SIEGE OPERATIONS.
THE ATTACK.
=68.= Siege operations include all the steps taken from the first
approach to the work up to its final capture. These taken in regular
order are as stated in Chapter II: the _investment_, the _distant
artillery attack_, the _construction of approaches_ and _parallels_,
_breaching by artillery or mines_, and the _final assault_.
For convenience in description the siege has been divided into three
periods. The _first period_ includes the preliminary operations up to
the completion of the investment.
The _second period_ includes all the operations between breaking
ground for the batteries of the first artillery position and the first
parallel, up to the completion of the most advanced parallel and the
occupation of a position near the foot of the glacis from which the
attack is to be made upon the breach, either by assault or sap.
The _third period_ comprises the advance from the last parallel, and
all subsequent operations up to the capture of the last entrenchment
and the surrender of the garrison.
The first and second periods are sometimes known as the “_distant_” and
the third period as the “_close attack_.”
FIRST PERIOD.
=69.= As a preliminary to the siege of any fortified place, all
possible information is obtained as to the strength and character of
its fortifications, the garrison, armament, stores of provisions and
ammunitions, water supply, water routes, telegraph and railroad lines,
manufactures, especially those which may be converted into factories
of arms and munitions, the character of the population of the place,
their probable food supply and their loyalty to their state; also the
topographical features and nature of the ground in the vicinity of
the work, the sites of camps and parks, the prevalent diseases of the
locality and the best means of preventing their attacks, etc., etc.
(see Bureau of Intelligence, Art of War, par. 128).
From these data the necessary materials and supplies are collected at
convenient points, the railroad or water routes selected, and the cars,
boats, wagons, etc., for their transportation provided; so that they
may arrive promptly and in the proper order when needed.
=70.= =The Investment.=--The investing force is brought
together, organized, and moved rapidly upon the place. When it is
available a large force of mounted troops may be used advantageously in
the investment, and be subsequently relieved by infantry and artillery.
When the investment is made, it adds greatly to the advantage of the
attack to completely surround and isolate the work, and to push the
investing line as near it as possible. When the investing force is
more or less dispersed, and is to be concentrated for the siege, the
temptation frequently exists to march them by converging lines upon the
place as a point of concentration.
While this may be advisable in some cases (as where the garrison is
very weak or under an inefficient commander), it will usually expose
the subdivisions of the investing force to be beaten in detail (Art
of War, par. 392). So also in surrounding the place; a premature
subdivision of the force into small fractions not protected by
field-works, or not within supporting distance each other, will afford
to an active defence an opportunity, by well-conducted sorties, to
inflict most severe losses upon the attack and very greatly delay
the investment. Keeping these dangers in view, the investing force
will move rapidly upon the work, seize, strengthen, and occupy strong
points as near the work as possible, and extend the lines to right
and left as rapidly as good judgment allows, until the place is
surrounded. Meanwhile detachments of greater or less size will scour
the ground around the place, seizing and carrying off or destroying,
so far as possible, all cattle, grain, lumber, etc., and everything
else which would be of use to the attack or defence. Under cover of
these detachments and escorts specially detailed for the purpose,
reconnoissances will be made to cover so much of the ground as can be
reached, especial efforts being made to examine the ground near the
works. These reconnoissances will necessarily be hurried and incomplete
but, must be as accurate as they can be made under the circumstances.
They should be directed principally to determining the heights and
directions of the principal points of the works, and their positions
with reference to prominent points that may be used as landmarks, in
verifying and correcting maps and information previously obtained, to
discovering the existing armament of the place and the steps already
taken for its defence, and to collecting all possible information
bearing upon the selection of the front of attack.
Systematic reconnoissances and surveys carried on throughout the siege
must be relied upon for checking and completing the work thus begun.
So soon as the supporting points for the investing force are secured,
a line of outposts is pushed forward towards the work and sentinels,
pickets, etc., are established (Art of War, pars. 167-194). The lines
of sentinels, pickets, and supports are placed as near the work as
practicable, and the line of resistance is advanced at every favorable
opportunity.
The usual rules for posting and relieving the outposts, establishing
day and night cordons, the use of patrols, etc., are applied, with such
modifications as circumstances render advantageous.
Any advanced points affording marked advantage to the attack which
have been seized are strengthened and held when possible, even
at considerable cost in men or with some delay in completing the
investment.
=71.= =Bringing up and Posting the Besieging Force.=--The
main besieging force, consisting principally of infantry, artillery,
and engineers, with the siege train, follows closely after the
investing force, and, upon arrival is encamped upon sites previously
selected, sending out at once, however, such reinforcements and
supports as are needed by the line of investment. Engineer and
artillery parks are established outside the zone of fire of the works
and in proximity to the main routes of communication. Branch railways
and tram-roads running through the parks, storehouses, repair shops,
etc. etc., are located and constructed. Sites for storage magazines
for ammunition are carefully selected at the most secure places,
and isolated when possible from the camps and parks by intervening
elevations of ground. The cover of these magazines, so far as possible,
is made up of wood and sand or earth free from stones large enough
to be dangerous projectiles in case of explosion. Rooms for loaded
shells and cartridges, and laboratories for making up ammunition are
constructed upon similar principles. Carefully studied arrangements for
the health and comfort of the men are made. Some of these are outlined
in Chapter VII.
=72.= =Fortifying the Camps, Parks, etc., etc.=--In former
sieges it was customary to completely surround the ground occupied
by the besieger with a continuous line of works of simple trace and
light profile called the “_line of circumvallation_;” and to construct
between the camps and the work another line, either continuous or with
intervals, called the “_line of countervallation_.” These lines were
placed respectively at about 200 yards in rear and in front of the
camps.
