet below the surface and the
other parts of the terre-plein may be sunk still lower. This gives
but little height of parapet, and the extra earth may be used for
giving additional thickness of cover to the splinter-proofs under the
traverses and flanks, and also to the magazines.

A great variety of plans and profiles may be adopted for batteries of
this class, the details of which need not be given, since they will be
modifications of those described in Field Fortifications and Permanent
Fortifications, and of the exposed battery to be next described. As
they are built under cover of screens and are not subject to fire
during construction, work upon them may be continuous and by day as
well as by night.

=46.= =Screens.=--The _natural screens_ used for cover are
elevations, woods, hedges, existing buildings, walls, etc., etc.

_Artificial screens_ may be made by setting out bushes to imitate
hedges or adopting similar devices, which, however, will usually fail
to deceive an active enemy. A trench with the earth thrown to the
front, forming a glacis-shaped parapet, will, however, generally be
effective. It must be made of such length that the enemy cannot know
the exact position of the battery, and of such height and thickness
that he cannot afford to expend enough ammunition to breach it.

This affords not only concealment during construction, but also a
remarkably efficient cover to the battery against hostile fire.

Screens, natural or artificial, should be from 50 to 100 yards in front
of the batteries, so that the enemy’s aim may not be corrected by
seeing the points struck by his shells.

Unless the screen is of material which will break up into injurious
splinters under hostile fire, only enough should be removed before
opening fire to unmask the target of each gun, leaving the remainder
for concealing the points struck by shells, even if it affords no cover
against their penetration.

=47.= =Exposed Sunken Battery.=--Before describing the
construction of this battery it is necessary to state that upon a site
fully exposed to the accurate concentrated fire of a work, directed
at night by light balls or electric lights, it will in general be
practicable to construct batteries only by sapping, and even then with
considerable losses. But these conditions seldom exist, since in the
distant attack it is usually possible to construct and arm the battery
before it is discovered by the defence, and in the close attack the
fire of the defence is generally so much reduced that some exposure
is justifiable. While the battery to be described is classed as an
“exposed battery,” it is understood that it may also be constructed
under cover of a parallel or other trench, and that in all cases when
practicable a natural or artificial mask is used to conceal the first
night’s work from the enemy. It is assumed from the results obtained in
practice that, with the material conveniently stored, the battery can
be traced, a central trench and splinter-proof covers be made during
the first night, and the battery finished and armed during the second.

The general design and details of this battery are due to the Royal
(British) Engineers.

=48.= =Tracing the Battery.=--The battery is traced under
the direction of an engineer officer by one or two tracing parties,
each composed as follows: 1 non-commissioned officer with a 6-foot
measuring-rod and tracing-lantern, and 4 sappers, one carrying a
measuring-tape and bundles of pickets, one a field-level, one several
tracing-tapes, and one a mallet or hand-axe; about 75 pickets and 1200
feet of tracing-tape should be provided. The line of fire of the first
gun of the battery (_xy_, Pl. V, Fig. 46) is accurately laid out and
marked by daylight. At dusk one party drives a picket at _I_, where the
directrix crosses the projection of the base of the interior slope,
and from this as an origin lays out the cutting lines of the central
trench, _I_, _II_, _III_, _IV_, _V_, _I_, making the trench 5 feet wide
and of the length required for the number of guns (= No. of guns ×
45'--10'); commencing then at a point _A_, 7' 6" to the left of _I_ and
in the rear cutting line, this party lays out the line _a_, _b_, _c_,
_d_, _e_, etc., ... _m_, _n_, _o_, as indicated, the direction _n_,
_o_, leading to the parallel.

The second party, beginning at _A_, lays out _A_, _B_, _C_,
communicating with the parallel, and then the inner cutting line of the
ditch _D_, _E_, _F_, _G_, _H_, _I_, allowing for a thickness of parapet
of 30 feet and an ultimate width of ditch of 12 feet (_D_, _E_, and
_H_, _I_).

Two parties should trace the battery in 25 minutes, one party in 45
minutes.

=49.= =Constructing the Central Passage and Splinter
Proofs.=--The first relief of working party for the central passage
is posted and commences work at once (Pl. V, Figs. 47-48). Each man’s
task is 5 feet in length and 4 feet in depth (giving 100 cubic feet).
It may be completed in 4 hours, and should be in 6 at most.

The second relief (Pl. V, Figs. 49-52) excavates the cartridge
recesses, trims up the work done by the first relief, lowers any earth
that stands too high, revets the slopes of the gun portions, puts in
frames and sheeting when needed in the splinter-proofs, places the
bearing planks and balks of the latter, which should be at least 9
inches thick and 9 feet long, except over the cartridge recesses, where
they are 12 feet, and when possible deepens the central passage under
the splinter-proofs to 5' 6" for a width of 2 feet to form a seat for
the men. It also places one or two planks along the passage to serve
as a bench for shells. The latter part of this work can be done by
daylight. The parapet formed by this excavation is about 2 feet high.
This is so masked or so inconspicuous as not to draw upon itself the
artillery fire of the defence. The construction of the battery will be
continued usually on the following night.

=50.= =Construction of the Battery= (Pls. V and VI, Figs. 53,
55, 60, 67).--Two reliefs are required for this. _The first relief_
receives its tools and arrives upon the ground at dusk. It is divided
into four parties, one for the front ditch, one for the gun portions,
one for the rear trench, and a reserve of ten per cent for substitutes
and casualties. They are posted and supervised by the engineer officer,
n. c. o^s., and sappers as described in paragraph 16, _ante_.

_The Front-ditch Party._--Each digger is assigned a task 5' wide, 6'
long, and 3' 6" deep. He throws the earth as far into the parapet as
he can. The shovellers, one to each two diggers, are posted 12 feet
from the cutting line of the ditch. They pass the earth back toward the
interior crest and the traverse, keeping the top surface nearly level.

_The gun-portion party_ is divided up equally among the gun portions,
each digger is allotted a task 4' wide, 7' 6" long, and 3' 6" deep.
The gabions around the gun portion are placed by the shovellers under
the direction of the engineer soldiers, a short one being placed at
the throat of the embrasure. The shovellers spread and level the earth
thrown out by the gun-portion parties and the rear-trench party. They
work in connection with the other shovellers to give to the traverses
and parapet near the interior crest the proper shape.

_The Rear-trench Party._--This party excavates to a width of 7' 6" the
rear trench and the communications with the parallel or approach. Each
digger has a task 4' wide, 7' 6" long, and 3' 6" deep. The two directly
in rear of each gun portion throw the earth to the rear, the others
throw it to the front, leaving a berm of 4' 6" at the rear of the
traverse. The men of the _reserve_ who are not otherwise occupied fill
sand-bags from the earth thrown to the rear, and cut a ramp 8 feet wide
and not steeper than 1/4, in rear of each gun-portion, when needed. It
is essential that the excavation of the gun-portion be finished by the
first relief, so that the platforms may be laid by the second relief in
time to allow the guns to be placed before daylight.

The first relief leaves in the battery the tools required by the second
and carries the rest back to the depot.

_The second relief_ is divided into three parties and a strong reserve
of one quarter or one fifth of its strength. The first, or _front-ditch
party_, works in the front ditch, widening it 6 feet and throwing the
earth back to form the front of the parapet. The shovellers, one to
each two diggers, spread and level it. The task of a digger is 5' wide,
6' long, and 3' 6" deep.

The second, or _platform party_, places the platforms and gives way to
the gun detachments.

The third, or _rear-trench party_, widens the trench 3' towards the
front by cutting off the rear of the traverses.

The _reserve_ completes any work left unfinished by the first relief,
fills sand-bags and places them around the gun portions, digs ditches
and drainage-pits when needed, and does any other work necessary for
the completion and arming of the battery.

When a tramway is laid in the trench for bringing up the guns and
carriages, the ramps in rear need not be cut.

=51.= =Alternative Construction in Position Very Much
Exposed.=--When the earth thrown up in making the splinter-proofs
cannot be concealed, it may attract such a severe fire from the defence
as to make the above-described construction impossible. In this case
the battery is traced as above described, the balks for covering the
splinter-proofs are placed in position resting on bearing-planks, and
the construction of the front ditch, gun portions, and rear trench
are commenced at once; and the battery is as nearly finished as time
allows, and armed if possible. The splinter-proofs are subsequently
mined out and the remaining necessary details finished before opening
fire.

=52.= =Splinter-proofs=, in addition to those in the central
trench, are usually constructed under the rear of the traverses (Pl.
VI, Figs. 65-67). These may be made during the construction of the
battery or after its completion. They are about 5 feet wide, 6 feet
deep, and 10 feet shorter than the width of the traverse. Their floor
is at 6 feet below the surface. The earth is held up by frames and
sheeting, and the roof is supported by cross-balks resting on posts
and running back into the traverse. The roof consists of railroad iron
or heavy timbers covered with earth, and access is given by steps from
the rear trench; the space not occupied by the steps may be shielded
with inclined posts or other covering if thought necessary. These
splinter-proofs differ in no essential from those described in Field
Fortifications. The finished battery is shown in Pl. VI, Figs. 62-64.

=53.= =Sunken Battery in a Parallel= (Pl. VII, Figs. 68
and 69).--A battery similar to the one above described is sometimes
constructed in a parallel. In this case the traverses have to be built
up, and therefore do not usually exceed 20 feet in thickness. Pickets
are driven at intervals of 35 feet along the banquette of the parallel
to mark the centres of the gun spaces, and the rest of the battery is
traced in the usual way. The steps of the parallel are cut away and
the slope revetted for the gun spaces and the central trench. Gabions
are placed along the back of the central trench and the sides of the
traverses. A rear trench 7' 6" wide is cut from the parallel at an
easy curve, so that its front cutting-line shall be 25 feet from the
foot of the interior slope; this, as before, is widened 3 feet by the
second relief cutting away the rear of the traverses. The reverse slope
of the parallel in rear of the gun portions is cut back to the rear
trench. A trench 2 feet wide and 2 feet deep is cut between the front
of the traverses and the foot of the interior slope, and the cartridge
recesses are excavated. The gabions of the traverses are filled,
balks placed over the central trench, and the tops of the traverses
and splinter-proofs are raised to the height of the parapet of the
parallel. A ditch in the front of the parallel 12' wide and 3' 6" deep,
traced at dusk, and excavated during the night, supplies earth to make
the parapet 30' thick and 4' 6" high. The work done in and behind the
parallel is not seen from the front, hence a great part of it may be
done by day, undetected by the enemy. The upper part of the traverses
is made by night, and the front ditch and front of the parapet are made
the same night or subsequently, depending upon the number of workmen
available.

Since the gabions of the traverses seriously obstruct the parallel,
they should not be placed in position until all arrangements are made
to open the rear trench.

In the special case of a battery on the crowning of the covered way,
the traverses have been already constructed in running the sap. The
splinter-proofs may be constructed by blinding portions of the sap, or
by mining them under the traverses. Owing to the height of the parapet,
embrasures of some depth will have to be cut through it. This is done
by a shallow sap started by one man, who is subsequently assisted
by a second, if the splay requires it. The cheeks are revetted with
sand-bags, covered with hides. The mouth of the embrasure is left
closed with the head parapet of the sap until fire is to be opened,
when the earth is dug away or blown away by the gun.

=54.= =Battery Behind the Crest of a Hill= (Pl. V., Figs.
57-59).--In a battery behind the crest of a hill the front ditch may
be omitted, the gun-portions may be entirely in excavation, and the
platforms given such a reference as to require a shallow groove to be
cut through the crest to allow the gun to fire. When the ground falls
away very rapidly to the rear it may be stepped under the traverses
to prevent their sliding, and the rear of the gun emplacement may
be raised when necessary to give the platform the proper slope. The
central trench is cut deep enough to give 5 feet of cover over the
splinter-proofs.

=55.= =Batteries on Sloping Ground= (Pl. VII., Figs.
70-72).--When the ground to be occupied by the battery slopes towards
or from the place or falls off on either side, the battery is
constructed essentially as upon level ground. The central passage is
driven, following the surface of the ground, the gun emplacements,
front and rear trench are excavated as before described, the additional
excavation or filling required in each gun emplacement to make the
platform horizontal is regulated for the particular site, any excess
of earth being used to give greater cover on the more exposed side,
and any deficiency being supplied from the front or rear trench, as
may be most convenient. Where the extra work imposed by the slope is
considerable, a third relief may be required to finish the battery, and
its arming may be necessarily postponed until the next night.

=56.= =Embrasures.=--Modern siege guns are generally
mounted either on “overbank” or “disappearing” carriages, firing over
parapets of sufficient height to give cover to the men. (The axis of
the trunnions of the U. S. 5" siege gun is 6" above the platform.)
Embrasures when used are generally shallow grooves cut in the top of
the parapet. In this case the bottom of these grooves must cut the
surface of the top of the parapet at or in rear of the highest line
visible to the enemy, so that no indentations which can be seen by him
will indicate the position of the guns. To effect this, the exterior
crest will usually be as high as and sometimes higher than the interior
crest, and the top of the parapet (“superior slope”) will be level or
will slope to the rear. In rare instances, however, deeper embrasures
with revetted cheeks must be made. The only serviceable revetment for
use with high-power guns is one of sand-bags wrapped in raw hides.
This may be made by laying down a hide, piling a number of sand-bags
upon it, and folding the free end back over them; placing another hide
on top of this with more sand-bags and so on. Or large packages may
be made by wrapping up a number of sand-bags in each hide and these
packages may be used for making the revetment.

The embrasure should be bottle-shaped in plan, shaped like a segment
of an ellipsoid immediately in front of the muzzle of the gun, then
drawn in like the neck of a bottle and narrowed to as small a mouth as
possible, so as to diminish the effect of the blast and give the least
possible exposure to the gun. When the battery is exposed to slant or
enfilading fire, instead of embrasures, bonnets of sand-bags may be
built upon the parapets to protect the guns.

=57.= =Observatories.=--Observatories or look-outs, as
previously stated, should as a rule be placed on high points well on
the flanks of the battery.[2] When this is impracticable, they may
be made by building up at the rear of the traverses, on the flanks,
or even in the gun portions, glacis-shaped covers pierced with a
sight-hole in all respects similar to a loop-hole for musketry, and
with just sufficient splay to include the desired field of view. A
number of these should be provided for each battery, so that the enemy
may not know which one is in use at any time. If subject to close and
accurate fire, the crest-line in their vicinity must be of the same
level as the tops of the look-outs, and provision must be made to
prevent the light showing through them.

=58.= =Drainage.=--After the completion and arming of the
battery, gutters should be cut on each side of the gun-portion leading
into one running along the reverse of the rear trench which carries
the water to low ground on the exterior, or which is provided with dry
wells or drainage-pits for collecting the water so that it may soak
into the ground or be pumped out with hand-pumps.

=59.= =Mortar Batteries.=--The introduction of rifled mortars
of all calibres, with the corresponding increase in accuracy of fire,
together with the destructive effects of shells charged with high
explosives, will doubtless lead to the extensive use of mortars in
future sieges.

In a distant attack the requirements of a mortar battery are very
simple, consisting principally of a stable platform, magazines for
ammunition, and bomb-proof covers for the gunners; since the battery
as a rule will be concealed from the view of the work by intervening
obstacles, and will in consequence not be subject to direct fire. When
the soil is favorable, cover against plunging fire will be most easily
obtained by sinking pits for the mortars to such depth as may be
necessary to furnish earth for a splinter-proof parapet surrounding
the pit, and for cover for the bomb-proof shelters for the men and the
magazines.

When ample space exists which is well concealed, and in which the
soil is good, a separate emplacement should be made for each mortar.
When necessary, however, two or more mortars may be placed in each
pit. The magazines, splinter and bomb proofs are similar to those
elsewhere described. When no natural mask exists, the battery may be
constructed behind an artificial screen, and be made of the general
type of the “exposed siege battery,” the gun portions being made with
front enough to accommodate one or two mortars as may be preferred, and
of such length only as is needed for working the mortar employed. The
terre-plein may be placed at any convenient depth below the surface of
the ground, and the revetment of the interior slope, if any be used,
will not ordinarily be carried higher than the muzzle of the mortar. As
the traverses are not subject to gun-fire, the splinter-proofs afforded
by the central passage may be added to by building others along
both sides of the traverse; and by deepening the mortar emplacement
sufficiently, they may be given enough cover to make them true
bomb-proofs.

A mortar battery fulfilling these conditions can hardly be silenced by
hostile fire.

The conditions under which the batteries may be constructed are,
however, so varied that detailed dimensions will not be given. No
difficulty will exist in making the battery of a size suitable for the
pieces to be employed.

The U. S. rifled siege mortar is of 7-inch calibre, about 5 feet
long, weighs 1715 lbs., and is designed to throw a 125-lb. shell with
a charge of 5½ lbs. of powder, giving an initial velocity of 685 f.s.
and a range of about 4000 yards. With reduced charges the range may be
reduced to about 650 yards without undue sacrifice of accuracy.

In the closer attack upon the work, batteries for the smaller siege
and field mortars may be readily constructed in front or rear
of the parallels, or in the parallels or approaches themselves;
splinter-proofs and temporary magazines being constructed by methods
previously indicated. In many cases, however, the lighter mortars,
field and Coehorn, which do not require fixed platforms, may be placed
behind any part of the trenches affording cover, and fire be opened and
continued until the fire of the enemy becomes too annoying, when the
mortars may be removed to some other locality.


MAGAZINES.

=60.= =Magazines= should be provided, at least two to each
battery, not only to localize the injury due to an explosion, but also
to prevent the battery being disabled by the explosion of a single one.

As previously stated (par. 43), they should contain 24 hours' supply
(from 150 to 200 rounds) for each gun which they are designed to
serve,[3] which may require a capacity in a single magazine of as much
as 6,000 lbs. of powder.

This amount should be reduced when possible by increasing the number
of magazines. The cartridges should be made up and packed in boxes at
the depots or parks, and the powder chambers in the magazines should be
of such size as to store these boxes with only such vacant space as is
necessary for ease in handling them.[4]

=61.= =Cover.=--The chamber should be covered with strong
balks or rails and enough earth to form a sloping roof; over this raw
hides or tarpaulin should be spread, and the remainder of the earth
filling be spread upon this and rammed solidly. The amount of earth
cover required for security must be determined from the principles
given in par. 21. The English engineers recommend as sufficient
protection against ordinary fire for a magazine 5 feet wide, two layers
of 9" × 9" fir laid crossing each other, or one layer of 12" × 12" oak,
covered with 5 feet of earth.

In experiments at Lydd in 1883, however, an 8-inch howitzer shell
falling at an angle of about 30° penetrated through a covering of
7 feet of soft clay and burst upon the timber roof of a magazine,
cutting it through. This shows that complete protection is not always
possible, and that the chances of hitting must be reduced by making
the horizontal area of the magazine chamber as small as possible,
and placing its smaller dimension in the line of the hostile fire.
The clear height of the magazine should be 4' 6" to 5' minimum, when
practicable, and the top of the covering balks should be at or below
the level of the ground.

=62.= =Location.=--A magazine should be located at such
distance from the battery that its explosion will not disable the
guns, injure the parapets or traverses, or seriously endanger the
cannoneers;[5] but, on the other hand, it should be near enough to
allow the ammunition boxes to be conveniently carried to the cartridge
recesses; and the communications for this purpose should be well
covered from hostile fire. The entrance to the magazine should be so
protected that splinters cannot enter the chamber. Any natural hollows,
banks, etc., in the immediate vicinity of the battery should be taken
advantage of to facilitate the construction of and give better cover to
the magazines. When nothing of this kind exists the magazines may be
placed on the flanks or in rear of the battery, and should be masked
and screened by the parapet of the parallel, approach, communications,
or battery, or by special glacis-shaped screens made, for the purpose;
which should be much longer than the width of the magazines that they
cover, so that the discovery of the location of the latter by the enemy
may be made more difficult. The magazines should not be located in rear
of the centre of the screens nor symmetrically with reference to the
battery, nor, when it can be avoided, directly in rear of a gun. The
passages leading to them should enter the battery in rear of a flank
or a traverse, and should be so directed as to escape enfilade. They
should be so graded that the surface water will run away from the door
of the magazine and be discharged upon lower ground or received in
drainage-pits placed at the lowest points.

=63.= =Construction of a Magazine Subject to Direct Fire
Only= (Pl. VII., Figs. 73-77.)--The method of tracing the
magazine and its approaches is too evident to need description. In
this example an earth cover of 5 feet against vertical and 20 feet
against horizontal fire is given. Should more or less be desired, a
corresponding change may be made in the plan, depth of excavation, and
depth and width of approaches; and the earth for additional cover may
be obtained from a ditch or pit in rear of the magazine. The excavation
for the chamber is given a width of 6', a depth of 5' 6", and a length
of 12', the entrance a width of 3', a depth of 5' 6", and a length of
6'.

The sides of the chamber and entrance are held up by frames 4' 9" high
and 2' 11" wide, outside measurement. The caps are 6" × 5", stanchions
4" × 5", and the ground sills 3" × 5"; sheeting 1" thick is inserted
between the frames and the earth. The covering balks are 9" × 6" and 10
feet long; their tops are flush with the surface of the ground; cleats
nailed on their under side keep the tops of the side frames from being
pushed in by the pressure of the earth. The earth cover is 5 feet high
at the centre and 4 feet at the crest of the outer slope. The passages
are 5' 6" deep, 3' wide at bottom, and 5' at the top. The entrance
is blinded by placing balks across the passage for such part of its
length as may be thought necessary, and extending the earth covering
over them, as shown in the section (Fig. 75). A door, swinging outside,
is hung on the outside frame. Heavy railroad iron may be substituted
for the timber balks with advantage. When thicker balks are used,
or when a second layer is added, the chamber and passage should be
correspondingly deepened.

=64.= =Manner of Executing the Work.=--The powder chamber and
passage are excavated and the frames and balks placed during the first
night, while the central passage of the battery is being constructed.
The excavated earth is thrown out far enough to allow the balks to be
put in position, and is so spread as not to be seen by the defence.
This may be done by one relief of 8 hours, or two reliefs of 4 hours
each. If the work is not completed during the night, the sheeting,
frames, and balks may be placed by day under cover of the earth thrown
out and the existing screens.

The passages are excavated and the earth cover completed on the second
night by two 4-hour reliefs, the first excavating to a depth of 3' 6",
and the second to 5' 6", trimming up the slopes and completing the
work. When necessary, the sides of the passage will be revetted by the
second and a third relief.

When the necessity for great haste exists, the excavation of the
powder-chamber, entrance, and passages may be carried on at the same
time, the excavated earth being thrown in front and on the sides of the
powder-chamber until the balks are in position, and then thrown back
upon them, levelled and rammed.

=65.= =Mined Magazine.=--When the soil, by absence of rock
and water, admits of mining, greater cover against vertical fire can be
obtained with less work by mining out the powder-chamber and passages
(Pl. VIII, Figs. 78, 79). The figures illustrate one of minimum
dimensions, which is constructed as follows: The entrance 10' × 5' by
5' 6" deep is first excavated, revetted with frames and sheeting and
covered with balks and earth as indicated. At 1 foot from the end
a shaft 2' × 5' is sunk to a depth of 12'. From the front of this a
gallery 2' × 5' 6" is driven for about 6'; at the end of this galleries
5' 6" × 2' are broken out on each side and driven so far as may be
necessary to store the requisite number of ammunition-boxes. (For
method of sinking shafts, driving galleries, etc., see Military Mining,
Arts. 25, 33, and 44-48.) The excavated earth is spread on top of the
magazine to increase the thickness of the cover already given by that
excavated from the passages. A ring-bolt is placed in the balk directly
over the shaft, for attaching a hoisting tackle for removing the earth
during construction and for hoisting and lowering ammunition-boxes
afterward.

A door opening outward may be hung at the entrance, and the passage
may be blinded as previously described, if it is thought necessary.
The communications are arranged in essentially the same way as for the
magazine previously described.

The dimensions given are the least which will allow moderately free
access and good cover. The magazine should be constructed, by good
miners, in two nights and the intervening day, and will store about
4000 pounds of cartridges in boxes. When time and the character of the
ground admit, and larger capacity is desired, the shaft may be made
wider and deeper, the gallery wider and longer, and the powder-chamber
deeper, longer, and wider, if desired.

The excavation for the entrance and approaches, the placing of balks,
and the levelling and ramming of the earth-cover, should be done by
night; the mining work can be carried on both night and day.

=66.= =Elevated Magazines.=--When the presence of rock or
water in the soil prevents sinking the magazines to the full depth
above given, they must be sunk so far as practicable and given the
least possible clear height of powder chamber, with the best attainable
overhead cover. This should be strengthened by the use of railroad iron
or rolled iron beams, when available. The cover against direct fire
should be increased up to 30 feet, and the front slope be made gentle,
like a glacis. A screen made of an earthen bank with a glacis slope
should also be used if possible. These precautions having been taken,
the depth of the powder-chamber in the direction of the hostile fire
should be reduced to a minimum, and the storage of large quantities
of powder be avoided, so far as possible, by constructing a number of
small magazines at the most convenient places in the vicinity of the
battery.

=67.= =Precautions against Dampness in Magazines for Siege
Batteries.=--Underground magazines of the character above described
are, of necessity, sometimes damp. The only ventilation usually
possible is obtained by leaving the door open, the air being changed
more or less by the men going in and out.

The passage leading to the powder-chamber should enter it at the
middle, and in the service of the guns one half of the chamber should
be emptied on one day and the other half on the next. This will usually
limit the time which a cartridge is exposed to the dampness of the
magazine to a maximum of one or two days.




