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.