The principal object of the first was to prevent by a small force
the entry of small reinforcing detachments and supplies; that of the
second was to resist vigorous sorties by the defence, or sudden attacks
from the outside by strong reinforcing parties. For this purpose the
detached works of the line of countervallation were so disposed as
to cover the main depots, parks, roads, etc., and to be in defensive
relations with each other.
The great development of the line which must be occupied by the
besieger, owing to modern methods of fortification and the range of
rifled cannon, prohibits the construction of complete lines of circum-
and countervallation. The besieger constructs in their stead one or
more lines of detached works upon advantageous points, and covers the
intervening ground more or less thoroughly by patrols, outposts, etc.
He then so disposes his main force as to be able to concentrate enough
to meet any sorties of the defence; and, if necessary, detaches a
force, called an “_army of observation_,” sufficiently large to meet
any relieving army and defeat it; or hold it in check until he can
concentrate the besieging force with the army of observation, and meet
the relieving army in a favorable position. As a rule, this position
will be one well outside the besieger’s cordon of works; since the
latter by its extent will necessarily be weak to resist a determined
attack (Art of War, par. 258), and by its proximity to the work will
render possible the co-operation of the garrison and the relieving
army. This, under the circumstances assumed, would seriously endanger
the besieging army.
In opposing sorties from the work, however, the conditions which fix
the point of conflict are reversed, and place it as near the work as
practicable. The shortening and strengthening of the line of investment
by closing it in upon the work make it imperative to hold all ground
gained; and this is generally best accomplished by intrenching the
line of outposts with continuous shelter trenches, strengthened at
intervals by batteries of field guns, and supported by field works of
considerable strength, placed within accurate cannon range of each
other, but not exposed to the direct fire of the guns of the place.
Behind the shelter trenches the outposts, supports, and reserves,
strengthened when necessary by troops from other points of the line,
should be able to hold their own against all ordinary sorties. The
main line of field works serves to resist a general attack made by the
mass of the garrison.
Placing the first intrenchments further back exposes the outposts to
the confusion resulting from falling back, frequently at night or in a
fog, and also enables the besieged to seize upon ground from which it
may be very difficult to dislodge them.
To allow the different parts of the line to be rapidly reinforced,
good roads protected from the fire of the work, and well marked with
sign-posts, etc., must be opened between the adjacent divisions of the
besieging force, and all streams must be provided with bridges secure
against floods, ice, etc.
=73.= =Distance of the Line of Investment from the
Work.=--This will result from conflicting conditions. Reasons
already given, which need not be repeated, lead to establishing it as
near as practicable. On the other hand, the accurate fire of the heavy
guns of the place, and vigorous sorties by the defence, cause much
annoyance and great loss to a line drawn too near the work. The more
recent sieges indicate about 3000 yards from the most advanced works,
as the least distance for the line of investment in open country and
with an active defence. It may be necessary in some cases to increase
this to 4500 or 5000 yards; but with ground favorable to the attack,
and a weak and demoralized defence, it may frequently be drawn nearer.
=74.= =Strength and Composition of the Besieging Force.=--In
former sieges when the place held out until the inner keep was breached
and carried by the regular progress of the siege, the ratio of the
necessary strength of the attack to the defence was estimated at 7 or
8 to 1, this large ratio resulting from the excessive labor in the
trenches and the losses incurred on the close attack. Modern writers
(arguing largely upon theoretical considerations) have reduced this
estimate to 4 or 5 to 1. No attack on a thoroughly-equipped and
well-defended strong place having been carried through all the steps of
a regular siege since the introduction of modern arms, absolute data
upon this subject are lacking.
The besieging force at Strasburg was about 60,000, garrison about
20,000, total length of siege 49 days. The defence was very weak.
Belfort, besieging force about 32,000, garrison about 16,000. After
a siege of 100 days the approaches were at about 1200 yards from the
works, which capitulated by reason of the general surrender of the
French. At Metz the besieging force was 150,000 men; the garrison,
demoralized by the previous defeat at Gravelotte, surrendered 173,000
men. At Paris the investing force was about 180,000, and the garrison
nominally between 300,000 and 400,000, of which perhaps 30,000 were
disciplined and effective soldiers; the remainder being made up of
remnants of defeated regiments and bodies of the Garde Mobile and
Garde Nationale. The investment of Paris was complete on September
19, 1870; its surrender from exhaustion of provisions took place
January 29, 1871. Several sorties were made, but the general defence
was paralyzed by the character of the troops and inhabitants. At
Plevna the Turks had at the outset about 56,000 men, at the surrender
40,000. The Russian force suffered great losses in its assaults, but
by continual reinforcement had at the end of the siege about 120,000
men. The defence by the Turks was desperate, but generally passive.
One determined sortie was made immediately before the surrender. The
surrender resulted from exhaustion of ammunition and provisions. The
works were field works only.
At Belfort the investing force was at first but 10,000 and the line of
investment 25 miles long, giving but 400 men to the mile. This force
was subsequently increased to 20,000 men, and when the besieging army
had all arrived, to 32,000 men.
At Paris (1870) the line of investment was about 3 miles from the
line of the forts, and about 53 miles in length, the investing force
180,000, giving a mean of about 2 men to the yard. The distribution
was, however, about 4 to the yard on the left bank and 1⅓ on the right
bank of the Seine.
At Plevna the line of investment was 2¾ miles from the forts, its
length 43½ miles, the investing force 100,000 men, about 1¼ men to the
yard.
