FIELD FORTIFICATIONS
=1140. Object.= The object of field fortifications is two-fold.
1. To increase the fighting power of troops by enabling the soldier to
use his weapons with the greatest possible effect.
2. To protect the soldier against the enemy's fire.
=1141. How these objects are accomplished.=
These objects are accomplished:
1. By means of shelters--trenches, redoubts, splinterproofs, etc.,
which protect the soldier from the enemy's fire.
2. By means of obstacles--wire entanglements, abatis, pits, etc.,
which delay the advance of the enemy.
=1142. Classification.= Field fortifications are usually divided into
three classes, =hasty intrenchments=, =deliberate intrenchments= and
=siege works=.
=Nomenclature of the Trench.= The following illustration shows the
names of the various parts of the trench.
[Illustration: Fig. 1]
=1143. Hasty intrenchments= include trenches dug by troops upon the
battlefield to increase their fighting power. They are usually
constructed in the presence of the enemy and in haste and embrace
three forms viz:--the =lying trench=, the =kneeling trench=, and the
=standing trench=.
=1144. Lying trench.= (Fig. 2.) This trench gives cover to a man lying
down. When intrenching under fire the rifle trench can be constructed
by a man lying down. He can mask himself from view in about 10 to 12
minutes and can complete the trench in 40 to 45 minutes. A good method
is to dig a trench 18 inches wide back to his knees, roll into it and
dig 12 inches wide alongside of it and down to the feet, then roll
into the second cut and extend the first one back. Conditions may
require men to work in pairs, one firing while the other uses his
intrenching tool. Duties are exchanged from time to time until the
trench is completed.
[Illustration: Fig. 2]
[Illustration: Fig. 2a
_Intrenching under fire_]
The height of the parapet should not exceed 1 foot. This trench
affords limited protection against rifle fire and less against
shrapnel.
=1145. Kneeling trench.= (Fig. 3.) Time permitting the lying trench
may be enlarged and deepened until the kneeling trench has been
constructed. The width of the bottom should be 2-1/2 feet--preferably
3 feet--and the relief (distance from bottom of trench to top of
parapet) is 3 feet--the proper height for firing over in a kneeling
position.
[Illustration: Fig. 3]
=1146. Standing trench= (Fig. 4) has a bottom width of 3 to 3-1/2 feet
and a relief of 4-1/2 feet which is the proper firing height for men
of average stature. As this trench does not give complete cover to men
standing in it a passage way should be constructed in rear of it not
less than 6 feet below the interior crest. This forms the complete
trench (Fig. 5). Figures 6-7-8 show simple standing trenches used in
the European War.
[Illustration: Fig. 4]
[Illustration: Fig. 5]
[Illustration: Fig. 6
Simple Standing Trench, Parapet Suppressed]
[Illustration: Fig. 7
Simple Standing Trench, Rocky Ground]
[Illustration: Fig. 8
Narrow Firing Trench with Parados]
=1147. Deliberate intrenchments= comprise trenches and works
constructed by troops not in line of battle and are usually intended
to enable a small force to resist a much larger one. It frequently
happens that hasty intrenchments are developed into deliberate
intrenchments and from this stage pass into the domain of siege works.
=1148. Fire trenches=,--the trenches which shelter the firing
line,--are of different types. No fixed type can be prescribed. The
type must be selected with due regard to the terrain, enemy, time,
tools, soil, etc., but all should conform to the requirements of a
good field of fire, and protection for the troops behind a vertical
wall, preferably with some head or over head cover.
The simplest form of fire trench is deep and narrow and has a flat
concealed parapet (Fig. 9). When time will permit the simple trench
should be planned with a view to developing it into a more complete
form (Figs. 10 and 11). In all trenches as soon as practicable a
passage way--2 feet wide at the bottom--should be provided, in rear of
the firing step, for the men carrying supplies, ammunition, etc., and
for the removal of the wounded.
[Illustration: Fig. 9]
[Illustration: Fig. 10]
[Illustration: Fig. 11]
When the excavated earth is easily removed a fire trench without
parapet may be the one best suited to the soil and other conditions
affecting the conditions of profile (Fig. 12). The enemy's infantry as
well as artillery will generally have great difficulty in seeing this
trench. Fig. 13 shows a squad trench. Fig. 14 shows a fire trench
provided with protection against shrapnel. This trench is used in the
European War.
