BATTERIES, OBSERVATORIES, AND MAGAZINES.
=42.= =Batteries= in siege operations are for field-guns,
siege-guns, howitzers, and mortars.
When the gun-platform is on or above the level of the ground they
are known as “_elevated batteries_,” when it is below the surface as
“_sunken batteries_.”
When they are concealed from the view of the enemy by natural
or artificial screens they are called “_screened_” or “_masked
batteries_,” and when on sites which can be seen by the enemy “_exposed
batteries_.”
GENERAL REQUIREMENTS OF SIEGE BATTERIES.
=43.= 1st. A good _platform_ for and sufficient space to work each
gun. The platform must be suited to the gun used. The space required is
about 15 feet front by 20 to 25 feet depth.
2d. A _parapet_ which cannot be penetrated by the projectiles which
will be fired against it, and which is high enough to afford cover to
the gun and its detachment against curved fire. A thickness of 30 feet
of earth will usually be enough for the most exposed batteries. A less
thickness may be used when the conditions justify it. The height of the
interior crest above the terre-plein should not be less than 7½ feet
when this is attainable and may sometimes be greater.
3d. _Traverses._ Each gun is usually separated from the next by a
traverse, whose thickness when subject to enfilade fire is the same as
that of the parapet (30 feet); under other circumstances the thickness
may be reduced if deemed advisable, but should, when practicable, be
such that a shell bursting at any point within it will blow out at the
top or on one side only.
4th. _Bomb_ and _splinter proofs_ sufficient to cover the gun
detachment and reserves against vertical fire. The thickness of cover
for these is to be regulated according to the principles laid down in
par. 21.
5th. _Magazines_ which will hold at least 24 hours' supply of
ammunition, besides recesses near the guns for shells and a few
cartridges.
6th. Easy and direct _communications_ for bringing up the guns and
placing them in position; including tramways, ramps, etc., etc.
7th. _Look-outs_ or _observatories_ from which the effect of the fire
can be seen. These when possible will be placed in high sheltered
places well on the flanks of the battery and preferably in advance of
it. They may be connected with it by signals, telegraph, or telephone,
when necessary.
8th. _Screens._--Earthen screens should when possible be thrown up in
front of all exposed batteries.
CONSTRUCTION OF BATTERIES.
=44.= =Batteries for Field Guns.=--When the place is
invested, the field artillery is placed in positions considered most
advantageous for repelling attacks from the garrison upon the investing
force. _Gun-pits_ (described in “Field Fortifications”) are usually
made at once for cover for the guns and their detachments. When any of
these sites are occupied during the siege the gun-pits may be connected
and converted into a battery as indicated by Pl. IV, Figs. 42-45.
A similar construction may sometimes be used during the siege when the
artillery fire of the place is weakened, and it is desirable to place
a field battery in position for reaching some point in the work. As
a rule, however, batteries for field guns will during the siege be
constructed in the same way as are those for siege guns and howitzers.
=45.= =Batteries for Siege Guns and Howitzers.=--These may
be _screened_ or _exposed_, _sunken_, or _elevated_. As a rule each
battery has a magazine on each flank. The amount of powder necessary to
serve two guns for 24 hours (150 to 200 rounds per gun = 2500 to 6000
lbs.) is as much as it is advisable to have in one magazine, in order
to limit so far as possible the disastrous effects of an explosion. For
this reason the number of guns in a battery is usually restricted to
four. This number may be increased when necessary, or when howitzers
firing small charges render it unobjectionable.
=Elevated batteries= require much more labor for their
construction and for obtaining cover for the men and material than the
sunken batteries. They are therefore used only when the target has to
be seen and the gun has to be raised for this purpose, or when owing
to the presence of rock or water in the soil, or the liability of the
site to be flooded it is impracticable to sink the platforms below
the surface. As a rule they can be constructed only when covered by a
screen either natural or artificial, and then with earth carried in
wheelbarrows, sand-bags, etc., etc.
=Sunken Batteries.=--When constructed under cover of a screen the
depth of the terre-plein of a sunken battery may be limited by the
presence of rock or water in the soil, the character of the guns and
carriages, and the time available for the work. In a hasty construction
the depth of the terre-plein is usually limited to from 3 to 4 feet,
which can be dug out in a short time. When more time is available the
gun platforms may be put at 5 to 6 feet below the surface and the
other parts of the terre-plein may be sunk still lower. This gives
but little height of parapet, and the extra earth may be used for
giving additional thickness of cover to the splinter-proofs under the
traverses and flanks, and also to the magazines.
