Military Instructors Manual by James P. Cole and Oliver Schoonmaker

J >> James P. Cole and Oliver Schoonmaker >> Military Instructors Manual

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Special instructions will be issued as to precautions against gas.

Selection of Site.

(a) Fire trench should be selected with due regard to tactical
requirements and the economy of men.

(b) Every fire trench should have a good field of fire, at least 250
yards.

(c) The trenches should have the best possible cover.

(d) The forward position on a slope for the first line has the best
advantage. The support trench should be on the reverse slope from 100
to 600 yards in rear of the first line to prevent direct observation
and to be practically free from artillery fire. The reserve trench is
usually from 1/2 to 1 mile in rear of the first line. Remember that
the first line, the support line, and the reserve line are all fire
trenches. Do not put them on a crest.

(e) The communicating trenches (boyaux) should be zigzagged, wide and
deep, and should follow the low ground. The longest straight trench
should not exceed thirty paces. The angle made by each turn should be
less than 140 degrees.

(f) The fire trenches should have salients and re-entrants so as to
flank the wire entanglements. The bays are usually 27 feet long with 9
feet of traverse.

(g) There are two problems in the siting of trenches, one for those to
be constructed under fire and another for those that will be
constructed without any danger from fire. Trenches built under fire
are usually made by connecting up individual shelters made by the
front line when forced to halt. Trenches built under quiet conditions
can be laid out according to the best possible plan.

Trench Construction.

Several kinds of difficulties face the trench digger: Sand, clay,
water and bullets. In order to overcome them he must be familiar with
the general arrangement of a trench, the principles which govern its
construction and the standard trench as it has been worked out in the
present war at the cost of thousands of lives.

General Arrangement.--A position is a combination of trenches,
consisting of: The fire trench, or first line, nearest the enemy; the
cover trench, just behind the first line, where all but sentinels of
the fire trench garrison are held in dugouts or shelters; the support
trench, from 150 to 200 yards in rear of the cover trench, and the
reserve, from 800 to 1,200 yards still further to the rear.

The support trench is placed far enough from the first line to prevent
the enemy from shelling both trenches at once. By a concentration of
artillery fire and a determined advance of the hostile infantry the
first line may be captured. The support trench must be so organized
that it will then act as a line of resistance upon which the enemy's
advance will break. Lieutenant Colonel Azan of the French army says:
"As long as the support trenches are strongly held, the position is
not in the hands of the enemy."

[Illustration: Plate #16]

The reserve is usually a _strong point_, so organized that it can
maintain independent resistance for several days if necessary, should
the enemy obtain control of adjacent areas.

Where possible trenches should be on reverse slopes, with the
exception of the first line; but usually the outline of a trench is
determined in actual combat, or is a part of hostile trench converted.
Under these circumstances it cannot be arranged according to tactical
ideals.

Artillery and the automatic gun are the determining factors in trench
warfare to-day. The effect of artillery fire must be limited in its
area as far as possible, and trenches are, therefore, cut by
_traverses_, which are square blocks of earth not less than nine feet
square, left every 27 feet along the trench. They should overlap the
width of the trench by at least one yard, thereby limiting the effect
of shell burst to a single _bay_, the 27-foot length of firing trench
between two traverses. Sharp angles have the same effect as traverses,
but angles of more than 120 degrees cannot be utilized in this way.

The sides of the trench are kept as nearly perpendicular as possible,
to give the maximum protection from shell burst and the fall of high
angle projectiles. The _parados_, the bank of earth to the rear of the
trench, has been developed during the war to give protection from
flying fragments of shells exploding to the rear, and to prevent the
figure of a sentinel from being outlined through a loop-hole against
the sky. The _berm_, a ledge or shelf left between the side of the
trench and the beginning of the parados, has come into general use in
order to take the weight of the parados off the earth at the immediate
edge of the trench, and so prevent the reverse slope from caving in
easily under bombardment or heavy rain.

[Illustration: Plate #16A]

Automatic guns have made it necessary to break the line of the trench
at every opportunity, in order to secure a flanking fire for these
arms. Auto-rifles and machine guns have tremendous effectiveness only
in depth, and flanking fire gives them their greatest opportunity.

Trench Construction.--The methods of building trenches are the same
whether the work is carried on under fire or not. In an attack, upon
reaching the limit of advance, the men immediately dig themselves in,
and later connect these individual holes to make a continuous line of
trench.

Most of the digging must be done at night, and must be organized to
obtain the most work with the least confusion. There are three ways of
increasing the efficiency of the men. In the first of these, squad
shifts, the squad leader divides his men into reliefs and gives each
man a limited period of intensive work. Reliefs may be made by squads
or by individuals. The second way of increasing efficiency is to
induce competition among the man and squads, thus making the work a
game in which each soldier's interest will be aroused in the effort to
do better than the others. The third method is to assign a fixed
amount of work to each man. An average task, which all ought to
accomplish in a given time, is found by experience, and those who
finish before their time is up are relieved from further work during
that shift, and allowed to return to their shelters.