In each of these sieges the place finally fell under the attack of a
force, in no case equal to 2½ times the garrison; but inferences drawn
from this fact are apt to be erroneous, since none of these places
was well fortified according to modern methods, well garrisoned, well
supplied, and defended to extremity.
The results show, however, that under similar circumstances, which are
apt to arise in any modern war, the attack of a strong place which can
be completely invested by a force of two or three times the strength
of the garrison, may promise success; which seems to be assured if
the defence allows the besieging force to complete the investment and
thoroughly intrench itself.
On the other hand, tactical considerations would indicate that a
well-equipped army, of good morale, under an active and aggressive
commander, covered by a modern intrenched camp, should be able to
prevent the investment; and by taking advantage of its interior lines,
its heavy guns and its strong _points d’appui_, should be able to beat
in detail a force very much greater than itself whose fractions, by
reason of the extent of the line of investment, are necessarily not
within supporting distance of each other.
These advantages of the defence evidently disappear, as above
indicated, when the attack is allowed to complete its fortifications,
since under their cover a small force can check even a determined
sortie until a sufficient force to beat it can be concentrated.
From these considerations it is evident that an investment, once
completed, may be maintained by a force less than that necessary to
establish it in the first place (see Investment of Plevna, Pierron,
Méthodes de Guerre Vol. III, pp. 647 _et seq._).
=75.= =The Point of Attack.=--From the information originally
in possession of the besieger, supplemented by that obtained by
reconnoissance, a decision is made as to the fronts of the work or
the particular detached works of the intrenched camp upon which the
approaches are to be made. The portion selected in either case is
called the “_point of attack_.” To reduce an intrenched camp, it will
in general be necessary to capture at least two of the detached works
and to silence the artillery fire of one or more on each side of those
taken. In an attack upon a strongly-fortified enceinte, the least that
is usually undertaken is to breach and capture one front with its
adjacent outworks, and to silence the fire of those which enfilade the
approaches and parallels or take them in reverse.
In selecting the point of attack the first consideration is, that
when taken, it shall afford material advantage to the besieger and
give him a foothold from which further approaches may be driven, if
necessary. This condition being fulfilled, the choice will result from
a careful study of the nature of the works and site. Those forts or
fronts resting upon precipices, bordering deep marshes or deep and
rapid streams, or which are so placed that approaches upon them will
be swept in flank and rear by the fire of the works, which cannot be
silenced, are considered impregnable by the ordinary operations of the
siege. Most serious difficulties are presented by those in which the
adjacent works are so disposed and of such strength that they can be
carried only in succession and by regular approaches; those provided
with wet ditches in which strong currents can be produced, those with
dry deep ditches, those which are mined, and those which present long
lines nearly straight, or even concave to the attack, and covering a
front nearly equal or even greater than can be occupied by the trenches
of the besiegers.
When the parallels and approaches have to be constructed upon ground
sloping downward towards the work, in soil containing large stones,
or in which the rock is close to the surface, in marshy ground or
that containing much water or liable to be flooded, the difficulty
of their construction and defilade are evident. The point of attack
considered most favorable to the besieger is one which, fulfilling the
first essential condition, is more or less salient, so that it can be
partially surrounded, and which admits of the approaches being driven
toward it in favorable soil, over ground sloping gently from the work,
or gently rolling with the crests and valleys of sufficient difference
of level to afford cover, and running generally in the direction of
the parallels.
A favorable location for parks, etc., with free, safe, and short
communications between them, also has great weight in selecting the
point of attack.
SECOND PERIOD.
=76.= =First Artillery Position.=--Every siege begins with
a bombardment, which is designed, as previously stated, to drive in
the outlying posts of the defence, to silence, so far as possible, the
artillery annoy and wear out the garrisons of the works to be attacked,
to interrupt the communications between them, break up bomb and
splinter proofs, destroy magazines and depots, and, if the enceinte can
be reached by the artillery, to bring a fire upon the population which
will lead to or hasten the surrender of the place.
The considerations which determine the location of the batteries for
the general bombardment have already been given (par. 7), as well as
the construction of the batteries and screens used (Chap. IV.). For the
systematic attack, however, the necessity of dismounting or silencing
the guns bearing upon the proposed approaches introduces the additional
condition that the batteries should be so located that besides their
general effect each shall fulfil, so far as practicable, its special
design by bringing an enfilading or reverse fire upon certain fronts;
or, in connection with other batteries, shall keep down the fire of
certain fronts by a preponderance of direct fire. Many batteries which
fulfil these last conditions occupy their original positions during
the entire siege. The requisite concentration of fire upon the point
of attack and its careful regulation for the special object in view
will frequently restrict the arc occupied by the batteries below
that desirable for a general bombardment only; and will necessitate
a closer grouping of the batteries for their easier control by the
artillery commanders. This line of batteries first established is
known as the “_first artillery position_” (Pl. VIII., Figs. 80, 81).
As the batteries must be secure against the attacks of the defence,
they must of necessity be outside the besiegers defensive line. Their
distance in yards will result from the character of the defence and
may vary from 2000 or 2500 yards for a weak defence, to 3500 or 4500
yards for an active one. On account of their long range and the object
to be obtained by their fire, they are armed with the heaviest rifles
and howitzers available, supplemented with rifled mortars of as large
calibre as can be obtained, firing, if practicable, torpedo shells
charged with high explosives.
Batteries of field guns which have already been favorably located for
the defence of the heavier batteries against attack, or for firing upon
the more advanced works, may, by modification of their gun pits into
finished batteries (par. 44), be used in conjunction with the heavy
batteries of the first artillery position.
