FIELD TRENCHES
The next element of the defensive position is the _first line fire
trenches_. These are located so as to have a good field of fire to
the front for several hundred yards and so constructed as to give the
greatest cover and protection from the fire of the enemy.
An unbroken, continuous trench would be exposed to enfilade fire. A
shell, shrapnel or grenade bursting therein would have widespread
effect. To overcome these elements the trench is constructed in short
lengths, with traverses between them, and technically known as the
_traverse type_.
Better defilade is thus secured and the material effect of any burst is
confined to narrow limits.
The trench interval between the traverses is known as the "bay," which
should not ordinarily be longer than 18 feet. Longer bays invite heavy
casualties in case the trench is enfiladed or a high explosive shell
finds its mark.
The illustration, Plate 14, shows a trace of the traversed type of fire
trench.
[Illustration:
_PLAN OF TRAVERSED TYPE OF FIRE TRENCH_
_PLATE 14._]
TYPE OF TRENCH
Formerly, protection from the enemy's fire was obtained by thickness of
parapet. In the trench warfare of today it is obtained by completely
concealing the riflemen in a deep, narrow trench with a very low
parapet.
The height over which the average man can fire is about 5 feet or about
five-sixths of his own height. This factor determines the height of the
parapet above the firing banquet of the trench or the height of bottom
of loophole above the same point, when the latter is employed.
[Illustration: Plate 15.--Simple standing trench.]
[Illustration: _PLATE 15a._]
The type of trench in general use today is the simple standing trench
shown in Plate 15.
DRAINAGE
If a trench is to be occupied for any length of time, especially if
much ground or falling water is to be encountered, drainage becomes
of prime importance. Many years ago a celebrated military authority
asserted that "nothing so saps the courage of a soldier as to wet the
seat of his breeches." This may be accepted as a true maxim, especially
in cold weather. The trench should therefore be made as dry as
possible. The floor of the trench should be given a sufficient slope to
the rear where an intercepting drain should carry the water to prepared
sumps or to a point from which it can be disposed of by drainage.
Provision should also be made to exclude surface drainage from the
trenches.
A scheme for trench drainage is shown in the illustrations (Plates 16,
17 and 18).
Overhead cover may be provided as shown in Plates 19 and 20.
Loopholes are made wherever head cover is provided. Where the enemy's
trenches are close, there is considerable danger in using them.
Collective firing takes place over the parapet. When loopholes are used
they should face half-right or half-left and not directly to the front.
[Illustration: Plate 16.--Method of draining trench.]
[Illustration: Plate 17. Details of trench drainage.]
[Illustration: Plate 18. Detail of trench drainage.]
[Illustration: Plate 19.--Overhead cover.]
[Illustration: Plate 19a.--Overhead cover.]
[Illustration: Plate 20.--Overhead cover.]
[Illustration: Plate 20a.--Overhead cover.]
The disadvantages of loopholes are:
1. The difficulty of concealing firing points. Loopholes give the
enemy's snipers an easy mark.
2. They lessen the number of rifles that can be used at a given point.
3. The necessary head cover makes it difficult to get out of the trench
quickly.
4. Damaged head cover often spoils a good firing point.
The three types of loopholes are:
1. Narrowest point of the opening nearest the marksman. This type is
most difficult to conceal, much of the parapet thickness is cut away
and, if of hard material, tends to deflect the bullets into the firer's
face. This defect may be remedied somewhat by stepping the surface of
the loophole.
2. Narrowest point to the front. Easiest to conceal but gives a limited
field of view.
3. Narrowest point midway between the front and rear. A compromise
between the first two types.
The following general remarks on the construction of loopholes are
taken from a work based upon the experience gained during the war in
Europe:
1. The angle of splay is usually 60 degrees. The thicker the parapet
the smaller must be the angle of splay.
[Illustration: Plate 21.--Types of loopholes.]
