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=.”