A great variety of plans and profiles may be adopted for batteries of
this class, the details of which need not be given, since they will be
modifications of those described in Field Fortifications and Permanent
Fortifications, and of the exposed battery to be next described. As
they are built under cover of screens and are not subject to fire
during construction, work upon them may be continuous and by day as
well as by night.
=46.= =Screens.=--The _natural screens_ used for cover are
elevations, woods, hedges, existing buildings, walls, etc., etc.
_Artificial screens_ may be made by setting out bushes to imitate
hedges or adopting similar devices, which, however, will usually fail
to deceive an active enemy. A trench with the earth thrown to the
front, forming a glacis-shaped parapet, will, however, generally be
effective. It must be made of such length that the enemy cannot know
the exact position of the battery, and of such height and thickness
that he cannot afford to expend enough ammunition to breach it.
This affords not only concealment during construction, but also a
remarkably efficient cover to the battery against hostile fire.
Screens, natural or artificial, should be from 50 to 100 yards in front
of the batteries, so that the enemy’s aim may not be corrected by
seeing the points struck by his shells.
Unless the screen is of material which will break up into injurious
splinters under hostile fire, only enough should be removed before
opening fire to unmask the target of each gun, leaving the remainder
for concealing the points struck by shells, even if it affords no cover
against their penetration.
=47.= =Exposed Sunken Battery.=--Before describing the
construction of this battery it is necessary to state that upon a site
fully exposed to the accurate concentrated fire of a work, directed
at night by light balls or electric lights, it will in general be
practicable to construct batteries only by sapping, and even then with
considerable losses. But these conditions seldom exist, since in the
distant attack it is usually possible to construct and arm the battery
before it is discovered by the defence, and in the close attack the
fire of the defence is generally so much reduced that some exposure
is justifiable. While the battery to be described is classed as an
“exposed battery,” it is understood that it may also be constructed
under cover of a parallel or other trench, and that in all cases when
practicable a natural or artificial mask is used to conceal the first
night’s work from the enemy. It is assumed from the results obtained in
practice that, with the material conveniently stored, the battery can
be traced, a central trench and splinter-proof covers be made during
the first night, and the battery finished and armed during the second.
The general design and details of this battery are due to the Royal
(British) Engineers.
=48.= =Tracing the Battery.=--The battery is traced under
the direction of an engineer officer by one or two tracing parties,
each composed as follows: 1 non-commissioned officer with a 6-foot
measuring-rod and tracing-lantern, and 4 sappers, one carrying a
measuring-tape and bundles of pickets, one a field-level, one several
tracing-tapes, and one a mallet or hand-axe; about 75 pickets and 1200
feet of tracing-tape should be provided. The line of fire of the first
gun of the battery (_xy_, Pl. V, Fig. 46) is accurately laid out and
marked by daylight. At dusk one party drives a picket at _I_, where the
directrix crosses the projection of the base of the interior slope,
and from this as an origin lays out the cutting lines of the central
trench, _I_, _II_, _III_, _IV_, _V_, _I_, making the trench 5 feet wide
and of the length required for the number of guns (= No. of guns ×
45'--10'); commencing then at a point _A_, 7' 6" to the left of _I_ and
in the rear cutting line, this party lays out the line _a_, _b_, _c_,
_d_, _e_, etc., ... _m_, _n_, _o_, as indicated, the direction _n_,
_o_, leading to the parallel.
The second party, beginning at _A_, lays out _A_, _B_, _C_,
communicating with the parallel, and then the inner cutting line of the
ditch _D_, _E_, _F_, _G_, _H_, _I_, allowing for a thickness of parapet
of 30 feet and an ultimate width of ditch of 12 feet (_D_, _E_, and
_H_, _I_).
Two parties should trace the battery in 25 minutes, one party in 45
minutes.
=49.= =Constructing the Central Passage and Splinter
Proofs.=--The first relief of working party for the central passage
is posted and commences work at once (Pl. V, Figs. 47-48). Each man’s
task is 5 feet in length and 4 feet in depth (giving 100 cubic feet).
It may be completed in 4 hours, and should be in 6 at most.