The total number of guns employed should be such as to give to the
attack a marked superiority over the defence at the opening of the
bombardment.
=77.= =Opening Fire.=--The batteries having been completed
and armed, the magazines finished and supplied, and the parks, depots
and communications put in such order that the batteries can be kept
fully supplied with ammunition; the fire of the batteries is commenced
simultaneously, the signal being given by a gun from some selected
battery. The fire once opened is continued day and night during the
siege, unless stopped by the commanding officer or from inability to
keep it up. It usually begins at daylight, in order to enable the
ranges to be corrected by the first shots, before the defence has
accurately located the batteries unmasked during the preceding night.
To open fire from a few batteries before the others are ready is
inexcusable, as it enables the defence to concentrate its fire upon
them and destroy them in succession. The targets of each battery and
gun and the rate of fire are prescribed before the fire is opened, and
these are changed only by subsequent orders or from sudden emergencies.
The fire is as a rule deliberate, seldom exceeding an average of 4
shots per hour for each gun by day, and 2 per hour at night. This rate
may be increased or diminished by the commanding officer for special
reasons and for a limited time.
The fire of the batteries is directed upon all the works of the place
within range, but with greater vigor upon the more important, and
especially upon those near the point of attack. The fire against
powder-magazines and storehouses should be uninterrupted, to prevent
the removal of powder and munitions. If the artillery of a part of the
work is silenced, the fire upon it may be slackened, but some fire,
especially vertical, should be kept up.
At night the fire is directed against the larger targets, such as
communications and covers, rather than upon the guns; but the fire
against the interior of the place (especially a city) is kept at about
the same rate day and night.
If preparations for a sortie are detected, the fire of the large
pieces is directed at the points of assembly, when known, and at the
openings through which the sortie is to be made. The field guns direct
their fire upon the troops in accordance with the tactical use of this
arm.
If the batteries of the first artillery position have the proper
preponderance over those of the place, they should soon clear away
the advanced posts, and keep down the fire of the works so that the
besieger may advance his outposts, control the exterior ground and
prepare to open the first parallel and establish the second artillery
position.
=78.= =Plan of Attack.=--By this time the reconnoissances and
surveys should be so far advanced and so thoroughly checked up that
the chief engineer will have been able to make, upon a large scale,
a map of the place and its surroundings with considerable accuracy,
and to locate upon it the proposed position of the first and second
parallels, the approaches, and the batteries of the second artillery
position. This map, with the accompanying memoirs, makes up the “_plan
of attack_,” which, when approved by the commanding general, serves as
a working plan for the prosecution of the siege, and is continually
corrected and added to as the siege progresses.
This map should be made in duplicate at least, and for accuracy in
the history of the siege should be corrected so far as possible by
redrawing or tracing, instead of by erasures.
=79.= =The First Parallel.=--The first parallel (Pl. VIII,
Figs. 80 and 81) serves as an intrenchment for the troops who protect
the second artillery position and who cover the workmen driving the
approaches. It also affords a covered communication between the
different lines of approaches.
Its length must be sufficient to cover all the batteries of the second
artillery position and protect their flanks; it must therefore extend
beyond the batteries which enfilade those faces of the fronts attacked
whose prolongations fall furthest out. Its flanks are usually more
or less refused, and terminated by strong earthworks. Emplacements
for batteries of field guns are provided at intervals to assist the
infantry in repelling sorties. When the length of the parallel is
very great, it is sometimes not continuous when first opened, but
the portions covering the groups of batteries are first made and
are subsequently connected. The ground between them is protected,
meanwhile, by a strong fire of small arms, field and other guns. When
communications covered by natural screens do not exist between the
first parallel, the batteries of the first artillery position, and the
parks, approaches are constructed at the same time as the parallel,
in sufficient number to give free passage to the troops, guns, and
materials.
These approaches (Pl. VIII, Figs. 80 and 81), as all others (par. 13),
are so directed as not to be enfiladed by the fire of the work, and
should be provided with portable or other tramways and cars, passing
switches being placed in the returns where needed.
=Its Distance from the Work.=--As a rule, it may be stated that
the first parallel is placed as near the work as possible. Most of the
batteries of the second artillery position are from 100 to 300 yards in
its rear, and the shorter their range the more effective is their fire.
The small-arm fire from the first parallel may also be an important
feature in modern sieges; to make it so requires the parallel to be
located within 1500 yards of the work, if possible. By placing the
parallel as near the work as possible, its length and that of the saps
are correspondingly reduced, the amount of work lessened, and generally
the fall of the place hastened. If an attempt be made to place it too
close to the work, however, the working parties will be discovered;
they will be within reach of strong sorties, and of the deadly fire of
small arms and machine guns; in consequence of which they may suffer
very great losses, be driven off, and the construction of the parallel
prevented. The minimum distance under the most favorable circumstances
is then about 600 to 700 yards. (This was the distance prescribed in
the day of smooth-bore guns, and was adopted as recently as 1870 at the
siege of Strasburg.) In an open, level country it may not be possible
to place the first parallel at a distance from the most advanced work
of less than 1800 to 2000 yards. When, however, it is necessary to
establish the first parallel at a very great distance, it will not, as
a rule, be made continuous, but in fractions covering approaches which
are driven forward. The first continuous parallel is then built at from
1000 to 1200 yards from the works, and behind this the second artillery
position is established.
