These things are bound to be discovered within a certain amount of time, and when you know the position of your listening post has been found by the enemy, which you will know very quickly, owing to the amount of bombs and rifle fire it will receive for one or two nights, until you can dig another one, it is a safe thing to build up a small parapet, taking it down every morning before dawn. It then becomes necessary to dig a new post, and this can be generally done by leading off from your old communication trench to some more favorable spot. When the new post is ready for occupancy, the old one should be filled in with barbed wire, or completely filled in again with dirt, and the sandbag parapet left to mislead as long as possible.
The first duty of a listening post is to listen and report. Most of the work is done at night, and no firing or sniping must be allowed from it during the day. Patrols generally come out via one listening post and return by another, so that all listening posts must be warned of the trench by which the patrol will come out and the approximate hour of departure and return. Patrols should never be sent out without definite orders as to what is required, and especially as to the listening post they leave and return by. Listening posts should fire without challenge at any one who approaches within sight, whether friend or enemy, unless it has been warned that a friendly patrol is out, in which event signals should be pre-arranged. Then the listening post will use the greatest caution and should challenge audibly when the patrol is close, and unless immediately satisfied, fire. Listening posts are connected with the fire trench by a cord or wire, and a simple code of tugs is arranged, or a bell fastened to the fire trench end for alarm in case of emergency, and here a sentry always stands to get any signals that may come from the listening post.
If a listening post has not been warned that a friendly patrol is out and fires on it without challenge, the L. P. is absolved from all blame.
When a hedge or ditch, which might easily provide cover to the enemy, is running parallel with the firing trench, it must be controlled at night by a machine or Lewis gun which is able to enfilade a frontal advance over open ground leading to it. If, as is often the case, the parallel hedge or ditch is easily approached along either hedges or ditches running at right angles to it, these angles must be protected by machine or Lewis gun firing down them.
When hedges or ditches running at right angles from the firing line and leading towards the enemy are in a sector of line, they should be protected from dusk to dawn by one or two men, generally only armed with bombs to protect against surprise, and great care must be taken that no more signs than possible are left to the occupancy of this position over night.
OBSERVATION POSTS
Loopholes for Firing. During an attack, firing is never possible through loopholes as it is too restricted to be of any value. All the firing then is done over the parapet. The difficulty of constructing new observation posts which are effectual and inconspicuous for any length of time has resulted in their not being made in a parapet, where, when located by the enemy, they are as often as not a source of danger. Moreover, promiscuous firing through loopholes by inefficient riflemen is of no value. Sniping is under the control and supervision of a sniping officer, and loopholes should only be used by men appointed by that officer. They are not used at night and should be only used during the day for enfilade fire, and be placed in the parapet as low down as is consistent with line of site. A piece of cloth or empty sandbag should be hung from the rear of the loophole, so that when the hole is not obstructed by the fire, no light can show through. No shots should be fired from those loopholes, except at a definite target, and ranges of targets or spots where targets may possibly appear, should be ascertained in advance, and necessary exposed movement, such as withdrawal of rifle, must be very slow and gradual. With care, and when only used by a skilled rifleman, a loophole will be of value for probably two weeks and good results obtained, but by a careless man the value of a loophole will not last a day and very likely result in casualties not only to the man shooting, but to others as well.
In the area from 20 to 100 yards behind the fire trench, there sometimes is, although very seldom, ground much higher than the actual fire trench, so that it is safe to allow even hastily trained men to use it for firing over the heads of the main front line trench, although it has happened that men in such a position have fired into their front line, thinking it the enemy line. This ground is generally used by building what are known as covering fire trenches. These to be of any value, should not be more than 20 yards behind the front line, as farther forward than 20 yards they become affected by artillery fire directed at the fire trenches; and farther back than 100 yards the covering fire, unless in the hands of very skilled and efficient riflemen, becomes very dangerous to the men in the front line.