The second relief (Pl. V, Figs. 49-52) excavates the cartridge
recesses, trims up the work done by the first relief, lowers any earth
that stands too high, revets the slopes of the gun portions, puts in
frames and sheeting when needed in the splinter-proofs, places the
bearing planks and balks of the latter, which should be at least 9
inches thick and 9 feet long, except over the cartridge recesses, where
they are 12 feet, and when possible deepens the central passage under
the splinter-proofs to 5' 6" for a width of 2 feet to form a seat for
the men. It also places one or two planks along the passage to serve
as a bench for shells. The latter part of this work can be done by
daylight. The parapet formed by this excavation is about 2 feet high.
This is so masked or so inconspicuous as not to draw upon itself the
artillery fire of the defence. The construction of the battery will be
continued usually on the following night.
=50.= =Construction of the Battery= (Pls. V and VI, Figs. 53,
55, 60, 67).--Two reliefs are required for this. _The first relief_
receives its tools and arrives upon the ground at dusk. It is divided
into four parties, one for the front ditch, one for the gun portions,
one for the rear trench, and a reserve of ten per cent for substitutes
and casualties. They are posted and supervised by the engineer officer,
n. c. o^s., and sappers as described in paragraph 16, _ante_.
_The Front-ditch Party._--Each digger is assigned a task 5' wide, 6'
long, and 3' 6" deep. He throws the earth as far into the parapet as
he can. The shovellers, one to each two diggers, are posted 12 feet
from the cutting line of the ditch. They pass the earth back toward the
interior crest and the traverse, keeping the top surface nearly level.
_The gun-portion party_ is divided up equally among the gun portions,
each digger is allotted a task 4' wide, 7' 6" long, and 3' 6" deep.
The gabions around the gun portion are placed by the shovellers under
the direction of the engineer soldiers, a short one being placed at
the throat of the embrasure. The shovellers spread and level the earth
thrown out by the gun-portion parties and the rear-trench party. They
work in connection with the other shovellers to give to the traverses
and parapet near the interior crest the proper shape.
_The Rear-trench Party._--This party excavates to a width of 7' 6" the
rear trench and the communications with the parallel or approach. Each
digger has a task 4' wide, 7' 6" long, and 3' 6" deep. The two directly
in rear of each gun portion throw the earth to the rear, the others
throw it to the front, leaving a berm of 4' 6" at the rear of the
traverse. The men of the _reserve_ who are not otherwise occupied fill
sand-bags from the earth thrown to the rear, and cut a ramp 8 feet wide
and not steeper than 1/4, in rear of each gun-portion, when needed. It
is essential that the excavation of the gun-portion be finished by the
first relief, so that the platforms may be laid by the second relief in
time to allow the guns to be placed before daylight.
The first relief leaves in the battery the tools required by the second
and carries the rest back to the depot.
_The second relief_ is divided into three parties and a strong reserve
of one quarter or one fifth of its strength. The first, or _front-ditch
party_, works in the front ditch, widening it 6 feet and throwing the
earth back to form the front of the parapet. The shovellers, one to
each two diggers, spread and level it. The task of a digger is 5' wide,
6' long, and 3' 6" deep.
The second, or _platform party_, places the platforms and gives way to
the gun detachments.
The third, or _rear-trench party_, widens the trench 3' towards the
front by cutting off the rear of the traverses.
The _reserve_ completes any work left unfinished by the first relief,
fills sand-bags and places them around the gun portions, digs ditches
and drainage-pits when needed, and does any other work necessary for
the completion and arming of the battery.
When a tramway is laid in the trench for bringing up the guns and
carriages, the ramps in rear need not be cut.
=51.= =Alternative Construction in Position Very Much
Exposed.=--When the earth thrown up in making the splinter-proofs
cannot be concealed, it may attract such a severe fire from the defence
as to make the above-described construction impossible. In this case
the battery is traced as above described, the balks for covering the
splinter-proofs are placed in position resting on bearing-planks, and
the construction of the front ditch, gun portions, and rear trench
are commenced at once; and the battery is as nearly finished as time
allows, and armed if possible. The splinter-proofs are subsequently
mined out and the remaining necessary details finished before opening
fire.
=52.= =Splinter-proofs=, in addition to those in the central
trench, are usually constructed under the rear of the traverses (Pl.