=80.= =Opening the Parallel.=--The profile of the parallel
is one of those already given (Pl. I, Figs. 7-13), and it is traced
and constructed as described (pars. 14, 18, and 19), by simple trench,
flying sap, or full sap, as may be most advantageous. In some cases,
however, it is constructed by enlarging the line of shelter trenches
already made by the outposts. To cover the working parties while
excavating the trench, when the parallel is near enough the work to be
endangered by a sortie, the outposts are advanced to about 300 yards
in front of the line, the pickets and supports are posted respectively
at about 100 and 200 yards in their rear, and are covered by rifle
pits and trenches made for this purpose during the preceding nights.
To conceal from the defence, if possible, the proposed location of the
parallel, these trenches and pits are constructed by all the outposts
in front of their positions. The reserves are held 800 to 1000 yards in
rear of the flanks, and the whole covering force should be equal to 1/2
or 2/8 the garrison of the place if an active defence is looked for.
At daylight the trenches will be far enough advanced to protect the
covering force which will occupy them. This force is from this time
known as the “_guard of the trenches_,” and is relieved usually every
24 hours, the time of relief being so chosen as not to interfere with
the working parties.
The working parties are, as previously indicated, divided into reliefs
of 4 or 8 hours.
For continuous work the besieging force should be large enough to allow
each man, after being one day in the guard of the trenches and one day
in the working party, to have one day in camp.
=81.= =The Second Artillery Position.=--By the second
artillery position previously referred to is meant the position
occupied by the guns of the attack, placed in batteries, accurately
located for breaching, enfilading, counter-battering or other specific
duty. These batteries are usually of the class described under the head
of “exposed sunken batteries” (Plates V, VI, VII), and are constructed
behind or in the parallels, as explained in pars. 48 to 55. When behind
a parallel they should be, if possible, at least 150 yards from it in
order that the blast of the guns shall not interfere too much with the
occupants of the parallel.
=82.= =Counter-batteries=, designed to dismount guns or
destroy embrasures of earth or masonry at ranges from 700 to 1000 yards
by direct fire may well be armed with 4½ or 5 inch rifles, since their
projectiles have sufficient energy for the desired result, and the
guns admit of a more rapid and long-continued fire than do those of
greater calibre. The batteries must be so placed as to look through the
embrasure attacked, and the number of guns pitted against any battery
must considerably exceed that in the battery.
Counter-batteries designed to silence by direct fire guns in turrets
or behind shields must be armed with guns of large calibre, mounted
with the best available cover, and must be aided by rapid fire guns
of moderate calibre, designed to disable the turret guns either by
embrasure shots or by oblique shots penetrating the parts which project
from the turret.
=83.= =Enfilading batteries= act in conjunction with
counter-batteries or independently; they are designed to take the
faces in flank or slightly in reverse, but are of necessity at times
limited to a slant fire. They are located as nearly as possible in
the prolongation of the terre-pleins. When the salients are obtuse
these prolongations lie near the adjacent faces for some distance, and
consequently the only possible emplacements of enfilading batteries
will give ranges which may vary from 1000 to 4000 yards. They are armed
with cannon of sufficiently large calibre to make their projectiles
efficient even at moderate velocities, and, when the faces enfiladed
are well provided with traverses, the charges are reduced so as to
give to the projectiles a large angle of fall. When the batteries are
on commanding heights higher velocities may be used.
=84.= =Breaching batteries=, except those established on
the crest of the counterscarp, can only breach the walls of modern
forts by “curved” or “indirect” fire. To obtain the necessary angle
of fall with the requisite accuracy and energy of blow, the guns must
be of considerable size and placed at comparatively long range; the
projectile must graze the crest of the glacis and strike the scarp wall
at an angle not too oblique. Experience seems to indicate that the best
effects are obtained, all things considered, when the vertical plane of
fire makes an angle of from 55° to 60° with the face of the scarp wall.
The distance of the battery from the wall to be breached is usually
from 1000 to 1500 yards.
The same considerations govern the construction and armament of
batteries designed to destroy réduits, barracks, gorge walls, city
gates, magazines, depots, bridges, locks, etc., etc.
=85.= =Batteries of rifled mortars or of howitzers for vertical
fire= should be so located, when possible, that the longest
dimension of the target will be in the direction of their fire. The
effect of their projectiles is greatest when they can be fired at
elevations, of 60° to 70° and with large charges. These considerations,
combined with those of good cover and easy supply, will govern their
location.
=86.= =Opening and conduct of fire from Second Artillery
position.=--The batteries which are ready on the morning of the
completion of the parallel open fire simultaneously upon the work,
and are supported by those of the first artillery position still
armed. The same rules govern the fire of the first and of the second
artillery position.
When the defence combines a number of batteries to silence one of the
attack a heavy fire is concentrated upon these batteries by those
from which the fire has been diverted. New batteries unmasked by
the defence, or established in intermediate or other works, should
receive prompt attention from the attack, with a view to silencing
them if possible before they correct their ranges. It is of the first
importance that the superiority of the artillery fire of the attack
shall be established at the opening of fire from the first artillery
position and be maintained throughout, and that the defence shall be
prevented from repairing any batteries which have been silenced. To
this end a few guns will keep up a slow fire upon these batteries so
long as it may be necessary.
Every gun of the defence must, if possible, be kept under a heavy fire,
and the fire upon the enceinte must be opened at the earliest possible
date and continued day and night, as previously described.
=87.= =Musketry fire= will be opened as soon as a parallel is
established at such distance as to make it effective; and this may be,
for a well-regulated fire of sharpshooters, at ranges of 1200 to 1500
yards, or in some cases even greater.
=88.= =The Advance from the First Parallel.=--It is assumed
that the fire from the first and second artillery positions will
silence almost completely the artillery fire of the work upon the
fronts attacked; but the defence will still be able to develop when
necessary a strong musketry fire, aided at times by machine and
rapid-fire or even some field guns. Consequently, the advance from the
parallel must be under cover.