CHAPTER V.

SIEGE OPERATIONS.


THE ATTACK.

=68.= Siege operations include all the steps taken from the first
approach to the work up to its final capture. These taken in regular
order are as stated in Chapter II: the _investment_, the _distant
artillery attack_, the _construction of approaches_ and _parallels_,
_breaching by artillery or mines_, and the _final assault_.

For convenience in description the siege has been divided into three
periods. The _first period_ includes the preliminary operations up to
the completion of the investment.

The _second period_ includes all the operations between breaking
ground for the batteries of the first artillery position and the first
parallel, up to the completion of the most advanced parallel and the
occupation of a position near the foot of the glacis from which the
attack is to be made upon the breach, either by assault or sap.

The _third period_ comprises the advance from the last parallel, and
all subsequent operations up to the capture of the last entrenchment
and the surrender of the garrison.

The first and second periods are sometimes known as the “_distant_” and
the third period as the “_close attack_.”


FIRST PERIOD.

=69.= As a preliminary to the siege of any fortified place, all
possible information is obtained as to the strength and character of
its fortifications, the garrison, armament, stores of provisions and
ammunitions, water supply, water routes, telegraph and railroad lines,
manufactures, especially those which may be converted into factories
of arms and munitions, the character of the population of the place,
their probable food supply and their loyalty to their state; also the
topographical features and nature of the ground in the vicinity of
the work, the sites of camps and parks, the prevalent diseases of the
locality and the best means of preventing their attacks, etc., etc.
(see Bureau of Intelligence, Art of War, par. 128).

From these data the necessary materials and supplies are collected at
convenient points, the railroad or water routes selected, and the cars,
boats, wagons, etc., for their transportation provided; so that they
may arrive promptly and in the proper order when needed.

=70.= =The Investment.=--The investing force is brought
together, organized, and moved rapidly upon the place. When it is
available a large force of mounted troops may be used advantageously in
the investment, and be subsequently relieved by infantry and artillery.

When the investment is made, it adds greatly to the advantage of the
attack to completely surround and isolate the work, and to push the
investing line as near it as possible. When the investing force is
more or less dispersed, and is to be concentrated for the siege, the
temptation frequently exists to march them by converging lines upon the
place as a point of concentration.

While this may be advisable in some cases (as where the garrison is
very weak or under an inefficient commander), it will usually expose
the subdivisions of the investing force to be beaten in detail (Art
of War, par. 392). So also in surrounding the place; a premature
subdivision of the force into small fractions not protected by
field-works, or not within supporting distance each other, will afford
to an active defence an opportunity, by well-conducted sorties, to
inflict most severe losses upon the attack and very greatly delay
the investment. Keeping these dangers in view, the investing force
will move rapidly upon the work, seize, strengthen, and occupy strong
points as near the work as possible, and extend the lines to right
and left as rapidly as good judgment allows, until the place is
surrounded. Meanwhile detachments of greater or less size will scour
the ground around the place, seizing and carrying off or destroying,
so far as possible, all cattle, grain, lumber, etc., and everything
else which would be of use to the attack or defence. Under cover of
these detachments and escorts specially detailed for the purpose,
reconnoissances will be made to cover so much of the ground as can be
reached, especial efforts being made to examine the ground near the
works. These reconnoissances will necessarily be hurried and incomplete
but, must be as accurate as they can be made under the circumstances.
They should be directed principally to determining the heights and
directions of the principal points of the works, and their positions
with reference to prominent points that may be used as landmarks, in
verifying and correcting maps and information previously obtained, to
discovering the existing armament of the place and the steps already
taken for its defence, and to collecting all possible information
bearing upon the selection of the front of attack.

Systematic reconnoissances and surveys carried on throughout the siege
must be relied upon for checking and completing the work thus begun.

So soon as the supporting points for the investing force are secured,
a line of outposts is pushed forward towards the work and sentinels,
pickets, etc., are established (Art of War, pars. 167-194). The lines
of sentinels, pickets, and supports are placed as near the work as
practicable, and the line of resistance is advanced at every favorable
opportunity.

The usual rules for posting and relieving the outposts, establishing
day and night cordons, the use of patrols, etc., are applied, with such
modifications as circumstances render advantageous.

Any advanced points affording marked advantage to the attack which
have been seized are strengthened and held when possible, even
at considerable cost in men or with some delay in completing the
investment.

=71.= =Bringing up and Posting the Besieging Force.=--The
main besieging force, consisting principally of infantry, artillery,
and engineers, with the siege train, follows closely after the
investing force, and, upon arrival is encamped upon sites previously
selected, sending out at once, however, such reinforcements and
supports as are needed by the line of investment. Engineer and
artillery parks are established outside the zone of fire of the works
and in proximity to the main routes of communication. Branch railways
and tram-roads running through the parks, storehouses, repair shops,
etc. etc., are located and constructed. Sites for storage magazines
for ammunition are carefully selected at the most secure places,
and isolated when possible from the camps and parks by intervening
elevations of ground. The cover of these magazines, so far as possible,
is made up of wood and sand or earth free from stones large enough
to be dangerous projectiles in case of explosion. Rooms for loaded
shells and cartridges, and laboratories for making up ammunition are
constructed upon similar principles. Carefully studied arrangements for
the health and comfort of the men are made. Some of these are outlined
in Chapter VII.

=72.= =Fortifying the Camps, Parks, etc., etc.=--In former
sieges it was customary to completely surround the ground occupied
by the besieger with a continuous line of works of simple trace and
light profile called the “_line of circumvallation_;” and to construct
between the camps and the work another line, either continuous or with
intervals, called the “_line of countervallation_.” These lines were
placed respectively at about 200 yards in rear and in front of the
camps.

The principal object of the first was to prevent by a small force
the entry of small reinforcing detachments and supplies; that of the
second was to resist vigorous sorties by the defence, or sudden attacks
from the outside by strong reinforcing parties. For this purpose the
detached works of the line of countervallation were so disposed as
to cover the main depots, parks, roads, etc., and to be in defensive
relations with each other.

The great development of the line which must be occupied by the
besieger, owing to modern methods of fortification and the range of
rifled cannon, prohibits the construction of complete lines of circum-
and countervallation. The besieger constructs in their stead one or
more lines of detached works upon advantageous points, and covers the
intervening ground more or less thoroughly by patrols, outposts, etc.
He then so disposes his main force as to be able to concentrate enough
to meet any sorties of the defence; and, if necessary, detaches a
force, called an “_army of observation_,” sufficiently large to meet
any relieving army and defeat it; or hold it in check until he can
concentrate the besieging force with the army of observation, and meet
the relieving army in a favorable position. As a rule, this position
will be one well outside the besieger’s cordon of works; since the
latter by its extent will necessarily be weak to resist a determined
attack (Art of War, par. 258), and by its proximity to the work will
render possible the co-operation of the garrison and the relieving
army. This, under the circumstances assumed, would seriously endanger
the besieging army.

In opposing sorties from the work, however, the conditions which fix
the point of conflict are reversed, and place it as near the work as
practicable. The shortening and strengthening of the line of investment
by closing it in upon the work make it imperative to hold all ground
gained; and this is generally best accomplished by intrenching the
line of outposts with continuous shelter trenches, strengthened at
intervals by batteries of field guns, and supported by field works of
considerable strength, placed within accurate cannon range of each
other, but not exposed to the direct fire of the guns of the place.
Behind the shelter trenches the outposts, supports, and reserves,
strengthened when necessary by troops from other points of the line,
should be able to hold their own against all ordinary sorties. The
main line of field works serves to resist a general attack made by the
mass of the garrison.

Placing the first intrenchments further back exposes the outposts to
the confusion resulting from falling back, frequently at night or in a
fog, and also enables the besieged to seize upon ground from which it
may be very difficult to dislodge them.

To allow the different parts of the line to be rapidly reinforced,
good roads protected from the fire of the work, and well marked with
sign-posts, etc., must be opened between the adjacent divisions of the
besieging force, and all streams must be provided with bridges secure
against floods, ice, etc.

=73.= =Distance of the Line of Investment from the
Work.=--This will result from conflicting conditions. Reasons
already given, which need not be repeated, lead to establishing it as
near as practicable. On the other hand, the accurate fire of the heavy
guns of the place, and vigorous sorties by the defence, cause much
annoyance and great loss to a line drawn too near the work. The more
recent sieges indicate about 3000 yards from the most advanced works,
as the least distance for the line of investment in open country and
with an active defence. It may be necessary in some cases to increase
this to 4500 or 5000 yards; but with ground favorable to the attack,
and a weak and demoralized defence, it may frequently be drawn nearer.

=74.= =Strength and Composition of the Besieging Force.=--In
former sieges when the place held out until the inner keep was breached
and carried by the regular progress of the siege, the ratio of the
necessary strength of the attack to the defence was estimated at 7 or
8 to 1, this large ratio resulting from the excessive labor in the
trenches and the losses incurred on the close attack. Modern writers
(arguing largely upon theoretical considerations) have reduced this
estimate to 4 or 5 to 1. No attack on a thoroughly-equipped and
well-defended strong place having been carried through all the steps of
a regular siege since the introduction of modern arms, absolute data
upon this subject are lacking.

The besieging force at Strasburg was about 60,000, garrison about
20,000, total length of siege 49 days. The defence was very weak.
Belfort, besieging force about 32,000, garrison about 16,000. After
a siege of 100 days the approaches were at about 1200 yards from the
works, which capitulated by reason of the general surrender of the
French. At Metz the besieging force was 150,000 men; the garrison,
demoralized by the previous defeat at Gravelotte, surrendered 173,000
men. At Paris the investing force was about 180,000, and the garrison
nominally between 300,000 and 400,000, of which perhaps 30,000 were
disciplined and effective soldiers; the remainder being made up of
remnants of defeated regiments and bodies of the Garde Mobile and
Garde Nationale. The investment of Paris was complete on September
19, 1870; its surrender from exhaustion of provisions took place
January 29, 1871. Several sorties were made, but the general defence
was paralyzed by the character of the troops and inhabitants. At
Plevna the Turks had at the outset about 56,000 men, at the surrender
40,000. The Russian force suffered great losses in its assaults, but
by continual reinforcement had at the end of the siege about 120,000
men. The defence by the Turks was desperate, but generally passive.
One determined sortie was made immediately before the surrender. The
surrender resulted from exhaustion of ammunition and provisions. The
works were field works only.

At Belfort the investing force was at first but 10,000 and the line of
investment 25 miles long, giving but 400 men to the mile. This force
was subsequently increased to 20,000 men, and when the besieging army
had all arrived, to 32,000 men.

At Paris (1870) the line of investment was about 3 miles from the
line of the forts, and about 53 miles in length, the investing force
180,000, giving a mean of about 2 men to the yard. The distribution
was, however, about 4 to the yard on the left bank and 1⅓ on the right
bank of the Seine.

At Plevna the line of investment was 2¾ miles from the forts, its
length 43½ miles, the investing force 100,000 men, about 1¼ men to the
yard.

In each of these sieges the place finally fell under the attack of a
force, in no case equal to 2½ times the garrison; but inferences drawn
from this fact are apt to be erroneous, since none of these places
was well fortified according to modern methods, well garrisoned, well
supplied, and defended to extremity.

The results show, however, that under similar circumstances, which are
apt to arise in any modern war, the attack of a strong place which can
be completely invested by a force of two or three times the strength
of the garrison, may promise success; which seems to be assured if
the defence allows the besieging force to complete the investment and
thoroughly intrench itself.

On the other hand, tactical considerations would indicate that a
well-equipped army, of good morale, under an active and aggressive
commander, covered by a modern intrenched camp, should be able to
prevent the investment; and by taking advantage of its interior lines,
its heavy guns and its strong _points d’appui_, should be able to beat
in detail a force very much greater than itself whose fractions, by
reason of the extent of the line of investment, are necessarily not
within supporting distance of each other.

These advantages of the defence evidently disappear, as above
indicated, when the attack is allowed to complete its fortifications,
since under their cover a small force can check even a determined
sortie until a sufficient force to beat it can be concentrated.

From these considerations it is evident that an investment, once
completed, may be maintained by a force less than that necessary to
establish it in the first place (see Investment of Plevna, Pierron,
Méthodes de Guerre Vol. III, pp. 647 _et seq._).

=75.= =The Point of Attack.=--From the information originally
in possession of the besieger, supplemented by that obtained by
reconnoissance, a decision is made as to the fronts of the work or
the particular detached works of the intrenched camp upon which the
approaches are to be made. The portion selected in either case is
called the “_point of attack_.” To reduce an intrenched camp, it will
in general be necessary to capture at least two of the detached works
and to silence the artillery fire of one or more on each side of those
taken. In an attack upon a strongly-fortified enceinte, the least that
is usually undertaken is to breach and capture one front with its
adjacent outworks, and to silence the fire of those which enfilade the
approaches and parallels or take them in reverse.

In selecting the point of attack the first consideration is, that
when taken, it shall afford material advantage to the besieger and
give him a foothold from which further approaches may be driven, if
necessary. This condition being fulfilled, the choice will result from
a careful study of the nature of the works and site. Those forts or
fronts resting upon precipices, bordering deep marshes or deep and
rapid streams, or which are so placed that approaches upon them will
be swept in flank and rear by the fire of the works, which cannot be
silenced, are considered impregnable by the ordinary operations of the
siege. Most serious difficulties are presented by those in which the
adjacent works are so disposed and of such strength that they can be
carried only in succession and by regular approaches; those provided
with wet ditches in which strong currents can be produced, those with
dry deep ditches, those which are mined, and those which present long
lines nearly straight, or even concave to the attack, and covering a
front nearly equal or even greater than can be occupied by the trenches
of the besiegers.

When the parallels and approaches have to be constructed upon ground
sloping downward towards the work, in soil containing large stones,
or in which the rock is close to the surface, in marshy ground or
that containing much water or liable to be flooded, the difficulty
of their construction and defilade are evident. The point of attack
considered most favorable to the besieger is one which, fulfilling the
first essential condition, is more or less salient, so that it can be
partially surrounded, and which admits of the approaches being driven
toward it in favorable soil, over ground sloping gently from the work,
or gently rolling with the crests and valleys of sufficient difference
of level to afford cover, and running generally in the direction of
the parallels.

A favorable location for parks, etc., with free, safe, and short
communications between them, also has great weight in selecting the
point of attack.


SECOND PERIOD.

=76.= =First Artillery Position.=--Every siege begins with
a bombardment, which is designed, as previously stated, to drive in
the outlying posts of the defence, to silence, so far as possible, the
artillery annoy and wear out the garrisons of the works to be attacked,
to interrupt the communications between them, break up bomb and
splinter proofs, destroy magazines and depots, and, if the enceinte can
be reached by the artillery, to bring a fire upon the population which
will lead to or hasten the surrender of the place.

The considerations which determine the location of the batteries for
the general bombardment have already been given (par. 7), as well as
the construction of the batteries and screens used (Chap. IV.). For the
systematic attack, however, the necessity of dismounting or silencing
the guns bearing upon the proposed approaches introduces the additional
condition that the batteries should be so located that besides their
general effect each shall fulfil, so far as practicable, its special
design by bringing an enfilading or reverse fire upon certain fronts;
or, in connection with other batteries, shall keep down the fire of
certain fronts by a preponderance of direct fire. Many batteries which
fulfil these last conditions occupy their original positions during
the entire siege. The requisite concentration of fire upon the point
of attack and its careful regulation for the special object in view
will frequently restrict the arc occupied by the batteries below
that desirable for a general bombardment only; and will necessitate
a closer grouping of the batteries for their easier control by the
artillery commanders. This line of batteries first established is
known as the “_first artillery position_” (Pl. VIII., Figs. 80, 81).
As the batteries must be secure against the attacks of the defence,
they must of necessity be outside the besiegers defensive line. Their
distance in yards will result from the character of the defence and
may vary from 2000 or 2500 yards for a weak defence, to 3500 or 4500
yards for an active one. On account of their long range and the object
to be obtained by their fire, they are armed with the heaviest rifles
and howitzers available, supplemented with rifled mortars of as large
calibre as can be obtained, firing, if practicable, torpedo shells
charged with high explosives.

Batteries of field guns which have already been favorably located for
the defence of the heavier batteries against attack, or for firing upon
the more advanced works, may, by modification of their gun pits into
finished batteries (par. 44), be used in conjunction with the heavy
batteries of the first artillery position.

The total number of guns employed should be such as to give to the
attack a marked superiority over the defence at the opening of the
bombardment.

=77.= =Opening Fire.=--The batteries having been completed
and armed, the magazines finished and supplied, and the parks, depots
and communications put in such order that the batteries can be kept
fully supplied with ammunition; the fire of the batteries is commenced
simultaneously, the signal being given by a gun from some selected
battery. The fire once opened is continued day and night during the
siege, unless stopped by the commanding officer or from inability to
keep it up. It usually begins at daylight, in order to enable the
ranges to be corrected by the first shots, before the defence has
accurately located the batteries unmasked during the preceding night.
To open fire from a few batteries before the others are ready is
inexcusable, as it enables the defence to concentrate its fire upon
them and destroy them in succession. The targets of each battery and
gun and the rate of fire are prescribed before the fire is opened, and
these are changed only by subsequent orders or from sudden emergencies.
The fire is as a rule deliberate, seldom exceeding an average of 4
shots per hour for each gun by day, and 2 per hour at night. This rate
may be increased or diminished by the commanding officer for special
reasons and for a limited time.

The fire of the batteries is directed upon all the works of the place
within range, but with greater vigor upon the more important, and
especially upon those near the point of attack. The fire against
powder-magazines and storehouses should be uninterrupted, to prevent
the removal of powder and munitions. If the artillery of a part of the
work is silenced, the fire upon it may be slackened, but some fire,
especially vertical, should be kept up.

At night the fire is directed against the larger targets, such as
communications and covers, rather than upon the guns; but the fire
against the interior of the place (especially a city) is kept at about
the same rate day and night.

If preparations for a sortie are detected, the fire of the large
pieces is directed at the points of assembly, when known, and at the
openings through which the sortie is to be made. The field guns direct
their fire upon the troops in accordance with the tactical use of this
arm.

If the batteries of the first artillery position have the proper
preponderance over those of the place, they should soon clear away
the advanced posts, and keep down the fire of the works so that the
besieger may advance his outposts, control the exterior ground and
prepare to open the first parallel and establish the second artillery
position.

=78.= =Plan of Attack.=--By this time the reconnoissances and
surveys should be so far advanced and so thoroughly checked up that
the chief engineer will have been able to make, upon a large scale,
a map of the place and its surroundings with considerable accuracy,
and to locate upon it the proposed position of the first and second
parallels, the approaches, and the batteries of the second artillery
position. This map, with the accompanying memoirs, makes up the “_plan
of attack_,” which, when approved by the commanding general, serves as
a working plan for the prosecution of the siege, and is continually
corrected and added to as the siege progresses.

This map should be made in duplicate at least, and for accuracy in
the history of the siege should be corrected so far as possible by
redrawing or tracing, instead of by erasures.

=79.= =The First Parallel.=--The first parallel (Pl. VIII,
Figs. 80 and 81) serves as an intrenchment for the troops who protect
the second artillery position and who cover the workmen driving the
approaches. It also affords a covered communication between the
different lines of approaches.

Its length must be sufficient to cover all the batteries of the second
artillery position and protect their flanks; it must therefore extend
beyond the batteries which enfilade those faces of the fronts attacked
whose prolongations fall furthest out. Its flanks are usually more
or less refused, and terminated by strong earthworks. Emplacements
for batteries of field guns are provided at intervals to assist the
infantry in repelling sorties. When the length of the parallel is
very great, it is sometimes not continuous when first opened, but
the portions covering the groups of batteries are first made and
are subsequently connected. The ground between them is protected,
meanwhile, by a strong fire of small arms, field and other guns. When
communications covered by natural screens do not exist between the
first parallel, the batteries of the first artillery position, and the
parks, approaches are constructed at the same time as the parallel,
in sufficient number to give free passage to the troops, guns, and
materials.

These approaches (Pl. VIII, Figs. 80 and 81), as all others (par. 13),
are so directed as not to be enfiladed by the fire of the work, and
should be provided with portable or other tramways and cars, passing
switches being placed in the returns where needed.

=Its Distance from the Work.=--As a rule, it may be stated that
the first parallel is placed as near the work as possible. Most of the
batteries of the second artillery position are from 100 to 300 yards in
its rear, and the shorter their range the more effective is their fire.
The small-arm fire from the first parallel may also be an important
feature in modern sieges; to make it so requires the parallel to be
located within 1500 yards of the work, if possible. By placing the
parallel as near the work as possible, its length and that of the saps
are correspondingly reduced, the amount of work lessened, and generally
the fall of the place hastened. If an attempt be made to place it too
close to the work, however, the working parties will be discovered;
they will be within reach of strong sorties, and of the deadly fire of
small arms and machine guns; in consequence of which they may suffer
very great losses, be driven off, and the construction of the parallel
prevented. The minimum distance under the most favorable circumstances
is then about 600 to 700 yards. (This was the distance prescribed in
the day of smooth-bore guns, and was adopted as recently as 1870 at the
siege of Strasburg.) In an open, level country it may not be possible
to place the first parallel at a distance from the most advanced work
of less than 1800 to 2000 yards. When, however, it is necessary to
establish the first parallel at a very great distance, it will not, as
a rule, be made continuous, but in fractions covering approaches which
are driven forward. The first continuous parallel is then built at from
1000 to 1200 yards from the works, and behind this the second artillery
position is established.

=80.= =Opening the Parallel.=--The profile of the parallel
is one of those already given (Pl. I, Figs. 7-13), and it is traced
and constructed as described (pars. 14, 18, and 19), by simple trench,
flying sap, or full sap, as may be most advantageous. In some cases,
however, it is constructed by enlarging the line of shelter trenches
already made by the outposts. To cover the working parties while
excavating the trench, when the parallel is near enough the work to be
endangered by a sortie, the outposts are advanced to about 300 yards
in front of the line, the pickets and supports are posted respectively
at about 100 and 200 yards in their rear, and are covered by rifle
pits and trenches made for this purpose during the preceding nights.
To conceal from the defence, if possible, the proposed location of the
parallel, these trenches and pits are constructed by all the outposts
in front of their positions. The reserves are held 800 to 1000 yards in
rear of the flanks, and the whole covering force should be equal to 1/2
or 2/8 the garrison of the place if an active defence is looked for.

At daylight the trenches will be far enough advanced to protect the
covering force which will occupy them. This force is from this time
known as the “_guard of the trenches_,” and is relieved usually every
24 hours, the time of relief being so chosen as not to interfere with
the working parties.

The working parties are, as previously indicated, divided into reliefs
of 4 or 8 hours.

For continuous work the besieging force should be large enough to allow
each man, after being one day in the guard of the trenches and one day
in the working party, to have one day in camp.

=81.= =The Second Artillery Position.=--By the second
artillery position previously referred to is meant the position
occupied by the guns of the attack, placed in batteries, accurately
located for breaching, enfilading, counter-battering or other specific
duty. These batteries are usually of the class described under the head
of “exposed sunken batteries” (Plates V, VI, VII), and are constructed
behind or in the parallels, as explained in pars. 48 to 55. When behind
a parallel they should be, if possible, at least 150 yards from it in
order that the blast of the guns shall not interfere too much with the
occupants of the parallel.

=82.= =Counter-batteries=, designed to dismount guns or
destroy embrasures of earth or masonry at ranges from 700 to 1000 yards
by direct fire may well be armed with 4½ or 5 inch rifles, since their
projectiles have sufficient energy for the desired result, and the
guns admit of a more rapid and long-continued fire than do those of
greater calibre. The batteries must be so placed as to look through the
embrasure attacked, and the number of guns pitted against any battery
must considerably exceed that in the battery.

Counter-batteries designed to silence by direct fire guns in turrets
or behind shields must be armed with guns of large calibre, mounted
with the best available cover, and must be aided by rapid fire guns
of moderate calibre, designed to disable the turret guns either by
embrasure shots or by oblique shots penetrating the parts which project
from the turret.

=83.= =Enfilading batteries= act in conjunction with
counter-batteries or independently; they are designed to take the
faces in flank or slightly in reverse, but are of necessity at times
limited to a slant fire. They are located as nearly as possible in
the prolongation of the terre-pleins. When the salients are obtuse
these prolongations lie near the adjacent faces for some distance, and
consequently the only possible emplacements of enfilading batteries
will give ranges which may vary from 1000 to 4000 yards. They are armed
with cannon of sufficiently large calibre to make their projectiles
efficient even at moderate velocities, and, when the faces enfiladed
are well provided with traverses, the charges are reduced so as to
give to the projectiles a large angle of fall. When the batteries are
on commanding heights higher velocities may be used.

=84.= =Breaching batteries=, except those established on
the crest of the counterscarp, can only breach the walls of modern
forts by “curved” or “indirect” fire. To obtain the necessary angle
of fall with the requisite accuracy and energy of blow, the guns must
be of considerable size and placed at comparatively long range; the
projectile must graze the crest of the glacis and strike the scarp wall
at an angle not too oblique. Experience seems to indicate that the best
effects are obtained, all things considered, when the vertical plane of
fire makes an angle of from 55° to 60° with the face of the scarp wall.
The distance of the battery from the wall to be breached is usually
from 1000 to 1500 yards.

The same considerations govern the construction and armament of
batteries designed to destroy réduits, barracks, gorge walls, city
gates, magazines, depots, bridges, locks, etc., etc.

