[Ill.u.s.tration: Plate No. 20.]

Shelters should not exceed six feet in width, but can be of any length. This will prevent the crushing in of the roof timber by the explosion of a projectile buried in the upper layer of earth. The principles of constructing shelters will be considered under "Dugouts," as they are similar for the two types.

Dugouts are chambers tunnelled into the ground with twenty feet or more of undisturbed earth above them. They are used in the cover trenches and sometimes in the first line. Enough of them must be built to shelter the garrison of each sector, allowing one man per yard of front. They must also be built for machine gun and trench mortar detachments.

Sentries must be stationed in observation posts which command the ground in front of each dugout. They must be connected with the dugouts by telephone or speaking tube.

Position.--Dugouts must always be on the side of the trench toward the enemy. This prevents flying sh.e.l.ls from falling into the entrances. They should connect with lateral trenches, not with boyaux, as men at the entrance obstruct traffic through the boyaux.

Entrances and exits must be well concealed, with not less than five feet of head cover. This should be provided with a bursting layer. All dugouts must have at least two openings, one on the opposite side of the traverse or angle from the other. It is well to have an exit behind the parados leading to a surprise position for a machine gun and bombers. All openings must have a sill 6 inches to 8 inches high, to prevent water from entering the dugout.

Galleries leading to dugouts should be built at an incline of 45 degrees. Their dimensions should be 2 feet 6 inches by 6 feet. Frames are of squared timber. The sill and two side posts should be not less than 6 inches square, and the frames in the pa.s.sageways 2 feet 6 inches by 4 feet 6 inches. They must be placed at right angles to the slope of the gallery, with distance pieces between uprights. In treacherous soil the frames rest on sills. Steps in the pa.s.sageway are 1 foot broad and 1 foot high.

Bomb-traps, extensions of the gallery about 3 feet long, should be dug beyond the point where the entrance to the dugout chamber leads off from the gallery. These will catch bombs thrown in from the surface and protect the chamber from the effects of their explosion.

Interior. The standard section is 6 feet by 8 feet, to allow for bunks on each side. Frames of 6 by 6 timber s.p.a.ced 2 feet 6 inches apart support the sides and roof. Roof planking should be 2 inches thick, and the sides should be covered with 1-1/2 inch plank or corrugated iron. Two shovels and two picks for emergencies should always be kept in each dugout. The construction of the chamber should be that of a very strong box, so that it will stand strain, if necessary, from within as well as from without.

Depots for Supplies must be near the headquarters of the platoon, company, battalion and regiment. Shelters may be made with ammunition boxes set into the side of the trench. Places should be provided for the following: Food, ammunition for rifles and auto-rifles, grenades, rockets, tools and other supplies. Places must also be arranged in the front line for ammunition, rockets and hand and rifle grenades.

Telephones. Communication is established as speedily as possible with the various units. In the forward trenches wires do not last long under bombardment and fire left open along the side of the trench, where quick repairs can be made. All soldiers must be taught to respect these wires and to care for them when they are found under foot or hanging. Conduits are dug for wires to battalion and regimental headquarters, and these are fairly safe from sh.e.l.l fire.

Departure Parallel. In preparing for an advance upon the enemy, a straight line trench without traverses, and with steps at the end for exit to the surface, is built in front of the first line trench. This line of departure is generally brought within about 200 yards of the hostile line by means of _saps_, short trenches run out from the front line to the new parallel. Since this line of departure can be seen by the enemy, it is sometimes better to construct steps in the front line trench itself, or when possible to build a _Russian sap_. This is a tunnel very near the ground, which can be broken through at a moment's notice when troops are ready to advance.

Machine Gun Emplacements.--Sh.e.l.l-holes with a good field of fire and emplacements along boyaux are the best location for machine guns. Few guns are placed in the front line, and these only at strong points in the line, which command a maximum field of effectiveness. Sh.e.l.l-holes may be imitated for machine gun emplacements, but in any case they should be connected by underground pa.s.sage with the trenches. Thus when trenches are destroyed by bombardment the machine guns remain intact. The field of fire for each machine gun should be carefully determined and marked by three stakes, one for the position of the gun, the other two for the limits of the field of fire. Using these as guides, the gun can be fired correctly at night. During the day it is never left in place nor fired from its actual emplacement.

[Ill.u.s.tration: No. 21]

Listening Posts.--These stations are usually carried out to the edge of the entanglements nearest the enemy. The listening station must be large enough for half a squad, and often has an automatic rifle and grenade thrower. There should be not more than two posts for each battalion. They are not occupied during the day. They are hard to defend and easily captured by a raiding party which cuts the wire to one of the flanks and comes in from the rear. The boyau leading to the post should be zig-zagged. The post itself should be deep enough for good head cover.

Wire Entanglements.--The object of the entanglement is not to stop completely the advance of the enemy, but to delay him at close range under machine gun, auto rifle and rifle fire, and within range of grenades and bombs. Entanglements should be concealed as much as possible from the enemy's trenches and from aerial observation. If possible, they should be placed on a reverse slope or in a dead angle.

