Sentinels in the listening posts should listen especially for the noise of crushed branches, stirring leaves, slight noise of arms or utensils. 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. If the night is dark, to avoid surprise, keep up firing: One man per section should fire in turn, from time to time varying the direction. 25.--Digging by enemy. If digging by the enemy is reported, cease firing. Have it located, throw bombs followed by volleys. Notify sappers for counter mining. 26.--Watch for light of enemy's fire. If enemy fires, note where light appears. 27.--Posting of sharpshooters. Locate sharpshooters in advantageous posts behind the trenches (trees, etc.). Have them fire into the enemy's listening posts and into the enemy's trench, especially wherever light appears. These posts should not be occupied during the day. 28.--Patrols. Send out patrols, stationary or mobile. PATROLLING. 29.--Functions of Patrols. The aim: to supplement the work of the listening posts and of the sentinels through more forward observation. To discover the movements and the operations of the enemy. To locate his emplacements. To keep in close touch with the enemy so as to take advantage of his possible weaknesses: lack of watchfulness, of ammunition, of sufficient troops. To verify, repair and complete advance defences. To get the exact range of enemy's positions. To bring back prisoners. 30.--Time to patrol. Patrols should be on duty through the night but be specially watchful before sunrise. 31.--Assignment of patrol duty. N. C. O. and men should be assigned to patrol duty by roster or as volunteers. In the former case, if there is reason to think that a patrol has not done its best to secure information, the same men should be sent out again. 32.--Sentinels should know about patrols. Neighboring companies should be notified of the departure, route and probable time of return of patrols. If several patrols are sent out at the same time they should know one another's itinerary. 33.--Dress and equipment of patrols.