2. The marksman holds his rifle in a line connecting the right
shoulder, the eye and the object, hence most of the body lies to the
left of the rifle. The loophole should be made to the right, with a
niche in the wall of the parapet from the hip to the armpit, to bring
the left shoulder well forward. It will be found that this permits the
right elbow to be placed on the edge of the parapet.
[Illustration: Plate 22.--Methods of constructing loopholes with
sandbags.]
3. Box loopholes with screens or blindage may be used, but should be
placed by a skilled marksman. The great disadvantage is that the enemy
notes these parapet alterations. Steel loophole plates are now provided
for this type of loophole. As the Germans sometimes use a steel bullet
with great penetrating power, it is advisable to place two plates
together to insure protection.
4. With every precaution that may be taken it is difficult to conceal a
loophole. A good plan is to deceive the enemy by using painted sandbags
and preparing plenty of dummy loopholes.
5. The minimum width of loopholes should be 2-1/2 inches. If narrower
than this, it is impossible to use both eyes to judge distances
correctly.
6. The parapet should be so sloped that there is a maximum grazing
fire when the rifle is fired as it lies on the parapet.
To insure that the bullet will not graze the parapet, although the
sights are clear, look through the barrel with the bolt removed.
COMMUNICATION TRENCH
In the first line fire trenches there are so many crooks and turns and
the trench itself is so narrow that passage along the same is very
difficult. To provide for this lateral communication a trench known
as the communication or supervision trench is dug. It runs generally
parallel to and a short distance in rear of the fire trench and is
connected therewith by zigzag approaches. The factor that determines
the distance between the fire trench and the communication trench is
that it should be at such a distance that a shell bursting in one of
the bays would not destroy the communication trench.
[Illustration: Plate 23.--Type of communication trench.]
The location of the communication trench with respect to the fire
trench and the arrangements of the approaches is shown in detail in
Plate 1.
The profile of the ordinary communication trench is shown in Plate 23.
DUGOUTS
During the artillery bombardment few men are left in the fire trenches.
The remainder of the garrison is held under cover a short distance
to the rear. This cover is provided by a system of dugouts connected
with the fire trench through underground passageways that lead to the
communication trench. This arrangement is shown in Plate 1.
A profile of the latest type of dugout is shown in Plate 24.
The solid earth cover is from 12 to 18 feet thick, which gives
protection from all but the very largest caliber shells.
[Illustration: Plate 24.--Type of dugout.]
Effective resistance is supplied by roofing materials as follows:
1. From shrapnel bullets: 2-inch planks covered with 12 inches of earth.
2. From 3-inch shells: 4-inch planks supporting 4 feet of earth with a
top layer of heavy stones to cause an early shell burst.
3. From howitzers of less than 6 inches caliber: 12-inch beams or logs
covered with 8 feet of earth.
4. From the largest caliber guns: 15 to 25 feet of earth.
The following table shows the penetration of the German S bullet at a
range of 200 yards:
_Inches_
Steel plate 3/8
Broken stone 6
Brickwork, cement and mortar 9
Brickwork, lime and mortar 14
Sandbags 24
Sand, loose 30
Hardwood, oak, etc. 38
Earth 50
Soft wood, poplar, etc. 58
Clay 60
Dry turf 80
In addition to the regular "dugouts" for the supports, the latest
type trenches have squad dugouts just in rear of the bays of the fire
trench. These provide shelter during bombardment for the members of the
squad not actually required on duty in the trench bay.
[Illustration: Plate 24a.--Section of traversed type of fire trench
showing entrance to squad dugout.]
COMMUNICATIONS
The fire trench is connected with the cover for supports by a system of
zigzag trenches having the profile shown in Plate 23. The arrangement
is shown in Plate 1.
[Illustration: Plate 25.--Profile of trench mortar emplacement.]
TRENCH MORTAR POSITIONS
Somewhere between the first line fire trench and the cover for the
supports is a line of emplacements for the trench mortars. Plate 25
shows a profile of the emplacement.
The arrangement of the position is shown in Plate 1.
[Illustration: Plate 25a.--Trench mortar.]