[Illustration: Fig. 12]
[Illustration: Fig. 13]
[Illustration: Fig. 14
Protection against Shrapnel]
In the European War the aim in constructing fire trenches seems to be
to minimize and localize artillery effect as far as possible. The main
excavation along the front is a continuous, very deep, communication,
not in itself prepared for active defense. The actual firing is done
from banquettes or firing steps just to the front of the passage or
from trenches dug as far as 5 or 10 feet in front of the main
excavation and reached by short passages. Figs 15 and 16 show the type
of this construction. Fig. 17 shows a fire trench with parades and
shelter.
[Illustration: Fig. 15
Two Methods for Communication Trenches in rear of Firing Trenches]
[Illustration: Fig. 16
Communication Trenches in rear of Firing Trenches
Recessed and Traversed Firing Trench]
[Illustration: Fig. 17
Trench Shelter]
=1149. Traverses.= Fire trenches are divided into sections or bays by
means of traverses which intercept side or enfilade fire and limit the
effect of shells, bombs or grenades, which burst inside of the trench.
The traverses should be wide enough to screen the full width of the
trench with a little to spare. The thickness of the traverse varies
from 3 to 6 feet or more. Six feet is the dimension generally found in
the traverses in the trenches on the European battle fronts.
=1150. Trench recesses; sortie steps.= It will be noted that in some
of the diagrams of the trenches now being used in the European War the
berm has been eliminated entirely. The object being to bring the firer
closer to the vertical wall thus giving him better protection from
shrapnel fire. There have also been added to the trench, recesses for
hand grenades. These recesses are similar to recesses dug in the front
wall of the trench for ammunition. One form of recess is shown in
(Fig. 18). In order to provide facilities for rapidly mounting from
the trench to charge, sortie steps and stakes have been provided in
some trenches as shown in (Fig. 16).
[Illustration: Fig. 18
_Store Recesses for Water, Hand-Grenades, Reserve Ammunition, Machine
Guns, Range Finders, Blankets, etc._ (From _Field
Entrenchments_--Solano.)]
=1151. Parados.= Instead of shrapnel, explosive shell is most
frequently used in the European War. This necessitates the addition of
a parados to the fire trench to protect against the back blast of high
explosives. This is shown in (Figs. 8 and 17).
An interesting development in cover for the firing line is shown in
dugouts constructed in the fire trenches in the European war. These
dugouts are deep underground and shelter from 3 to 8 men each (Fig.
19). These dugouts will be discussed more in length under cover
trenches.
[Illustration: Fig. 19]
=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.
[Illustration: Fig. 20]
[Illustration: Fig. 21]
[Illustration: 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.
[Illustration: Fig. 23]
[Illustration: Fig. 24]
[Illustration: Fig. 25]
[Illustration: 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 Japanese in Manchuria and Fig. 29 that used by the
Russians.
[Illustration: Fig. 27]
[Illustration: Fig. 28]
[Illustration: 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.
[Illustration: Fig. 30]
[Illustration: 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, grass down, or straw, or grain sacks over the platform before
putting on the earth, to prevent the latter from sifting through.
[Illustration: Fig. 32]
[Illustration: Fig. 33]
[Illustration: Fig. 34]
[Illustration: Fig. 35]
=The thickness of overhead cover= depends upon the class of fire
against which protection is desired, and is sometimes limited by the
vertical space 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.
[Illustration: Fig. 36]
[Illustration: Fig. 37]
[Illustration: 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 passage 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 passage 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.
[Illustration: Fig. 39
_Typical Passage 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.
[Illustration: 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
spaces 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.
=1161. Location.= There are two things to be considered in locating
trenches: (1) The tactical situation, and (2) the nature of the
ground. The first consideration requires that the trenches be so
located as to give the best field of fire. Locating near the base of
hills possesses the advantage of horizontal fire, but, as a rule, it
is difficult to support trenches so located and to retreat therefrom
in case of necessity. While location near the crest of hills--on the
"military crest"--does not possess the advantage of horizontal fire,
it is easier to support trenches so located and to retreat therefrom.
