Every boyau should be marked where it meets a trench with a sign indicating the place and trench. Without this messengers, reliefs and re-enforcements may easily be lost in the maze of trenches.
Latrines should be run out about 20 feet from boyaux at points directly in rear of lateral trenches. If possible they should be placed so that men cannot enter them without passing near the platoon leaders. This will prevent men from leaving the front line, under the pretense of going to latrines, during bombardments or mining operations. The trench leading to a latrine should be constructed like a boyau, and the pit should be close to the side nearest the enemy, to give the best possible protection from shell fire. There are three types of trench latrines: Deep boxes which are covered and have rough seats; short straddle trenches or trenches equipped with a single horizontal bar, and portable cans, used where the ground or the limited space make it impossible to dig pits. These cans should be emptied daily into holes behind the trenches, which are covered after the cans are emptied into them.
Urinals should be separate from the latrines. They may be either holes about three feet deep filled with stone, troughs with a covered pit at the end, or portable cans.
Shelters. For the protection of men not actually on duty three forms of shelters are used. The splinter-proof is a form of light shelter whose covering affords protection only against splinters. These are usually on the reserve line. About 12 inches to 20 inches of earth over a roof of logs or planks will afford protection from splinters and shrapnel. Curved sheets of iron may also be used. The deep shelter or bomb-proof is a chamber constructed by digging from the surface and constructing a roof. To protect against eight-inch shells the top of the chamber should be twenty feet below the surface. Heavy beams or sections of railroad iron are laid across the roof. Above them is a layer of earth several feet thick; then another layer of timber extending to undisturbed ground on the sides with concrete, crushed stone, metal, etc., above to make a percussion surface for exploding projectiles that penetrate the upper layer of earth. This layer fills in the rest of the space to the level of the ground.
Shelters should not exceed six feet in width, but can be of any length. This will prevent the crushing in of the roof timber by the explosion of a projectile buried in the upper layer of earth. The principles of constructing shelters will be considered under "Dugouts," as they are similar for the two types.
Dugouts are chambers tunnelled into the ground with twenty feet or more of undisturbed earth above them. They are used in the cover trenches and sometimes in the first line. Enough of them must be built to shelter the garrison of each sector, allowing one man per yard of front. They must also be built for machine gun and trench mortar detachments.