Approaches are, therefore, broken out from the parallel and pushed
forward towards the work, the workmen being protected by the fire of
the guards of the trenches. Usually at least three lines of approaches
are constructed, concentrating upon the point of attack and following
generally the lines of the capitals of the adjacent salients.
When attacking a line of detached works two or more lines of approaches
may be constructed towards each work attacked. The approaches are run
in zigzags, each branch so directed as to pass a short distance (30
or 40 yards) outside the most advanced work of the defence from which
it could be enfiladed; at each change of direction of the zigzags a
return of 10 or 20 yards is made to cover the approach in rear (Pl.
VIII, Figs. 80 and 81). The length of the branches is so regulated as
not to mask too much of the front of the parallel; they consequently
grow shorter as they approach the work and vary ordinarily between 200
and 50 yards, seldom exceeding 100 yards when near the work. The heads
of the different approaches are advanced at about equal speed so as to
afford mutual support.
=89.= =The Second Parallel.=--The second parallel is located
nearer to the first parallel than to the covered way, sometimes very
much nearer. It is constructed and occupied by the guard of the
trenches. The principle followed is that the guards of the trenches
shall always be nearer to the head of the sap than is the enemy
in his most advanced place of arms; so that, in case of a sortie,
the advantage will lie with the besieger. The flanks of the second
parallel are refused and strengthened like those of the first, or are
even carried back to the first parallel, to guard them against flank
attacks.
The second parallel having been completed and occupied, serves as a
base for further advance, which is conducted according to the same
methods, “_demi-parallels_” (Pl. VIII, Fig. 81) being run out to the
right and left of the approaches when they are well advanced beyond the
second parallel. These demi-parallels are sometimes joined, forming
a third parallel, from which the approaches are advanced as before,
with additional parallels when needed, until the foot of the glacis
or exterior of the counter-mines is reached. The number of parallels
is determined by the distance at which the first is established and
the vigor of the defence; formerly three were considered all that
were needed, and this number was used at Strasburg, 1870. At other
modern sieges a larger number has frequently been required. At
Belfort (1870-71) the third parallel was established at 1200 yards
from the place. Five parallels were used at the siege of Fort Wagner
(July-September, 1863).
The approaches are driven in zigzags by simple trench, flying or full
sap, until the direct advance becomes equal to about one third of the
length of trench; and from this point they are driven directly upon
the work by double-traversed sap (Pl. III, Figs. 28-35), the latter
being, as a rule, used only in advancing from the foot of the glacis,
or during the third period of the siege.
THIRD PERIOD.
=90.= =The Third Period of the Siege= frequently called the
“_close attack_,” includes all the steps between establishing the last
parallel and the surrender of the place. These are the capture and
crowning of the covered way, breaching the scarps and counter-scarps,
passing the ditch, capturing and crowning the breaches of the outworks
and main works in succession, and the final reduction of the interior
retrenchments, or keep.
All these operations are carried on within close and deadly range of
small arms and shells of Coehorn mortars, and many of them within
range of hand grenades and upon ground honeycombed with mines and
countermines, or liable to be flooded or inundated. They are slow in
progress, uncertain in results, and require an extravagant expenditure
of men and material. They can be pushed to a successful issue only when
the artillery fire of the place is silenced and its small-arm fire is
almost completely kept down by the fire of the attack.
The conditions of modern warfare are such, however, that by the time
the attack has reached the foot of the glacis the losses and exhaustion
of the garrison are frequently so great as to preclude an obstinate,
close defence; and, in the majority of cases, the place is compelled to
surrender before the close attack is commenced.
=91.= =The capture and crowning of the covered way= is
accomplished by _assault_ or by _sap_. The former is an extremely
hazardous and bloody operation, which all authorities unite in
condemning, and which should be undertaken only in extreme cases. It
is carried out usually at night, by forming an assaulting party in the
parallel, who rush forward to the crest of the covered way; capture, if
possible, its guards, and under any attainable cover open a fire upon
the crest of the work. All available small-arm and machine-gun fire
combines with this to keep down the fire of the defence; and under
cover of this fire the working parties construct, by flying sap, a
trench crowning the covered way, and the communications between it and
the parallel.
The trench is occupied as soon as it affords cover, and is subsequently
completed and prepared for the reception of its guns and infantry guard.
In crowning the covered way by sap (Pl. IV, Fig. 36), the saps are
broken out from the parallel, a circular place of arms is constructed,
which gives additional communication and serves as a depot for trench
materials, the traversed sap is pushed forward, and the covered way
crowned as previously described (par. 36). It will frequently be
necessary to run out at right angles to this sap short branches of
parallels (Pl. IX, Fig. 83), to serve as places of arms, or as trenches
of departure for mines or galleries, for underground warfare or for
breaching walls.
=92.= =Breaching the Scarps and Counter-scarps.=--The
counter-scarp, as a rule, and the scarp at times is breached by mining.
(See Military Mining, pars. 91-93). When practicable, however, the
scarp is breached with artillery and preferably by guns of the second
artillery position; since a breaching battery on the crowning of the
covered way, which must be provided with most ample splinter-proofs to
protect the gunners from flying splinters of masonry and shot, is in
general constructed only with great losses and delays; and the guns in
this position must be fired under great angles of depression, requiring
very deep embrasures to avoid exposing the cannoneers. When the ditch
is deep and narrow it may be necessary to blow down the counter scarp
and part of the glacis, in order to expose the scarp-wall to the fire
of the breaching battery, whether on the glacis or at a distance. This
necessity should be foreseen and provided for in locating the batteries.