=85.= =Batteries of rifled mortars or of howitzers for vertical
fire= should be so located, when possible, that the longest
dimension of the target will be in the direction of their fire. The
effect of their projectiles is greatest when they can be fired at
elevations, of 60° to 70° and with large charges. These considerations,
combined with those of good cover and easy supply, will govern their
location.

=86.= =Opening and conduct of fire from Second Artillery
position.=--The batteries which are ready on the morning of the
completion of the parallel open fire simultaneously upon the work,
and are supported by those of the first artillery position still
armed. The same rules govern the fire of the first and of the second
artillery position.

When the defence combines a number of batteries to silence one of the
attack a heavy fire is concentrated upon these batteries by those
from which the fire has been diverted. New batteries unmasked by
the defence, or established in intermediate or other works, should
receive prompt attention from the attack, with a view to silencing
them if possible before they correct their ranges. It is of the first
importance that the superiority of the artillery fire of the attack
shall be established at the opening of fire from the first artillery
position and be maintained throughout, and that the defence shall be
prevented from repairing any batteries which have been silenced. To
this end a few guns will keep up a slow fire upon these batteries so
long as it may be necessary.

Every gun of the defence must, if possible, be kept under a heavy fire,
and the fire upon the enceinte must be opened at the earliest possible
date and continued day and night, as previously described.

=87.= =Musketry fire= will be opened as soon as a parallel is
established at such distance as to make it effective; and this may be,
for a well-regulated fire of sharpshooters, at ranges of 1200 to 1500
yards, or in some cases even greater.

=88.= =The Advance from the First Parallel.=--It is assumed
that the fire from the first and second artillery positions will
silence almost completely the artillery fire of the work upon the
fronts attacked; but the defence will still be able to develop when
necessary a strong musketry fire, aided at times by machine and
rapid-fire or even some field guns. Consequently, the advance from the
parallel must be under cover.

Approaches are, therefore, broken out from the parallel and pushed
forward towards the work, the workmen being protected by the fire of
the guards of the trenches. Usually at least three lines of approaches
are constructed, concentrating upon the point of attack and following
generally the lines of the capitals of the adjacent salients.

When attacking a line of detached works two or more lines of approaches
may be constructed towards each work attacked. The approaches are run
in zigzags, each branch so directed as to pass a short distance (30
or 40 yards) outside the most advanced work of the defence from which
it could be enfiladed; at each change of direction of the zigzags a
return of 10 or 20 yards is made to cover the approach in rear (Pl.
VIII, Figs. 80 and 81). The length of the branches is so regulated as
not to mask too much of the front of the parallel; they consequently
grow shorter as they approach the work and vary ordinarily between 200
and 50 yards, seldom exceeding 100 yards when near the work. The heads
of the different approaches are advanced at about equal speed so as to
afford mutual support.

=89.= =The Second Parallel.=--The second parallel is located
nearer to the first parallel than to the covered way, sometimes very
much nearer. It is constructed and occupied by the guard of the
trenches. The principle followed is that the guards of the trenches
shall always be nearer to the head of the sap than is the enemy
in his most advanced place of arms; so that, in case of a sortie,
the advantage will lie with the besieger. The flanks of the second
parallel are refused and strengthened like those of the first, or are
even carried back to the first parallel, to guard them against flank
attacks.

The second parallel having been completed and occupied, serves as a
base for further advance, which is conducted according to the same
methods, “_demi-parallels_” (Pl. VIII, Fig. 81) being run out to the
right and left of the approaches when they are well advanced beyond the
second parallel. These demi-parallels are sometimes joined, forming
a third parallel, from which the approaches are advanced as before,
with additional parallels when needed, until the foot of the glacis
or exterior of the counter-mines is reached. The number of parallels
is determined by the distance at which the first is established and
the vigor of the defence; formerly three were considered all that
were needed, and this number was used at Strasburg, 1870. At other
modern sieges a larger number has frequently been required. At
Belfort (1870-71) the third parallel was established at 1200 yards
from the place. Five parallels were used at the siege of Fort Wagner
(July-September, 1863).

The approaches are driven in zigzags by simple trench, flying or full
sap, until the direct advance becomes equal to about one third of the
length of trench; and from this point they are driven directly upon
the work by double-traversed sap (Pl. III, Figs. 28-35), the latter
being, as a rule, used only in advancing from the foot of the glacis,
or during the third period of the siege.


THIRD PERIOD.

=90.= =The Third Period of the Siege= frequently called the
“_close attack_,” includes all the steps between establishing the last
parallel and the surrender of the place. These are the capture and
crowning of the covered way, breaching the scarps and counter-scarps,
passing the ditch, capturing and crowning the breaches of the outworks
and main works in succession, and the final reduction of the interior
retrenchments, or keep.

All these operations are carried on within close and deadly range of
small arms and shells of Coehorn mortars, and many of them within
range of hand grenades and upon ground honeycombed with mines and
countermines, or liable to be flooded or inundated. They are slow in
progress, uncertain in results, and require an extravagant expenditure
of men and material. They can be pushed to a successful issue only when
the artillery fire of the place is silenced and its small-arm fire is
almost completely kept down by the fire of the attack.

The conditions of modern warfare are such, however, that by the time
the attack has reached the foot of the glacis the losses and exhaustion
of the garrison are frequently so great as to preclude an obstinate,
close defence; and, in the majority of cases, the place is compelled to
surrender before the close attack is commenced.

=91.= =The capture and crowning of the covered way= is
accomplished by _assault_ or by _sap_. The former is an extremely
hazardous and bloody operation, which all authorities unite in
condemning, and which should be undertaken only in extreme cases. It
is carried out usually at night, by forming an assaulting party in the
parallel, who rush forward to the crest of the covered way; capture, if
possible, its guards, and under any attainable cover open a fire upon
the crest of the work. All available small-arm and machine-gun fire
combines with this to keep down the fire of the defence; and under
cover of this fire the working parties construct, by flying sap, a
trench crowning the covered way, and the communications between it and
the parallel.

The trench is occupied as soon as it affords cover, and is subsequently
completed and prepared for the reception of its guns and infantry guard.

In crowning the covered way by sap (Pl. IV, Fig. 36), the saps are
broken out from the parallel, a circular place of arms is constructed,
which gives additional communication and serves as a depot for trench
materials, the traversed sap is pushed forward, and the covered way
crowned as previously described (par. 36). It will frequently be
necessary to run out at right angles to this sap short branches of
parallels (Pl. IX, Fig. 83), to serve as places of arms, or as trenches
of departure for mines or galleries, for underground warfare or for
breaching walls.

=92.= =Breaching the Scarps and Counter-scarps.=--The
counter-scarp, as a rule, and the scarp at times is breached by mining.
(See Military Mining, pars. 91-93). When practicable, however, the
scarp is breached with artillery and preferably by guns of the second
artillery position; since a breaching battery on the crowning of the
covered way, which must be provided with most ample splinter-proofs to
protect the gunners from flying splinters of masonry and shot, is in
general constructed only with great losses and delays; and the guns in
this position must be fired under great angles of depression, requiring
very deep embrasures to avoid exposing the cannoneers. When the ditch
is deep and narrow it may be necessary to blow down the counter scarp
and part of the glacis, in order to expose the scarp-wall to the fire
of the breaching battery, whether on the glacis or at a distance. This
necessity should be foreseen and provided for in locating the batteries.

A full or semi-detached scarp-wall will be breached when the battery is
on the glacis by making vertical cuts at the ends, and a horizontal cut
at about one third or one fourth its height from the bottom, and then
firing shells into the part to be brought down, continuing the fire
until the large masses of masonry are broken up, and the slope is made
gentle and smooth enough to admit of easy ascent. A detached scarp-wall
will be breached by a glacis battery, or any scarp-wall by a distant
battery, by continued battering, which will not only knock down the
wall, but also break up the fragments and make a practicable ramp.

=93.= =The Capture and Crowning of the Breach.=--The decision
as to whether the breach shall be captured and crowned by _assault_
or by _sap_ will be governed by considerations similar to those which
determined the character of the attack upon the covered way. The
difficulties and dangers of the assault are perhaps greater than in
that case. The =assault=, if undertaken, will be carried out in
a similar manner, previous preparations having been made by making a
practicable breach at least 25 to 30 yards wide, a practicable descent
into the ditch of equal width, and a covered place of assembly for the
working party and a depot of trench materials in immediate proximity to
the breach.

The artillery defence of the ditch, whether from caponières, flank
embrasures or casemates, or from adjacent works, must of course be
silenced before crossing the ditch either by assault or by regular
approach. This is accomplished by counter-batteries on the glacis, by
heavy field guns located in temporary batteries in the trenches, by
mines, or by overhead or indirect fire from the distant batteries, or
from light mortars in the advanced trenches, as may be necessary.

If the interior arrangement of the work is known by the besieger the
assault maybe made by night; but if it is unknown, the confusion
resulting from a night attack will be so great as to render its success
almost hopeless, and the assault will have to be delivered by day.

The assaulting columns will be made up of an advanced line of
skirmishers (selected men, good shots, and generally volunteers),
followed by a working party of sappers to clear away obstacles,
these closely followed by the columns of assault; while the supports
and reserves move forward in the trenches to join in the assault as
circumstances require. The troops who first gain the crest establish
themselves there and hold the breach until those coming after them
pass and engage the garrison, while some detachments strive to capture
and open one gate or more to admit the reserves. The assaulting force
should be equal at least to once and a half or twice the garrison, and
simultaneous attacks should be made upon other breaches or accessible
parts of the work to divide the attention of the defence.

These false attacks are sometimes successful, and preparations for
taking advantage of this contingency should not be omitted. The
subdivisions of the assaulting force should each receive explicit
instructions as to its special object, and under no circumstances
should their lines of march intersect. Unmistakable signals of
recognition should be prescribed to prevent conflicts arising between
the different parties meeting within the work. The bombardment
preceding the attack should not cease, and thus notify the defence
when the assault is to be made; but the guns should be directed upon
adjacent parts of the work until the assault penetrates the work or is
repulsed.

=94.= In the =attack by the sap= the method of crossing the
ditch adapted to the circumstances is used (pars. 39-41, Pl. IV, Figs.
37-41) and the sap is started at the foot of the breach, driven up it,
and the breach is crowned according to the methods previously described
(par. 36).

The sappers are protected from small sorties by the fire from the
crowning of the covered way and any other points bearing on the head
of the sap. Fireballs, electric lights and other means will be used
during the night to light up the parapets of the work and expose the
defenders, in this as in the previous operations of the siege. The
crowning of the breach will be extended and converted into a place
of arms, from which further sapping can be carried on in a similar
manner, until the breach in the last retrenchment is crowned and the
preparations for the final attack upon the garrison are made, or the
place surrenders. If the garrison takes refuge in an interior keep and
continues the defence the keep must be reduced by similar methods.

=95.= =Additional Operations in the Attack of an Intrenched
Camp.=--The operations above described are those necessary to
reduce a fortified place of the older type, or a detached work of an
intrenched camp. The latter, though of less extent and with a smaller
garrison, offers as a rule greater resisting power, since it is usually
subject to front fire only, has more complete bomb-proof cover, and is
free from the presence of non-combatants.

While a great advantage is gained by the capture of two or more of
the advanced forts, the resisting power of the intrenched camp is
by no means destroyed. These forts are subject to the fire of the
collateral works, of which frequently two or more must be silenced
before a further advance can be made. The beleaguered army may still
be in condition to recapture the forts by vigorous assaults; and in
almost every case, before the fall of the works of the outer line, a
line of provisional fortifications of high resisting power, connected
by trenches, will have been constructed by the defence in rear of the
captured works, with its flanks secured by the collateral works of the
outer line. An assault against works of this class offers no prospect
of success. The besieger is therefore obliged, as soon as he captures
a detached fort, to put it in condition to withstand the assaults of
the besieged army and to afford protection from the artillery fire
of the collateral works, and then to push forward his approaches
against the successive positions prepared by the defence, which will
as a rule present a front equal to or greater than that which can be
occupied by the attack. The gorges of the captured works are repaired
and strengthened, covered communications are made through the faces,
either through the breaches or in more convenient points, traverses
are repaired or built to protect against the fire of the collateral
works, and the captured works are connected by trenches which afford
emplacements for batteries and form a new parallel from which the saps
can be driven in attacking the intermediate works. Simultaneously with
this attack, it is usually advisable to advance from the flanks of the
first or second parallel upon the forts of the outer line which form
the flanks of the intermediate line. The approaches can generally be
driven with comparative ease owing to these works having already been
partly disabled and now being subject to a flank and reverse fire from
the newly-established batteries.

The flanks of the intermediate line being turned by the capture
of these works, a portion or the whole of it will of necessity be
abandoned. The subsequent operations up to the capture of the enceinte
will be of the same nature as those already described.

=96.= =Occupation of a Conquered Place.=--Immediately upon
the fall of the place it must be occupied by a force (chosen when
possible from the reserve which has not participated in the final
assault) sufficient to control not only the inhabitants, but also the
disorderly soldiers of the attacking force. All pillaging, wanton
destruction, and abuse of the conquered must be restrained with a
strong hand, immediate and exemplary punishment being inflicted upon
offenders. The orderly portion of the defenders must be protected,
and such steps taken for supplying their needs as humanity requires;
while the disorderly ones must be repressed with such severity as may
be necessary. So soon as order is established a careful inventory of
captured property is made, and it is stored subject to the orders of
the government. When the possibility exists of the place being attacked
or besieged by the enemy, all its resources which are available for
defence are collected, repaired, and stored for use.


VAUBAN’S MAXIMS.

=97.= Marshal Vauban, the great French military engineer (born
1633, died 1707), whose experience and success in sieges made him the
great authority on the subject, formulated certain maxims for governing
the conduct of a siege, the observance of which led to almost certain
success, and the departure from them almost invariably resulted
disastrously. The most of these are as applicable to sieges of to-day
as they were to those of his own time. The following[6] bear upon the
second and third periods of the attack:

1st. To delay the opening of the trenches until the besieging forces
are all well posted and made secure by fortifications from an attack
either from the garrison or from a succoring force; and until
everything requisite for carrying on the work vigorously has been
collected and is ready at hand when wanted.

2d. To make a single attack rather than a double one, unless the
two attacks can be well connected and the besieging force exceeds
considerably in strength the garrison. This, as a matter of course,
excludes false attacks, and double separate attacks, unless the
superiority of the besieging force is very great. By a single attack
is understood one by which it is proposed to gain possession of the
main work by a single breach at some point; by a double attack it is
proposed to effect two breaches of the main work. The advantage of the
latter lies in forcing the garrison to divide their strength for the
defence of the two breaches, whilst the assailing forces, being under
one leadership, can at any moment concentrate if necessary upon the
point most favorable to their assault.

3d. To embrace within the parallels and approaches all the defences
which bear upon the site to be occupied by the besieger’s works, in
order to have secure positions for establishing the batteries that may
be required to silence the fire of these defences.

4th. To multiply the approaches, with the view of giving mutual
support, less encumbered communications, and dividing the fire of the
defences, which, if concentrated upon a single one, might soon destroy
it.

5th. To throw up at least three main lines of parallels, placing
them in the best positions for mutual support and for guarding the
approaches and batteries from sorties of the besieged.

6th. To avoid attacking a point upon which the approaches can be run
only on a narrow front, or one which can only be approached over marshy
ground, or on causeways.

7th. To be careful not to push forward any portion of the trenches
until they are well flanked and protected by trenches in their rear,
which are completed and occupied by troops.

8th. To avoid encumbering the approaches with trench materials, tools,
workmen, or troops; placing all of these in the parallels, on the right
and left of the approaches, so as to be ready at hand when wanted, and
to be rapidly sent forward through the trenches of the approaches,
which should be kept free for this purpose.

9th. To place the ricochet (enfilading) batteries in such positions
that they can have an enfilading and slant reverse fire upon the guns
of the defences to be attained by them.

10th. To refrain from opening fire from any series of batteries until
it can be done at the same moment from all of them.

[In connection with this and other siege operations, Vauban remarks
that precipitation in sieges does not hasten the close of them, but
often prolongs them and renders them more bloody.]

11th. To employ the fire of the batteries and trenches, rather than
open assaults, to drive the besieged from their defences, before
attempting to occupy them by the besieging force.

12th. When it is decided to make an open assault, to do so by day, if
there is no portion of the fire of the defences which bears upon the
point to be carried that is not completely kept under by the fire of
the batteries and trenches; but, in the contrary case, when the fire of
the defences is not completely kept under, to make a night assault.

13th. Not to attempt an obstinate resistance to an open assault of the
besieged upon any unfinished portion of the trenches; but rather to
withdraw the workmen and the few troops near them to some point behind
the parallel immediately in rear, and then to open a vigorous fire from
it upon the assailing force.

14th. To keep within the cover of the parallel when the assailant is
advancing to the assault, and leave him to expose himself to its fire
as long as he pleases, and then, when he is well cut up, and has got
thrown into confusion, as he necessarily will at night, in the trenches
that he may have carried, to fall upon him with the bayonet and drive
him out.

15th. Not to push such charges too far from the parallel, but to retire
promptly, so soon as the assailant has fairly taken to flight, within
the cover of the parallel, so as not to draw the fire of the besieged
works.


JOURNAL OF THE ATTACK.

=98.= In connection with the plan of attack previously referred
to (par. 78), a complete _Journal of the Attack_ will be kept in which
will be recorded day by day a detailed record of the daily progress
of the siege, giving the day and hour of starting and completing each
battery, parallel, approach, etc., with their daily progress, dates
of opening fire from each battery, and, generally, every incident
connected with the siege. This journal will be supplemented by journals
kept by the chiefs of engineers and artillery, in which will be
consolidated the daily reports of all subordinate commanders of these
respective arms, giving the expenditure of ammunition, the performance
of the guns, carriages, etc.; the modification made in details of
parapets, batteries, magazines, etc., with their value; the results of
trials of new devices, and special reports upon any points connected
with the siege. These journals will be carefully preserved and copies
transmitted to the War Department from time to time for future use.




CHAPTER VI.

THE DEFENCE.


=99.= =Preliminary Considerations.=--The defence of a
fortified place is entrusted to a commanding officer, who, when the
siege is established, is generally known as the “Governor of the
Place.” His duties become more exacting and his powers more absolute
from the beginning of hostilities until the place is invested and
cut off from communication with the exterior, when, since the whole
responsibility of the defence rests upon him, his powers over
both the garrison and the inhabitants of the place, of necessity
become autocratic in all matters affecting the defence, directly or
indirectly. He, of course, avails himself of the counsel and advice of
his subordinate officers and may make up a “Council of Defence” from
his second in command and the commander of the engineers and of the
artillery; but the ultimate decision of all questions must rest with
him alone.

During peace and after the beginning of hostilities up to the near
approach of the investing force, the civil authorities retain their
ordinary jurisdiction, unless martial law is declared by proper
authority; but after the place is invested, martial law (or state of
siege) exists from necessity, and the police power, the control of
provisions and supplies of all kinds, public and private, buildings,
animals, vehicles, etc., and everything necessary for the defence of
the place fall into the hands of the governor, who also is empowered
to direct who shall be sent out and who shall be retained within the
place, and what necessary service or labor shall be performed by the
inhabitants. Having been selected for these onerous and exacting
duties, he, under no circumstances, allows himself to be cut off
from his post, and is therefore debarred from leading his troops in
person in the active operations outside the work or exposing himself
unnecessarily or recklessly during any period of the siege.

=100.= =The Garrison.=--The garrison should consist of
artillery and infantry, and, in an intrenched camp, of enough mounted
troops for escort, messenger, and a limited vedette service.

The strength of the infantry is generally regulated so as to give a
suitable garrison to each detached work, and about 1½ to 2 men for each
yard of the front of attack. The artillery is allowed about 12 men for
each gun. The number of engineers is determined for each place by the
probable amount of engineer work that will be required. These troops
make up about one-third of the entire force.

A general reserve of all arms (principally, however, foot troops)
makes up the other two-thirds, and is held as “a fighting force”
for preventing the investment of the place, or for breaking up the
investing lines when established. This reserve is called upon for
work on the front of attack or in the trenches only when it cannot be
avoided.

In smaller places the portion of the garrison called upon for the
outer line of defence may be increased to one-half or two-thirds, and
the general reserve be reduced to one-half or one-third of the entire
force. When the investment is strongly established the general reserve
will usually be combined with the other troops.

The troops engaged on the front of attack are usually assigned to the
different sectors of attack and are divided into reliefs (ordinarily
three), each relief having as a rule a tour of one day in the front
lines, one in the immediate supports, and one in the reserve and
in interior fatigue duty. The Governor, however, so regulates the
details as to impose upon the troops the least work consistent with an
energetic defence.

=101.= =Armament.=--The guns for arming the place should be
placed in position or in store within the works before the beginning
of hostilities. There should be mounted in commanding positions a
sufficient number of high-power guns to hold the enemy’s first works
at a distance and to fire upon his camps, etc., if placed too near.
In addition to these, a full supply of light guns, including machine
and rapid-fire guns, should be at all times equipped and supplied for
immediate use in meeting an assault or surprise. Their emplacements,
platforms, etc., should be in readiness for use at any moment.

In large places and for an active defence there will be needed also
enough field-guns to properly equip the general reserve (about 4 guns
per 1000 men). These should be considered a part of the equipment of
the reserve.

It being, from economical considerations, impossible to supply guns to
fully arm all the fronts of a place, enough only are usually provided
to thoroughly equip the sector of attack and to replace those disabled.
These are stored within the place where they are secure against
deterioration or injury, and are mounted in the sector of attack
when it is definitely determined. The numbers of high-powered guns,
howitzers, mortars, and machine and rapid-fire guns needed must be
determined from the size of the place, its garrison, and the character
of attack which may be expected.

=102.= =Ammunition, Provisions and Supplies.=--A plentiful
supply of ammunition, especially of projectiles, for all the guns
should be kept constantly on hand. The projectiles, which may be stored
for an indefinite term without deterioration, may be distributed in
magazines in proximity to their batteries; the powder should be so
stored as to preserve its properties, and be distributed to the service
magazines at such times and in such quantities as may be necessary.
Other equipments will be stored and handled in accordance with the same
principles.

The utmost care will be taken in storing and issuing the provisions and
supplies belonging to the troops; and in cases of necessity during the
siege the sales of provisions to the inhabitants by the dealers will be
regulated, both in prices and quantities, by the military governor.

=103.= =Sanitation and Hygiene.=--The most rigid sanitary
measures and rules of hygiene should be enforced from the beginning of
the siege, under the direction of the military governor, whose medical
officers should join with the health officers of the place (if any
exist) in guarding not only the troops but all the inhabitants from all
avoidable causes of epidemic diseases. Extreme rigor in carrying out
these regulations in not only allowable, but is most urgently required.

=104.= =Preparations for Defence.=--An active defence
being presupposed, all possible measures for its execution should be
taken before the near approach of the enemy interferes with them. The
principal ones are as follows, viz.: Advanced posts are established
as far from the work as is prudent, say 3500 to 4000 yards, placed at
points which may be easily defended or which would be advantageous
positions for the enemy’s batteries, etc. These, when possible, should
be so placed that the ground between them is swept by their infantry
fire and by the artillery of the place. They should be provided with
good cover for the troops, and parapets for infantry and field-guns.
When not naturally strong, field-works should be built. Quarries,
ditches, sunken roads, villages, woods, etc., should be taken advantage
of, either as points of defence, passive obstacles, or covers for
communications, as may be best. Lines of retreat to the work as
secure as possible from hostile fire should be provided. All supplies
in the vicinity of the work which will be useful during the siege
should be collected and taken into the place. Means of communicating
with the exterior by telegraph, telephone, signal flags, lanterns
and heliotropes, carrier-pigeons and balloons, should be secured.
Search-lights for illuminating the exterior should be obtained, and
as soon as practicable bomb-proofs and shelters for the inhabitants
should be prepared in the body of the place; and in connection with the
civil authorities the fire department of the place should be organized
and taught how to extinguish fires with dry earth and by pulling down
buildings when water is not available.

The service of security and information should be extended to the
furthest possible limit, not only by outposts, etc., but by telegraph
operators and reliable correspondents at long distances from the place;
and preparations should be made to retard the approach of the enemy by
the destruction of the roads, bridges, etc.

=105.= =Defence during the First Period of the Siege.=--Upon
the approach of the enemy each work should receive its permanent
garrison, and the fighting reserve should go out to occupy the advanced
posts and to take full advantage of its interior lines to hold him back
and punish any careless or ill-advised advance, being aided in this
when possible by the fire of the heavy guns of the place. Care must
be taken to avoid too great dispersion of the troops, and exposing
advanced parties to being cut off and captured by pushing them too far
to the front or holding their positions too long; but no opportunity
should be missed of attacking and destroying or beating back hostile
detachments when tactical conditions warrant it.

The defence during the first part of this period differs but little
from the ordinary defence of an intrenched battle-field. The principal
differences arise from the fact that the flanks of the advanced lines
and the lines of retreat to the work are so well covered that with
ordinary precautions they may be considered secure, and all energies
may be directed to meeting the front attack and executing offensive
returns. So soon as the point of attack selected by the enemy becomes
known the advanced positions may be more fully manned and equipped;
trenches with inconspicuous parapets, or preferably without any, may
be made to cover the infantry, field-guns, and sometimes siege-guns on
travelling carriages. These positions may be, as previously stated,
2500 to 3000 yards from the permanent works, and the intervals between
them may be swept by the heavy guns of the latter.

