: Fig. 20]

[Illustration: Fig. 21]

[Illustration: Fig. 22]

The position of the throat may vary. If on the outside, it is less
conspicuous but more easily obstructed by injury to the parapet and
more difficult to use, since in changing aim laterally the man must
move around a pivot in the plane of the throat. If the material of
which the loophole is constructed presents hard surfaces, the throat
should be outside, notwithstanding the disadvantages of that position,
or else the sides must be stepped as in Fig. 22. In some cases it may
be best to adopt a compromise position and put the throat in the
middle, Fig. 22. Figs. 23 to 26 show details and dimensions of a
loophole of sand bags.

[Illustration: Fig. 23]

[Illustration: Fig. 24]

[Illustration: Fig. 25]

[Illustration: Fig. 26]

A serviceable form of loophole consists of a pyramidal box of plank
with a steel plate spiked across the small end and pierced for fire.
Fig. 27 shows a section of such a construction. It is commonly known
as the =hopper loophole=. The plate should be 3/8 in. thick, if of
special steel; or 1/2 in., if ordinary metal. Fig. 28 shows the
opening used by the Japanese in Manchuria and Fig. 29 that used by the
Russians.

[Illustration: Fig. 27]

[Illustration: Fig. 28]

[Illustration: Fig. 29]

The construction of a notch requires only the introduction of some
available rigid material to form the sides; by adding a cover the
notch becomes a loophole. Where the fire involves a wide lateral and
small vertical angle, loopholes may take the form of a long slit. Such
a form will result from laying logs or fascines lengthwise on the
parapet, supported at intervals by sods or other material, Fig. 31, or
small poles covered with earth may be used, Fig. 30.

[Illustration: Fig. 30]

[Illustration: Fig. 31]

=1154. Overhead cover.= This usually consists of a raised platform of
some kind covered with earth. It is frequently combined with
horizontal cover in a single structure, which protects the top and
exposed side. The supporting platform will almost always be of wood
and may vary from brushwood or light poles to heavy timbers and plank.
It is better, especially with brush or poles, to place a layer of
sods, grass down, or straw, or grain sacks over the platform before
putting on the earth, to prevent the latter from sifting through.

[Illustration: Fig. 32]

[Illustration: Fig. 33]

[Illustration: Fig. 34]

[Illustration: Fi