e of the hostile infantry the
first line may be captured. The support trench must be so organized
that it will then act as a line of resistance upon which the enemy's
advance will break. Lieutenant Colonel Azan of the French army says:
"As long as the support trenches are strongly held, the position is
not in the hands of the enemy."

[Illustration: Plate #16]

The reserve is usually a _strong point_, so organized that it can
maintain independent resistance for several days if necessary, should
the enemy obtain control of adjacent areas.

Where possible trenches should be on reverse slopes, with the
exception of the first line; but usually the outline of a trench is
determined in actual combat, or is a part of hostile trench converted.
Under these circumstances it cannot be arranged according to tactical
ideals.

Artillery and the automatic gun are the determining factors in trench
warfare to-day. The effect of artillery fire must be limited in its
area as far as possible, and trenches are, therefore, cut by
_traverses_, which are square blocks of earth not less than nine feet
square, left every 27 feet along the trench. They should overlap the
width of the trench by at least one yard, thereby limiting the effect
of shell burst to a single _bay_, the 27-foot length of firing trench
between two traverses. Sharp angles have the same effect as traverses,
but angles of more than 120 degrees cannot be utilized in this way.

The sides of the trench are kept as nearly perpendicular as possible,
to give the maximum protection from shell burst and the fall of high
angle projectiles. The _parados_, the bank of earth to the rear of the
trench, has been developed during the war to give protection from
flying fragments of shells exploding to the rear, and to prevent the
figure of a sentinel from being outlined through a loop-hole against
the sky. The _berm_, a ledge or shelf left between the side of the
trench and the beginning of the parados, has come into general use in
order to take the weight of the parados off the earth at the immediate
edge of the trench, and so prevent the reverse slope from caving in
easily under bombardment or heavy rain.

[Illustration: Plate #16A]

Automatic guns have made it necessary to break the line of the trench
at every opportunity, in order to secure a flanking fire for these
arms. Auto-rifles and machine guns have tremendous effectiveness only
in depth, and flanking fire gives them their