=1152. Head cover= is the term applied to any horizontal cover which may be provided above the plane of fire. It is obtained by notching or loop-holing the top of the parapet so that the bottoms of the notches or loopholes are in the desired plane of fire. The extra height of parapet may be 12 to 18 inches and the loopholes may be 3 to 3-1/2 feet center to center.

Head cover is of limited utility. It increases the visibility of the parapet and restricts the field of fire. At close range the loopholes serve as aiming points to steady the enemy's fire and may do more harm than good at longer ranges. This is especially the case if the enemy can see any light through the loophole. He waits for the light to be obscured, when he fires, knowing there is a man's head behind the loophole. A background must be provided or a removable screen arranged so that there will be no difference in the appearance of the loophole whether a man is looking through it or not. Head cover is advantageous only when the conditions of the foreground are such that the enemy can not get close up.

=1153. Notches and loopholes=, Figs. 20-22, are alike in all respects, except that the latter have a roof or top and the former have not. The bottom, also called =floor= or =sole=, is a part of the original superior slope. The sides, sometimes called =cheeks=, are vertical or nearly so. The plan depends upon local conditions. There is always a narrow part, called the =throat=, which is just large enough to take the rifle and permit sighting. From the throat the sides diverge at an angle, called the =splay=, which depends upon the field of fire necessary.

[Ill.u.s.tration: Fig. 20]

[Ill.u.s.tration: Fig. 21]

[Ill.u.s.tration: Fig. 22]

The position of the throat may vary. If on the outside, it is less conspicuous but more easily obstructed by injury to the parapet and more difficult to use, since in changing aim laterally the man must move around a pivot in the plane of the throat. If the material of which the loophole is constructed presents hard surfaces, the throat should be outside, notwithstanding the disadvantages of that position, or else the sides must be stepped as in Fig. 22. In some cases it may be best to adopt a compromise position and put the throat in the middle, Fig. 22. Figs. 23 to 26 show details and dimensions of a loophole of sand bags.

[Ill.u.s.tration: Fig. 23]

[Ill.u.s.tration: Fig. 24]

[Ill.u.s.tration: Fig. 25]

[Ill.u.s.tration: Fig. 26]

A serviceable form of loophole consists of a pyramidal box of plank with a steel plate spiked across the small end and pierced for fire.

Fig. 27 shows a section of such a construction. It is commonly known as the =hopper loophole=. The plate should be 3/8 in. thick, if of special steel; or 1/2 in., if ordinary metal. Fig. 28 shows the opening used by the j.a.panese in Manchuria and Fig. 29 that used by the Russians.

[Ill.u.s.tration: Fig. 27]

[Ill.u.s.tration: Fig. 28]

[Ill.u.s.tration: Fig. 29]

The construction of a notch requires only the introduction of some available rigid material to form the sides; by adding a cover the notch becomes a loophole. Where the fire involves a wide lateral and small vertical angle, loopholes may take the form of a long slit. Such a form will result from laying logs or fascines lengthwise on the parapet, supported at intervals by sods or other material, Fig. 31, or small poles covered with earth may be used, Fig. 30.

[Ill.u.s.tration: Fig. 30]

[Ill.u.s.tration: Fig. 31]

=1154. Overhead cover.= This usually consists of a raised platform of some kind covered with earth. It is frequently combined with horizontal cover in a single structure, which protects the top and exposed side. The supporting platform will almost always be of wood and may vary from brushwood or light poles to heavy timbers and plank.

It is better, especially with brush or poles, to place a layer of sods, gra.s.s down, or straw, or grain sacks over the platform before putting on the earth, to prevent the latter from sifting through.

[Ill.u.s.tration: Fig. 32]

[Ill.u.s.tration: Fig. 33]

[Ill.u.s.tration: Fig. 34]

[Ill.u.s.tration: Fig. 35]

=The thickness of overhead cover= depends upon the cla.s.s of fire against which protection is desired, and is sometimes limited by the vertical s.p.a.ce available, since it must afford headroom beneath, and generally should not project above the nearest natural or artificial horizontal cover. For splinter proofs a layer of earth 6 to 8 ins.

thick on a support of brush or poles strong enough to hold it up will suffice if the structure is horizontal. If the front is higher than the rear, less thickness is necessary; if the rear is higher than the front, more is required. For bombproofs a minimum thickness of 6 ins.

of timber and 3 ft. of earth is necessary against field and siege guns, or 12 ins. timber and 6 ft. of earth against the howitzers and mortars of a heavy siege train, not exceeding 6 inches in caliber.

In determining the area of overhead cover to be provided, allow 6 sq.

ft. per man for occupancy while on duty only, or 12 sq. ft. per man for continuous occupancy not of long duration. For long occupation 18 to 20 sq. ft. per man should be provided.

It is not practicable to give complete cover to rifle positions that will successfully withstand the heavy artillery of today. The use of overhead cover is usually limited to that sufficient for protection against rifle fire, machine gun fire, and shrapnel.