If these positions can be so strongly held as to compel the besieger
to attack them with his heavy guns, he will be compelled to establish
his first artillery position at a very great distance--possibly 5000
to 6000 yards from the work. [At Belfort, 1870, positions of this kind
were taken only after seventy-seven days of siege.]

As the advanced positions may be subject to the fire of the heaviest
class of siege-guns, if any parapet is made it should be of the nature
of a glacis of gentle slope and little command. Infantry trenches
should be made narrow and deep as a protection against shells and
shrapnel (Pl. IX, Fig. 84), and gun-emplacements should be as small as
practicable and almost entirely in excavation, for the same reason.
Positions so prepared suffer very little from gun-fire, and will
frequently require attack by systematic approaches.

An efficient outpost service must be maintained in front of these
positions to prevent their being taken by surprise.

When but a limited number of troops are available for defence it is
of course impossible to push out the advanced posts so far to the
front. In all cases, however, they should be placed at the greatest
practicable distance.

=106.= =Opening of Artillery-fire by the Defence.=--The
artillery-fire of the defence should be opened upon the besieger’s
batteries, etc., before they are ready for action, so that the ranges
may be obtained and the tables of fire corrected without interference
by the hostile fire. If this can be accomplished, the increased effect
due to the accurate fire of the defence may more than counterbalance
the numerical superiority of the attack, and result in preventing the
completion of some of his batteries and in silencing others.

If, on the other hand, the attack anticipates the defence in obtaining
the range, his superiority in numbers and accuracy will frequently
necessitate abandoning some emplacements and mounting the guns in
others, where they may be used in the later stages of the siege.

=107.= =Defence during the Bombardment and Assault.=--The
amount of ammunition which can be profitably expended by the defence
during the bombardment must be determined by the quantity on hand and
the advisability of exposing by their fire the positions of the guns.

The infantry troops and the light guns are held under cover, ready to
be moved forward to meet the assault if made. Special care will be
taken to avoid being deceived by false attacks; and the assault, if
made, will be met as previously described (par. 6).

If the attack is repulsed, an offensive return may be made by the
general reserve, assisted, when necessary, by the local reserves of
the front of attack; but the garrisons of the permanent works should
not be withdrawn from them for this purpose, as it is always possible
that they may be needed to protect the works and cover a retreat. If
the assault succeeds, the defenders will retire to their positions in
rear, from which the strongest possible fire will be directed upon the
pursuing troops and upon the captured position to render its possession
difficult or impossible. If the assailants are driven off, the position
is immediately reoccupied by the defence.

=108.= =Defence during the Second Period of the Siege.=--The
point of attack having been definitely determined by the preliminary
steps of the attack in opening the parallels and establishing the
batteries, the besieged will at once proceed to mount extra guns
and reinforce the troops upon the threatened fronts. He will keep
his outposts or sentinels during this and the subsequent periods as
far to the front as possible, to prevent surprises and to keep out
reconnoitring parties spies, etc., etc.

From observations previously established, he will locate at the
earliest possible moment the batteries, etc., of the attack, and will
prevent their completion and arming by the use of shells and case-shot
charged with high explosives, fired from howitzers and mortars. He will
use his long guns for counter-battering those of the besieger, and
generally for direct fire upon exposed targets.

By taking the initiative he may frequently obtain the upper hand in
the artillery duel, and possibly be able to prepare the way for strong
sorties, and the destruction of the besieger’s works. In any case he
must at this stage develop the full fire of his guns and work them to
their maximum value.

If, however, the superiority of the artillery of the attack is
pronounced, and it becomes impracticable to serve any battery
advantageously, it will be better to dismount its guns and remount them
in other positions, as indicated in the preceding paragraph (par. 106).

All efforts will be made to prevent the construction of the parallels
and approaches, their positions being discovered by the use of the
search and other lights, and the work upon them retarded by direct and
curved fire. For the latter light rifled mortars promise to be very
effective.[7]

The trenches connecting the detached and intermediate works will be
strengthened, and counter-approaches will when practicable be driven
out to afford positions for enfilading the approaches. The field and
machine guns will be held in constant readiness for use, and will
be brought into action at every favorable opportunity; but will be
withdrawn and placed under cover previously prepared so soon as the
fire upon them becomes too severe to be endured.

Meanwhile a new position in rear, with its flanks supported upon the
adjacent detached works, will be selected and made ready for defence in
case the front line is taken.

The general reserve will be used for offensive movements, which are
made whenever favorable opportunities arise, particularly in making
counter-attacks after unsuccessful assaults.

=109.= =Defence during the Third Period.=--The defence of
the detached works of an intrenched camp during the Third Period will
be conducted, so far as the general reserve is concerned, in very much
the same manner as during the Second Period; but in the immediate
defence of the detached work itself, owing to the close approach of the
besieger, its character will change. The artillery except the field
and machine guns will be silenced, and the latter will usually be
only available for defending the ditches and for repelling assaults.
Light guns will, however, be held in readiness for temporary use when
practicable.

The outposts will of necessity be drawn in and replaced by a chain of
sentinels along the parapets of the covered way or the main parapet,
who will pick off the besiegers at every possible chance, and will be
reinforced by the rest of the garrison when an assault is imminent.
All flanking defences will be kept in as good condition as possible,
and in readiness to prevent the crossing of the ditch, or to repulse
an assault. Grenades and shells will be kept in readiness to roll into
the ditch, the breaches will be obstructed and mined if practicable,
counter-mines will be brought into play, and all other possible
measures taken to retard the approach of the besieger to the breach
and to repel his assaults. When, however, the work is reduced to such
a state as to make its defence hopeless, it should not be held at the
expense of great losses to the defence, unless the besieger’s works can
be considerably delayed by doing so. When the position consists of an
enceinte with ordinary outworks, the investment during the Third Period
of the siege will be closer, the opportunities for using the general
reserve will usually disappear, and its troops will be merged with
those of the general defence.

When, in this case, the place is to be defended to the last, all
measures will be taken for the defence of the breach; and after this is
carried, for the final defence of the inner retrenchments or keeps.

The tactical handling of the garrison for this purpose is in accordance
with the principles already laid down (par. 6, and Art of War, pars.
282-84.)

The sorties recommended during a siege are, when made by the general
reserve and in large bodies, usually carried out by moving the troops
from the collateral works upon the flanks of the besieger’s works. In
the close attack, however, they may be made by small parties moving
to the front from the nearest outpost or salient. The object in all
cases is the same--to destroy the enemy’s works, delay his advance, and
inflict upon him all possible loss.


THE CAPITULATION.

=110.= Should the defensive policy of the state not require a
place to be held to extremity, the governor must be fully informed
of the fact, and the extent of the defence and the conditions of
capitulation must be fully understood by him before the investment.
As a rule, however, no excuse will be received for the surrender of a
place until every means of defence is exhausted, and further resistance
is not only hopeless, but impossible, the only rule which can guide
the governor being that “one additional day of defence may be of
incalculable benefit to his country.” The old rule, copied from the
French, but no longer observed by them, requires the defence to sustain
at least one assault on a practicable breach in the body of the place.

Within recent years, in civilized warfare, no cases have occurred in
which such assaults have been made, the places having been reduced by
the more distant attack; but assuming such an assault to be repulsed,
it will not justify the surrender of the place so long as a possibility
of repulsing similar assaults exists. The garrison must withstand all
attacks of whatever nature to the last extremity, and continue the
defence up to the full requirements of duty and honor--surrendering
only when nothing else is possible.


JOURNAL OF THE DEFENCE.

=111.= =A Journal of the Defence=, entirely similar to
that of the attack, will be kept by the besieged for use by the War
Department in case of a successful defence. Nothing should be entered
in the journal which might be of special value to the besieger in case
the place is taken, but a separate journal of such matter should be
kept in cipher, or should be destroyed before the surrender of the
place.




CHAPTER VII.

PARKS AND DEPOTS, SHELTERS AND HUTS, KITCHENS, OVENS, SINKS, LATRINES,
WATER-SUPPLY, ETC.


PARKS AND DEPOTS.

=112.= =The Engineer and Artillery Parks and Depots= are
located and arranged for security against the artillery-fire and the
attack, by surprise or otherwise, of the defence, and also for facility
in receiving, storing, and distributing materials and supplies.

The first condition is fulfilled by placing them at a safe distance,
concealing them from the view of the defence if possible, and guarding
them against attack, and the access of incendiaries, etc., by strict
application of ordinary defensive tactics, and a most thorough system
of interior guards. Powder depots, trains, etc., especially are guarded
against the access of all unauthorized persons.

The second condition, when railroad communication is used, is satisfied
by making the park conform to the best-planned railroad terminals and
freight-yards. A type arrangement is given in Plate IX, Fig. 85, in
which switches from the main line give access to as many side-tracks,
_a_, _b_, _c_, _d_, etc., and spurs, 1, 2, 3, etc., as may be needed.
When practicable, these sidings should connect at each end with
the main line in order to afford free ingress and egress from both
directions. They should be placed at such distances apart as to allow
loading-platforms and the desired room for sheds, piles of materials,
etc., between them; large areas being left for light, and small for
heavy, materials. The spurs, 1, 2, 3, etc., should preferably be short;
but if long, should be connected by switches. A Υ, as indicated, is
frequently convenient for reversing complete trains without uncoupling
the cars, and is indispensable when a turn-table is not available.

When the powder-depot is separated from the main park it is better
to reach it by a special track branching from the main line at some
distance from the park, so that the ammunition-trains will not pass
through or near the latter. The sketch given is proposed as a type
only, since the park may occupy one or both sides of the main line, be
long and narrow, short and broad, regular or irregular in outline, as
may best conform to the ground available.

Standard-gauge roads will, when practicable, be laid between the main
park and the smaller depots. When this is not feasible, narrow-gauge
tram-roads will be used instead, and will also connect the smaller
depots with the trenches and batteries. The portable tramways used by
contractors are well fitted for use in the trenches.

When the park is located upon navigable water a number of piers and
wharves are occupied. They should be provided with derricks or cranes,
and tracks and cars upon which materials may be loaded directly from
the ships. The park may then be arranged on the general plan above
indicated. The switches are so arranged as to allow empty cars to
return to the wharves on a track different from that used by the loaded
ones.

In storing materials and supplies in the park care must be taken to
place each class by itself, and to so pile them that they can be
readily inventoried and inspected, and be removed or replaced without
disturbing other piles. This requires the piles to be arranged in
regular order, with unobstructed passages between them, and prohibits
piling articles of different kinds or sizes on top of each other.


SHELTERS AND HUTS.

=113.= In a regular siege, the besieging army will, as a regular
rule, eventually be provided with tents or portable huts for shelter;
but before this is accomplished much suffering and consequent disease
may result from exposure, which could be avoided by the construction of
temporary shelters, huts, and screens from materials available for this
purpose.

In severe winter weather tents and thin wooden huts do not afford
sufficient protection, and it may be necessary to substitute for them
others with walls of logs, sods, sand-bags, adobe, or other materials,
or even huts partly or entirely sunk into the earth. The greatest care
must be exercised in enforcing proper ventilation and cleanliness
in huts of this class. If this is not done serious fevers and other
camp diseases are almost sure to occur. (Art of War, Art. 352-3.)
The figures given (Plate IX, Figs. 86-94) have been selected from a
great many examples to serve as suggestions. They may be modified or
combined, as circumstances require. Their construction is evident from
the figures, and requires no description. Ditches surrounding the huts
are made to carry off rain-water. Heavy roofs are supported by poles
set up inside the hut as needed. Fireplaces are dug in the sides of the
excavation, or are built up of sods, clay, etc. It is better to make
two, as shown, to obtain a good draught in any wind. Chimneys are made
of sods or of sticks plastered with clay, unless drain-tiles, tin cans,
or other suitable materials can be found. Great care must be taken to
prevent their setting the roof on fire.

In many cases water-proof roofing felts and papers may be obtained
and used for roofs, etc., in huts and shelters. The lumber from
packing-boxes, tin from canned vegetables, and wire from baled forage
may frequently be utilized for doors, chimneys, ties, etc. Straw mats
for mattresses, etc., are economical in the use of straw and conduce to
cleanliness, as they can be easily taken up and replaced. The method
of making them is shown in Pl. IX, Fig. 95. When twine is not at hand,
they may be woven of straw rope. They, as well as all other bedding,
should be taken out and sunned every dry day. Ordinary hurdles laid
upon the ground or raised a few inches above it protect the blankets,
etc., from the moisture of the earth.

It cannot be too strongly impressed upon officers, that all devices of
the kind above indicated, which add to the comfort of the men, add also
to their health, morale, and efficiency.


KITCHENS AND OVENS.

=114.= In our service a company will usually have a camp-cooking
outfit sufficient for its needs, and generally of good pattern; but
these are not always on hand when needed, and small detachments are
frequently deprived of them for days or weeks. In ordinary soil,
kitchens, and in a clay soil ovens, can be constructed, which, with a
few kettles and cans, will enable the men to prepare for themselves
fairly good meals without unnecessary waste of fuel. A few of these are
figured in Pls. IX, X, Figs. 96-103. The banks of the trench shown in
Fig. 96 afford support for cross-bars, and protect the fire from the
wind. The type shown in Figs. 97, 102, 103 take the place of a stove,
require but little fuel, and secure a steady heat. To obtain a good
draught they should be so built that the wind blows toward the chimney.
For this purpose they may radiate from a central chimney. (The flues
of those not in use may be temporarily stopped up with sods.) The arch
of the oven shown in Pl. X, Fgs. 98-101, may be built over a piece of
sheet iron if it can be obtained; if not, over a hurdle well smeared
with clay. A slow fire will, under favorable conditions, dry and bake
the clay arch so that it will stand after the brushwood of the hurdle
is burned out. They may then be heated and used for baking.


LATRINES, SINKS, ETC.

=115.= Latrines and sinks for the reception of garbage, etc.,
are objects of the greatest importance in all camps, temporary or
permanent; and, unless properly made and cared for, they speedily make
their presence known, and become a most prolific source of discomfort
and disease.

For permanent camps liable to be occupied for a long time special
arrangements for the disinfection, removal, and destruction of garbage
and excreta must be made. For temporary camps it will suffice to
provide pits with suitable conveniences and screens; covering with a
thin layer of the excavated earth all deposited garbage and excreta
before they become offensive. When, as is sometimes the case, these
pits cannot be kept free from water, it may be necessary to use in
addition lime, copperas, carbolic acid, or other chemical disinfectants
and deodorizers.

The ordinary constructions used in temporary camps are shown in Pl.
X, Figs. 104-107. Separate latrines for officers are constructed and
screened. The seat shown in Fig. 107, when one can be obtained, adds
much to their comfort.

In more permanent camps the latrines may be roofed and screened with
canvas or boards, and board seats be provided for the men. Uninclosed
sinks and latrines should have earthen banks all around them, to
indicate their position and to prevent men walking into them at night.
Upon abandoning a camp all sinks and latrines are to be disinfected and
filled up.


WATER-SUPPLY.

=116.= The problem of obtaining a sufficient and wholesome
water-supply for a besieging army is usually one difficult of solution.
The precautions which are necessary in ordinary camps (Art. of War,
352 and 358) become of still greater importance in this case, owing
to the choice of the source of supply being limited to those which
are not controlled by the besieged, and to the constantly increasing
danger of pollution of all ground waters by the bodies of the dead men
and animals and the refuse and filth of the camps. The evils arising
from these sources may be largely or entirely removed by boiling the
drinking-water, and the disagreeable tastes and smells may be removed
by filtering through good filters. It is very difficult, however, to
compel the men to boil the water, or to drink it after it is boiled,
unless it is properly aerated and filtered. All available measures
should, therefore, be adopted to supply them with wholesome water.

The results of the most recent researches show that properly conducted
_intermittent filtration_ with sand-filters will render a polluted
water almost if not entirely safe. (See reports of Massachusetts State
Board of Health on Purification of Sewage and Water, 1890.) And the
analysis of water sterilized by a steam-jet at the Columbian Exposition
in Chicago, 1893, gives reason to believe that this process may be
very effective in removing disease germs. (See report of Allen Hazen,
Chemist, Department of Water-supply, published in _Engineering News_,
March 29, 1894.) In camps of some permanence one or both of these
processes may be well worth applying.

Small filters for limited amounts of water may be bought in the market,
or may be improvised and set up for officers or company messes. Figs.
108-110, Pl. X, are given as suggestions; they serve as strainers in
any case. If used intermittently they _may_ have a high sanitary value,
and if made up partly of either animal or wood charcoal they remove
more or less completely any offensive taste or odor which water may
have. Security, however, requires doubtful water to be boiled.

In all cases arrangements should be made to protect the water from
surface pollution, for convenient access for the men, and for watering
horses.

(See the following books, treating on Military Hygiene in Camp and
Garrison: Parker’s Practical Hygiene; Traité d’Hygiène Militaire,
Morache; Manuel d’Hygiène militaire, Viry; Military Hygiene, Woodhull;
the Soldier’s Pocket-book, Wolseley; etc., etc.)




PART II.

_MILITARY MINING, BLASTING, AND DEMOLITION._




CHAPTER I.

NOMENCLATURE AND THEORY.


=1.= =Military Mining= includes all the operations necessary
for placing charges of explosive underground and exploding them at the
time desired, for the purpose of destroying the men, materials, or
works in their vicinity, or for breaking up the surface of the ground
either to advance or retard the operations of a siege.

The excavation for receiving the _charge_ is called the _chamber_. The
approaches leading to the chamber when horizontal or somewhat inclined
are called _galleries_, and when vertical are known as _shafts_. When
very steep they are sometimes called _slopes_. The charge, chamber, and
approaches taken together constitute a _mine_.

The pit formed by the explosion is called the _crater_.

When the ground is homogeneous and its surface horizontal, the
intersection of its surface by the crater is approximately a circle,
the radius of which is called the _crater radius_, _AB_, Pl. XI, Fig. 1.

The right line joining the centre of the charge with the nearest point
of the surface toward which the explosion will take place, generally
the surface of the ground, is called the _line of least resistance_
(written generally L. L. R.), _C B_, Pl. XI, Fig. 1.

A right line from the centre of the charge to the edge of the crater is
called the _radius of explosion_, _C D_, Pl. XI, Fig. 1.

The distance from the centre of the charge at which an ordinary mining
gallery will be broken in by the explosion is called the _radius of
rupture_, _C L_, Pl. XI, Fig. 3. The radius of rupture varies in length
with its inclination to the horizontal.

Craters whose _diameters_ are once, twice, etc., their lines of least
resistance are called _one-lined_, _two-lined_, etc., craters.

Mines in which the L. L. R. is equal to the _crater radius_ are called
_common mines_. (Their craters are _two-lined_.) Those in which the
crater radius exceeds the L. L. R. are called _overcharged mines_
or _globes of compression_; when it is less, they are _undercharged
mines_; and when the charge is so small that no exterior crater is
formed, they are known as _camouflets_.

=2.= In the explosion of military mines on land it may safely be
assumed that the circumstances of combustion of the charge when fired
are such that the energy developed is directly proportional to the
charge. A portion of this energy is generally lost by the escape of the
compressed gases into the air, by the heat given up to the surrounding
media, and by the transmission of earth-waves or shock; the remainder
and greater part, however, is expended in rupturing the case containing
the charge, compressing the soil in its immediate vicinity, separating
that lifted up from that forming the sides of the crater, breaking up
the portion thrown out into large or small fragments, projecting them
to a greater or less distance, and disintegrating the soil around the
crater to a distance which varies with the soil and with the quantity
and character of the explosive used.

As the proportional part of the energy expended in each of the
effects above named cannot be determined in any particular case,
and as each case differs in some respect from every other, it is
manifestly impossible to express in any mathematical formula a rule for
determining the exact amount of explosive required for any particular
mine.

From the results of long experience, however, engineers have concluded
that computations sufficiently exact for practical purposes can be made
upon the hypothesis that _for common mines and those approximating
closely to them in form_, the volumes of the craters are directly
proportional to the charges used.

=3.= In order to apply this rule in practice the volumes of
craters formed by known charges must be measured; but since the soil
in the immediate vicinity of the crater is more or less disintegrated,
and the crater itself is partly filled up by the material which falls
back into it, the outlines of the original crater cannot usually be
recognized or its exact geometrical figure be determined. Besides, the
craters formed under circumstances seemingly identical differ more or
less among themselves.

For convenience in computation, however, several simple geometrical
figures have been assumed as giving with sufficient accuracy the form
of the crater of a common mine. See Pl. XI, Fig. 1. Among these Vauban
assumed a cone, _ACD_, with its vertex at the centre of the charge;
Valière a paraboloid of revolution, _AHD_, with its focus at the centre
of the charge; Müller truncated this paraboloid by a horizontal plane
through its focus; while Gumpertz and Lebrun adopted the form in common
use at their time, and which has been generally accepted since, viz.,
a frustum of a cone, _AEFD_, the smaller base of which passes through
the centre of the charge and has a radius, _EC_, equal to one-half the
crater radius, _AB_ (or one-half L. L. R., _CB_).

The volumes of these figures are as follows:

  Vauban’s cone                    1.05 (L. L. R.)^3,
  Valière’s paraboloid             1.90 (L. L. R.)^3,
  Müller’s truncated paraboloid    1.84 (L. L. R.)^3,
  The frustum of a cone            1.83 (L. L. R.)^3 = nearly (11/6)(L. L R.)^3.

The cone of Vauban (lately assumed also by Höfer) was abandoned as
unsatisfactory, because it did not conform to the craters produced,
and, as treated by Höfer, because the charges computed by its use were
found to be too small (an error in the wrong direction). The paraboloid
of Valière or Müller would seem to conform more nearly to the actual
shape assumed by the crater; but it will be observed that the volume of
the latter is sensibly the same as that of the truncated cone, and as
the volume of earth thrown out is the quantity to be considered, the
truncated cone will be assumed as the measure for it.

=4.= The principle that “the volumes of the craters are
proportional to the charges used” is the general statement of the
_miner’s rule_. Assume _C_ and _C´_ to represent the charges of two
mines whose volumes are _V_ and _V´_, lines of least resistance _l_ and
_l´_, and crater radii _r_ and _r´_. Assume also that the craters are
frustums of cones, the radii of whose larger bases are twice those of
the smaller. Then

  _C_ : _C´_ :: _V_ : _V´_ :: (11/6)(_lr_^2) : (11/6)(_l´r_´^2),

or

  _C´_ = _C_ (_V´_/_V_) = _C_[(11/6)(_l´r_´^2)/(11/6)(_lr_^2)] = _C_[(_l´r´_^2)/(_lr_^2)] ... (1)

Equation (1) is applicable to _mines in which r does not differ
materially from l or r´ from l´_.

From an experimental mine giving a crater of this general type the
relations between _C_, _l_, and _r_ may be determined, and assuming any
two of the quantities _C´_, _l´_, and _r´_ for a mine with a crater
nearly similar in form, the other may be found from eq. (1).

When _l_ = _r_ and _l´_ = _r´_, we have

  _C_ : _C´_ : :(11/6)_l_ : (11/6)_l_´^3,

  and

  _C´_ = _C_[(11/6)(_l_´^3)/(11/6)(_l_^3)] = _C_[(_l_´^3)/(_l_^3)] (2)

Equation (2) is applicable to common mines, and shows that _in common
mines the charge varies as the cube of the line of least resistance_.

Assuming _C__{´}_ as the charge which will produce a crater with a
volume of unity, equations (1) and (2) become, by omitting the primes
from _l_ and _r_,

  _C_ = _C__{´}_(11/6)_lr_^2,  (3)

  and

  _C_ = _C__{´}_(11/6)_l_^3  (4)

Equation (4) gives the rule for determining the charge for common mines
whose L. L. R. is given, viz.: _Multiply 11/6, the cube of the line of
least resistance in yards, by the quantity of explosive required to
throw out one cubic yard_.

The latter quantity is determined by experiment. A similar rule may be
written out from eq. (3) for mines differing but little from common
mines.

=5.= The quantity of gunpowder required to throw out a cubic yard
of material has been calculated from a great number of mines fired
in different kinds of soil. The following table gives the quantities
required according to Lebrun and Macaulay, respectively the French and
English authorities on the subject:[8]

TABLE A.

  Number. Description of Earth, Rock, or   Weight per   Charge,   Charge,   Proportional
     Masonry.                              cubic foot.  Gumpertz  Macaulay.   value
                                                      and Lebrun.            of charge.

                                                lbs.    lb. oz.    lb. oz.
   1 Light sandy earth (_common earth,           85     1.8        1.13       1.12
       Lebrun_)

   2 Hard sand                                  111     1.10¾      2.0        1.25

   3 Fat earth mixed with sand and gravel
        (_common earth, Macaulay_)              116     1.5⅓       1.10       1.00

   4 Wet sand                                   118     1.12       2.2        1.30

   5 Earth mixed with stones                    118     1.14       2.4        1.40

   6 Clay mixed with tufa                       124     2.1        2.8        1.55

   7 Fat earth mixed with pebbles               143     2.4        2.12       1.69

   8 Rock                                       143     3.0        3.10       2.25

   9 New or old moist brickwork or masonry                          2.2       1.30

  10 Inferior brickwork or masonry                                 2.11       1.66

  11 Good, new ditto                                               3.10       2.25

  12 Good, old ditto                                                4.1       2.50

  13 Roman ditto, or other equally good
        in warm climates                                             4.11     2.90

=6.= For _common mines_ in _ordinary earth_ a convenient rule,
very generally used, and which gives results nearly the same as those
deduced from the table, is:

_The charge of gunpowder in pounds is equal to one tenth the cube of
the line of least resistance in feet_, or

  _C_ lbs. = (1/10)_l_^3 ft.     (5)


OVERCHARGED AND UNDERCHARGED MINES.