VI, Figs. 65-67). These may be made during the construction of the
battery or after its completion. They are about 5 feet wide, 6 feet
deep, and 10 feet shorter than the width of the traverse. Their floor
is at 6 feet below the surface. The earth is held up by frames and
sheeting, and the roof is supported by cross-balks resting on posts
and running back into the traverse. The roof consists of railroad iron
or heavy timbers covered with earth, and access is given by steps from
the rear trench; the space not occupied by the steps may be shielded
with inclined posts or other covering if thought necessary. These
splinter-proofs differ in no essential from those described in Field
Fortifications. The finished battery is shown in Pl. VI, Figs. 62-64.
=53.= =Sunken Battery in a Parallel= (Pl. VII, Figs. 68
and 69).--A battery similar to the one above described is sometimes
constructed in a parallel. In this case the traverses have to be built
up, and therefore do not usually exceed 20 feet in thickness. Pickets
are driven at intervals of 35 feet along the banquette of the parallel
to mark the centres of the gun spaces, and the rest of the battery is
traced in the usual way. The steps of the parallel are cut away and
the slope revetted for the gun spaces and the central trench. Gabions
are placed along the back of the central trench and the sides of the
traverses. A rear trench 7' 6" wide is cut from the parallel at an
easy curve, so that its front cutting-line shall be 25 feet from the
foot of the interior slope; this, as before, is widened 3 feet by the
second relief cutting away the rear of the traverses. The reverse slope
of the parallel in rear of the gun portions is cut back to the rear
trench. A trench 2 feet wide and 2 feet deep is cut between the front
of the traverses and the foot of the interior slope, and the cartridge
recesses are excavated. The gabions of the traverses are filled,
balks placed over the central trench, and the tops of the traverses
and splinter-proofs are raised to the height of the parapet of the
parallel. A ditch in the front of the parallel 12' wide and 3' 6" deep,
traced at dusk, and excavated during the night, supplies earth to make
the parapet 30' thick and 4' 6" high. The work done in and behind the
parallel is not seen from the front, hence a great part of it may be
done by day, undetected by the enemy. The upper part of the traverses
is made by night, and the front ditch and front of the parapet are made
the same night or subsequently, depending upon the number of workmen
available.
Since the gabions of the traverses seriously obstruct the parallel,
they should not be placed in position until all arrangements are made
to open the rear trench.
In the special case of a battery on the crowning of the covered way,
the traverses have been already constructed in running the sap. The
splinter-proofs may be constructed by blinding portions of the sap, or
by mining them under the traverses. Owing to the height of the parapet,
embrasures of some depth will have to be cut through it. This is done
by a shallow sap started by one man, who is subsequently assisted
by a second, if the splay requires it. The cheeks are revetted with
sand-bags, covered with hides. The mouth of the embrasure is left
closed with the head parapet of the sap until fire is to be opened,
when the earth is dug away or blown away by the gun.
=54.= =Battery Behind the Crest of a Hill= (Pl. V., Figs.
57-59).--In a battery behind the crest of a hill the front ditch may
be omitted, the gun-portions may be entirely in excavation, and the
platforms given such a reference as to require a shallow groove to be
cut through the crest to allow the gun to fire. When the ground falls
away very rapidly to the rear it may be stepped under the traverses
to prevent their sliding, and the rear of the gun emplacement may
be raised when necessary to give the platform the proper slope. The
central trench is cut deep enough to give 5 feet of cover over the
splinter-proofs.
=55.= =Batteries on Sloping Ground= (Pl. VII., Figs.
70-72).--When the ground to be occupied by the battery slopes towards
or from the place or falls off on either side, the battery is
constructed essentially as upon level ground. The central passage is
driven, following the surface of the ground, the gun emplacements,
front and rear trench are excavated as before described, the additional
excavation or filling required in each gun emplacement to make the
platform horizontal is regulated for the particular site, any excess
of earth being used to give greater cover on the more exposed side,
and any deficiency being supplied from the front or rear trench, as
may be most convenient. Where the extra work imposed by the slope is
considerable, a third relief may be required to finish the battery, and
its arming may be necessarily postponed until the next night.
=56.= =Embrasures.=--Modern siege guns are generally
mounted either on “overbank” or “disappearing” carriages, firing over
parapets of sufficient height to give cover to the men. (The axis of
the trunnions of the U. S. 5" siege gun is 6" above the platform.)