=1155. Cover trenches= are constructed to provide safe cover for the supports or reinforcements of the fire trenches or to provide cooking and resting facilities for the garrison of the neighboring fire trenches. The important point in cover trenches is safety. They vary in design from the simple rectangular trenches to elaborately constructed trenches having overhead cover, kitchens, shelters, latrines, dressing stations, etc. Cover trenches must not be mistaken for a secondary position, they are cover for the firing line, supports and reserves until they are required in the fire trenches. The cover trench requires a depth of at least 6 feet to protect men standing.

Greater depths may be used when necessary. Fig. 36 is a section of an open cover trench and Fig. 37 of a closed one. This section may be used for a communicating trench. Fig. 38 shows a cover trench close to a fire trench. The character of overhead cover for trenches is shown in the diagrams under overhead cover. The distance of the cover trenches varies with the situation. The experience of the European war places the cover trenches from 15 to 50 yards in rear of the fire trenches. These trenches furnish shelter for at least 2/3 of the firing line and supports.

[Ill.u.s.tration: Fig. 36]

[Ill.u.s.tration: Fig. 37]

[Ill.u.s.tration: Fig. 38]

The reserves are furnished yet more elaborate shelter, with plenty of room for the men to lie down and rest and when practicable, bathing facilities are provided.

=1156. Dugouts.= An elaborate system of dugouts has developed along the lines occupied by the troops in the European war. These dugouts are located from 14 to 40 feet below the ground and are reached by stairs in timbered pa.s.sage ways. At the foot of the stairs a tunnel or corridor runs forward and on either side or at the end, rooms have been dug out varying in size. Most of these rooms have been timbered and lined. Many are electrically lighted. In some of these underground shelters, accommodations for several hundred men have been prepared with all of the necessary facilities for making them comfortable. It must be understood that such elaborate preparations can only be made when troops face each other in trenches where operations have developed into practically a siege.

=1157. Communicating trenches.= These trenches as the name implies are for the purpose of providing safe communication between the cover and fire trenches. They may be also constructed just in rear of a series of fire trenches to provide a means of communication from one to the other. Communicating trenches also extend to the rear of the cover trenches and provide safe pa.s.sage to fresh troops or supplies. These trenches are usually laid out in zig zag or curved lines (Fig. 39), to prevent enfilade fire from sweeping them. As a general rule excavated earth is placed on both sides of the trench to afford protection, the depth is usually from 6 to 7 feet. (Fig. 15) shows a typical communicating trench.

[Ill.u.s.tration: Fig. 39

_Typical Pa.s.sage Trench from Supports to Firing Line._

(From _Field Entrenchments_--Solano)]

=1158. Lookouts.= To enable the garrison of a trench to get the greatest amount of comfort and rest, a _lookout_ should be constructed and a sentinel stationed therein.

The simplest form would consist of two sandbags placed on the parapet and splayed so as to give the required view, and carefully concealed.

Better forms may be constructed, with one side resting on the berm by using short uprights with overhead cover, a slit on all sides being provided for observation.

At night, lookouts are usually posted at listening points located in or beyond the line of obstacles. These will be discussed under obstacles.

=1159. Supporting Points.= In some cases small supporting points may have to be established close behind the general line of trenches for the purpose of breaking up a successful attack on the trenches and to aid in delivering a counter attack. These points are strongly entrenched and have all around wire entanglements and are garrisoned by from 20 to 40 picked men or by larger forces if the situation demand it. In some cases machine guns are added to the force in the supporting point.

=1160. Example of trench system.= Having discussed trenches and obstacles somewhat in detail, let us take a combination of the whole showing a complete system such as is used today. (Fig. 40) is a good example.

[Ill.u.s.tration: Fig. 40

FIRST LINE FIRING TRENCH]

Beginning at the front we have the line of wire entanglements or obstacles with their listening posts X, for guarding them. Connecting the listening posts to the fire trenches are the communicating trenches. The fire trenches are shown by the heavy black line running about 60 feet in rear of the obstacles. Note the many traverses shown by the indentations in the line. Points marked M with arrows projecting to the flanks are machine guns, so located as to sweep the front of the position with a cross fire. Points marked S are underground shelters for from 3 to 6 men. Points marked S' are shelters for 30 men. In rear of the firing trenches at a distance varying from 100 to 200 feet is the line of cover trenches. This line is connected with the fire trenches by the zig zagged line of communicating trenches. Note that the latrines (L) and first aid stations (F) are just off from the communicating trenches, while the larger shelter for men (S') are near the cover trenches. As the note on the diagram shows, the trench requires 250 men to occupy it with double that number in support. The trench has 108 loopholes with s.p.a.ces between provided with a higher banquette so that the whole parapet may be manned for firing.

On the battlefields of Europe today there are generally three lines of fire trenches. This permits the defender to fall back to a 2nd or 3rd prepared position in case he is driven out of his first trench. On a hill we find a fire trench near the foot of the slope, one just forward of the military crest, and the third on the reverse slope of the hill.

In many instances the first line trenches consist of as many as four or five lines of trenches running in a general lateral direction and connected by deep narrow communicating trenches. The depth between the first and last of these trenches is, in some instances, not over a hundred yards. Sign boards are necessary at short intervals to prevent the soldiers from getting lost. The effect of having so many alternative firing trenches is to make it extremely difficult for an enemy to advance from, or even to hold one of them, even when he gains a footing, as he would be swept by fire from the supporting trenches in rear and also by flanking fire from the adjacent trenches.