Depending upon circumstances, there are times when it will be better
to intrench near the base of hills and there are other times when it
will be better to intrench on the "military crest," which is always in
front of the natural crest. The construction of trenches along the
"military crest" does not give any "dead space"--that is, any space to
the front that can not be reached by the fire of the men in the
trenches.
Whether we should construct our trenches on high or low ground is a
matter that should always be carefully considered under the particular
conditions that happen to exist at that particular time, and the
matter may be summarized as follows:
The advantages of the high ground are:--
1. We can generally see better what is going on to our front and
flanks; and the men have a feeling of security that they do not enjoy
on low ground.
2. We can usually reenforce the firing line better and the dead and
wounded can be removed more easily.
3. The line of retreat is better.
The disadvantages are:--
1. The plunging fire of a high position is not as effective as a
sweeping fire of a low one.
2. It is not as easy to conceal our position.
The advantages of low ground, are:--
1. The low, sweeping fire that we get, especially when the ground in
front is fairly flat and the view over the greater part of it is
uninterrupted, is the most effective kind of fire.
2. As a rule it is easier to conceal trenches on low ground,
especially from artillery fire.
3. If our trenches are on low ground, our artillery will be able to
find good positions on the hill behind us without interfering with the
infantry defense.
The disadvantages are:--
1. As a rule it will be more difficult to reenforce the firing line
and to remove the dead and wounded from the trenches.
2. On a low position there will usually be an increase of dead space
in our front.
3. The average soldier acting on the defensive dreads that the enemy
may turn his flank, and this feeling is much more pronounced on low
ground than on high ground. Should the enemy succeed in getting a
footing on our flank with our trenches on top of the hill, it would be
bad enough, but it would certainly be far worse if he got a footing on
top of the hill, on the flank and rear, with our company on low ground
in front. We, therefore, see there are things to be said for and
against both high and low ground, and the most that can be said
without examining a particular piece of ground is: Our natural
inclination is to select high ground, but, as a rule, this choice will
reduce our fire effect, and if there is a covered approach to our fire
trenches and very little dead ground in front of it, with an extensive
field of fire, there is no doubt the lower ground is better. However,
if these conditions do not exist to a considerable degree, the moral
advantage of the higher ground must be given great weight, especially
in a close country.
The experience of the European war emphasizes the fact that the
location of rifle trenches is today, just as much as ever, a matter of
compromise to be determined by sound judgment on the part of the
responsible officers. The siting of trenches so that they are not
under artillery observation is a matter of great importance, but, it
has yet to be proven that this requirement is more important than an
extensive field of fire. There are many instances where to escape
observation and fire from the artillery, trenches were located on the
reverse slopes, giving only a limited field of fire. This restricted
field of fire permitted the enemy to approach within a few hundred
yards of the trench and robbed them of the concealment they had hoped
to gain. The choice between a site in front, and one in rear of a
crest, is influenced by local conditions which govern the
effectiveness of our own and the enemy's fire. In general, the best
location for effective fire trenches, lies between the military crest
of rising ground and the lowest line from which the foreground is
visible. If the position on the military crest is conspicuous, it is
inadvisable.
With regard to the nature of the ground, trenches should, if
practicable, be so located as to avoid stony ground, because of the
difficult work entailed and of the danger of flying fragments, should
the parapet be struck by an artillery projectile.
To locate the trace of the trenches, lie on the ground at intervals
and select the best field of fire consistent with the requirements of
the situation.
Trenches should be laid out in company lengths, if possible, and
adjoining trenches should afford each other mutual support. The flanks
and important gaps in the line should be protected by fire trenches
echeloned in rear.