Embrasures when used are generally shallow grooves cut in the top of
the parapet. In this case the bottom of these grooves must cut the
surface of the top of the parapet at or in rear of the highest line
visible to the enemy, so that no indentations which can be seen by him
will indicate the position of the guns. To effect this, the exterior
crest will usually be as high as and sometimes higher than the interior
crest, and the top of the parapet (“superior slope”) will be level or
will slope to the rear. In rare instances, however, deeper embrasures
with revetted cheeks must be made. The only serviceable revetment for
use with high-power guns is one of sand-bags wrapped in raw hides.
This may be made by laying down a hide, piling a number of sand-bags
upon it, and folding the free end back over them; placing another hide
on top of this with more sand-bags and so on. Or large packages may
be made by wrapping up a number of sand-bags in each hide and these
packages may be used for making the revetment.
The embrasure should be bottle-shaped in plan, shaped like a segment
of an ellipsoid immediately in front of the muzzle of the gun, then
drawn in like the neck of a bottle and narrowed to as small a mouth as
possible, so as to diminish the effect of the blast and give the least
possible exposure to the gun. When the battery is exposed to slant or
enfilading fire, instead of embrasures, bonnets of sand-bags may be
built upon the parapets to protect the guns.
=57.= =Observatories.=--Observatories or look-outs, as
previously stated, should as a rule be placed on high points well on
the flanks of the battery.[2] When this is impracticable, they may
be made by building up at the rear of the traverses, on the flanks,
or even in the gun portions, glacis-shaped covers pierced with a
sight-hole in all respects similar to a loop-hole for musketry, and
with just sufficient splay to include the desired field of view. A
number of these should be provided for each battery, so that the enemy
may not know which one is in use at any time. If subject to close and
accurate fire, the crest-line in their vicinity must be of the same
level as the tops of the look-outs, and provision must be made to
prevent the light showing through them.
=58.= =Drainage.=--After the completion and arming of the
battery, gutters should be cut on each side of the gun-portion leading
into one running along the reverse of the rear trench which carries
the water to low ground on the exterior, or which is provided with dry
wells or drainage-pits for collecting the water so that it may soak
into the ground or be pumped out with hand-pumps.
=59.= =Mortar Batteries.=--The introduction of rifled mortars
of all calibres, with the corresponding increase in accuracy of fire,
together with the destructive effects of shells charged with high
explosives, will doubtless lead to the extensive use of mortars in
future sieges.
In a distant attack the requirements of a mortar battery are very
simple, consisting principally of a stable platform, magazines for
ammunition, and bomb-proof covers for the gunners; since the battery
as a rule will be concealed from the view of the work by intervening
obstacles, and will in consequence not be subject to direct fire. When
the soil is favorable, cover against plunging fire will be most easily
obtained by sinking pits for the mortars to such depth as may be
necessary to furnish earth for a splinter-proof parapet surrounding
the pit, and for cover for the bomb-proof shelters for the men and the
magazines.
When ample space exists which is well concealed, and in which the
soil is good, a separate emplacement should be made for each mortar.
When necessary, however, two or more mortars may be placed in each
pit. The magazines, splinter and bomb proofs are similar to those
elsewhere described. When no natural mask exists, the battery may be
constructed behind an artificial screen, and be made of the general
type of the “exposed siege battery,” the gun portions being made with
front enough to accommodate one or two mortars as may be preferred, and
of such length only as is needed for working the mortar employed. The
terre-plein may be placed at any convenient depth below the surface of
the ground, and the revetment of the interior slope, if any be used,
will not ordinarily be carried higher than the muzzle of the mortar. As
the traverses are not subject to gun-fire, the splinter-proofs afforded
by the central passage may be added to by building others along
both sides of the traverse; and by deepening the mortar emplacement
sufficiently, they may be given enough cover to make them true
bomb-proofs.
A mortar battery fulfilling these conditions can hardly be silenced by
hostile fire.
The conditions under which the batteries may be constructed are,
however, so varied that detailed dimensions will not be given. No
difficulty will exist in making the battery of a size suitable for the
pieces to be employed.
The U. S. rifled siege mortar is of 7-inch calibre, about 5 feet
long, weighs 1715 lbs., and is designed to throw a 125-lb. shell with
a charge of 5½ lbs. of powder, giving an initial velocity of 685 f.s.
and a range of about 4000 yards. With reduced charges the range may be
reduced to about 650 yards without undue sacrifice of accuracy.
