Fig. A. Fig. B.
Barrage trench for miners.—If the enemy passes in spite of everything, the explosion should at least have been foreseen. The enemy's attack must be limited or stopped, and this is always possible after the explosion of the charge, which may explode well in advance of our lines and act only as a strong means of launching his attack. The barrage trench is established at from 40 to 50 meters in rear of the salient T (Fig. B). In front of the parapet T, wire entanglement R, and two machine-gun positions M1 and M2 are placed. When the enemy's explosion is near, only a few men are left to occupy the salient. The German explosion does not bury anyone, and when the attack is launched it breaks down at the entanglement R.
Camouflet.—The sector commander is warned when the defense is about to explode a camouflet. About 10 meters on each side of the gallery are evacuated as a precaution. The only danger is in having several sandbags fall on the sides of the gallery entrance. Warn the working party charged with the relief, in order that they may not block the passage of men in the first line. Do not fire or make any changes in that part of the trench, in order that the enemy may not locate the position. Do not fire rockets before a given time. The camouflet sometimes shakes the ground and dust is visible. Nine times out of ten the camouflet is used at night.
When the enemy explodes a camouflet, fire a quantity of rockets to locate the positions. Fire grenades and throw bombs at the presumable position of the gallery. Send several men in front of the parapet to listen to what is going on in the enemy trench.
Offensive galleries.—These are intended to pass under the adversary's defenses. Depth.—Start at first line when it is far enough away from the enemy. Start at second line, or at special communication trench about 20 meters in the rear of the first line, when the enemy trench is too near. (See preceding.) A depth of 15 to 18 meters should be attained. The work is done as in ordinary galleries.
Fig. C.
Superimposed galleries.—This procedure gives splendid results in deceiving the enemy, who thinks he is protecting himself. The defensive gallery starts at the first line and the offensive gallery starts in rear of it. Both galleries are on the same vertical plane, the second being more advanced in the direction of the enemy than the first. An enemy listener easily confuses one with the other, and the offensive gallery passes under him. (See Fig. C.) Distances D and D1 are the same. The miner, M, confuses the two sounds, and the offensive gallery passes under him.
Mine chambers.—They are of special interest to the Engineer Corps from a technical point of view. The best hours for exploding them are 4 a. m. and 7 p. m. When an attack is launched at a great distance, or when there is to be no attack, the explosion is preceded by several minutes of noise in the trenches. We commence firing and show several bayonets over the parapet. The enemy believes an attack is coming, comes out of his shelter, and mans his trenches. After the explosion we fire on the mine crater for four hours with artillery, grenades, and bombs. This fire should cover all the area exploded by the mine chamber and should prevent any help to the wounded or buried.