=1162. Concealment of trenches.= Owing to the facilities for
observation that the aeroplanes and other air craft afford, and to the
accuracy and effect of modern artillery fire, every possible means
should be taken to conceal trenches, gun implacements, and other
works. The aim should be to alter the natural surface of the ground as
little as possible and to present a target of the smallest possible
dimensions. Covering the parapet with brush or grass will afford
temporary concealment. If the new earth can be sodded it aids greatly
in concealing the trench. In some cases troops have gone to the extent
of painting canvas to resemble the ground and have placed it over
trenches, guns, etc. Straw and grass placed in the bottom of trenches
make them less conspicuous to air scouts. When trenches are dug on a
fairly steep slope care must be used to conceal the back of the
trench, which, being higher than the parapet, will stand out as a scar
on the hillside. Grass or brush may be used to conceal the back of the
trench.
=1163. Dummy trenches.= May be constructed which attract the enemy's
attention and draw his fire, or at least a part of it. The extent to
which this method may be used may include the construction of dummy
obstacles and guns, and even hats may be placed on the parapets.
=1164. Length of trench.= The usual minimum allowance of trench space
is one yard per man, although in some tests, two feet was found
sufficient for men to fire satisfactorily. Ordinarily one squad will
occupy the space between two traverses which experience has shown
should be about 15 feet apart.
=1165. Preparation of the foreground.= One of the first principles in
improving the foreground is that an enemy attacking the trenches shall
be continually exposed to fire especially in the last 400 or 500
yards. This requires a clearing of the foreground and a filling in of
depressions or leveling of cover. Dead space may be swept by fire of
trenches specially located for that purpose. Those features of the
ground which obstruct the field of fire, restrict the view, or favor
or the enemy's approach, should be removed as far as possible. On the
other hand, features which favor the concealment of the trenches or
increase the difficulty of the attack would better be left standing,
especially when it is possible to fire through or over them.
=1166. Revetments.= By a revetment we mean a facing placed against the
front or back wall of a trench to keep the earth in place.
When trenches are to be occupied for any length of time, they must be
revetted. There are many forms of revetments. Sod revetments, stakes
with brush behind them, stakes with planks, boards, or poles behind
them and a common form seen in the trenches in Europe chicken wire
with brush or canvas behind it.
=1167. Drainage.= All trenches should be dug so as to drain in case of
rain. In favorable locations the trench may be constructed to drain
automatically, by constructing it with an incline to one end. Under
ordinary circumstances dry standing has to be provided in trenches by
raising the foot level by the use of brush, boards, poles, etc.
Bailing will have to be resorted to in most cases to drain the trench.
=1168. Water Supply.= At least 1/2 a gallon of water per man per day
should be supplied. The supply is almost invariably liable to be
contaminated, therefore, it should be sterilized by boiling or by
treating. These are usually located just off from the communicating
trenches. Some form of receptacle should be used and all deposits
covered with chemicals.
=1169. Latrines.= Numerous latrines must be constructed in the
trenches' earth. These receptacles are removed from time to time and
emptied in pits dug for that purpose. Urinal cans must also be
provided and cared for in a similar manner.
=1170. Illumination of the Foreground.= Battlefield illumination is a
necessity where night attacks may be expected, and also as a
protection to the line of obstacles. Portable searchlights have become
an accepted part of every army. In addition to these, trenches must be
supplied with reflector lights, star bombs, rockets and flares,
arranged so that they can be put into action instantaneously when the
enemy approaches.
The foreground should be entirely illuminated, leaving the defenders
in the shadow. If the light is too close to the defenders parapet,
they are illuminated and become a good target. Some flares will burn
for 20 minutes and may be thrown to the front as grenades, fired as
rockets, shot from small mortars, or placed well to the front to be
set off by trip wires close to the ground. The best light devised is
one that can be fired well to the front from a small mortar and then
hung suspended from an open parachute above the enemy. Bonfires can be
laid ready for lighting when no other means is at hand. Whatever form
of illumination is adopted, it should withstand bad weather conditions
and prolonged bombardment.
=1171. Telephones.= When armies have been forced to trench warfare and
time has permitted an elaborate system of trenches to be constructed,
telephone communication is established as soon as possible. The
central station, with the switch-board is located in a shelter in rear
of the cover trenches and lines are run to all trenches, lookout
stations and listening points.
=1172. Siege works.= Comprise devices used by besiegers and besieged
in attack and defense of strong fortifications and especially those
devices enable troops to advance under continuous cover.