=7. For overcharged and undercharged mines= in which the L. R.
R. and crater radius differ materially in length the results deduced
from the preceding equations are not applicable. For such mines the
following equations, due to Gumpertz and Lebrun, are in common use,
viz.:

For an overcharged mine,

  _C_ = _C__{´}_(11/6)[_l_ + (7/8)(_r_ - _l_)]^3.     (6)

For an undercharged mine,

  _C_ = _C__{´}_(11/6)[_l_ + (7/8)(_l_ - _r_)]^3.   (7)

In which _C_ = charge of explosive in pounds, _l_ = L. L. R. in yards,
_r_ = crater radius in yards, _C_{´}_ = amount of explosive in pounds
necessary to throw out one cubic yard of earth in a common mine in the
same soil.

These formulæ are deduced as follows, viz.:

It was found by experiments made independently by Belidor and Marescot
that 3660 lbs. of powder in a mine with L. L. R. equal to 4 yards gave
a crater with a radius of 12 yards in earth requiring for a common mine
1½ lbs. of powder per cubic yard. The charge for a common mine in the
same soil with L. L. R. equal 4 yards is

  (11/6)(4 yds.)^3 × (1½) = 176 lbs.

Representing by _l_ the L. L. R. for a common mine requiring a charge
of 3660 lbs., since the charges of common mines are proportional to the
cubes of their lines of least resistance, we have

  176 : 3660 :: 4^3 : _l_^3 = 1330.8,

whence

  _l_ = 11^_y_;  11^3 = 1331.

To find from these data the relations between charges for overcharged
mines, construct Figs. 2 and 2_a_, (Pl. XI.)

Fig. (2) gives mines with crater radii of 4^_y_ and 12^_y_ and a common
L. L. R. of 4^_y_.

Divide the distance between _A_ and _B_ into four equal parts, and
assume the points of division as the extremities of the crater radii
of overcharged mines, each of which exceeds the one next smaller by
(¼)_AB_, and all corresponding to a L. L. R. of 4^_y_.

Fig. (2_a_) gives common mines with lines of least resistance of 4^_y_
and 11^_y_. Divide the distance _A´B´_ also into four equal parts, and
assume the points of division as the extremities of the crater radii of
common mines each of which exceeds the one next smaller by (¼)_A´B´_.

Since the charges for the common mines whose lines of least resistance
are respectively 4^_y_ and 11^_y_ are identical with those of the
overcharged mines whose crater radii are 4^_y_ and 12^_y_ respectively,
it is assumed that the charges for the intermediate common mines are
the same as would be required to produce the corresponding intermediate
overcharged mines.

The increment of the crater radius and line of least resistance of any
one of these common mines is equal to 7/8 the increment of the crater
radius of the corresponding overcharged mine; consequently the charge
which gives an overcharged mine whose L. L. R. and crater radius are
_l_´ and _r_´, respectively, will produce a common mine whose L. L. R.
_l_ will be given by the equation

  _l_ = _l_´ + (7/8)(_r_´ - _l_´).      (_a_)

Since the charge for a common mine is obtained from equation (4), _C_ =
_C__{1}(11/6)_l_^3, the charge for the overcharged mine will be

  _C_ = _C_{1}(11/6)[_l_´ + (7/8)(_r_´ - _l_´]^3,

as above.

For ordinary earth and gunpowder, when L. L. R. is measured in feet,
eqs. (6) and (7) become, respectively:

For an overcharged mine,

  _C_ = (1/10)[_l_ + (7/8)(_r_ - _l_)]^3      (6´)

For an undercharged mine,

  _C_ = (1/10)[_l_ - (7/8)(_l_ - _r_)]^3      (7´)

=8.= Giving to _l_ the same value in equations (4), (6), and (7),
we have

_C_´ = _C_((7/8)[_r_/_l_] + (1/8))^3,       (8)

In which _C_ = charge for _common mine_ with L. L. R. and crater radius
= _l_. _C_´ = charge for _over_ or _undercharged mine_ with L. L. R.
= _l_ and crater radius _r_. Equations (6), (7), and (8) having been
deduced from the relations existing between _C_, _l_, and _r_ for
mines varying from common mines up to those in which _r_ = 3_l_ may
safely be used for _overcharged_ mines up to this limit.[9] In their
applications to _undercharged_ mines they become uncertain when _r_ =
(½)_l_; and when _r_ = (⅜)_l_ the computed charge generally produces a
camouflet.

These computed charges are:

  for _r_ = (½)_l_, _C_´ = 0.1779_C_; for _r_ = (⅜)_l_, _C_´ = O.1636_C_.

A rule of the French engineers states that a charge which will produce
a common mine with L. L. R. = _l_ will produce a camouflet if the L.
L. R. is increased to (7/4)_l_. At this depth _C_´ = 0.187_C_, and the
formula gives a crater radius of 25/49.

As a safe “rule of thumb,” we may assume that _a charge which will give
a common mine with L. L. R. = l_ will give a camouflet with L. L. R. =
2_l_ (_r_´ from formula = (3/7)_l_). Conversely, _a camouflet will be
produced by ⅛ of the charge which will produce a common mine_.

=9. Radius of Rupture.=--The determination of the _radius of
rupture_ is an important consideration in underground warfare, since,
when it is known, miners may so place their chambers as to break in the
galleries of the enemy without injuring their own.

As different mining galleries, however, differ from each other so much
in strength to resist crushing, and as the cost of an exhaustive series
of experiments to determine their relative strength would be so great
both in time and money, but little well-established data exist upon
which to found a rule for determining the radius of rupture.

=10.= The rule deduced by Gumpertz and Lebrun, however, from
the material available at their time corresponds very nearly with
the results of later experiments and observations, and is generally
admitted as sufficiently near correct for practical use.

This rule is based upon the theory that the surface of rupture is an
oblate spheroid, (Pl. XI, Fig. 3), with its axis of revolution vertical
and its centre at the centre of the charge; the intersection with the
surface of the ground _AD_ coinciding with the edge of the crater. The
ratio between the semi-transverse axis _CF_ and the semi-conjugate
axis _CH_ of the generating ellipse of this assumed spheroid is the
same as that between the radius of explosion _CD_ and L. L. R., _CK_.
The rule is, that _the radius of rupture in any direction is equal the
corresponding radius of this spheroid_.

From the conditions assumed the following values of the semi-transverse
and semi-conjugate axes _h_ and _v_ (which are the horizontal and
vertical radii of rupture) are obtained, viz.:[10]

  _h_ = _l_√(1 + 2(_r_/_l_)^2);

  _v_ = _l_√[(1 + 2(_r_/_l_)^2)/(1 + (_r_/_l_)^2)].

For common mines these formulas give:

  _h_ = 1.732_l_ = (7/4)_l_ = (7/4)_r_;

  _v_ = 1.225_l_ = (5/4)_l_ = (5/4)_r_.

For six-line craters,

  _h_ = 4.358_l_ = (35/8)_l_ = (3/2)_r_;

  _v_ = 1.378_l_ = (11/8)_l_ = (1/2)_r_.

=11.= The English authorities adopt the value of (7/4)_l__{´} for
the horizontal and _l__{´} √(2) = 1.41421 _l__{´} = (7/5)_l__{´} for
the vertical radius of rupture of all classes of mines. In which
_l__{´} = L. L. R. of an equivalent common mine = _l_ + (7/8)(_r_-_l_),
etc.

Some later experiments at Chatham have given

  _v_ = (5/3)_l_ for a 4-lined crater;

  _v_ = 2_l_ for a 5-lined crater;

  and

  _v_ = (5/2)_l_ for a 7½-lined crater.

=12.= There are other good reasons for believing that Lebrun’s
value for the vertical radius is too small; but as its use leads to
increasing the charges designed to produce crushing effects, the error,
if it exists, is in the right direction, and justifies the use of the
formula until more exact data are available.


EXPLOSIVES.

=13.= No military mining operations of note have been carried
on since the introduction of dynamite and other high explosives;
consequently our knowledge of their value for work of this kind
rests entirely upon the results obtained from experimental mines.
Unfortunately but few experiments seem to have been made, and the
published results of these are very meagre.

=14.= Two mines fired at Krems in 1873 with L. L. R. of 12 ft. in
earth weighing 100 lbs. per cubic foot and charged, one with 173 lbs.
gunpowder, the other with 58 lbs. dynamite (kind not stated), gave
crater radii, respectively, of 12.75 and 10.25 feet. Lebrun’s formulas
applied to these give to gunpowder and dynamite the ratio 1 : 1.688.

Two powder-mines and one dynamite-mine, each of 12 ft. L. L. R., were
fired at Willet’s Point in 1878. The powder-mines were each charged
with 200 lbs. cannon-powder and the dynamite mine with 82 lbs. dynamite
No. 1.

No. 1 powder-mine gave a crater radius of 15½ ft.

No. 2 powder-mine gave a crater radius of 15¼ ft., or a mean of 15⅜ ft.

The dynamite-mine gave a crater radius of 14½ ft.

The relative values of cannon powder and dynamite resulting from the
application of the same formulas to these mines is 1 : 1.997.[11]

=15. Choice of Explosive.=--From these experimental mines it may
be concluded that for forming craters in ordinary earth dynamite is not
quite so efficient as double its weight of good gunpowder. For breaking
up hard rock, blowing up strong masonry, and especially in demolitions
where tamping is usually defective, this ratio does not hold; but
the relative effect of the high explosive increases continually with
the lack of tamping and the intensity of the local blow desired,
until a point is reached at which the effect of gunpowder is almost
imperceptible, while the high explosive does efficient work. This
property of the high explosives renders them extremely valuable for
use in hasty demolitions, such as blowing up palisades or barriers,
destroying guns, etc., etc.

Owing to their varying values in different conditions the choice of
explosive to be used in any particular case must evidently depend upon
the circumstances attending it.

In underground explosions both gunpowder and high explosives give out
noxious gases which penetrate the soil, and which entering a gallery
in sufficient quantity would suffocate the miners. Of these gases the
carbonic oxide given off by some of the high explosives is probably the
most dangerous to human life, and if mixed with the proper proportion
of air forms an explosive mixture, resembling in this respect the
fire-damp of the coal-mines. Whether in practical mining operations it
would ever be retained in the soil in such quantities as to produce
this effect remains to be seen.

Some of the high explosives, on the other hand, seem to produce
relatively small quantities of noxious gases. The gases produced by
gunpowder, while suffocating in their nature, have the advantage of
always making their presence known by their odor.

=16.= For use in overcharged mines designed to break in the
enemy’s galleries, the high explosives, from the violent character of
their explosion and from the phenomena exhibited in submarine mining,
promise to give relatively greater radii of rupture than gunpowder; but
sufficient data are not available to state this positively.[12]

=17.= Beside the considerations above stated, which refer to the
effects produced by the explosive when fired, there are others equally
important relating to the safety and facility with which the explosive
may be transported, handled, and placed in the mines. The latter will
frequently have greater weight than the former in determining the
explosive to be used in any particular case which may arise in the
practical operations of mining. Of the latter considerations some
of the most important in deciding whether to use gunpowder or high
explosives are the following, viz.:

Gunpowder is easily obtained, and most enlisted men are more or less
familiar with its properties.

It explodes when ignited by fire.

It does not ordinarily explode when struck by a bullet.

It is injured by moisture and destroyed by thorough wetting.

It is not affected by ordinary changes of temperature.

It requires thorough tamping to produce good effects.

Many high explosives are not injured by moisture, and some are
unaffected by total immersion in water.

They generally burn without detonation if ignited by flame.

Some of them do not explode when struck by a bullet. The more sensitive
ones do.

The properties of some of them are materially changed by freezing.

On account of their greater strength, the same effects may be produced
by smaller charges, requiring smaller chambers and cases.

By reason of the violence of their action they produce good results
even if imperfectly tamped.

The last two considerations, together with the possibility of using
them in wet places without protection against moisture, lessen greatly
the time required to excavate, charge, and tamp a mine, and may
frequently enable the one using them to anticipate an enemy using
gunpowder and thus secure success, when the use of gunpowder would
reverse the situation. In mining operations and in expert hands the
high explosives, upon the whole, seem to cause fewer accidents than
gunpowder.




CHAPTER II.

PRACTICAL OPERATIONS AND DETAILS.


=18. Tools and Appliances.=--The different operations of mining
are carried on by the use of picks, shovels, bars, saws, axes, hammers
(large and small), chisels, wheel and hand barrows, windlasses, ropes,
wooden or leather buckets, gauge-sticks, mason’s levels (Pl. XI, Fig.
4), plumb-lines, candles, closed lanterns, tin pipes, rubber and canvas
hose, canvas, nails, etc., etc., of the kinds in common use; and the
following special tools and appliances, viz.:

The _Miner’s Pick_. Smaller and lighter than the common pick. Neither
its head nor its handle exceeds 2 feet in length.

The _Miner’s Shovel_. Similar in shape to a common shovel, but not
exceeding 2 feet in length.

The _Push Pick_ (Pl. XI, Fig 5), which has a lance-shaped blade about
3½ in. wide and 6 in. long attached to a handle about 2 feet long.

The _Field Level_ (Pl. XI, Fig 6), which consists of three strips of
wood about 2" × ½", arranged as shown. The strip _A_ is 4' between
centres of pins; _B_ and _C_ are 2', 9-15/16"; the angle at a = 90°.
A spirit-level is inserted in piece _C_, and a plumb-line attached as
shown. The markings on _A_ are used for gentle slopes, those on _B_ for
steep ones.

The other sides of _B_ and _C_ are divided into degrees of arc, the
centre being at the middle point of the outside edge of _A_.

The _Slope Block_, which is a wooden cube used in connection with a
mason’s level for fixing slopes.

_Angle Templets_ (Pl. XI, Fig. 7), making a definite angle, used in
laying out galleries.

The _Miner’s Truck or Car_. A small, four-wheeled wagon with fixed
axles and very short wheel-base; exterior dimensions about 20" wide,
18" to 20" high, and 30" long. Used for carrying earth through
galleries, and usually hoisted up the shaft and dumped outside,
replacing the buckets used in sinking the shaft.

The _Miner’s Bellows_ (Pl. XI, Fig. 8). A leather bag with wooden top
and bottom, provided with inlet and outlet valves, from the latter of
which the air is led off in pipes or hose. In using the bellows the
miner stands upon the lower handles and works the bellows with his
hands by the upper ones.

This is frequently replaced by a common blacksmith’s bellows or the
rotary blower from a portable forge; and sometimes by an improvised
air-pump, consisting of a large open cask filled with water and
another smaller one, with one head removed and the other provided with
outlet and inlet valves and an air-tube, inverted over the large cask,
supported by a spring-pole and worked up and down by hand in the water
of the lower cask.

The _Miner’s Candlestick_ (Pl. XI, Fig. 9), which holds a candle, and
may be driven into the side or bottom of a gallery.

_Miner’s Lamps_ (Pl. XI, Fig. 10), can be used only when the
ventilation is good, as they give off more smoke than candles.

When an electric-light plant is available, incandescent lamps will be
used for mining.

_Earth Augers_, similar to those used for boring post-holes, but of
different diameters, are sometimes used for placing camouflets. Their
shanks are made in short lengths, which can be joined together to allow
of boring a deep hole from a narrow shaft or gallery.


GALLERIES AND SHAFTS.

=19. The Dimensions of Galleries and Shafts= are determined by the
use to be made of them, the necessity of ventilation, and the minimum
space in which a man can work.

They are usually about as follows, viz.:

                                            Height,    Width,
                                             feet.      feet.

  1. Great or grand galleries                    6       7
  2. Common galleries                            6       3½
  3. Half galleries                              4½      3
  4. Branches                                    3½      2½
  5. Small branches (_rameaux de combat_).       2½      2

Shafts vary in size--from the smallest in which a man can work (about
2' × 4'), to any size that may be required, seldom exceeding 10' × 10'.

Great galleries are used for descent into a ditch, and when it is
wished to pass cannon through them.[13]

Common galleries are used for descent into a ditch, and for
communications. Troops can pass through them “by twos.”

Half galleries answer for general purposes of attack. They allow the
miner to work freely in different positions without being cramped,
but are small enough to admit of rapid driving. Branches and small
branches are driven out from the galleries to the mine-chambers, etc.
They can be driven rapidly for short distances (10 to 20 feet); but
when of greater length the earth is removed from them with difficulty,
they are not easily ventilated, and are too small for use as
communications.

=20. Shaft and Gallery Linings.=--In very firm soil it is
sometimes practicable to drive small shafts and galleries short
distances without lining them; but if these are to stand for any length
of time, there is always danger of their falling in, particularly
if shaken by the explosion of mines in their vicinity. When it is
considered safe to use them, however, the shafts should be elliptical
in plan, and the roofs of the galleries should be pointed arches. As
a rule, however, both shafts and galleries should be lined. Those
which are permanent in their character--as the main galleries of the
countermines of a permanent work--are lined with masonry. Masonry
linings may be of brick, stone, or concrete walls and arches. The
smaller galleries constructed during a siege, and all the shafts and
galleries of the attack, are lined with wood. Wooden linings are of two
general types, known as _cases_, and _frames and sheeting_.

=21.= _Cases_ (Pl. XI, Figs. 11 and 12) are made of plank, from
6" to 12" wide, each case consisting of a cap-sill, a ground-sill, and
two stanchions. The cap and ground-sills are cut to a length equal to
the clear width of the shaft or gallery plus twice the thickness of
the stanchions; a rectangular notch is cut in each end to receive a
corresponding tenon cut on the stanchion. The length of the stanchions
between shoulders is equal to the clear length of the shaft or height
of the gallery. The length of the tenons is generally equal to the
thickness of the cap and ground sill (usually 2´´), and their width
about three inches. Notches are cut in the sides of all the pieces of
the case, as shown in the figure, for convenience in handling them.

In grand galleries the tenons at the top of the stanchions are usually
shorter than the thickness of the cap-sill, and those at the bottom, as
well as the mortises in the ground-sill, are omitted. The stanchions
are kept from collapsing by blocks nailed to the ground-sills. These
blocks are 2" thick, and wide enough (about 9´´) to so guide the wheels
of a gun-carriage as to prevent the axle striking the stanchions.

In cases for smaller galleries also the tenons are sometimes omitted
at the bottom of the stanchions, the mortises in the ground-sills cut
an inch or two deeper, and the stanchions kept from collapsing by keys
driven in the mortises (Pl. XI, Fig. 13).

=22. Shaft and Gallery Frames= (Pl. XI, Figs. 14, 15, and 16)
are made of scantlings, halved together at the ends, as shown in the
figures. _Sheeting_ is made of boards or planks of the necessary
thickness, sawn to proper lengths, and bevelled at the ends. When sawn
lumber is not available, the frames may be made of saplings, and in
some cases poles may be used for sheeting.

The middle of each cap and ground sill, both in frames and cases, is
distinctly marked by a shallow saw cut or otherwise.

=23.= The following table gives the dimensions, in inches, usually
adopted for the pieces of cases, frames, and sheeting, for galleries of
different sizes, viz.:

  ----------------+------------------------------------+---------------------------------------------
                  |               Cases.               |            Frames and Sheeting.
                  +------------+-----------+-----------+------------+-----------+---------+----------
                  |Ground-sill.|Stanchions.| Cap-sill. |Ground-sill.|Stanchions.|Cap-sill.|Sheeting.
  ----------------+------------+-----------+-----------+------------+-----------+---------+----------
                  |    In.     |    In.    |    In.    |    In.     |    In.    |   In.   |   In.
  Great galleries |     3      |     4     |     5     |   6 × 4    |   6 × 6   |  6 × 9  |    2
  Common galleries|     2      |     2     |     2     |   6 × 3    |   6 × 6   |  6 × 8  |    1½
  Half galleries  |     2      |     2     |     2     |   5 × 3    |   5 × 5   |  5 × 7  |    1½
  Branches        | 1½ or 2    | 1½ or 2   | 1½ or 2   |   4 × 3    |   4 × 4   |  4 × 5  |  1 or 1½
  Small branches  | 1 to 2     | 1 to 2    |   1 to 2  |   3 × 3    |   3 × 3   |  3 × 4  |    1
  ----------------+------------+-----------+-----------+------------+-----------+---------+----------

The cases of branches and small branches are sometimes made very
strong, with a view to resist rupture by the explosion of neighboring
mines. For this purpose cases made of oak plank 4" thick are used,
and the branch near its end is packed full of scantlings provided
with rope-handles at their ends for withdrawing them after the mine
is fired. This packing is, however, of doubtful utility, since a
compression of the case sufficient to call the resistance of the
packing into play is very apt to produce a permanent deformation of the
cases, which will jam the scantlings and prevent their removal. For
convenience in use the pieces of cases should be of uniform width.

=24. Relative Advantages of Cases, and Frames and Sheeting.=--In
favorable soil, cases, when they can be obtained, allow of more rapid
progress and give a lining with a smooth interior. In very bad soil
they cannot be used for the larger galleries.

Frames and sheeting can be used in all soils which admit of mining
operations, and can usually be improvised from materials found in the
vicinity.

=25. Sinking a Shaft by Frames and Sheeting.=--The size and
position of a shaft are usually determined by the character and
direction of the gallery which is to start out from it. It is evident
(Pl. XI, Fig. 17) that the clear width of the shaft must be enough
greater than the outside width of the gallery to allow the side
sheeting of the gallery to be freely inserted outside the frames of the
gallery and inside those of the shaft; also, that the shaft frames must
be so spaced as to leave a clear space at the bottom for the gallery.
This space must be equal to the clear height of the gallery, increased
by the thickness of the cap-sill, the sheeting, and one or two inches
for easy working. This and the thickness of one frame being deducted
from the depth of the shaft, the remainder may be divided up into a
number of equal or unequal parts called _shaft intervals_. In order
that the sheeting may not yield under the pressure of the earth, these
intervals seldom exceed 4 feet.

The length of the shaft must be great enough to allow the miners to
work freely, and to insert the sheeting for the first gallery interval.

The sheeting for both shafts and galleries is cut in lengths about 1
foot greater than the interval between frame centres.

=26.= The size and position of the shaft having been fixed, the
top frame (Pl. XI, Fig. 15) is placed in position and secured by pegs,
and the direction of its axis is accurately fixed by the score marks
at the middle of the end pieces. The side and end pieces of this frame
are respectively about 3 feet longer than those of the other frames,
and are so halved together as to make of their ends four projecting
_horns_, 1½' long, which keep the frame in place during the excavation
of the first interval.

This frame is usually placed with its top flush with the surface of the
ground. The miner proceeds to excavate the shaft with pick and shovel,
making it large enough in plan to admit the sheeting outside the frame.
Usually the first interval can be excavated without supporting the
earth at the sides, which are vertical or slightly undercut, so that
at the bottom of the interval the shaft will be large enough to admit
the second frame, the sheeting of the first interval, and a system of
wedges which hold this sheeting out from the second frame a distance
somewhat greater than the thickness of the sheeting of the second
interval. The verticality of the sides is determined by the plumb-line,
and the size of the shaft by two gauge-sticks cut respectively to the
outside length and width of the excavation, and distinctly marked at
their centres.

To avoid the inconvenience of working under the top frame, the first
interval is frequently marked out and excavated before the frame is
fixed in its position.

When the shaft is deep enough the second frame is put in place and
nailed together; the notches in the ends of the side pieces turned
upward and those of the end pieces downward. The top and second frame
are connected by nailing to them four battens of proper length (two on
each side), which suspend the second frame from the top frame at the
established interval. The second frame is placed vertically below the
top frame by using the plumb-line and the scores in the frames.

The sheeting is inserted outside the top frame, bevelled end first,
bevel outside, and pushed down until its top is flush with the top
frame. The lower end of the sheeting is held out from the lower frame
by suitable wedges, and the excavation of the second interval is
commenced.

In ordinary soil the sides of the shaft will now require support.
Sheeting is therefore introduced and pushed down as the excavation
proceeds, and the wedges previously placed are removed to make room for
the sheeting.

=27.= If the pressure of the earth becomes great enough to spring
the sheeting-planks inward, an _auxiliary frame_ is introduced. This is
a frame similar to the shaft frames, but from 4 to 6 inches larger in
outside dimensions.

The sheeting rests directly against the outside of this frame, and is
thus held out far enough to allow the third frame to be placed and the
wedges to be inserted as before.

The auxiliary frame is then removed and used in the next interval.

=28.= Successive frames are placed in the same manner until the
one directly over the gallery is reached. Great care is taken to place
this frame at exactly the right height, and the shaft is then continued
to the required depth. A frame is placed at the bottom with its top at
the level of the floor of the gallery, and the sheeting is allowed to
rest directly against the outside of this frame. When the soil will
allow it, the sheeting is omitted wholly or in part over the portion of
the shaft which is to form the gallery entrance.

=29. Precautions.=--In sinking shafts especial care must be taken
to make the excavation no larger than is required for placing the
lining, since if a vacant space is left outside the lining the sides of
the shaft may give way through its entire height, and fall against the
lining with a blow which will crush it in.

_This is often the cause of fatal accidents both in shafts and
galleries._

=30. Partly-lined Shafts=, i.e., those in which the
sheeting-planks are separated from each other by greater or less
intervals, should only be used for small depths and when they are
expected to stand for a very short time.