These trench mortars are used to hurl charges of high explosives
varying from 25 to 100 pounds into the enemy's lines. They have a
range of from 300 to 1,800 yards.
[Illustration: Plate 25b.--Improvised catapult.]
COVER FOR SUPPORTS
At a variable distance to the rear of the first line fire trench is
located the cover for supports, which is organized much in the same
manner as the first line system of trenches and affords a second
position in the system to fall back to in case of necessity. These
trenches are provided with overhead cover and numerous dugouts for the
protection of the men.
MACHINE GUNS
At every available place throughout the defensive position machine guns
are located, typical positions of which are shown in Plate 1.
The typical types of cover are shown in Plates 26 and 27.
Machine guns are a very potent factor in trench warfare. They are
now being employed to a far greater extent than ever before, and the
number is increasing on all the battle fronts as fast as they can be
manufactured. The machine-gun positions are carefully concealed from
the enemy, and fire is not opened until it is certain that it will be
effective.
[Illustration: Plate 26.--Profile of type of cover for machine gun.]
[Illustration: Plate 27.--Type of cover for machine guns.]
The selection of the sites for the emplacements should be made with a
view to bringing a powerful enfilade or oblique fire on the attacking
enemy at effective range, to provide a flanking fire for supporting
troops, and to sweep gaps in the line of obstacles.
Their fire should come as a surprise to the attacking party.
In the construction of cover for machine guns the following points
should be observed:
1. They must have a platform for the gun and gunner. This may be
provided for in the construction of the emplacement or built up with
sandbags. The platform should be 3 feet wide and 6-1/2 feet in length.
2. If head cover is provided, it should not differ in appearance from
that constructed elsewhere in the trenches. The loopholes must be
blinded with gunny sacks.
3. The front of the emplacement should be cut under to receive the
leg of the tripod, thus bringing the gun up closer to the parapet and
furnishing more cover for the gunner.
4. Splinter-proof shelters should be provided near at hand for the
members of the gun detachment.
5. Where the enemy's trenches are near, the position for the
emplacement should be selected by day and the actual work done under
cover of darkness.
6. The guns should be located so that they support each other by their
fire. Alternate positions should be constructed.
7. When located to enfilade straight lines of trenches, special
capioniers should be constructed.
SUPPORTING POINTS
At intervals from 800 to 1,500 yards along the first line, supporting
points are established. They may consist of a fortified village or
a specially prepared position having a "labyrinth" of trenches and
rendered well-nigh impregnable to infantry assault by every defensive
device known to modern warfare. They are designed to bring a flanking
fire to bear upon the intervening intervals with the idea that troops
cannot pass beyond them until they are reduced.
VILLAGE DEFENSE
The following was the actual scheme employed for the defense of a
French village and exemplifies the thoroughness with which defenses
must be organized.
The village was about 700 yards in rear of the front line, and had
three keeps surrounded with wire entanglements and independent of each
other, but with an elaborate system of communication trenches. Water
and four days' rations were stored in each keep, and wells dug. Each
of the keeps held about one company. The communication trenches were
about 6 feet deep, used as far as possible as fire trenches, and well
traversed. Firing platforms were revetted with brushwood, and shelters
made all over the village. In addition to keeps, a series of lines
existed in the rear of the front line, intercommunicating and provided
with barbed wire. A small wood on one point of the front was defended
by a network of low wire entanglements and a line of high wire netting.
Every officer had to know all about his section and its communications
with right and left. Telephone wires were laid low down in
communication trenches and fastened a few inches from ground with
wooden pickets.
Machine guns were placed so as to flank salients. A 65-mm. field gun
was placed in the front line to sweep the village, and an observation
station placed in a tree. The observer wore a green mask and green
sheet.
Great use was made of brushwood and undergrowth to revet steps of
firing platform.
All work was carried out by regimental officers and men without help
from the engineers, who were fully employed in mining. The garrison of
the village and the front line trenches in the vicinity was about one
battalion, but the fire trenches were sufficient for three battalions.