In the closer attack upon the work, batteries for the smaller siege
and field mortars may be readily constructed in front or rear
of the parallels, or in the parallels or approaches themselves;
splinter-proofs and temporary magazines being constructed by methods
previously indicated. In many cases, however, the lighter mortars,
field and Coehorn, which do not require fixed platforms, may be placed
behind any part of the trenches affording cover, and fire be opened and
continued until the fire of the enemy becomes too annoying, when the
mortars may be removed to some other locality.
MAGAZINES.
=60.= =Magazines= should be provided, at least two to each
battery, not only to localize the injury due to an explosion, but also
to prevent the battery being disabled by the explosion of a single one.
As previously stated (par. 43), they should contain 24 hours' supply
(from 150 to 200 rounds) for each gun which they are designed to
serve,[3] which may require a capacity in a single magazine of as much
as 6,000 lbs. of powder.
This amount should be reduced when possible by increasing the number
of magazines. The cartridges should be made up and packed in boxes at
the depots or parks, and the powder chambers in the magazines should be
of such size as to store these boxes with only such vacant space as is
necessary for ease in handling them.[4]
=61.= =Cover.=--The chamber should be covered with strong
balks or rails and enough earth to form a sloping roof; over this raw
hides or tarpaulin should be spread, and the remainder of the earth
filling be spread upon this and rammed solidly. The amount of earth
cover required for security must be determined from the principles
given in par. 21. The English engineers recommend as sufficient
protection against ordinary fire for a magazine 5 feet wide, two layers
of 9" × 9" fir laid crossing each other, or one layer of 12" × 12" oak,
covered with 5 feet of earth.
In experiments at Lydd in 1883, however, an 8-inch howitzer shell
falling at an angle of about 30° penetrated through a covering of
7 feet of soft clay and burst upon the timber roof of a magazine,
cutting it through. This shows that complete protection is not always
possible, and that the chances of hitting must be reduced by making
the horizontal area of the magazine chamber as small as possible,
and placing its smaller dimension in the line of the hostile fire.
The clear height of the magazine should be 4' 6" to 5' minimum, when
practicable, and the top of the covering balks should be at or below
the level of the ground.
=62.= =Location.=--A magazine should be located at such
distance from the battery that its explosion will not disable the
guns, injure the parapets or traverses, or seriously endanger the
cannoneers;[5] but, on the other hand, it should be near enough to
allow the ammunition boxes to be conveniently carried to the cartridge
recesses; and the communications for this purpose should be well
covered from hostile fire. The entrance to the magazine should be so
protected that splinters cannot enter the chamber. Any natural hollows,
banks, etc., in the immediate vicinity of the battery should be taken
advantage of to facilitate the construction of and give better cover to
the magazines. When nothing of this kind exists the magazines may be
placed on the flanks or in rear of the battery, and should be masked
and screened by the parapet of the parallel, approach, communications,
or battery, or by special glacis-shaped screens made, for the purpose;
which should be much longer than the width of the magazines that they
cover, so that the discovery of the location of the latter by the enemy
may be made more difficult. The magazines should not be located in rear
of the centre of the screens nor symmetrically with reference to the
battery, nor, when it can be avoided, directly in rear of a gun. The
passages leading to them should enter the battery in rear of a flank
or a traverse, and should be so directed as to escape enfilade. They
should be so graded that the surface water will run away from the door
of the magazine and be discharged upon lower ground or received in
drainage-pits placed at the lowest points.
=63.= =Construction of a Magazine Subject to Direct Fire
Only= (Pl. VII., Figs. 73-77.)--The method of tracing the
magazine and its approaches is too evident to need description. In
this example an earth cover of 5 feet against vertical and 20 feet
against horizontal fire is given. Should more or less be desired, a
corresponding change may be made in the plan, depth of excavation, and
depth and width of approaches; and the earth for additional cover may
be obtained from a ditch or pit in rear of the magazine. The excavation
for the chamber is given a width of 6', a depth of 5' 6", and a length
of 12', the entrance a width of 3', a depth of 5' 6", and a length of
6'.
The sides of the chamber and entrance are held up by frames 4' 9" high
and 2' 11" wide, outside measurement. The caps are 6" × 5", stanchions
4" × 5", and the ground sills 3" × 5"; sheeting 1" thick is inserted
between the frames and the earth. The covering balks are 9" × 6" and 10
feet long; their tops are flush with the surface of the ground; cleats
nailed on their under side keep the tops of the side frames from being
pushed in by the pressure of the earth. The earth cover is 5 feet high
at the centre and 4 feet at the crest of the outer slope. The passages
are 5' 6" deep, 3' wide at bottom, and 5' at the top. The entrance
is blinded by placing balks across the passage for such part of its
length as may be thought necessary, and extending the earth covering
over them, as shown in the section (Fig. 75). A door, swinging outside,
is hung on the outside frame. Heavy railroad iron may be substituted
for the timber balks with advantage. When thicker balks are used,
or when a second layer is added, the chamber and passage should be
correspondingly deepened.