They are a constant menace to the miners, owing to the danger of their
caving in, and in a much greater degree to the probability of stones,
etc., falling from the unprotected parts and seriously injuring or
killing the men at the bottom.

=31. Driving a Gallery with Frames and Sheeting.=--The direction
of the gallery has already been marked by the scores on the shaft
frames; but it must be verified by plumb-lines, and two small pickets
be driven on the line of its axis, which is located exactly by small
nails, one driven in the head of each picket.

Two gauge-rods are prepared, giving the extreme height and breadth of
the excavation, i.e., the height of the frame plus two thicknesses of
top sheeting, and the breadth of the frame plus four thicknesses of
side sheeting. The middle of each gauge-rod is also plainly marked.

A gallery frame is set up against the side of the shaft (Pl. XI, Fig.
17), its ground-sill flush with the bottom frame of the shaft; or its
stanchions may rest upon the shaft frame as a ground-sill.

The gallery frame is carefully located and fastened in position with
battens and braces. The shaft sheeting is then forced down two or three
inches with a bar, and the top sheeting of the gallery inserted and
driven in until its end is supported by the earth. It is given the
proper upward pitch by a scantling laid across it and secured to the
shaft frames. The shaft sheeting is forced further down, the earth at
the top excavated, and the top gallery sheeting advanced. As this work
proceeds the side sheeting-planks are successively inserted and driven
forward.

In this way the gallery is advanced one gallery interval, usually
about 4 feet, when a second frame is placed. Its position is verified
by the score marks; for direction, by a line; for grade, by a spirit,
mason’s, or field level; and for verticality, by a plumb-line. It is
then secured in place by nailing battens to it and the preceding frame.
Wedges are inserted between the frame and the sheeting, and the gallery
is continued by the same methods (Pl. XII, Fig. 19). When the sheeting
is advanced only by hard driving the frames are slightly inclined to
the rear at first, and are afterwards driven forward until vertical.

=32.= If, while advancing the sheeting, the pressure upon it
becomes so great as to spring it, a _false frame_ (Pl. XII, Fig.
18) must be used. This consists of a cap-sill, ground-sill, and two
stanchions, connected by mortises and tenons. The stanchions have
tenons and the sills mortises at each end. The cap-sill is usually
rounded on top and, for facility in setting up and removing, its
mortises are longer than the width of the tenons. The latter are held
in place by wedges when the frame is in position. The false frame is
usually made of the same height as the common frames and, when side
sheeting is used, wider by twice the thickness of this sheeting. When
side sheeting is not used, its outside width may be equal to the clear
width of the gallery.

In using the frame (Pl. XII, Fig. 19) the ground-sill is first placed
accurately in position at a half interval in advance, the stanchions
are set up, and the cap-sill placed upon them and wedged. The whole
frame is then raised about 2 inches by folding wedges placed under
each end of the ground-sill, and is secured by battens. The sheeting
will now rest directly upon the cap-sill and stanchions, and have the
proper inclination to clear the next frame by its own thickness, as is
required.

The next frame is then set up, the wedges driven under the sheeting,
and the false frame removed; which is easily done, owing to its
construction.

=33.= When the soil is very bad a _shield_ (Pl. XII, Fig. 20)
is used to prevent the earth in front and above from caving into
the gallery. In starting out from the shaft the following method is
adopted: As soon as the top sheeting is sufficiently advanced and the
shaft sheeting is forced down about 1 foot, the top plank of the side
sheeting is inserted and driven forward about 2 feet, and the earth
at the top of the gallery is excavated for from 6 inches to 1 foot
in advance. A piece of plank a foot wide and in length equal to the
width of the gallery is then placed directly under the top sheeting
and against the face of the excavation, and is held in place by braces
at its ends secured to the shaft lining. The shaft sheeting is then
lowered another foot, the next plank of the side sheeting inserted, the
earth excavated, and a second plank of the shield placed in the same
way as before. This is continued until the entire face is covered. The
top and side sheeting are then driven forward, and the top plank of the
shield is removed and replaced in advance; after which each plank is
removed and replaced in succession, as above described.

=34. Inclined Galleries.=--_Method of fixing the slope._--If the
gallery instead of being horizontal is _ascending_ (Pl. XII, Fig. 21)
or _descending_ (Fig. 22), the proper slope is obtained by using a
_slope-block_ whose edge is equal to the rise or fall of the gallery
in one interval. This is placed upon the lower of two consecutive
ground-sills, and the proper height of the other is determined by a
mason’s or spirit level (Fig. 21). If a field-level or a mason’s level
properly marked for the slope is used, the slope-block may be dispensed
with (Fig. 22).

=35. Position of Frames.=--In driving _descending galleries_
better progress will be made and less material used if the frames are
set at right angles to the axis of the gallery (Pl. XII, Fig. 22);
and this is the usual custom. In driving _ascending galleries_ this
is impracticable, and the frames are set vertically (Fig. 21). In all
other respects inclined galleries are driven in the same manner as
horizontal ones.

=36. Partly-lined Galleries.=--In very firm soil side sheeting may
be omitted entirely, and in that less firm the side planks need not be
in contact. When the side sheeting is omitted the width of excavation
may be reduced to the clear width of the gallery, and the stanchions
be let into the side wall flush with its surface. In this case the
ground-sills are frequently omitted, the stanchions resting upon wooden
blocks, stones,or directly upon the earth.

To save material, the planks of the top sheeting are sometimes more
or less separated also. This can only be recommended when rapid and
temporary work is required with limited materials; and in these cases
the earth between the planks should be supported by a packing of
sticks, brush, etc., etc.

=37. Change of Direction in Galleries.=--In changing the
direction of a gallery, the new direction is laid off by using
a carefully made angle-templet (Pl. XI, Fig. 7) or slope-block,
field-level, etc., and it is prolonged in the new direction by the
methods already described. When the soil is firm enough to stand safely
while excavating and lining one gallery interval, even if somewhat
short, no difficulty exists in changing the direction of a gallery in
either a vertical or horizontal plane, since the excavation in the new
direction may be made so large that the miner working in it can place
the new frames and introduce the sheeting and wedges. The gallery can
then be carried on without diminution in size.

When the soil is bad, however, special arrangements must be made for
introducing the sheeting.

=38. Change of Slope.=--To pass from a horizontal to an
_ascending_ gallery (Pl. XII, Fig. 21) it is only necessary to give
the top sheeting the proper angle by holding down its back end with a
piece of scantling placed across the gallery for that purpose; and, to
give the side sheeting the proper inclination, cutting trenches in the
bottom of the gallery for the lower pieces, if necessary.

In passing from a horizontal to a _descending_ gallery (Pl. XII, Fig.
22) the roof may be carried forward horizontally, and the floor given
the desired pitch by increasing the height of the consecutive frames,
until enough head-room is obtained to allow the top sheeting for the
descending gallery to be inserted at the proper height and angle. The
frame at this point is made with a cap-sill (upon which the sheeting
rests directly), and a second cross-piece below it, serving as a
cap-sill for the descending gallery. From this point forward the frames
may be set perpendicular to the axis of the gallery, as previously
stated.

If the descending gallery is very steep and the horizontal pressure of
the soil great, it may be necessary to strengthen the stanchions of the
last two or three vertical frames by cross-pieces near their upper ends.

=39. Change of Direction Horizontally.=--Slight changes of
direction of narrow galleries, either to right or left, may be made
in a manner entirely similar to that above described for descending
galleries, by widening the frames until the side sheeting can be
inserted at the required angle, and strengthening the cap-sills, when
necessary, with additional stanchions.

When the gallery is wide or the changes of direction abrupt, however,
it is customary to drive the gallery entirely beyond the turning-point,
and then break out a gallery in the new direction from the side of the
original gallery.

=40. Returns.=--A gallery starting out from the side of another
is called a _return_, and is _rectangular_ or _oblique_ according to
the angle made by its axis with that of the original gallery, which is
called the _gallery of departure_.

That the return may be broken out, the interval between the frames of
the gallery of departure at this point must be such as to admit between
the stanchions a frame and the side sheeting of the return (Pl. XII,
Fig. 23). This part of the gallery of departure is called a _landing_,
and its floor is made horizontal.

If the return is oblique (Fig. 24), its width measured along the
gallery of departure will be determined by an oblique section, and may
be so great that the strength of the lining of the gallery of departure
will not allow the necessary length of landing. In this case a short
rectangular return is first broken out from the side of the gallery
of departure, and the new gallery is broken out from the side of
this return (Fig. 25). The latter method diminishes the length of the
landing when the change of direction is less than 45°.

=41.= The floor of a return is started at the level of the floor
of its landing. In firm soils which will stand for a short time without
support the first frame may be set up entirely outside the gallery of
departure (Pl. XII, Figs. 24 and 25) and may be of the same height in
clear as this gallery. When the soil is bad, however, and side sheeting
is required in the gallery of departure, the first frame of the return
must be set up against this sheeting in the interval between the
stanchions of the landing (Fig. 23). This makes the clear height of the
return at this frame less than that of the gallery of departure by a
little more than the thickness of the sheeting.

The first frame of an oblique return should be so made that the sides
of the stanchions will be parallel to the side walls of the return,
thus giving a good bearing to the side sheeting.

In very bad soil, the first few frames of a return must be firmly
braced to resist the backward thrust of the earth, by battens
connecting them together and by struts across the gallery of departure.
The latter are removed when the return is sufficiently advanced.

=42. A Complete Map= must be made of every system of mines,
showing the centres of shafts, and the axes and slopes of all
galleries; giving also the references and lengths of all landings, and
the locations, references, and dimensions of all mine chambers.

=43. Working Drawings= must also be made from which sheeting can
be cut to proper lengths and angle-templets, etc., cut and framed.

These can be easily and accurately drawn by remembering that, to
allow the miners to insert the sheeting, every return must have such
dimensions outside its sheeting that, if it were free to move, its
lining could be slid back across its landing as a drawer slides in a
table. The size of the landings and dimensions of frames having thus
been determined, the parts of the galleries between them may be divided
into intervals, which, for convenience, should be equal, since this
will allow the sheeting to be cut to a uniform length.

=44. Sinking a Shaft with Cases.=--(Pl. XII, Figs. 26 and 27.)--A
case of the required size is put together and accurately placed upon
the site of the shaft, whose dimensions are marked upon the ground
outside it. The case is then removed and the earth excavated to the
depth of the case, which is placed in the excavation with its top flush
with the surface of the ground. Its position is carefully verified, and
it is secured in position by packing earth around it. The excavation is
then continued for the depth of another case, which is put in place as
follows, viz.:

One end piece is placed in position, the tenons of the two side pieces
are inserted in the mortises at its ends, and the side pieces are
pushed back into position; a pocket-shaped excavation is made with a
push-pick beyond the end of one of the side pieces and running back
three or four inches into the side wall; the remaining end piece is
inserted in this far enough to allow the mortise at its other end to
slip over its corresponding tenon; it is then drawn back, and the
tenons at both ends fitted into their mortises. The notches cut in the
sides of the pieces allow them to be easily handled.

The next case is placed in the same way, care being taken not to
excavate two consecutive pockets at the same angle.

When practicable, it is well to fill up these pockets by stuffing in
sods from below before placing the next case.

Some miners prefer to place one tenoned piece first, then the two
mortised pieces, leaving a wedge-shaped opening behind one of them, and
insert the other tenoned piece last, drawing the mortised piece forward
upon its tenon.

When the sides of the cases are tenoned at one end only and secured by
wedges at the other, they are easily placed in position without cutting
out behind them.

=45.= Upon reaching the level of the top of the gallery, the
pieces on the gallery side of the shaft are omitted if the ground is
firm, but if it needs support these pieces are put in place and secured
by cleats or braces, but the tenons are not inserted in the mortises.

=46. Driving a Gallery with Cases= (Pl. XII, Fig. 27).--This is
practicable only when the soil is somewhat firm. In breaking out from
the side of the shaft, a frame is first placed inside the shaft to
support the ends of the shaft cases resting against the pieces which
are to be removed. The latter pieces are then taken out and grooves
are cut in the earth for the ground-sill, stanchions, and cap-sill of
the gallery, and these are put in place in a manner entirely analogous
to that described for sinking a shaft. This case is set flush with
the inside of the shaft and supports the side pieces, whose tenons
rest upon its stanchions. The projecting earth is then cut away and
grooves are cut for the next case, which is placed in position and the
excavation continued as before.

=47.= When the earth shows a tendency to cave, which it frequently
will in great galleries, the cap-sill must be put in position and
supported while the miner excavates the grooves for the ground-sill and
stanchions.

To support the cap-sill, two crutches are used. A _crutch_ (Pl. XII,
Fig. 28) consists of an upright piece of timber carrying a cross-piece
whose length is equal to the width of two cases. The upright piece
rests upon the ground-sill of the case already placed, and is raised to
the proper height by wedges. The part of the cross-piece which projects
in advance is made 2 inches higher than the rear part, to support the
cap-sill somewhat above its final level, so as to allow the tenons of
the stanchions to be easily inserted. The rear part of the cross-piece
is attached to the upright by an iron rod or short chain.

So soon as the case is set and adjusted to position the crutches are
taken down by removing the wedges, and are replaced under the next
cap-sill.

=48.= In very firm soil shafts and galleries are frequently
driven with cases not in juxtaposition, but separated by greater or
less intervals. Pieces of planks (which may be parts of cases) placed
vertically and resting against the sides and ends of the cases in
shafts, or horizontally and resting upon the cap-sills in galleries,
and somewhat separated from each other, are used to support the earth
between the cases.

The same remarks apply to this construction as to the similar one
sometimes used when mining with frames and sheeting.

=49. Change of Direction in Galleries Lined with Cases.=--Slight
changes in direction in a horizontal plane can be easily and gradually
made by setting each case a little obliquely to the one preceding
it, and separating the stanchions on one side while they touch on the
other, supporting the roof in the wedge-shaped openings, if necessary,
with pieces of wood, etc. For an abrupt change, it is better to break
out a rectangular return from the side of the gallery and pass from
this into the required direction by gradual change.

If the return is to be of the same height as the gallery of departure,
the cap-sills of the latter, for a distance equal to the width of the
return, are lifted off the tenons of the stanchions by struts and
wedges, and the first case of the return is set as in breaking out from
a shaft; the ground-sill is, however, narrowed by the thickness of the
stanchions of the gallery of departure so that the face of the case of
the return is flush with the inside of the gallery of departure, and
the ends of the cap-sills of the latter rest upon the cap-sill of the
first case of the return.

=50. Change of Slope.=--In passing from a horizontal to a
_descending gallery_ the change may be made gradually, in a manner
similar to that described for a change in horizontal direction, and the
cases remain normal to the axis of the gallery. (Pl. XII, Fig. 31.)

To pass to an _ascending gallery_ by the method above described would
require the earth at the face of the gallery to be undercut in order to
introduce the case, and this undercutting would be continued so long as
the cases were normal to the axis of the gallery. This construction is,
as a rule, impracticable. In ascending galleries, therefore, the cases
are set with their stanchions vertical, while their cap and ground
sills lie in the slope of the roof and floor of the gallery.

=51.= To conform with this requirement, and for convenience in
setting up, the ends of the stanchions receive the proper bevel, while
the sides of the tenons and mortises are made parallel to the sides of
the stanchions. (Pl. XII, Fig. 12.)

=52. Shafts à la Boule.=--In order to place a charge of explosive
directly under the ground occupied, or for other reasons, it is
frequently necessary to sink a small shaft in the least possible time.
For this purpose a modified form of cases is sometimes used, in which
the ends are halved together instead of being tenoned and mortised.
(Pl. XII, Fig. 29.) They are spaced at greater or less distances apart,
according to the nature of the ground, and are connected together by
battens. Stones, pieces of wood, etc., etc., are driven between them
and the sides of the shaft to support the latter.

This construction is called a shaft à la Boule. It is expected to stand
for a few days at most. Many other extemporized linings may be used for
similar purposes.

=53. Blinded Galleries.=--Galleries cannot be successfully driven
with less than 3 to 3½ feet of undisturbed earth over their sheeting.
In making a descent into a ditch, or in pushing forward an approach
in siege operations, it is often impracticable to lower the bottom
of the trench of departure sufficiently to give the requisite cover
for starting a gallery at once. In these cases _blinded descents_ or
_galleries_ may be used, the tops and sides of which are supported by
_blindage-frames_, or _blinds_, each of which consists of two side
parts of 4" × 6" scantling 9' long, united by two cross-pieces of
the same section 3' 8" long, which are mortised or halved into them,
leaving horns at each end 1' long. (Pl. XII, Fig. 30.)

=54.= The galleries are constructed as follows (Pl. XII, Fig.
31): A double sap with a width of 8' is broken out from the side of
the trench in the direction required and is driven forward in the
usual manner, but with a continual increase in depth, at a slope not
exceeding 1/4. The side slopes are as steep as the earth will allow.
Two blindage-frames are set up vertically on the sides of the sap, 7'
apart in clear, with their tops at the level of the tops of the trench
gabions, their bottom horns resting in holes dug for them. These frames
are prevented from falling inward by another frame placed crosswise
upon them, with its horns resting on their cross-pieces. The side of
this top frame toward the front may be held up by a stake or crutch,
and the second pair of frames be placed at such an interval that their
horns will interlock with those of the top frame. Successive frames
may be placed in the same manner. The covering or “roof” is formed by
three or four layers of fascines placed across the trench on top of
the frames, and covered with earth thrown back upon them as the work
proceeds. The sides of the gallery are held up by fascines, etc., laid
along outside the frames.

As soon as the bottom of the blinded gallery has reached the proper
depth a mine-gallery may be started and carried forward.

=55.= The blindage-frames described above give to the gallery a
clear width and height of 7'. For smaller galleries the blinds may all
be made shorter and of lighter scantling; or, if desired, those for the
sides may be of a different length from those for the top.

=56. Rate of Advance of Galleries.=--The following table gives an
estimate of the men and tools required for shafts and galleries, with
the probable rate of advance in good soil:

  KEY:
  NC O   = N. C. Officer.
  M      = Miners.
  P      = Picks.
  MP     = Miners' Picks.
  P-p    = Push-picks.
  Sh     = Shovels.
  MS     = Miners' Shovels.
  MT     = Miner’s Truck.
  F-l    = Field-levels.
  M-r    = Measuring-rod 6´.
  T-l    = Tracing-line.
  M S    = Mauls or Sledges.
  CB     = Canvas Buckets.
  R-l    = Rope-ladder.
  W-b    = Wheel-barrows.
  MB     = Miners' Bellows.
  Pr.    = Progress, ins. per. hour.
  -------------------+-----------+----------------------------------------------------------------
                     |   Men.    |                        Tools.
    Kind of Gallery, +----+------+---+---+---+---+---+-----+---+---+---+---+---+---+---+---+------
      etc.           |NC O|  M   | P | MP|P-p| Sh| MS|  MT |F-l |M-r|T-l|M S|CB |R-l|W-b|MB | Pr.
  -------------------+----+------+---+---+---+---+---+-----+----+---+---+---+---+---+---+---+------
  Great gallery or } |    |      |   |   |   |   |   |     |    |   |   |   |   |   |   |   |
   Blinded gallery } | 1  |12[14]| 4 | 2 | 2 | 8 |   |     | 1  | 1 | 1 | 1 |   |   | 4 |   |  12
  Common gallery     | 1  | 4    |   | 1 | 1 | 2 | 1 | 1   | 1  | 1 | 1 | 1 |   |   |   | 1 |  12
  Half gallery       | 1  |4[15] |   | 1 | 1 | 2 | 1 | 1   | 1  | 1 | 1 | 1 |   |   |   | 1 |  16
  Branch gallery     | 1  |4[15] |   | 1 | 1 | 2 | 1 | 1   | 1  | 1 | 1 | 1 |   |   |   | 1 |  24
                     |    |      |   |   |   |   |   |     |    |   |   |   |   |   |   |   |{ 30
  Small branch       | 1  | 3    |   | 1 | 1 |   | 2 |1[16]|[17]| 1 | 1 | 1 |   |   |   | 1 |{ to
                     |    |      |   |   |   |   |   |     |    |   |   |   |   |   |   |   |{ 36
                     |    |      |   |   |   |   |   |     |    |   |   |   |   |   |   |   |
  Shaft              | 1  |4[18] |   | 1 | 1 | 2 | 1 |     | 1  | 1 | 1 | 1 | 1 | 1 |   |   |{ 18
                     |    |      |   |   |   |   |   |     |    |   |   |   |   |   |   |   |{ 24
  -------------------+----+------+---+---+---+---+---+-----+----+---+---+---+---+---+---+---+------


VENTILATION OF MINES.

=57.= The gases resulting from firing mines and from the lamps,
bodies, and candles of the miners so vitiate the air in galleries that,
unless means for ventilating them are adopted, the miners must eventually
abandon them or become asphyxiated.

In ordinary circumstances, when no powder gases are present, a gallery
cannot be driven safely more than 60 feet without ventilation.

The measures adopted for ventilating galleries consist, 1st, in forcing
in fresh air; 2d, in drawing out foul air; and, 3d, in assisting the
natural diffusion and circulation of the air through them.

=58.= The first is accomplished by forcing air through pipes,
which may be of tin, wood, or common hose, leading to the point where
ventilation is required. The air is forced in by the use of the miner’s
bellows or other apparatus already described. This method is simple
in its application and places the fresh air where it is needed, but
drives the foul air back into the galleries occupied by other miners.
It is the only practicable method of ventilating single, long, narrow
galleries and branches.

=59.= The second method may be applied to a system consisting
of a number of galleries connected by transversals, by so placing
an exhausting fan as to draw the air out through one gallery, while
by light wooden or canvas doors and screens the other galleries are
so arranged that the fresh air, entering from the exterior, sweeps
through the galleries occupied by the miners, and escapes through the
unoccupied gallery leading to the fan, carrying the gases with it.

In this method a single large gallery may be ventilated by using a
canvas partition placed near the top or on one side, so that the fresh
air will go in on one side around the end of the partition and back by
the other side to the fan.

This method has the advantage of carrying the gases away from the
galleries occupied by the men, and supplying fresh air throughout those
which are occupied.

The exhaust may be produced by a fire constantly burning at the foot of
a shaft instead of by a fan.

The method is, however, complicated in its application, and can seldom
be used for military mines.

=60.= The third method, or assisting natural ventilation, is
carried out by cutting numerous cross-galleries connecting those which
are near each other, by making air-shafts and bore-holes connecting the
galleries with the surface of the ground, and, when practicable, by
placing the openings of the shafts and galleries at different levels.
This method will serve for a few men working leisurely in preparing
countermines before an attack, but is entirely inadequate during active
mining operations.

=61.= By the use of masks covering the face, and supplied with
fresh air either through hose or from a reservoir of compressed air
carried with him, a miner may work in galleries in which the air is
irrespirable. The advantages which may frequently result from the time
thus saved justify providing apparatus of this kind for use in mining
operations.


MINE-CHAMBERS.

=62. Mine-chambers= to contain the charge of explosive are
preferably nearly cubical in form, and if not charged at once, or if of
large size, must have sufficient lining to support the roof and sides.

When they are above the level of the gallery they are arranged to drain
into it. They are made large enough to contain the receptacle for the
charge and to allow the charge to be placed in it. They are, as a rule,
placed in short returns at one side of the branch or gallery, but may
be at its end, above or below it. The mine-chamber frequently consists
of so much of the end of the gallery as is necessary to contain the
charge.


LOADING AND FIRING MINES.

=63. Preparing the Charge.=--The weight of the charge necessary
to produce the desired effect is determined by the rules previously
given. Its volume, if of powder or compressed gun-cotton, may be found
by allowing 30 cubic inches to the pound; and if of dynamite, about 20
cubic inches.

If the mine-chamber is perfectly dry, and the mine is to be fired at
once, a layer of straw may be placed upon the floor of the chamber and
the charge contained in canvas bags laid upon it. When the ground is
more or less wet, or when the mine is not to be fired immediately, the
charge should have a water-proof covering, which may be a thoroughly
calked and pitched box, an ale-barrel or beer-keg, the metal barrels
in which powder is shipped, or India-rubber or pitched-canvas
bags,--depending upon the amount of moisture present and the time that
the charge is to remain in place. Many of the high explosives are not
affected by dampness, and but little if any by water; but to secure
the fuse and its connections from injury, and to remove all danger of
misfires, the explosive should in all cases be protected from water if
practicable.

=64. Distribution of Fuses in the Charges.=--Gunpowder will
explode with full effect if ignited, but to prevent the explosion of
the central part of a large charge scattering the exterior portion
before it is ignited a number of fuzes should be used. They may
convey fire only, but must all be ignited by the firing apparatus,
and simultaneously. One fuze to each 100 lbs. of powder is not too
great an allowance; but when lack of time or appliances does not admit
of placing a number of fuzes, the desired effect may be obtained by
increasing the charge of powder and using one fuze. (See Abbot, Prof.
Papers Corps of Engineers, No. 23, 1881, p. 62, for number of fuzes
needed; and pp. 244-51 for simultaneous ignitions.)