Continual care must be used to check up the tools on hand, as the men
are prone to leave them where they were working rather than carry them
back and forth to work. Each unit must guard its property from
appropriation by neighbors on its flanks.

System of Laying Out Trenches.--The trace of the trench is first
staked out, particularly at traverses and corners when the work is to
be done at night. Measurements should be exact, and the men should be
required to line the limits of each trench so as not to exceed them
in digging. All sod should be taken up carefully and used on the
parapet for concealment or on the berm to make a square back wall for
the dirt of the parapet. If possible this should be done with the
parados wall, so as to make it as inconspicuous as possible from the
front.

Men should begin to dig at the center of the trench and throw the dirt
as far out on the sides as possible, so that as they go deeper the
earth can be thrown just over the berm. The slope of the sides will be
kept steep and the men prevented from widening the trench as they dig.
In sandy soil the sides of the trench should be allowed to reach their
angle of repose (which is wider at the top than required), then the
trench walls supported with _revettments_ to the proper width, which
are filled in behind with sand. Always dig to full depth before
beginning to revet, as it is impossible to dig deeper afterwards
without loosening the revetting.

Revettments.--Every trench at points needs support, and this
_revetting_ may be done with any of the following materials: Sod;
corduroy of logs laid lengthwise; sand bags (size 20 in. x 10 in. x 5
in.); galvanized iron; chicken wire and cloth made in a frame about
six feet long; _hurdles_, wicker mats made by driving three-inch
stakes into the ground, leaving uprights as high above the ground as
the depth of the trench, then weaving withes and slender saplings
between the uprights; expanded metal; _gabions_, cylindrical baskets
made like hurdles except that the stakes are driven in a circle;
_fascines_, bundles of faggots about 10 inches in diameter by 9 feet
long. The faggots are laid together on a horse or between stakes
driven in the ground, then "choked," or bound tightly together, by a
rope 3 feet 8 inches long with loops at each end, tightened with two
stiff levers. The bundle is then bound with wire at intervals of two
feet. The circumference of a fascine should be 25 inches.

[Illustration: Plate #17]

Capt. Powell of the C.E.F. found during 18 months' service in the
trenches, that a separate construction for the bottom and firing step
from that of the parapet made repair much simpler when the trench was
damaged by shell fire. The upper part of the trench usually suffers
most, while the bottom section, if unattached, often remains intact
and the drainage system needs only to be cleared out. If the portion
above the firing step is one piece with that below, however, the whole
trench has to be reconstructed.

There is nothing more important than the supports used to keep
revetting in place. With sods, sand bags, concrete and gabions, a
proper arrangement in the first place will make other support
unnecessary.

Sod should be placed carefully, with a slope of not more than one
inch on four, with the vegetation uppermost. This type is least
affected by rain.

Sand Bags should be used like brickwork, laid in alternate headers
(binders) and stretchers. Their use should be confined as far as
possible to emergency and repair work, because after a few weeks the
bags rot and cannot be moved about. If the trench wall has been
demolished by artillery fire, the particles of cloth make digging out
the bottom of the trench a very difficult matter.

Concrete Work has been used extensively by the Germans, but the
chips fly like bullets under shell explosion, and the concrete cracks
and disintegrates in severe weather. It is used in the bottom of
trenches for drainage and for the firing step.

Gabions may be set into the wall of the trench and filled with
earth, or used at corners to prevent the wearing down of the edge,
which reduces the protective effect of the trench. Set in at a slight
angle they will hold the side without further re-enforcement.

With the other forms of revetting some secondary support is required.
This is usually furnished by sinking stakes into the bottom of the
trench and securing their upper ends to a "dead man"--a stake or log
sunk in the ground more than three feet away. The tendency is to sink
the dead men too near to the trench, and to attach too many wires to
one of them. It is important to sink the stakes at least one foot
below the bottom of the trench. By digging holes for them instead of
driving them in directly, the sides of the trench need not be
disturbed by the concussion of driving the stakes. This is especially
important in sandy soils. Stakes should be placed about two feet
apart. Dead men should be buried deeply enough to prevent cutting by
shell explosions.

Trench Armament.--A few machine guns are set in concealed
emplacements along the trench to cover important salients. The
automatic rifle is used over the parapet. Besides these there is the
rifle grenade and trench mortar. The rifle grenade has a simple
emplacement. After securing the proper elevation, the butt of the
rifle is placed between posts or blocks of wood and the muzzle rested
against a log on the wall of the trench. A trench mortar emplacement
is dug in the rear wall of the trench, or a shell hole is utilized,
care being taken to conceal it from aerial observation.

