g. 35]

=The thickness of overhead cover= depends upon the class of fire
against which protection is desired, and is sometimes limited by the
vertical space available, since it must afford headroom beneath, and
generally should not project above the nearest natural or artificial
horizontal cover. For splinter proofs a layer of earth 6 to 8 ins.
thick on a support of brush or poles strong enough to hold it up will
suffice if the structure is horizontal. If the front is higher than
the rear, less thickness is necessary; if the rear is higher than the
front, more is required. For bombproofs a minimum thickness of 6 ins.
of timber and 3 ft. of earth is necessary against field and siege
guns, or 12 ins. timber and 6 ft. of earth against the howitzers and
mortars of a heavy siege train, not exceeding 6 inches in caliber.

In determining the area of overhead cover to be provided, allow 6 sq.
ft. per man for occupancy while on duty only, or 12 sq. ft. per man
for continuous occupancy not of long duration. For long occupation 18
to 20 sq. ft. per man should be provided.

It is not practicable to give complete cover to rifle positions that
will successfully withstand the heavy artillery of today. The use of
overhead cover is usually limited to that sufficient for protection
against rifle fire, machine gun fire, and shrapnel.

=1155. Cover trenches= are constructed to provide safe cover for the
supports or reinforcements of the fire trenches or to provide cooking
and resting facilities for the garrison of the neighboring fire
trenches. The important point in cover trenches is safety. They vary
in design from the simple rectangular trenches to elaborately
constructed trenches having overhead cover, kitchens, shelters,
latrines, dressing stations, etc. Cover trenches must not be mistaken
for a secondary position, they are cover for the firing line, supports
and reserves until they are required in the fire trenches. The cover
trench requires a depth of at least 6 feet to protect men standing.
Greater depths may be used when necessary. Fig. 36 is a section of an
open cover trench and Fig. 37 of a closed one. This section may be
used for a communicating trench. Fig. 38 shows a cover trench close to
a fire trench. The character of overhead cover for trenches is shown
in the diagrams under overhead cover. The distance of the cover
trenches varies with the situation. The experience of the European war
places the cover trenches from 15