Sentinels must be informed of the sending out of patrols, the approximate hour of departure and return, and the general direction that the patrol is to follow.
Watcher. Each platoon in the trenches, from the first line to the rear, must have some watchers, whose duty it is to give the alarm both day and night against attack. These watchers do not observe the enemy as do the sentinels. They walk in the trench in which the platoon is placed, especially at the entrance of the dugouts or shelters occupied by this platoon. When they hear a signal of alarm given by a sentinel or by a messenger, they wake the platoon as quickly as possible. In general, they give to the chief of the platoon all the information that they have obtained during the time of their duty. When an officer or private from another sector enters the trench, it is the duty of the watchers to ascertain the purpose of his visit. Watchers receive special orders to give the alarm against a gas attack, and must sound the alarm gongs and bells for this purpose.
The watcher may have his rifle, without bayonet, resting on the side of the trench at the entrance of a dugout.
Observer. The observers are specially trained men whose duty is to observe the hostile position and to gain all the information that they can obtain of the enemy’s activities.
Each man in the company can be used as a sentinel or as a watcher, but not all as observers. To become an observer, a man must have a special capacity for this task. Each platoon should have at least six such observers of proper qualification; good eyesight and hearing, patient, and a good shot. They are relieved every two hours. Observation duty is carried out in daylight.
The observers are of two kinds:
(1) In each company the platoon observers are distributed in a number of observation posts especially chosen for this purpose. These posts are located in the support point of the company which may be in advance of the firing line, in the firing line, or in any point within the position that has a wide view of the front. These observers employ periscopes or field glasses. Everything of note that is observed is recorded and from this data the captain makes out his daily observation report.
(2) Also, in the sector, there are special observatories belonging to the headquarters of the regiment, under the command of the intelligence officer of the sector. There are usually two or three observatories, from which the information is transmitted directly to the colonel. These observatories are furnished with field glasses, maps, and telephones.
In general, all observers are required to obtain all possible information of the enemy, to record all modifications of the hostile position in its works and wire entanglements, all the movements that they can observe, all working parties that they can discover. Also, they receive special orders for the cases they must report to the commander, as for instance: shelling of the position by artillery or trench mortars, gas attacks, signal rockets fired in the front line, activities of the aviation services, whether of friend or enemy.