em.

Care must be taken not to leave them too long in action.

540. They are valuable to a rear guard which seeks to check a vigorous
pursuit or to gain time.

541. In attack, if fire of position is practicable, they are of great
value. In this case fire should not be opened by the machine guns
until the attack is well advanced. At a critical period in the attack,
such fire, if suddenly and unexpectedly opened, will greatly assist
the advancing line. The fire must be as heavy as possible and must be
continued until masked by friendly troops or until the hostile
artillery finds the machine guns.

542. In the defense, machine guns should be used in the same general
manner as described above for the attack. Concealment and patient
waiting for critical moments and exceptional opportunities are the
special characteristics of the machine gun service in decisive
actions.

543. As part of the reserve, machine guns have special importance. If
they are with the troops told off to protect the flanks, and if they
are well placed, they will often produce decisive results against a
hostile turning movement. They are especially qualified to cover a
withdrawal or make a captured position secure.

544. Machine guns should not be assigned to the firing line of an
attack. They should be so placed that fire directed upon them is not
likely to fall upon the firing line.

545. A skirmish line can not advance by walking or running when
hostile machine guns have the correct range and are ready to fire.
Machine-gun fire is not specially effective against troops lying on
the ground or crawling.

546. When opposed by machine guns and without artillery to destroy
them, infantry itself must silence them before it can advance.

An infantry command that must depend upon itself for protection
against machine guns should concentrate a large number of rifles on
each gun in turn and until it has silenced it.

_AMMUNITION SUPPLY._

547. The method of supply of ammunition to the combat trains is
explained in Field Service Regulations.

548. The combat train is the immediate reserve supply of the
battalion, and the major is responsible for its proper use. He will
take measures to insure the maintenance of the prescribed allowance at
all times.

In the absence of instructions, he will cause the train to march
immediately in rear of his battalion, and, upon separating from it to
enter an engagement, will cause the ammunition therein to be