Loopholes.--Loopholes are still much in use for observation, but
they are employed less and less for firing, as they are difficult to
conceal from the enemy and almost useless when the enemy is close.
They should cut the parapet diagonally, not directly to the front, and
should be concealed by vegetation and by a curtain over the opening
when they are not in use. Sheet steel plates with small peep holes are
used on the parapet. They are set up with a slope to the rear to
deflect bullets.

Trench Bottoms.--In clay or hard soil special arrangements must be
made for drainage. Where possible the trench should have a convex
surface and should be smooth. A rough bottom means delay in reliefs,
and possible injuries. Where trenches are used for long periods
board walks should be constructed. Under these drains or sink holes
can be placed to collect water. A sink hole may be constructed by
digging a pit filled with small stones, or a barrel may be sunk into
the ground and filled with stone. Where there is not sufficient slope
to carry off the water, or at the lowest point of a drainage system, a
water hole should be dug in front of the trench large enough to handle
the drainage water.

[Illustration: Plate #18]

Communication Trench (or Boyau).--Running to the rear and joining
the different parallel resistance trenches are communication trenches
or boyaux. These are for transportation of men and material as well as
for communication. Communication trenches should be made wide enough
to allow travel for men with loads, should be at least seven feet deep
and as smooth as possible on the bottom. Rough places will delay
traffic. They are dug with turns every 20 or 30 yards to prevent their
being swept by gun fire. When boyaux are built by night sharp zig-zag
corners should be used, or the angles will not be acute and protection
will be lost. During daylight when the directions can be seen, the
construction may be a serpentine curve, with no stretch of more than
30 yards visible from one point.

Boyaux are sometimes used for lateral defence and often emplacements
for automatic guns are arranged to cover stretches of them. Bombing
stations are placed near by to protect the guns and to clear the boyau
of the enemy. At these points the boyau is left straight for a short
distance in front. Where provision is made for lateral or frontal
defence by rifle fire, firing steps are constructed. If this is
inconvenient for movement along the boyau, individual emplacements
must be made in the side wall for firing. Sentry posts are dug at
right angles to the boyau.

Arrangements for passage of men moving in opposite directions may be
made by extending short spurs at the corners, enlarging the boyau at
the bends, digging niches or passing points here and there, or
constructing island traverses with the boyau running around on each
side.

[Illustration: Plate #19]

Every boyau should be marked where it meets a trench with a sign
indicating the place and trench. Without this messengers, reliefs and
re-enforcements may easily be lost in the maze of trenches.

Latrines should be run out about 20 feet from boyaux at points
directly in rear of lateral trenches. If possible they should be
placed so that men cannot enter them without passing near the platoon
leaders. This will prevent men from leaving the front line, under the
pretense of going to latrines, during bombardments or mining
operations. The trench leading to a latrine should be constructed like
a boyau, and the pit should be close to the side nearest the enemy, to
give the best possible protection from shell fire. There are three
types of trench latrines: Deep boxes which are covered and have rough
seats; short straddle trenches or trenches equipped with a single
horizontal bar, and portable cans, used where the ground or the
limited space make it impossible to dig pits. These cans should be
emptied daily into holes behind the trenches, which are covered after
the cans are emptied into them.

Urinals should be separate from the latrines. They may be either holes
about three feet deep filled with stone, troughs with a covered pit at
the end, or portable cans.

Shelters. For the protection of men not actually on duty three forms
of shelters are used. The _splinter-proof_ is a form of light shelter
whose covering affords protection only against splinters. These are
usually on the reserve line. About 12 inches to 20 inches of earth
over a roof of logs or planks will afford protection from splinters
and shrapnel. Curved sheets of iron may also be used. The _deep
shelter_ or _bomb-proof_ is a chamber constructed by digging from the
surface and constructing a roof. To protect against eight-inch
shells the top of the chamber should be twenty feet below the surface.
Heavy beams or sections of railroad iron are laid across the roof.
Above them is a layer of earth several feet thick; then another layer
of timber extending to undisturbed ground on the sides with concrete,
crushed stone, metal, etc., above to make a percussion surface for
exploding projectiles that penetrate the upper layer of earth. This
layer fills in the rest of the space to the level of the ground.

[Illustration: 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 shells 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 passageways 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 passageway 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 spaced 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 shell 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.--Shell-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. Shell-holes
may be imitated for machine gun emplacements, but in any case they
should be connected by underground passage 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.

[Illustration: 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 classified 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 muffled, and metal screw posts are used when near the
enemy's line. Posts are placed in two parallel lines, two yards apart,
spaced 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.

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