The high explosives detonate with full force only when exploded with
a detonating fuze. Under favorable conditions one fuze will detonate
a very large charge, but cases arise in which a portion of the charge
explodes and the remainder does not. To insure the best results,
therefore, it is desirable to distribute fuzes throughout a large
charge, at the rate of perhaps one fuze to each 50 lbs. These fuzes
should contain from 20 to 30 grains of fulminate of mercury, which is
itself very sensitive to shock, and has in a high degree the power of
detonating the other explosives. One fuze only (or, for safety against
defects, two or three) need be connected with the firing apparatus, the
others serving to reinforce and carry on the wave of explosion after it
is started--differing in this respect from their use with charges of
gunpowder.[19]

=65. Character and Construction of Fuzes.=--Formerly, for firing
mines, trains of powders put up in linen tubes, quick-match, and other
similar devices were used. Electric-blasting apparatus is now in such
common use that it will always be available for any extended mining
operations. For single mines with small charges it may, however, be
necessary sometimes to resort to the older method of firing, the
apparatus for which can be readily improvised. But even in these cases
“Bickford” or “Safety” fuze will usually be available, and may be used
alone for firing gunpowder, or with a common fulminate-of-mercury
“blasting-cap” for high explosives. It burns at the rate of about 4
feet per minute. Very quick-burning fuzes are also made which may be
used at times (e. g., _Bickford Instantaneous_, which burns at the rate
of 120 feet a second; _Gomez Lightning_, which burns so rapidly that it
may almost be said to detonate; etc.) Great care must be taken not to
mistake them for the common Bickford.

=66. Electric Fuzes= are made of three general classes: First,
those which are fired by a spark from a high-tension machine; second,
those which are ignited by a current from a battery or “dynamo;” third,
those which can be fired by either. (Abels, etc.)

=67.= Those of the second class are manufactured in large
quantities, and, in connection with a portable dynamo or
“blasting-battery,” are almost universally used for blasting operations
throughout the United States.

These fuzes (Pl. XII, Fig. 32) are made up of two insulated copper
wires, _A_, _A_, passing through a small cylindrical block of
insulating material, _B_, and terminating about 1/16 inch above its
end. A very fine platinum wire, _C_, about 1/1000 inch in diameter and
1/8 inch long, connects the ends of the insulated wires. Surrounding
the platinum wire is a small quantity of gun-cotton, mealed powder, or
fulminate of mercury, _D_. A copper capsule containing 15 to 30 grains
of fulminate of mercury, _E_, is pressed down over the cylindrical
block far enough to bring the fulminate in contact with the material
surrounding the platinum wire, and the whole fuze is then coated with a
water-proof composition. The insulated copper wires are cut to various
lengths for convenience in connecting with the conductors or lead wires
from the battery.

=68.= Fuzes of the first and third classes are now but little
used. Many of them are unsatisfactory and dangerous. They differ in
construction from those of the second class principally in that the
platinum-wire bridge is omitted, and the exploding spark or current
passes from one insulated copper wire to the other through a material
which is ignited by it.

=69. Placing the Fuses in the Charges.=--A certain number of
cartridges or packages should be selected, each fuse inserted and well
packed in the explosive, and the wires or free end of the safety fuse
brought out through the opening, which should be made water-proof, if
necessary, by securely closing and thoroughly pitching it. The wires
or exterior part of the fuse should then be securely fastened to the
outside of the cartridge, so that an accidental strain upon them will
not break the waterproofing or move the fuse from its place. They are
then coiled up and remain so until the cartridge is placed in the
general charge of the mine.

=70.= Several of the high explosives congeal at a temperature
above the freezing-point of water, and in this state are less sensitive
to shock, and explode with difficulty if closely packed in cartridges
as usually delivered from the factories. They explode more readily when
in the form of a powder. When using them in cold weather, therefore,
each fuse should be put in a cartridge loosely filled with the powdered
explosive, or with some high explosive not affected by cold. Others
need special primers to cause detonation. The fuses should, of course,
be placed in these primers.

=71. Placing the Charges.=--The charge is placed in the
mine-chambers, either in the dark, by light reflected through the
galleries, by closed lanterns carefully placed and guarded, or, when
practicable, by incandescent electric lights. It is carried through low
and narrow galleries on men’s backs or in miner’s cars, and should for
this reason be put up in packages not exceeding 50 lbs. in weight.

It is packed in the chamber with great care, and under the immediate
supervision of the responsible officer. The packages containing the
fuses are distributed uniformly throughout the mass, and the wires
uncoiled and led back into the gallery, the free ends of the two wires
of each fuse having been previously twisted together for safety against
electric currents and for identification.

These wires, which must be long enough to reach through the tamping,
are all collected together and led back through it in a wooden or other
conduit, which protects them from injury while tamping the mine.

When electric lights are used, great care must be taken to remove the
light and all its conducting wires before the wires of the fuses are
uncoiled and laid along the gallery.

=72. Tamping.=--Mines are tamped with sods and earth, wood and
earth, sand-bags, etc., etc.

When sods are used the branch is filled for about 3 feet with sods
carefully laid and packed with the joints filled with earth. About 3
feet of earth is solidly packed against this, then alternate layers
of sods and earth until the desired length of tamping is obtained. To
tamp with wood and earth or sand-bags, a wooden shield is first placed
across the branch and firmly braced; behind this, earth is solidly
packed or sand-bags carefully laid until the required length of tamping
is obtained. Sometimes a second shield is put up behind the earth
tamping, and firmly braced in position. The strength of the tamping is
also increased by pieces of timber crossing each other diagonally, with
their ends resting against the sides of the branch. Sand-bags make the
best tamping, as they offer high resistance and are easily placed and
removed.

The tamping should have a length equal to at least 1½ times the line of
least resistance of a common mine corresponding to the charge, and if
not of the best quality, to twice this line.

=73. Firing Mines.=--If electric fuses are used the main
conductors or lead wires coiled upon a reel are taken in and the
ends properly joined to the fuse wires; they are then led through
the galleries, attached to the battery, and fired at the designated
instant. Under no circumstances should the main lead wires be connected
to the battery or dynamo until everything is ready for firing.

If a Bickford fuse is used its length is regulated to the desired time
of firing from its known rate of burning. The miner lights the end and
retires; the explosion takes place approximately at the calculated
time. With the “Lightning Gomez” or similar fuses a length reaching to
the firing-point may be used. It is lighted at the desired time, and
burns with such rapidity that for lengths not exceeding 300 or 400 feet
the time of burning is inappreciable.

Instead of using great lengths of these fuses, they may be cut
shorter and their ends be brought together and inserted in a little
mealed powder which is fired by a piece of safety-fuse, slow match or
port-fire, etc., long enough to give the miner time to retire to a safe
distance after igniting it.

Bickford fuse is best ignited by a piece of cotton wicking soaked in
oil and loosely tied around it. This, when lighted, will burn through
the covering and set fire to the composition. By this device many fuses
may be ignited in a short time. A slow match or “touch-paper” for
igniting quick-burning fuses or powder-trains may be made by soaking
common paper in a strong solution of nitre and drying it.


CAMOUFLETS BY BORING.

=74.= In favorable soil a camouflet or small mine may sometimes be
placed and fired very quickly by the following process:

A hole 2" to 3" in diameter and of the desired depth is bored in the
proper direction with an auger or boring-bar. A cartridge containing
from ½ lb. to 2 lbs. of dynamite is pushed down to the bottom and
fired. The explosion increases the diameter of the hole somewhat
throughout, and obstructs it more or less with loose earth. At the
same time it enlarges the part near the seat of the charge into a
bottle-shaped cavity, whose size varies with the charge used and the
nature of the soil. The hole is rapidly cleared out with a long-handled
scoop, the cavity filled with powder, primed, and fired.

The enlargement made by the charges of dynamite above given may contain
from 50 to 100 lbs. of gunpowder under favorable circumstances.

=75.= In stony soil this method becomes very difficult if not
impracticable; and when it can be used the preliminary explosion of
dynamite vitiates to a greater or less degree the air of the shaft or
gallery from which the boring is made, and also informs the enemy of
the progress and intention of the miner.

To remove the latter objections, the English authorities recommend the
use of holes 6" or 8" in diameter, bored with earth-augers, charged to
a length of 2 or 3 calibres, and well tamped. When applicable, this
method is manifestly a great improvement upon the other; but the auger
is so liable to be stopped by stones which a boring-bar might break or
push to one side, that it can only be applied in very favorable soil.




CHAPTER III.

ORGANIZATION AND TACTICS OF MINES.


=76. Organization of Mines.=--Underground warfare is conducted in
the dark, in bad air, with constant danger of caving earth, suffocation
by noxious gases, destruction of men and galleries by intentional
explosions of hostile mines or accidental ones of our own, in addition
to the usual dangers and difficulties of opening and supplying the
mines under the close fire of the enemy.

These considerations necessitate the rejection of all complicated
systems in the attack, and in the work carried on by the defence during
the siege.

Ignorance of the point to be selected for attack, and the great expense
of permanent countermines, also require those prepared beforehand by
the defence to conform to simple and economical systems.

For this reason it is not necessary to give in detail the systems
proposed by the older writers. They are described in most of the
extended treatises on military engineering.

=77. The Attack.=--The object of the attack is to advance his
galleries in the most rapid manner possible, with the best available
system of ventilation, and to place his mines in such position as to
break up the galleries and destroy the men, materiel, and works of the
defence, both above and below ground; or to form connecting craters
which may be occupied and converted into parallels, trenches, etc.

=78.= To accomplish this, when no natural ravine exists, a deep
trench or “_lodgment_” is made, usually connecting the entrances of all
the galleries and serving as a communication between them, and as a
depot for such supplies as must always be at hand.

From this lodgment the galleries are started by a shaft, blinded
descent, or mining-gallery; the method depending upon the depth to be
reached and the thickness of cover required.

The entrance of each gallery is protected from horizontal and vertical
fire, and from splinters, by a bomb-proof cover and traverses of
sufficient thickness and strength.

The galleries are generally driven in lines nearly parallel, and at
such distance apart that the hostile miners working at any point
between them will be heard, either from the main galleries or from
returns called “_listening-galleries_” or “_listeners_.”[20]

Depending upon the depth at which they are placed and other
circumstances arising in different cases, the main galleries in various
sieges have been placed at distances apart varying from about 8 to 30
yards.

These galleries are connected at intervals by “_transverse galleries_”
or “_transversals_,” which assist the ventilation very much and give
additional communication between them.

Branches for placing mines are driven in prolongation of the gallery
or obliquely to the right or left, and, when the gallery is at a low
level, inclining upward so as to shorten the line of least resistance,
economize powder, and diminish the injury to the gallery and branches,
resulting from the explosion of the mine.

=79.= When the hostile miners come within striking distance of
each other, each strives to run his galleries directly toward the
other in order to avoid exposing its flank to the hostile mine; thus
diminishing as much as possible the injury resulting from its explosion.

=80.= The mines of the attack are generally overcharged in order
to do the greatest possible injury to the mines of the defence, and to
open large craters, but undercharged mines and camouflets are also used
at times.

=81. The Defence.=--The object of the defence is to retard or stop
the advance of the attack, by the destruction of his mines and miners,
without forming craters which will assist him in making his parallels
and approaches.

=82.= For this purpose his galleries must satisfy nearly the
same conditions as those of the attack. They usually start out from
the counter-scarp gallery or from a parallel gallery a little in
advance of it, and extend to a greater or less distance from the work,
according to the time and expense allowable for their construction.
For permanent works they are frequently prepared in time of peace, and
lined with masonry. It is particularly for this class of countermines
that many elaborate systems have been designed for completely covering
the ground, and for throwing up the same earth several times by mines
placed at different depths and exploded in succession. For reasons
previously given, these cannot be recommended.

=83.= A simple system of galleries placed as far below the
surface as practicable, parallel or slightly diverging, connected
when necessary by transversals whose lines prolonged pass inside the
enceintes, and with branches fulfilling the same conditions driven out
for listening-galleries, will, under the direction of an energetic
officer, fulfil the conditions of defence as well, probably, as any
that can be devised.

The branches leading to mine-chambers can be driven out from the main
galleries, transversals, or listeners, as may be desired; and if the
hostile miners obtain possession of any part of the system and blow it
up, the lines of craters formed will be so swept by the fire of the
work that they can hardly be occupied by the enemy.

=84.= As a rule, the mines of the defence will be undercharged or
camouflets, to avoid the formation of exterior craters, but the rule is
not without exceptions.

=85. Shaft Mines=, mines placed in vertical shafts, are used
by both attack and defence for destroying galleries, etc., in their
vicinity. By the attack they are usually placed in craters already
formed, or in other places protected from hostile fire. A shaft is sunk
rapidly, generally “à la Boule,” heavily “overcharged,” filled up with
earth, and fired.

The defence may use the same method or may sometimes prepare them
beforehand, tamping them and leaving a tubular opening through the
tamping for loading and firing them.


MINE TACTICS.

=86.= The tactics of mine warfare result directly from the
consideration above given. The special details of attack and defence
vary in each particular case. The reports of mining operations in
different sieges[21] supply precedents and give suggestions for future
operations of a like character.

=87. Todleben’s Rules.=--The general principles of mine tactics
have been laid down by General Todleben from his experiences at
Sebastopol (in Royal Engineers Occasional Papers, vol. i., 1877). They
may be summarized as follows:

=88. The Attack.=--The besieger should advance by several
galleries, securing those on the flank by listeners. He must be active
and persistent, as the enemy will use every available moment to develop
his countermines. When he receives the first camouflet of the defence
he must hasten to fire his overcharged mines in the uninjured branches,
in order to destroy the hostile countermines. He will generally suffer
losses more or less heavy from this epoch forward, but must submit to
them; since too much circumspection and delay will almost always result
in complete failure.

Before firing the overcharged mines he must have everything in
readiness to occupy and intrench himself in the craters formed; to open
communication from the trenches to the craters either by sap or by
forming a line of connecting craters; and for constructing shelters for
the party occupying the craters and holding them against the sorties of
the defence.

After occupying the craters, he should drive forward his galleries from
them at once, unless the besieged has anticipated him and surrounded
the craters with branches--which may be assumed to be the case if any
delay has occurred in occupying it. In this case he should sink shafts
à la Boule, heavily overcharged, and fire them, and immediately occupy
the new crater and push out from it; and thus progress as rapidly as
possible, by constantly placing and firing overcharged mines, whose
craters will, with little alteration, form both communications and
parallels.

When the fire of the defence upon the crater is so severe that a deep
shaft cannot well be sunk, a shallower one with correspondingly small
charge is first sunk and fired, and a deeper one is sunk from the
crater thus formed.

The overcharged mines should be well tamped when time permits. If
not well tamped the charge should be increased (_or high explosives
used._--J. M.).

=89. The Defence.=--The defence should push out his galleries as
far as possible and at the earliest practicable date, connecting them
by transversals for ventilation, and holding them at a level below any
likely to be reached by the attack.

When near the enemy, he should stop work several times a day and listen
for sounds from the hostile miners which will locate their position.

Hearing the sound of the enemy’s miner, he may work toward him
noiselessly, or prepare and charge a chamber and await the approach
of the miner toward it, listening at the point where the hose trough
(_tube for fuse wires._--J. M.) comes through the tamping until the
enemy is near enough to justify firing. Judgment as to distances must
be formed from practice obtained while driving the countermines.

To avoid forming craters on the surface, and to do the greatest
possible damage to the besieger’s works, the besieged should not fire
his mine until the enemy’s distance from it is less than the line of
least resistance reckoned toward the surface.

When this condition is fulfilled, he may give to his camouflet a charge
of from 3/10 to 4/10 the charge for a common mine placed at the same
depth, since the charge will produce its principal effect upon the
enemy’s gallery, and but little upon the surface.

Special care must be exercised by the defence to avoid premature
explosions, since a mine fired at too great range damages only his own
branch, and may make a crater; thus working directly to the advantage
of the attack, who may prepare an overcharged mine or sink a shaft à la
Boule in the crater thus made.

As successive explosions of necessity damage the branch in use, to
avoid falling back, another one should be prepared as a reserve before
the first is disabled, and at a little distance from it.

After the attack has fired his overcharged mine, the defence, by a
strong fire of canister, musketry, etc., should prevent him from
occupying the craters, and if he takes possession, should drive him
out by a continuous mortar fire, keeping him from completing his
communications by fire from guns.

The defence should push forward branches and establish himself under
the slope of the craters, in front and on both flanks, and by exploding
camouflets prevent the attack from driving galleries or sinking shafts
à la Boule.

When the nature of the soil admits, many of the camouflets will be
placed by boring. Should the defensive measures above and below ground
not debar the enemy from establishing himself in the crater, the
defence may establish overcharged mines immediately in its front, with
a view to destroying the advancing galleries of the attack, blowing up
the men and their lodgment in the crater, and opening up the latter to
the fire of the work.

Shafts à la Boule being very dangerous for the countermines, the
defence should do his best to prevent their use, by artillery and
musketry fire above ground, and by camouflets placed by boring under
ground. In addition, he must take advantage of every favorable
opportunity to delay the progress of the attack by sorties from the
works.

=90. Remark.=--In underground warfare the besieger has a decided
advantage, but the besieged, by a cool consideration in handling his
mines, and by persistently holding back the attack, foot by foot, may
very greatly retard it, or even cause such losses and delays as to lead
to its being abandoned.


BREACHING BY MINES.

=91.= The attack having reached the scarp of the work, mines are
prepared for breaching the counter-scarp and scarp.

Experience shows that the charges are best located in rear of the
counterforts when they exist, or at equal intervals along plain walls.
The charge should not be placed immediately in contact with the
masonry, but in the earth behind it, and at a depth below the top of
the wall equal at least to 1½ the L. L. R., measured to the face of the
wall.

The charge should be estimated by the rules already given, and
increased by 20 to 30 per cent, so as not only to throw down the walls,
but also to break up the earth and form a practicable breach.

=92.= The galleries for placing the chambers behind the
counterscarp are branches from the gallery of descent into the ditch;
those behind the scarp may branch out from a gallery driven under the
ditch, when water or rock do not forbid, or from a gallery driven
through the scarp wall after crossing the ditch by sap or by a bridge.

=93.= To start the gallery through the scarp wall, a miner is
“_attached_” to the wall by protecting him from fire along the ditch,
from sorties, and from loaded shells, etc., rolling down upon him from
the parapet by suitable traverses and splinter-proof.

This operation is of course very dangerous, and is generally impossible
unless the fire of the defence along the ditch is previously silenced.
To expedite the work of the miner a gun is sometimes brought down
through the gallery, and the face of the wall is shattered by its fire
before the miner is “=attached=.”




CHAPTER IV.

BLASTING AND DEMOLITIONS.


BLASTING.

=94. Blasts= are small mines used generally for breaking up rocks,
or masonry in demolitions.

=95.= Holes for placing the charges are drilled usually with
_drill-bars_ or _churn-drills_, known also as _jumpers_.

These are steel bars sharpened to a chisel edge. The _drill-bar_ is
usually held by one man and struck with a hammer by another; it is
turned slightly after each blow in order to make a round hole.

For small holes the driller holds the drill in one hand and strikes
with the other.

The _churn-drill_ is a longer bar, generally sharpened at both ends
and enlarged in the middle. It is used for drilling vertical holes by
raising and dropping it in the holes, turning it slightly after each
blow.

=96.= The _charge_ may be gunpowder or high explosive. If the
former, it must be thoroughly tamped. If the latter, tamping will
greatly increase its effect; but it is in some cases preferable to
obtain the desired effect by increasing the charge and saving the time
taken in tamping.

=97.= Blasts are fired by electric fuses, Bickford fuse,
firing-tubes, needles, etc.

The fuses have been already described.

The _firing-tube_ is a very small iron pipe, which is inserted in the
powder charge and the tamping rammed around it.

After the tamping is finished the tube may be filled with fine powder
poured in it if the hole is vertical or inclined downward, or straws
filled with powder may be inserted if it inclines upward or is
horizontal. A “squib” of wet powder is also sometimes placed in the
tube and ignited, when it passes down the tube like a rocket and fires
the charge.

The _needle_ is a smooth copper wire, longer than the depth of the
hole. It has a ring handle, by which it may be turned around and
withdrawn. It is inserted in the charge, the tamping is well rammed
around it, and it is withdrawn, leaving a pipe in the tamping, through
which fire may be communicated, as described for the firing-tube.

=98. Tamping.=--The best and safest tamping is perfectly dry
silicious sand, poured in the hole so as to fill it completely, but not
rammed. It cannot be used in holes which incline upward nor when the
needle is used.

In such cases moist clay, brick-dust, etc., are used. The first layers
are pressed in upon the charge, and the subsequent ones thoroughly
rammed down with a copper tamping-bar. A hammer is used with the bar,
when necessary, in deep holes and hard rock.

_With high explosives no tamping should be used except dry sand or
water. Holes which incline upwards should receive an extra charge and
be untamped._

=99. Determining the Charge.=--The charge of gunpowder or high
explosive required for any particular hole in ordinary blasting can
be best estimated by an experienced blaster. If one is not to be
obtained, an approximate estimate for the first experiment may be
made from the formulas (counting the high explosives about four or
five times as strong as gunpowder for ordinary use), and the charges
for subsequent blasts may be estimated from the effects of those first
fired.

=100. Precautions.=--If a _tamped_ hole misses fire _it should
never be cleared out for recharging_. A new hole should be drilled
near, but not breaking into it.

Electric fuses or Bickford fuses (with blasting-caps for high
explosives) should always be used when they can be obtained.


DEMOLITIONS.

=101. Deliberate Demolitions=, such as the destruction of walls,
casemates, etc., in time of peace, or at a distance from the enemy in
time of war, should be so made as to economize powder and work. To
accomplish this, the mines and blasts should be located where they
will produce the best effects attainable, and the charges should be
proportioned to the work required from them.

The table previously given (p. 124) will serve as a guide for computing
the first charges used, and from the results of these the charges of
subsequent ones may be determined.

Judgment must be used in placing the charges, so that, when possible,
they will destroy the supports and allow the superstructure to break up
by falling.

The charges will usually be placed in chambers under or hollowed out in
the masonry. Sometimes they are more advantageously placed in a trench
outside and close to the foot of the walls. They should always be well
tamped: when in mine-chambers, by methods previously described; when
in trenches, or laid along the exterior of walls, by loading them with
earth, etc., until the line of least resistance passes through the wall
to be destroyed.

=102. Hasty Demolitions= are made when the time available for the
work is limited.

The structures usually destroyed are houses, walls, stockades, bridges,
tunnels, canal-locks, railroads, rolling-stock, etc., etc.

The time does not usually allow the charge to be placed in the most
advantageous position or to be properly tamped. For this reason the
high explosives are best suited for this kind of work, and large
charges are a necessity.

=103. Houses and Magazines= are best destroyed by placing several
charges with connecting trains inside and along the walls, laying
strong timbers upon them, with struts from the timbers to the floors
and roof above; barricading the doors and windows from within, and
firing the powder from a safe distance without.

=104. Walls.=--A wall not exceeding 3 or 4 feet in thickness may
be breached by charges of gunpowder placed at intervals along it.
Calling the thickness of the wall in feet _t_, the charge in pounds may
be 3_t_^3, placed at intervals of 2_t_.

For gun-cotton the Woolwich rule calls for charges in pounds of from
⅓_t_^2 to ½_t_^2 per running foot. Experiments made in New York with
dynamite indicate that the charges should be at least ½_t_^2 per
running foot, and for very good masonry should exceed this.

A charge of dynamite of ½_t_^2 per running foot will be given by a
cylindrical cartridge whose diameter in inches equals the thickness
of the wall in feet.[22] The effect of the charge will be very much
increased by throwing over it even a very light tamping of earth or
sand.

=105. Stockades.=--A strong stockade or palisade may be broken
down by charges of from 40 to 60 lbs. of gunpowder placed in contact
with it, and preferably covered with sand-bags. 10 or 15 lbs. of high
explosive should produce about the same effect.

=106. Bridges.=--Arched bridges are best attacked in the piers if
high and thin, or at the haunches and crown of the arch. Two or more
charges in the length of the pier, or width of the roadway, will be
more effective than the same amount in a single charge at the middle.

The charges should be placed in chambers cut in the piers or down
through the roadway to the back of the arch.

The abutments of single-span arches are generally very strong, and
the haunches well covered with earth and masonry. In hurried work,
therefore, the crown will generally be selected, a trench dug down
to it across the roadway, the charge placed in the trench, tamped if
possible, and fired.[23]

High explosives, from their shattering effect, are perhaps most
advantageously used by suspending them beneath and in contact with
the arch at the crown and haunches. The plank or timber upon which
they are placed should be as heavy as possible, in order to act as a
partial tamping, and should be drawn up so that the explosive will be
in actual contact with the soffit of the arch.

Under these circumstances they should produce as great an effect as
four or five times their weight of gunpowder.

Iron and wooden truss-bridges should be thrown down by breaking the
main braces near the piers, or the chords near the centre, by charges
placed in a joint if possible. High explosives are particularly
valuable for this purpose.

In wooden bridges they may be placed in auger-holes bored for them,
and in iron bridges inside the hollow members, between eye-bars, or in
other similar places.

=107. Tunnels, Canal-locks=, and similar constructions must be
attacked with large charges, so placed as to temporarily or permanently
disable the work, as may be considered necessary. The location of
each charge should be determined and its amount computed from these
considerations before the destruction is attempted.

A temporary obstruction is frequently all that is necessary or
desirable for these works, and the damage done to them should be
carefully regulated with a view to their subsequent repair and use.

=108. Railroads.=--Railroads are temporarily disabled by tearing
up the track, making hot fires of piles of ties, placing the rails upon
them so that they will heat and bend by their own weight; or, better
still, twisting the rails while hot by suitably-shaped steel hooks and
wooden levers of the kind devised by General Haupt (Pl. XII, Fig. 33).
Rails so twisted cannot be again used until re-rolled.

