(1) The activity of the enemy:
His infantry will send out more numerous and aggressive patrols and reconnaissance parties.
His artillery will increase its daily destructive fire.
It will multiply its number of registering shots, establish barrage fires in the interior of your position, and begin to concentrate on communication routes.
His air service will take on unusual activities.
(2) Vigilant observation of roads and territory behind the enemy’s lines may reveal convoys carrying troops and supplies, the assembling of troops in woods, etc. (smoke from their kitchens), accumulation of materials in depots (often accompanied by explosions in artillery dumps).
(3) The observation service may discover new hostile works, such as the contraction of parallels of departure out in front of his first line. There may be also successive parallels behind the nearest jumping-off trench.
(4) Prisoners and deserters, who become more numerous because of the approaching offensive, may give valuable information concerning the coming attack.
The task of discovering the enemy’s preparation for an attack is incumbent upon all ranks, but above all, this duty devolves particularly upon the information service, balloon and air service, and artillery observers. In the sector, the intelligence officer must perfect his system of observation to the highest degree. The information in the daily reports is carefully sorted and tested.
Preventive Measures before the Attack. During this time, each chief of area takes all preventive measures possible against the coming attack. The attack is an expected event for which all must be prepared. The preparation simply consists in perfecting and carrying out of the original plan of defense.