A full or semi-detached scarp-wall will be breached when the battery is
on the glacis by making vertical cuts at the ends, and a horizontal cut
at about one third or one fourth its height from the bottom, and then
firing shells into the part to be brought down, continuing the fire
until the large masses of masonry are broken up, and the slope is made
gentle and smooth enough to admit of easy ascent. A detached scarp-wall
will be breached by a glacis battery, or any scarp-wall by a distant
battery, by continued battering, which will not only knock down the
wall, but also break up the fragments and make a practicable ramp.
=93.= =The Capture and Crowning of the Breach.=--The decision
as to whether the breach shall be captured and crowned by _assault_
or by _sap_ will be governed by considerations similar to those which
determined the character of the attack upon the covered way. The
difficulties and dangers of the assault are perhaps greater than in
that case. The =assault=, if undertaken, will be carried out in
a similar manner, previous preparations having been made by making a
practicable breach at least 25 to 30 yards wide, a practicable descent
into the ditch of equal width, and a covered place of assembly for the
working party and a depot of trench materials in immediate proximity to
the breach.
The artillery defence of the ditch, whether from caponières, flank
embrasures or casemates, or from adjacent works, must of course be
silenced before crossing the ditch either by assault or by regular
approach. This is accomplished by counter-batteries on the glacis, by
heavy field guns located in temporary batteries in the trenches, by
mines, or by overhead or indirect fire from the distant batteries, or
from light mortars in the advanced trenches, as may be necessary.
If the interior arrangement of the work is known by the besieger the
assault maybe made by night; but if it is unknown, the confusion
resulting from a night attack will be so great as to render its success
almost hopeless, and the assault will have to be delivered by day.
The assaulting columns will be made up of an advanced line of
skirmishers (selected men, good shots, and generally volunteers),
followed by a working party of sappers to clear away obstacles,
these closely followed by the columns of assault; while the supports
and reserves move forward in the trenches to join in the assault as
circumstances require. The troops who first gain the crest establish
themselves there and hold the breach until those coming after them
pass and engage the garrison, while some detachments strive to capture
and open one gate or more to admit the reserves. The assaulting force
should be equal at least to once and a half or twice the garrison, and
simultaneous attacks should be made upon other breaches or accessible
parts of the work to divide the attention of the defence.
These false attacks are sometimes successful, and preparations for
taking advantage of this contingency should not be omitted. The
subdivisions of the assaulting force should each receive explicit
instructions as to its special object, and under no circumstances
should their lines of march intersect. Unmistakable signals of
recognition should be prescribed to prevent conflicts arising between
the different parties meeting within the work. The bombardment
preceding the attack should not cease, and thus notify the defence
when the assault is to be made; but the guns should be directed upon
adjacent parts of the work until the assault penetrates the work or is
repulsed.
=94.= In the =attack by the sap= the method of crossing the
ditch adapted to the circumstances is used (pars. 39-41, Pl. IV, Figs.
37-41) and the sap is started at the foot of the breach, driven up it,
and the breach is crowned according to the methods previously described
(par. 36).
The sappers are protected from small sorties by the fire from the
crowning of the covered way and any other points bearing on the head
of the sap. Fireballs, electric lights and other means will be used
during the night to light up the parapets of the work and expose the
defenders, in this as in the previous operations of the siege. The
crowning of the breach will be extended and converted into a place
of arms, from which further sapping can be carried on in a similar
manner, until the breach in the last retrenchment is crowned and the
preparations for the final attack upon the garrison are made, or the
place surrenders. If the garrison takes refuge in an interior keep and
continues the defence the keep must be reduced by similar methods.
=95.= =Additional Operations in the Attack of an Intrenched
Camp.=--The operations above described are those necessary to
reduce a fortified place of the older type, or a detached work of an
intrenched camp. The latter, though of less extent and with a smaller
garrison, offers as a rule greater resisting power, since it is usually
subject to front fire only, has more complete bomb-proof cover, and is
free from the presence of non-combatants.
While a great advantage is gained by the capture of two or more of
the advanced forts, the resisting power of the intrenched camp is
by no means destroyed. These forts are subject to the fire of the
collateral works, of which frequently two or more must be silenced
before a further advance can be made. The beleaguered army may still
be in condition to recapture the forts by vigorous assaults; and in
almost every case, before the fall of the works of the outer line, a
line of provisional fortifications of high resisting power, connected
by trenches, will have been constructed by the defence in rear of the
captured works, with its flanks secured by the collateral works of the
outer line. An assault against works of this class offers no prospect
of success. The besieger is therefore obliged, as soon as he captures
a detached fort, to put it in condition to withstand the assaults of
the besieged army and to afford protection from the artillery fire
of the collateral works, and then to push forward his approaches
against the successive positions prepared by the defence, which will
as a rule present a front equal to or greater than that which can be
occupied by the attack. The gorges of the captured works are repaired
and strengthened, covered communications are made through the faces,
either through the breaches or in more convenient points, traverses
are repaired or built to protect against the fire of the collateral
works, and the captured works are connected by trenches which afford
emplacements for batteries and form a new parallel from which the saps
can be driven in attacking the intermediate works. Simultaneously with
this attack, it is usually advisable to advance from the flanks of the
first or second parallel upon the forts of the outer line which form
the flanks of the intermediate line. The approaches can generally be
driven with comparative ease owing to these works having already been
partly disabled and now being subject to a flank and reverse fire from
the newly-established batteries.