=109. Rolling-stock.=--Railroad cars may be disabled by breaking
one or more wheels with sledges, or may be destroyed by burning.
Locomotives may be disabled temporarily by carrying away the smaller
parts of the mechanism, or permanently by breaking the engine-cylinders
with sledges; bursting the boilers or burning out their fire-boxes by
drawing out nearly all their water, fastening down the safety-valves,
and building a hot fire in the furnaces; or by making a hot fire under
them so as to heat and thus bend or warp the reciprocating parts of the
machinery.

=110.= In all hasty demolitions with explosives the charges should
be well in excess of those computed by the ordinary rules: first,
because the explosives will not be so placed as to act to the greatest
advantage; and, second, because the demolition should be _immediate_
and _complete_.




INDEX.


  A

                                                                  PAGE
  Additional operations--intrenched camps,                          91

  Advance from first parallel,                                      84

  Advanced positions,                                              104

  Advantage lies with attack,                                      176

  Ammunition,                                              44, 57, 101

  Angle template,                                             137, 148

  Approaches,                                                       16

  Approaches, execution of,                                       20-3

  Approaches, tracing,                                              18

  Approaches, over-ground,                                          31

  Ascending galleries,                                             148

  Armament,                                                        100

  Army of observation,                                              69

  Artillery, first position,                                   75, 104

  Artillery, first position opening fire,                           67

  Artillery, second position,                                       81

  Artillery, second position opening fire,                          83

  Artillery-fire, opening, by defence,                             104

  Assault,                                                           4

  Assault, defence against,                                          7

  Assault, dispositions for,                                         5

  Assault of breach,                                                89

  Attaching a miner,                                               177

  Attack by mines,                                             169-171

  Attack by sap,                                                    91

  Attack, close,                                                   107

  Attack, journal of,                                               97

  Attack, plan of,                                                  78

  Attack, point of,                                                 73

  Attack, successive steps of,                                      64

  Auger, earth,                                                    138

  Auxiliary frame,                                                 144


  B

  Battery, alternative construction,                                50

  Battery behind crest of hill,                                     53

  Battery, breaching,                                               83

  Battery, construction of,                                         48

  Battery, constructing centre passage of,                          48

  Battery, counter,                                                 82

  Battery, definitions,                                             42

  Battery, electric,                                             163-6

  Battery, enfilading,                                              82

  Battery, exposed sunken,                                          46

  Battery for field-guns, construction of,                          43

  Battery for siege-guns and howitzers,                             44

  Battery for siege-guns, ammunition required,                      44

  Battery, general requirements of siege,                           42

  Battery, location of,                                          9, 75

  Battery, mortar,                                                  55

  Battery of rifled mortars and howitzers,                          83

  Battery on sloping ground,                                        53

  Battery, sunken, in a parallel,                                   51

  Battery, tracing the,                                             47

  Belfort, siege of,                                     71-2, 86, 104

  Besieging force, bringing up and posting,                         67

  Besieging force, strength and composition,                      70-2

  Blasts,                                                          178

  Blasting and demolitions,                                     178-84

  Blindage-frames or blinds,                                       156

  Blinded descents or galleries,                          38, 156, 170

  Blinded sap,                                                      38

  Blinded sap, traverse by,                                         35

  Blinds or screens,                                                45

  Blockade,                                                          1

  Bombardment,                                                       8

  Bombardment, defence against,                                     10

  Bombardment, defence during,                                     105

  Bomb-proofs and traverses,                                   25, 170

  Branches,                                                     170-72

  Breach, capture and crowning of,                                  89

  Breaching batteries,                                              83

  Breaching by mines,                                            176-7

  Breaching galleries,                                             177

  Breaching the scarp and counter-scarp,                            88

  Breaking out a full sap from a parallel,                          30

  Breaking out a double sap from a parallel,                        33

  Bridge, demolition of,                                           182

  Bridge, floating--passage of ditch,                               40

  Brigade or detachment of sappers,                                 28

  Bringing up and posting the besieging force,                      67


  C

  Camps, fortifying,                                                68

  Camouflet,                                        120, 167, 171, 172

  Canal locks, demolition of,                                      183

  Capitulation, the,                                               109

  Capture and crowning of breach,                                   89

  Capture and crowning of covered way,                              87

  Cases, mining,                                                139-41

  Chamber, definition,                                             119

  Chamber, form and location,                                      160

  Changing direction of double sap,                                 33

  Changing direction of galleries,                       148, 150, 154

  Changing slope of galleries,                                149, 155

  Charge, definition,                                              119

  Charge, excess to be used in demolitions,                        184

  Charge for over- or under-charged mines,                         125

  Charge for blasts, weight determined,                            179

  Charge for blasts, when tamped,                                178-9

  Charge for common mines,                                       122-4

  Charge for mines, placing,                                       165

  Charge for mines, preparing,                                     161

  Choice of explosives,                                            132

  Churn-drill,                                                     178

  Circular place of arms,                                           31

  Conquered place, occupation of,                                   93

  Common mine defined,                                             120

  Common mine volumes and charges,                               120-4

  Construction of battery for field-guns,                           43

  Construction of battery, sunken,                               48-50

  Construction of central passage,                                  48

  Construction of magazine,                                         60

  Construction of simple trench,                                    20

  Construction of trench by flying sap,                             22

  Counter-battery,                                                  82

  Cover for bomb and splinter proofs,                            23-25

  Cover for magazines,                                              58

  Covered way, crowning of the,                                     35

  Crater, definitions,                                             119

  Crater, assumed form of,                                         121

  Crater relation between volume and charge,                     120-7

  Crater radius, definition,                                       119

  Crowning the covered way,                                         35

  Crutch,                                                          154


  D

  Dampness, precautions against,                                    63

  Defence, the,                                                 99-111

  Defence against assault,                                      7, 105

  Defence against bombardment,                                 10, 105

  Defence against surprise,                                          4

  Defence, ammunition for,                                         101

  Defence, armament for,                                           100

  Defence by mines,                                              171-2

  Defence, council of,                                              98

  Defence during bombardment and assault,                          105

  Defence during first period,                                     103

  Defence during second period,                                    106

  Defence during third period,                                     107

  Defence, garrison for,                                            99

  Defence, journal of,                                             110

  Defence, opening artillery fire by,                              104

  Defence, preliminary considerations,                              98

  Defence, preparations for,                                       101

  Defence, provisions and supplies,                                101

  Demi-parallels,                                                   86

  Demolitions, deliberate,                                         180

  Demolitions, hasty,                                              181

  Descending galleries,                                            147

  Detachment or brigade of sappers,                                 28

  Detonation,                                                      162

  Dispositions for an assault,                                       5

  Distribution of fuzes in charge,                                 161

  Distance of line of investment,                                   70

  Ditch, passage of,                                                37

  Double sap,                                                       32

  Double sap, breaking out, from a parallel,                        33

  Double sap, changing direction of,                                33

  Double sap, execution of,                                         32

  Drainage,                                             16, 24, 55, 59

  Drawings, working,                                               151

  Drill-bars and drills,                                           178

  Dynamite, etc.,                                                132-5

  Dynamite, freezing of,                                           165

  Dynamite, tamping,                                               179


  E

  Earth auger,                                                     138

  Electric batteries, wires, and lights,                         165-6

  Elevated and sunken batteries,                                    44

  Elevated magazine,                                                62

  Embrasures,                                                       53

  Enfilading batteries,                                             82

  Execution of double sap,                                          32

  Execution of single sap,                                          28

  Experimental mines,                                    125, 131, 133

  Explosion, theory of,                                            120

  Explosive, charge for blasts,                                    179

  Explosive, charge for mines,                                   122-5

  Explosive, choice of,                                          132-5

  Explosive, expenditure of energy,                                120

  Explosive, freezing of,                                          165

  Explosive, noxious gases from,                              133, 158

  Explosive, relative strength of,                            131, 179

  Explosive, tamping of,                                         178-9

  Exposed sunken battery,                                           46


  F

  False frame,                                                     146

  Field kitchens and ovens,                                        114

  Field-level, description,                                        136

  Field-level, use,                                      146, 148, 149

  Filtration of water,                                             117

  Fire, musketry,                                                   84

  Fire, opening by attack,                                          76

  Fire, opening by defence,                                        104

  Fire, opening from second artillery position,                     83

  Firing blasts,                                                   178

  Firing and loading mines,                                      161-6

  Firing-tubes and needles,                                      178-9

  First artillery position,                                         75

  First parallel,                                                   78

  First period of the siege,                                        65

  Flying sap,                                                       20

  Flying sap, construction of,                                      22

  Fort Wagner,                                                      86

  Form and volume of crater,                                       121

  Fortifying camps, parks, etc.,                                    68

  Frames and sheeting compared with cases,                         141

  Frames and sheeting, use in shafts,                           139-45

  Frames and sheeting, use in galleries,                        145-51

  Freezing of high explosives,                                     165

  Full sap,                                                         28

  Full sap, driving of,                                             28

  Full sap, breaking out from a parallel,                           30

  Fuzes,                                                 161, 164, 166


  G

  Galleries, blinded,                                              156

  Galleries, change of direction of,                     148, 150, 154

  Galleries, change of slopes of,                             149, 154

  Galleries, definitions and dimensions,                      119, 138

  Galleries, direction in attack,                                  171

  Galleries, distance apart,                                       170

  Galleries, for breaching,                                        177

  Galleries, inclined,                                      147-9, 155

  Galleries, listening,                                            170

  Galleries of departure,                                          150

  Galleries, partly lined,                                         148

  Galleries, rate of advance of,                                   157

  Galleries, transverse,                                           170

  Gallery linings,                                              139-41

  Gallery with frames and sheeting,                             145-51

  Gallery with cases,                                            153-6

  Garrison of place,                                                99

  Gases generated in mines,                                   133, 158

  General requirements of siege batteries,                          42

  Globe of compression defined,                                    120

  Governor of the place,                                            98

  Guns, field, batteries for,                                       43

  Guns and howitzers, batteries for,                                44

  Guns, ammunition required,                                     44-57

  Guns for armament,                                               100

  Guns of first artillery position,                                 76

  Guns, positions of, to be changed,                               106

  Gunpowder, amount per cubic yard,                      123, 124, 178


  H

  Hasty demolitions,                                               181

  High explosives compared with gunpowder,                       131-5

  High explosives, freezing of,                                    165

  High explosives, use in blasting,                             179-80

  Houses and magazines, demolition of,                             181

  Howitzer batteries,                                               44

  Howitzers for vertical fire,                                      83

  Huts and shelters,                                               113


  I

  Inclined galleries,                                               47

  Infantry trenches,                                               104

  Intrenched camp, attack upon,                                     91

  Investment,                                                    9, 65

  Investment, distance of line of,                               70-72


  J

  Journal of the attack,                                            97

  Journal of the defence,                                          110

  Jumper,                                                          178


  K

  Kitchens and ovens,                                              114


  L

  Landings,                                                      150-1

  Latrines, sinks, etc.,                                           115

  Line of investment, distance of,                                  70

  Line of least resistance = L. L. R.,                             119

  Listening galleries or listeners,                             170-72

  Loading and firing mines,                                        161

  Location of batteries,                                         9, 75

  Location of magazine,                                             58

  Lodgement,                                                       170


  M

  Magazines,                                                        57

  Magazines, construction of,                                       60

  Magazines, cover for,                                             58

  Magazines, drainage of,                                           59

  Magazines, elevated,                                              62

  Magazines, execution of the work upon,                            61

  Magazines, location of,                                           58

  Magazines, mined,                                                 61

  Magazines, precautions against dampness,                          63

  Maps,                                                            151

  Masks for batteries, etc.,                                        45

  Masks, air-tight, for exploring mines,                           160

  Maxims, Vauban’s,                                                 94

  Mine defined,                                                    119

  Mine-chamber,                                                    160

  Mine, common,                                                  120-5

  Mine, overcharged and undercharged,            120, 125, 131, 171-72

  Mines of attack,                                            169, 171

  Mines of defence,                                              171-2

  Mines, organization of,                                          169

  Mine tactics,                                                  172-6

  Mined magazine,                                                   61

  Mining, military, object of,                                     119

  Miner, attaching a,                                              177

  Miner’s bellows,                                                 137

  Miner’s candlestick,                                             137

  Miner’s lamp,                                                    137

  Miner’s pick and shovel,                                         136

  Miner’s rule,                                                    122

  Miner’s truck or car,                                            137

  Mortar batteries,                                             55, 83

  Mortars, siege,                                              57, 107

  Musketry fire,                                                    84


  O

  Observatories,                                                    54

  Occupation of conquered place,                                    93

  Opening fire, attack,                                             76

  Opening fire, defence,                                           104

  Opening fire from second artillery position,                      83

  Opening the first parallel,                                       80

  Organization and duties of brigade of sappers,                    28

  Organization and tactics of mines,                            169-76

  Ovens and kitchens,                                              114

  Overcharged and undercharged mines,                  120, 125, 171-2

  Overground approaches,                                            31


  P

  Parallels,                                                        15

  Parallels, demi-,                                                 86

  Parallels, execution of,                                        20-3

  Parallel, first,                                                  78

  Parallel, first, opening,                                         80

  Parallel, first, advance from,                                    84

  Parallel, second,                                                 85

  Parallel, third, etc.,                                            86

  Parallel, tracing a,                                              17

  Parks, camps, etc., fortifying,                                   68

  Parks and depots,                                                111

  Partly-lined galleries,                                          148

  Paris, siege of,                                                71-2

  Passage, central, of battery,                                     48

  Passage of the ditch,                                             37

  Period, first, of siege,                                     65, 103

  Period, second, of siege,                                    75, 106

  Period, third, of siege,                                     86, 107

  Pick and shovel, miner’s,                                        136

  Pick, miner’s, distance heard,                                   170

  Placing fuzes in charge,                                         164

  Placing the charge,                                         165, 176

  Plan of attack,                                                   78

  Plevna, siege of,                                             71, 72

  Point of attack,                                                  73

  Posting besieging force,                                          67

  Posting working parties,                                          18

  Powder-boxes,                                                     58

  Powder for siege batteries,                                   44, 57

  Precautions against dampness,                                     63

  Precautions in blasting,                                         180

  Preliminary considerations of defence,                            98

  Preparations for defence,                                        101

  Preparing the charge,                                            161

  Progress of the siege,                                            12

  Proofs, bomb,                                                     25

  Proofs, splinter,                                         23, 48, 50

  Provisions and supplies,                                         101

  Push pick,                                                       136


  R

  Radius of explosion,                                             119

  Radius of rupture,                                     120, 128, 131

  Railroads, demolition of,                                        183

  Rate of advance of galleries,                                    157

  Rate of advance of sap,                                           29

  Regular approaches,                                               12

  Requirements, general, of siege batteries,                        42

  Returns,                                                       150-1

  Rifled mortars and howitzers, batteries of,                       83

  Rolling-stock, demolition of,                                    184


  S

  Sand-bag fork,                                                    13

  Sap, attack by,                                                   91

  Sap, definition,                                                  27

  Sap, blinded,                                                     35

  Sap, breaking out from a parallel,                                30

  Sap, double,                                                    32-3

  Sap-fork,                                                         13

  Sap, flying,                                                  20, 22

  Sap, full,                                                     28-30

  Sap, shallow,                                                     31

  Sap-shield,                                                   13, 23

  Sap, traversed,                                                 33-5

  Sap, widening the,                                                30

  Sapping, definitions, etc.,                                       27

  Sapping, former methods,                                          36

  Scraper,                                                          13

  Screens,                                                          45

  Second artillery position,                                        81

  Second artillery position, opening fire from,                     83

  Second parallel,                                                  85

  Shaft, definitions and dimensions,                          119, 138

  Shaft à la Boule,                                           156, 172

  Shaft intervals,                                                 142

  Shaft linings,                                               139-141

  Shaft mines,                                                     172

  Shaft, sinking, with cases,                                    152-4

  Shaft, sinking, with frames and sheeting,                      141-5

  Shaft in a lodgement,                                            170

  Shallow sap,                                                      31

  Shelters and huts,                                               113

  Shield for covering ditch,                                     38-40

  Shield for driving gallery,                                      147

  Shovel and pick, miner’s,                                        136

  Siege, definitions, etc.,                                     12, 64

  Siege batteries,                                               42-53

  Siege, first period of,                                      65, 103

  Siege, second period of,                                     75, 106

  Siege, third period of,                                      86, 107

  Siege, length of,                                                 71

  Siege of Belfort, Fort Wagner, Paris, Plevna,
      and Strasburg,                                       71, 86, 104

  Simple trench,                                                    20

  Sinking shaft with frames and sheeting,                        141-5

  Sinking shaft with cases,                                      152-4

  Sinks and latrines,                                              115

  Slope, defined,                                                  119

  Slope-block,                                                137, 148

  Slope, change of,                                           149, 155

  Slope, method of fixing,                                         147

  Squibs,                                                          178

  Splinter-proofs,                                          23, 48, 56

  Sterilizing water,                                               117

  Stockades, demolition of,                                        182

  Strasburg, siege of,                                          71, 86

  Sunken battery,                                                45-53

  Supplies and provisions,                                         101

  Surprise,                                                          2

  Surprise, defence against,                                         4

  Surrender of the place,                                          109


  T

  Tamping blasts,                                                178-9

  Tamping mines,                                                   166

  Third period of siege,                                            86

  Todleben’s rules,                                                173

  Tools and appliances,                                        10, 136

  Tracing approaches,                                               18

  Tracing a battery,                                                47

  Tracing lanterns, pickets, tapes, etc.,                           14

  Tracing parallels,                                                17

  Transverse galleries or transversals,                            170

  Traverse by blinded sap,                                          35

  Traverse, cube,                                                   34

  Traverses, length of,                                             34

  Traversed sap,                                                    33

  Trenches,                                                         15

  Trench cavalier,                                                  36

  Trenches, guard of the,                                           15

  Trench, infantry,                                                104

  Trench, simple,                                                   20

  Tunnels, demolition of,                                          183


  U

  Underground warfare,                                             169


  V

  Vauban’s maxims,                                                  94

  Ventilation of mines,                                         158-60

  Vertical fire, batteries for,                                     83

  Volume and form of craters,                                      121

  Volume and weight of charge,                                161, 181


  W

  Wagner, Fort, siege of,                                           86

  Walls, demolition of,                                            181

  Water-supply,                                                    116

  Weight and volume of charge,                                161, 181

  Wet ditch, passage of,                                         38-40

  Working drawings,                                                151


[Illustration:

  _Plate I._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate II._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate III._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate IV._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate V._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate VI._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate VII._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate VIII._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate IX._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _Plate X._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _MILITARY MINING Plate XI._

  _Bradley & Poates, Engr’s, N. Y._]

[Illustration:

  _MILITARY MINING Plate XII._

  _Bradley & Poates, Engr’s, N. Y._]




BOOKS FOR

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FOOTNOTES:

[1] In the siege of Strasburg, 1870, a bridge of beer casks was built
across the ditch of Lunette No. 52, between nightfall and 10 P. M.,
September 21st. The ditch was about 66 feet wide and 9 to 10 feet deep.
This bridge gave access to the lunette. It was subsequently sunk by the
fire of the work and was replaced by a causeway.--Franco-German War,
Official Account, Part 2, vol. 1., pp. 88, 89.

[2] One of a group of trees may frequently serve for this purpose.

[3] The charge for the 5" siege gun is 15 lbs. of powder; 200 rounds =
3,000 lbs.; 2 guns, 6,000 lbs.

[4] No special box has been adopted in our service. The English box is
1' 9" × 1' 5½" × 1' 5" outside, metal lined, and holds almost 100 lbs.
of made-up cartridges.

[5] The crater radius of a mine with L. L. R. of 6' to 12' and a charge
of 6,000 lbs. of powder would be about 44 feet (Art. 7, Military
Mining). The radius of the mound of earth thrown out would probably be
three times this.

[6] Quoted from Mahan’s Siege Operations.

[7] A shell from a 9" .45 rifled mortar has in experimental firing
produced in moderately hard ground a crater 8 feet deep and 19½ feet in
diameter.

[8] From the unpublished records of three experimental mines fired at
 Willet’s Point in 1877-83 it would seem that the quantities given in
 this table are greater than those required if good American powder is
 used. These mines, in a soil of modified drift,
 with a L. L. R. of 12 ft. required 1.02 lbs. per cu. yd. = 1 lb. ⅓ oz.; and
 with a L. L. R. of 17 ft. required 1.15 lbs. per cu. yd. = 1 lb. 2½ oz.

[9] Six-lined craters (_r_ = 3_l_) are generally considered as the
practical limit of overcharged mines, although at Chatham mines have
been fired giving _r_ = (3-3/4)_l_. The published data concerning them
indicate that they required charges larger than the formulas above
given call for.

[10] Describe the semicircle _BMNF_. Then

  _OD_ : _ON_ :: _CH_ : _CM_;

  _l_ : _ON_ :: _v_ : _h_.

  _ON_^2 = (_h_^2 _l_^2) / _v_^2.      (1)

  _BO_ : _ON_ :: _ON_ : _OF_;

  _h_ + _r_ : _ON_ :: _ON_ : _h_ - _r_.

  _ON_^2 = _h_^2 - _r_^2      (2)

  _CF_ : _CH_ :: _CD_ : _CK_;

  _h_ : _v_ :: √(_r_^2 + _l_^2) : _l_.

  (_h_^2)(_l_^2)/_v_^2 = _r_^2 + _l_^2      (3)

  ∴ Eqs. (1), (2), and (3), _r_^2 + _l_^2 = _h_^2 - _r_^2.

  _h_^2 = _l_^2 +2_r_^2      (4)

  _h_ = √(1 + 2(_r_/_l_)^2).

         *       *       *       *       *

  Eqs. (3) and (4), (_l_^2 + 2_r_^2)_l_^2 = _v_^2(_r_^2 + _l_^2).

  _v_^2 = (_l_^2 +2_r_^2)/(1+_r_^2/_l_^2) = _l_^2(1+2(_r_^2/_l_^2))/(1+_r_^2/_l_^2);

  _v_ = _l_(√((1+2(_r_/_l_)^2)/(1+(_r_/_l_)^2))).


[11] General Abbot’s experiments in submarine mining fix the relative
values of cannon powder and dynamite No. 1 in water, measured by the
pressure exerted by them (not by the craters formed), as 1 : 2.45. The
characters of the media and the explosives would naturally lead to the
inference that the superiority of dynamite over powder would be greater
in water than in earth.--J. M.

[12] The 82 lb. dynamite-mine at Willet’s Point produced almost exactly
the same effect upon the gallery of access as the 200-lb. cannon-powder
mine, while its external crater was considerably less in diameter.
Its crater was surrounded, however, by concentric cracks spaced at
intervals of 3 or 4 feet to a distance of about 40 feet from the centre
of the crater. No such effect was produced by the powder-mine.

On the other hand, the actual radii of rupture produced by five
experimental mines fired at Olmutz in 1871-2 agree very closely with
the values which result from applying Lebrun’s formulas to craters
of the same size and shape produced by gunpowder, and indicate that
charges of dynamite and gunpowder which produce identical craters
will also have identical radii of rupture. The somewhat contradictory
results given by the Willet’s Point and Olmutz mines show the necessity
for further experiments.

[13] To pass a 5" siege-gun, mounted upon a high or “overbank” carriage
(model 1887), requires a gallery 7' × 7' in clear.

[14] Four of these may be unskilled laborers.

[15] No. required at commencement of gallery. Beyond 4 feet add one
man, and one additional for every 20 feet of gallery.

[16] Instead of a truck a canvas bag may be used. A large hoe or drag
may be used to draw back the earth from the face of the gallery.

[17] One mason’s level.

[18] These numbers are for small shafts of about 2' by 4'; large
shafts require a larger force. They advance at about the same rate as
galleries of equal cross-section.

[19] In the blasting at Hell Gate, 1870-76, several cases occurred,
both with nitro-glycerine and compressed gun-cotton, in which a part
of the charge exploded, breaking the blast-hole nearly to the bottom,
and leaving the remainder of the charge unexploded in the bottom of the
hole, from which it was subsequently recovered. Similar results were
obtained in experiments, conducted by Capt. (now Major) Heuer, 1875-6,
with long tubes filled with nitro-glycerine. See also Encyc. Brit.,
vol. xvi, “Mining,” for similar information.

[20] In compact soil the sound of a pick can be heard up to about 40
feet, and at about 20 feet when the miners are working as quietly as
possible.

[21] E.g., the sieges of Candia (1667-9), Schweidnitz (1762),
Silistria and Brailow (1828-9), Sebastopol (1854-5), Vicksburg (1863),
Petersburg (1864), etc., etc., and the experimental mining operations
at Graudenz in 1862. See Woolwich and Chatham Text-books, Mahan’s Field
Fortifications, Guerre de Siège Blanchecotte et Chauvot Fontainebleau,
etc., etc.

[22] A dynamite cartridge 1" in diameter weighs ½ lb. per running foot;
2" in diameter, 2 lbs. per ft.; etc.

[23] Capt. Schaw’s (R. E.) rule for an untamped charge of gunpowder
placed as above described is _C_ lbs. = ⅔ L. L. R.^2 × _B_, in which
_C_ = charge in pounds, _B_ = breadth of bridge in feet, and L. L. R. =
line of least resistance in feet, measured through the arch.


[Transcriber’s Note:

Obvious printer errors corrected silently.

Inconsistent spelling and hyphenation are as in the original.]





End of Project Gutenberg's Attack of Fortified Places., by James Mercur