er.

Concrete Work has been used extensively by the Germans, but the
chips fly like bullets under shell explosion, and the concrete cracks
and disintegrates in severe weather. It is used in the bottom of
trenches for drainage and for the firing step.

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. W