The flanks of the intermediate line being turned by the capture
of these works, a portion or the whole of it will of necessity be
abandoned. The subsequent operations up to the capture of the enceinte
will be of the same nature as those already described.
=96.= =Occupation of a Conquered Place.=--Immediately upon
the fall of the place it must be occupied by a force (chosen when
possible from the reserve which has not participated in the final
assault) sufficient to control not only the inhabitants, but also the
disorderly soldiers of the attacking force. All pillaging, wanton
destruction, and abuse of the conquered must be restrained with a
strong hand, immediate and exemplary punishment being inflicted upon
offenders. The orderly portion of the defenders must be protected,
and such steps taken for supplying their needs as humanity requires;
while the disorderly ones must be repressed with such severity as may
be necessary. So soon as order is established a careful inventory of
captured property is made, and it is stored subject to the orders of
the government. When the possibility exists of the place being attacked
or besieged by the enemy, all its resources which are available for
defence are collected, repaired, and stored for use.
VAUBAN’S MAXIMS.
=97.= Marshal Vauban, the great French military engineer (born
1633, died 1707), whose experience and success in sieges made him the
great authority on the subject, formulated certain maxims for governing
the conduct of a siege, the observance of which led to almost certain
success, and the departure from them almost invariably resulted
disastrously. The most of these are as applicable to sieges of to-day
as they were to those of his own time. The following[6] bear upon the
second and third periods of the attack:
1st. To delay the opening of the trenches until the besieging forces
are all well posted and made secure by fortifications from an attack
either from the garrison or from a succoring force; and until
everything requisite for carrying on the work vigorously has been
collected and is ready at hand when wanted.
2d. To make a single attack rather than a double one, unless the
two attacks can be well connected and the besieging force exceeds
considerably in strength the garrison. This, as a matter of course,
excludes false attacks, and double separate attacks, unless the
superiority of the besieging force is very great. By a single attack
is understood one by which it is proposed to gain possession of the
main work by a single breach at some point; by a double attack it is
proposed to effect two breaches of the main work. The advantage of the
latter lies in forcing the garrison to divide their strength for the
defence of the two breaches, whilst the assailing forces, being under
one leadership, can at any moment concentrate if necessary upon the
point most favorable to their assault.
3d. To embrace within the parallels and approaches all the defences
which bear upon the site to be occupied by the besieger’s works, in
order to have secure positions for establishing the batteries that may
be required to silence the fire of these defences.
4th. To multiply the approaches, with the view of giving mutual
support, less encumbered communications, and dividing the fire of the
defences, which, if concentrated upon a single one, might soon destroy
it.
5th. To throw up at least three main lines of parallels, placing
them in the best positions for mutual support and for guarding the
approaches and batteries from sorties of the besieged.
6th. To avoid attacking a point upon which the approaches can be run
only on a narrow front, or one which can only be approached over marshy
ground, or on causeways.
7th. To be careful not to push forward any portion of the trenches
until they are well flanked and protected by trenches in their rear,
which are completed and occupied by troops.
8th. To avoid encumbering the approaches with trench materials, tools,
workmen, or troops; placing all of these in the parallels, on the right
and left of the approaches, so as to be ready at hand when wanted, and
to be rapidly sent forward through the trenches of the approaches,
which should be kept free for this purpose.
9th. To place the ricochet (enfilading) batteries in such positions
that they can have an enfilading and slant reverse fire upon the guns
of the defences to be attained by them.
10th. To refrain from opening fire from any series of batteries until
it can be done at the same moment from all of them.
[In connection with this and other siege operations, Vauban remarks
that precipitation in sieges does not hasten the close of them, but
often prolongs them and renders them more bloody.]
11th. To employ the fire of the batteries and trenches, rather than
open assaults, to drive the besieged from their defences, before
attempting to occupy them by the besieging force.
12th. When it is decided to make an open assault, to do so by day, if
there is no portion of the fire of the defences which bears upon the
point to be carried that is not completely kept under by the fire of
the batteries and trenches; but, in the contrary case, when the fire of
the defences is not completely kept under, to make a night assault.
13th. Not to attempt an obstinate resistance to an open assault of the
besieged upon any unfinished portion of the trenches; but rather to
withdraw the workmen and the few troops near them to some point behind
the parallel immediately in rear, and then to open a vigorous fire from
it upon the assailing force.
14th. To keep within the cover of the parallel when the assailant is
advancing to the assault, and leave him to expose himself to its fire
as long as he pleases, and then, when he is well cut up, and has got
thrown into confusion, as he necessarily will at night, in the trenches
that he may have carried, to fall upon him with the bayonet and drive
him out.
15th. Not to push such charges too far from the parallel, but to retire
promptly, so soon as the assailant has fairly taken to flight, within
the cover of the parallel, so as not to draw the fire of the besieged
works.
JOURNAL OF THE ATTACK.
=98.= In connection with the plan of attack previously referred
to (par. 78), a complete _Journal of the Attack_ will be kept in which
will be recorded day by day a detailed record of the daily progress
of the siege, giving the day and hour of starting and completing each
battery, parallel, approach, etc., with their daily progress, dates
of opening fire from each battery, and, generally, every incident
connected with the siege. This journal will be supplemented by journals
kept by the chiefs of engineers and artillery, in which will be
consolidated the daily reports of all subordinate commanders of these
respective arms, giving the expenditure of ammunition, the performance
of the guns, carriages, etc.; the modification made in details of
parapets, batteries, magazines, etc., with their value; the results of
trials of new devices, and special reports upon any points connected
with the siege. These journals will be carefully preserved and copies
transmitted to the War Department from time to time for future use.