actual emplacement.

[Illustration: No. 21]

Listening Posts.--These stations are usually carried out to the edge
of the entanglements nearest the enemy. The listening station must be
large enough for half a squad, and often has an automatic rifle and
grenade thrower. There should be not more than two posts for each
battalion. They are not occupied during the day. They are hard to
defend and easily captured by a raiding party which cuts the wire to
one of the flanks and comes in from the rear. The boyau leading to the
post should be zig-zagged. The post itself should be deep enough for
good head cover.

Wire Entanglements.--The object of the entanglement is not to stop
completely the advance of the enemy, but to delay him at close range
under machine gun, auto rifle and rifle fire, and within range of
grenades and bombs. Entanglements should be concealed as much as
possible from the enemy's trenches and from aerial observation. If
possible, they should be placed on a reverse slope or in a dead angle.
They should be from 50 to 100 yards in front of the trench, so that
artillery fire directed upon the trench will not be effective on the
wire. At the same time the wire must not be far enough advanced so
that the enemy's raiding parties can cut the entanglements.

Wire entanglements are classified as high entanglements, low
entanglements and loose wire.

High Entanglements are strung on metal or wood posts about four feet
high, both wire and posts being painted for camouflage. The driving of
posts must be muffled, and metal screw posts are used when near the
enemy's line. Posts are placed in two parallel lines, two yards apart,
spaced alternately so that the posts in one line are opposite the
middle of the interval in the other.

Tracing Entanglements is done by a sergeant followed by two stake
placers, two holders and two drivers, who in turn are followed by men
attaching wire. Two men carry each roll of wire, and each pair (there
are twelve pairs in all) strings one wire. A panel between stakes is
composed of four strands. Each wire should be wrapped around each
post. The same arrangement of panels should run between the two lines
of posts. The entanglements are in three lines about 20 yards apart,
the nearest being 20 yards from the front line trench. The
entanglement nearest the enemy should be constructed first, so that
men always work nearest their own trenches. All wire entanglements
should be at all po