The dotted line is the ground level: the uneven line is the course that would be taken by a man walking along the bottom of the chain of craters, and keeping in the centre. Actually, of course, (on patrol) one would not keep in the centre where the crater contained water, but would skirt the water by going to one side of it. The “bridges” are important, as they are naturally the easiest way across the craters; a bombing patrol, for instance, could crawl over a bridge, without having to go right down to the bottom level, and (which is more important) will not have a steep climb up over very soft and spongy soil. These bridges are the “lips” of the larger craters where they join the smaller; looking at a crater-chain in plan X is a “bridge,” whereas Y and Z are “lips” rising above ground level.
This crater-chain being understood, the system of sentries is easily grasped. Originally, before mining commenced, our front line ran (roughly) from left to right along Rue Albert up 80 A Street and along to the top of 76 Street in a straight line. Then began the great game of mining under the enemy parapet and blowing him up; and its corollary countermining, or blowing up the enemy’s mine galleries before he reached your parapet. Such is the game as played underground by the tunnelling companies, R.E. To the infantry belongs the work (if not blown up) of consolidating the crater, whether made by your or an enemy mine, that is to say, of seizing your side of the crater and guarding it by bombing-posts in such a way as to prevent the enemy from doing anything except hold his side of the crater.
For instance, take a single crater, caused by us blowing up the German gallery before it reaches our parapet. If we do nothing, the enemy digs a trench into the crater at A, and can get into the crater any time he likes and bomb our front line, and return to his trench unseen. This, of course, never happens, as we dig a sap into the crater from our side, and the result is stale-mate; each side can see into the crater, so neither can go into it.
That is all. 83 B, 81 A, the Matterhorn sap, the Loop, the Fort—they are all saps up to crater-edges, in some cases joined up along the edge (as between 83 B and 83 A, or at the Loop and the Fort.) And these saps are held by bombing-posts. Where there are no craters in front (as, for instance, between the Fort and the Loop), there the trench is held by sentry groups in the ordinary way. The most important bombing-posts are at the “bridges,” which are the points that most want guarding.
Each platoon has so many posts to “find” men for. No. 5 Platoon has three posts between the Lewis-gun position and the top of 76 Street; No. 6 finds two in the Fort and one between the Fort and the Loop; there is another post before you reach the Loop, found by No. 7, who also finds two in the Loop itself; while No. 8 finds the Matterhorn post and the top of 80 A. All these posts are composed of one bomber, who has a box of bombs with him and his rifle without bayonet fixed, and one bayonet man. There is no special structure about a “post”: it is just the spot in the trench where the sentries are placed. Sometimes one or two posts could be dispensed with by day, if one post could with a periscope watch the ground in front of both. The sentry groups are relieved every two hours by the platoon N.C.O. on trench duty. There is always an N.C.O. on trench duty, going the rounds of his sentry groups, in every platoon; and one officer going round the groups in the company. Thus is secured the endless chain of unwinking eyes that stretches from Dunkirk to Switzerland.
There were two Lewis guns to every company. One had a position at the Fort, covering the ground between the Fort and the Loop; the other was just to the right of 80 A, where it had a good position sweeping the craters. The Lewis-gun teams found their sentries independently of the platoons, and had their dug-outs. A nice compact little affair was a Lewis-gun team; always very snug and self-contained.
Company Headquarters were at Trafalgar Square, though later we changed to a dug-out half-way up 76 Street. Each platoon had a dug-out about fifty yards behind the front line, and as far as possible one arranged to get the men a few hours’ sleep in them every day; but only a certain percentage at a time. There were four stretcher-bearers and two signallers also at Trafalgar Square. Also a permanent wiring-party had its quarters here, a corporal and five men; they made up “concertina” or “gooseberry” wire by day, and were out three or four hours every night putting it out. They were, of course, exempt from other platoon duties. Each platoon had a pioneer to attend to sanitary arrangements, and other odd jobs such as fetching up soup; and each platoon had an orderly ready to take messages. At Company Headquarters, besides the officers’ servants, were the company orderly, and company officers’ cook. An officer on trench duty was accompanied by his servant as orderly.