They should be from 50 to 100 yards in front of the trench, so that artillery fire directed upon the trench will not be effective on the wire. At the same time the wire must not be far enough advanced so that the enemy's raiding parties can cut the entanglements.

Wire entanglements are cla.s.sified as high entanglements, low entanglements and loose wire.

High Entanglements are strung on metal or wood posts about four feet high, both wire and posts being painted for camouflage. The driving of posts must be m.u.f.fled, and metal screw posts are used when near the enemy's line. Posts are placed in two parallel lines, two yards apart, s.p.a.ced alternately so that the posts in one line are opposite the middle of the interval in the other.

Tracing Entanglements is done by a sergeant followed by two stake placers, two holders and two drivers, who in turn are followed by men attaching wire. Two men carry each roll of wire, and each pair (there are twelve pairs in all) strings one wire. A panel between stakes is composed of four strands. Each wire should be wrapped around each post. The same arrangement of panels should run between the two lines of posts. The entanglements are in three lines about 20 yards apart, the nearest being 20 yards from the front line trench. The entanglement nearest the enemy should be constructed first, so that men always work nearest their own trenches. All wire entanglements should be at all points commanded by the flanking fire of machine guns. High entanglements (known as abatis) may be made by felling trees toward the enemy, and similar entanglements made of brushwood are useful in emergency.

Low Entanglements are formed of pickets two feet high, 2-1/2 inches in diameter, wired in all directions. Vegetation renders the entanglement invisible from the enemy and from aerial observation.

This type may also be placed in shallow excavations which are concealed from the enemy and partly protected from artillery fire.

Sharpened stakes, with their points hardened by fire, driven obliquely into the ground, may also be used.

Loose Wire in the form of loops of small diameter fastened to stakes, or wire laid along the ground and attached at the ends, or spirals of barbed wire in racks, is used for entanglements. It is reported that this form is coming into considerable use, but the details have not been published. Such entanglements are much harder to locate by aerial observation.

The following are a number of criticisms made by Lieut. Henri Poire of the French army, detailed as instructor at Plattsburg, upon the system of field works constructed by the 17th and 18th Provisional Training Regiments. The ground was of loose sand, with some gravel at a depth of about six feet.

1. Dimensions of trenches as laid out were not followed.

(a) Bottom of trenches behind firing steps too narrow.

(b) Firing step too deep. It should never be more than 3 feet 4 inches below berm of parapet.

(c) Parapet much too thin in most cases. It should be at least three feet thick.

(d) Communication trenches (boyaux) generally too narrow.

(e) Islands in communication trenches should never be less than 10 x 12 yards--otherwise one sh.e.l.l will demolish the entire pa.s.sageway.

2. Revettment work not well anch.o.r.ed. In some cases too many wires from supports fastened to one dead man. Another fault is that dead men were not buried deeply enough in the ground, nor far enough back from the trench. In one case a dead man (a stake) supported all four sides of an island in a communication trench. The destruction of this post would have completely blocked every pa.s.sage around the island.

Furthermore, dead men rot quickly and tend to break off. It is necessary, therefore, to have a number of them, each holding only a portion of the weight. All projecting branches and irregularities along a trench should be removed by occupying troops.

3. Too many loop-holes. Except for snipers, riflemen and automatic riflemen fire over the parapet.

4. Machine gun loop-holes not wide enough. They should not be less than 36 inches wide. There must be vegetation planted in front and a curtain hung over the loop-holes to prevent detection. The growing plants in front will be easily swept away at the first discharge.

5. Remember never to imitate sh.e.l.l-holes until after a real bombardment by the enemy.

6. The dugouts made were never deep enough and afforded no protection. In fact it would be far better to have none than to be caught inside when a sh.e.l.l exploded in a shallow one, because the confinement of the explosion would intensify the effect.

7. Shelters were all too wide. Six feet is the maximum.

The platoon headquarters dugout should be of the same width as the trench, not over three feet, but as long as necessary. Company headquarters is six feet wide and of whatever depth required.

8. In digging, not enough care was used to conceal the fresh earth from the enemy. Make false emplacements to utilize this dirt; also dig dummy trenches about one foot deep, leaving the sides sharp so that they will show clearly on aerial photographs.

9. In using plants as camouflage, distinct care must be exercised not to put growing plants too freely nor to place them where they never existed. The actual ground conditions must be copied.

10. Some latrines were not arranged with the stools close beneath the wall nearest the enemy. This caused the loss of protection, which it is imperative to consider, as many casualties occur here.

11. Too many listening posts. They are easily captured by hostile fighting patrols. There should never be more than two listening posts to a battalion.

12. The observation stations in many instances had no good field of fire or were outlined against the sky on the crest of some rise. The site for an observation post should always be placed over the crest and have a good field of fire for use in case of attack.

Occupation.