If enemy is detected, these sentinels should hasten back to fire trench to give the alarm quietly so that the enemy may be surprised.
They should fire only if they are themselves caught unawares.
Listening posts should not be too numerous, about two per battalion.
If there are no listening posts, patrols should be sent out to favorable spots especially at sundown and before sunrise.
22.—Enemy sighted or heard, fire.
If the night is clear and the terrain is open, proceed as during the day: If the enemy is sighted or heard, fire in short volleys. In case of doubt throw grenades with the first volley.
23.—Otherwise no firing.
Otherwise, absolute silence should be observed. No firing whatever.
24.—Unless night is dark.