Military Instructors Manual

by J. P. Cole; Oliver Schoonmaker

Gabions may be set into the wall of the trench and filled with earth, or used at corners to prevent the wearing down of the edge, which reduces the protective effect of the trench. Set in at a slight angle they will hold the side without further re-enforcement.

With the other forms of revetting some secondary support is required. This is usually furnished by sinking stakes into the bottom of the trench and securing their upper ends to a "dead man"—a stake or log sunk in the ground more than three feet away. The tendency is to sink the dead men too near to the trench, and to attach too many wires to one of them. It is important to sink the stakes at least one foot below the bottom of the trench. By digging holes for them instead of driving them in directly, the sides of the trench need not be disturbed by the concussion of driving the stakes. This is especially important in sandy soils. Stakes should be placed about two feet apart. Dead men should be buried deeply enough to prevent cutting by shell explosions.

Trench Armament.—A few machine guns are set in concealed emplacements along the trench to cover important salients. The automatic rifle is used over the parapet. Besides these there is the rifle grenade and trench mortar. The rifle grenade has a simple emplacement. After securing the proper elevation, the butt of the rifle is placed between posts or blocks of wood and the muzzle rested against a log on the wall of the trench. A trench mortar emplacement is dug in the rear wall of the trench, or a shell hole is utilized, care being taken to conceal it from aerial observation.

Loopholes.—Loopholes are still much in use for observation, but they are employed less and less for firing, as they are difficult to conceal from the enemy and almost useless when the enemy is close. They should cut the parapet diagonally, not directly to the front, and should be concealed by vegetation and by a curtain over the opening when they are not in use. Sheet steel plates with small peep holes are used on the parapet. They are set up with a slope to the rear to deflect bullets.

Trench Bottoms.—In clay or hard soil special arrangements must be made for drainage. Where possible the trench should have a convex surface and should be smooth. A rough bottom means delay in reliefs, and possible injuries. Where trenches are used for long periods board walks should be constructed. Under these drains or sink holes can be placed to collect water. A sink hole may be constructed by digging a pit filled with small stones, or a barrel may be sunk into the ground and filled with stone. Where there is not sufficient slope to carry off the water, or at the lowest point of a drainage system, a water hole should be dug in front of the trench large enough to handle the drainage water.

Communication Trench (or Boyau).—Running to the rear and joining the different parallel resistance trenches are communication trenches or boyaux. These are for transportation of men and material as well as for communication. Communication trenches should be made wide enough to allow travel for men with loads, should be at least seven feet deep and as smooth as possible on the bottom. Rough places will delay traffic. They are dug with turns every 20 or 30 yards to prevent their being swept by gun fire. When boyaux are built by night sharp zig-zag corners should be used, or the angles will not be acute and protection will be lost. During daylight when the directions can be seen, the construction may be a serpentine curve, with no stretch of more than 30 yards visible from one point.

Boyaux are sometimes used for lateral defence and often emplacements for automatic guns are arranged to cover stretches of them. Bombing stations are placed near by to protect the guns and to clear the boyau of the enemy. At these points the boyau is left straight for a short distance in front. Where provision is made for lateral or frontal defence by rifle fire, firing steps are constructed. If this is inconvenient for movement along the boyau, individual emplacements must be made in the side wall for firing. Sentry posts are dug at right angles to the boyau.

Arrangements for passage of men moving in opposite directions may be made by extending short spurs at the corners, enlarging the boyau at the bends, digging niches or passing points here and there, or constructing island traverses with the boyau running around on each side.