=64.= =Manner of Executing the Work.=--The powder chamber and
passage are excavated and the frames and balks placed during the first
night, while the central passage of the battery is being constructed.
The excavated earth is thrown out far enough to allow the balks to be
put in position, and is so spread as not to be seen by the defence.
This may be done by one relief of 8 hours, or two reliefs of 4 hours
each. If the work is not completed during the night, the sheeting,
frames, and balks may be placed by day under cover of the earth thrown
out and the existing screens.
The passages are excavated and the earth cover completed on the second
night by two 4-hour reliefs, the first excavating to a depth of 3' 6",
and the second to 5' 6", trimming up the slopes and completing the
work. When necessary, the sides of the passage will be revetted by the
second and a third relief.
When the necessity for great haste exists, the excavation of the
powder-chamber, entrance, and passages may be carried on at the same
time, the excavated earth being thrown in front and on the sides of the
powder-chamber until the balks are in position, and then thrown back
upon them, levelled and rammed.
=65.= =Mined Magazine.=--When the soil, by absence of rock
and water, admits of mining, greater cover against vertical fire can be
obtained with less work by mining out the powder-chamber and passages
(Pl. VIII, Figs. 78, 79). The figures illustrate one of minimum
dimensions, which is constructed as follows: The entrance 10' × 5' by
5' 6" deep is first excavated, revetted with frames and sheeting and
covered with balks and earth as indicated. At 1 foot from the end
a shaft 2' × 5' is sunk to a depth of 12'. From the front of this a
gallery 2' × 5' 6" is driven for about 6'; at the end of this galleries
5' 6" × 2' are broken out on each side and driven so far as may be
necessary to store the requisite number of ammunition-boxes. (For
method of sinking shafts, driving galleries, etc., see Military Mining,
Arts. 25, 33, and 44-48.) The excavated earth is spread on top of the
magazine to increase the thickness of the cover already given by that
excavated from the passages. A ring-bolt is placed in the balk directly
over the shaft, for attaching a hoisting tackle for removing the earth
during construction and for hoisting and lowering ammunition-boxes
afterward.
A door opening outward may be hung at the entrance, and the passage
may be blinded as previously described, if it is thought necessary.
The communications are arranged in essentially the same way as for the
magazine previously described.
The dimensions given are the least which will allow moderately free
access and good cover. The magazine should be constructed, by good
miners, in two nights and the intervening day, and will store about
4000 pounds of cartridges in boxes. When time and the character of the
ground admit, and larger capacity is desired, the shaft may be made
wider and deeper, the gallery wider and longer, and the powder-chamber
deeper, longer, and wider, if desired.
The excavation for the entrance and approaches, the placing of balks,
and the levelling and ramming of the earth-cover, should be done by
night; the mining work can be carried on both night and day.
=66.= =Elevated Magazines.=--When the presence of rock or
water in the soil prevents sinking the magazines to the full depth
above given, they must be sunk so far as practicable and given the
least possible clear height of powder chamber, with the best attainable
overhead cover. This should be strengthened by the use of railroad iron
or rolled iron beams, when available. The cover against direct fire
should be increased up to 30 feet, and the front slope be made gentle,
like a glacis. A screen made of an earthen bank with a glacis slope
should also be used if possible. These precautions having been taken,
the depth of the powder-chamber in the direction of the hostile fire
should be reduced to a minimum, and the storage of large quantities
of powder be avoided, so far as possible, by constructing a number of
small magazines at the most convenient places in the vicinity of the
battery.
=67.= =Precautions against Dampness in Magazines for Siege
Batteries.=--Underground magazines of the character above described
are, of necessity, sometimes damp. The only ventilation usually
possible is obtained by leaving the door open, the air being changed
more or less by the men going in and out.
The passage leading to the powder-chamber should enter it at the
middle, and in the service of the guns one half of the chamber should
be emptied on one day and the other half on the next. This will usually
limit the time which a cartridge is exposed to the dampness of the
magazine to a maximum of one or two days.