Whistle Signals.
[42.] Attention to orders. A short blast of the whistle. This signal is used on the march or in combat when necessary to fix the attention of troops, or of their commanders or leaders, preparatory to giving commands, orders, or signals.
When the firing line is firing, each squad leader suspends firing and fixes his attention at a short blast of his platoon leader's whistle. The platoon leader's subsequent commands or signals are repeated and enforced by the squad leader. If a squad leader's attention is attracted by a whistle other than that of his platoon leader, or if there are no orders or commands to convey to his squad he resumes firing at once.
Suspend firing. A long blast of the whistle.
All other whistle signals are prohibited.
Arm Signals.
[43.] The following arm signals are prescribed. In making signals either arm may be used. Officers who receive signals on the firing line "repeat back" at once to prevent misunderstanding.
Forward, march. Carry the hand to the shoulder; straighten and hold the arm horizontally, thrusting it in direction of march.
This signal is also used to execute quick time from double time.