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. [Illustration: 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 D^1 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. _Launching an attack by means of mining._--The mine is an irresistible means of launching an attack. In a mined sector the best troops completely lose their bearings for several seconds after an explosion. These several seconds prevent the machine gun from firing, and the assailant gains a foothold in the first line and often in the second. A mine attack should be prepared in the following manner: Several days beforehand the attacking troops are sent to the rest camp. The plan of the jumping-off trenches, the trenches to be attacked, the ground trace of the crater, and the zone of the searchlights are drawn on the ground with chalk. Each attacking fraction is placed in position, with the materiel to be carried. Each fraction's line of advance is marked out in chalk, as well as the section of the enemy's trench to be occupied and the position of the barrage. Every detail is studied thoroughly, and the exercise repeated a dozen times. The attack is then carried out as planned.