will
remain with little loss for a long time. To make sure of prompt
ignition gas lines are laid in the ditches. When turned on the gas
readily ignites and the resulting fire produces great heat. Wire or
barbed wire looped in the ditches and staked down makes this a
formidable obstacle.

=1197. Grenades and bombs= are containers, designed to be thrown by
hand, by a sling, fired as a rocket or from specially constructed
mortars, or dropped from aerial craft. They burst by time or
percussion fuses and may be improvised in a variety of forms and are
most useful in close attack or defense. Their effect is local but they
are very demoralizing to men's nerves.

=1198. Hand grenades= are designed to be thrown by the hand and vary
greatly in construction. In general, however, they consist of a
container filled with bullets or pieces of iron or other metal in the
center of which is a charge of high explosive which scatters the
bullets or fragments with deadly effect. The three methods of
discharging a hand grenade are:

_By time fuse_ which is lighted by hand. About 5 to 9 seconds is the
time from ignition until the grenade bursts. This does not give the
defender time to pick up the bomb and throw it out of the trench.

_By friction primer and fuse._ In this form of hand grenade a strap on
the wrist with a short line attached with a hook on the end of it
serves, when the hook is engaged in the ring of the grenade, to jerk
the primer when the grenade is thrown. This automatically ignites the
fuse which bursts the grenade in from 4 to 5 seconds.

_By percussion._ In this form of grenade the charge is fired when the
grenade strikes the ground or object at which it is thrown. In this
form of grenade a safety pin holds the plunger from the cap. When the
grenade is to be thrown the safety pin is withdrawn.

As a general rule fuse burns at the rate of 1 inch in 1 and 1/4
seconds; however each lot of fuse should be tested.

Figs. 1 and 2 show two forms of improvised grenades. Common cans, such
as preserved fruits and vegetables are shipped in commercially, make
good containers. The usual weight of a hand grenade is about 1-1/2
pounds.

[Illustration: Fig. 1

Hair Brush Bomb]

[Illustration: Fig. 2

Hand Grenade]

=1199. Other methods of throwing grenades.= Many grenades have been
designed to be fired from the ordinary rifle. This grenade has a rod
which is inserted in the barrel of the rifle. A special charge of
powde