Vauban showed how to breach the escarp with the least expenditure of
ammunition. This was done by making, with successive shots placed close
together (which was feasible even in those days from a position so close
as the crest of the covered way) horizontal and vertical cuts through
the revetment wall. The portion of revetment enclosed by the cuts being
thus detached from support was overturned by the pressure of the earth
from the rampart. Ricochet fire was also the invention of Vauban. He
showed how, in enfilading the face of a work, by using greatly reduced
charges a shot could be made to drop over the crest of the parapet and
skim along the terreplein, dismounting guns and killing men as it went.
18th-century principles of defence.
The constant success of Vauban must be ascribed to method and thorough
organization. There was a deadly certainty about his system that gave
rise to the saying "Place assiegee, place prise." He left nothing to
chance, and preferred as a rule the slow and certain progress of saps
across the ditch and up the breach to the loss and delay that might
follow an unsuccessful assault. His contemporary and nearest rival
Coehoorn tried to shorten sieges by heavy artillery fire and attacks
across the open; but in the long run his sieges were slower than
Vauban's.
So much a matter of form did the attack become under these conditions,
that in comparing the supposed defensive powers of different systems of
fortification it was usual to calculate the number of days that would be
required in each case before the breach was opened, the time being
measured by the number of hours of work required for the construction of
the various trenches and batteries. It began to be taken as a matter of
course that no place under any circumstances could hold out more than a
given number of days; and naturally, when the whole question had become
one of formula, it is not surprising to find that places were very often
surrendered without more than a perfunctory show of resistance.
The theory of defence at this time appeared to be that since it was
impossible to arrest the now methodical and protected progress of the
besiegers' trenches, no real resistance was possible until after they
had reached the covered way, and this idea is at the root of the
extraordinary complications of outworks and multiplied lines of ramparts
that characterized the "systems" of this period. No doubt if a successor
to Vauban could have brought the same genius to bear on the actual
defence of places as he did on the attack, he would have discovered that
the essence of successful defence lay in offensive action outside the
body of the place, viz. with trench against trench. For want of such a
man the engineers of the defence resigned themselves contentedly to the
loss of the open ground outside their walls, and relied either upon
successive permanent lines of defence, or if these did not exist, upon
extemporized retrenchments, usually at the gorge of the bastion.
[Illustration: FIG. 68.--Double Sap.]
It is curious that such experienced soldiers as most of them were should
not have realized the fatal effect upon the minds of the defenders which
this almost passive abandonment of line after line must needs produce.
Even a civilian--Machiavelli--had seen into the truth of the matter
years before when he said (_Treatise on the Art of War_, Book vii.):
"And here I ought to give an advice ... to those who are constructing a
fortress, and that is, not to establish within its circuit
fortifications which may serve as a retreat to troops who have been
driven back from the first line.... I maintain that there is no greater
danger for a fortress than rear fortifications whither troops can retire
in case of a reverse; for once the soldier knows that he has a secure
retreat after he has abandoned the first post, he does in fact abandon
it and so causes the loss of the entire fortress."
[Illustration: FIG. 69.--Direct advance by Double Sap.]
It must, however, be remembered that in those days when soldiers were
mostly of a separate or professional caste, the whole thing had become a
matter of business. Fighting was so much regulated by the laws and
customs of war that men thought nothing of giving up a place if,
according to accepted opinion, the enemy had advanced so far that they
could no longer hope to defend it successfully. Once this idea had set
in it became hopeless to expect successful defences, save now and then
when some officer of very unusual resolution was in command. This is the
real reason for the feeble resistance so often made by fortresses in the
17th and 18th centuries, which has been attributed to inherent weakness
in fortifications. Custom exacted that a commandant should not give up a
place until there was an open breach or, perhaps, until he had stood at
least one assault. Even Napoleon recognized this limitation of the
powers of the defence when in the later years of his reign he was trying
to impress upon his governors the importance of their charge. The
limitation was perfectly unnecessary, for history at that time could
have afforded plenty of instances of places that had been successfully
defended for many months after breaches were opened, and assault after
assault repulsed on the same breach. But the same soldiers of the 17th
and 18th centuries who had created this artificial condition of affairs,
established it by making it an understood thing that a garrison which
surrendered without giving too much trouble after a breach had been
opened should have honourable consideration; while if they put the
besiegers to the pains of storming the breach, they were liable to be
put to the sword.
[Illustration: FIG. 70.--Later Stages of the Attack (Vauban).]
Peninsular War.
It has been necessary to dwell at some length on the siegecraft of
Vauban and his time, not merely for its historical interest, but because
the system he introduced was practically unaltered until the end of the
19th century. The sieges of the Peninsular War were conducted on his
lines; so was that of Antwerp in 1830; and as far as the disposition of
siege trenches was concerned, the same system remained in the Crimea,
the Franco-German War and the Russo-Turkish War. The sieges in the
Napoleonic wars were few, except in the Iberian peninsula. These last
differed from those of the Vauban period and the 18th century in this,
that instead of being deliberately undertaken with ample means, against
fortresses that answered to the requirements of the time, they were
attempted with inadequate forces and materials, against out-of-date
works. The fortresses that Wellington besieged in Spain had rudimentary
outworks, and escarps that could be seen and breached from a distance.
At that time, though the power of small arms had increased very slightly
since the last century, there had been a distinct improvement in
artillery, so that it was possible to breach a visible revetment at
ranges from 500 to 1000 yds. Wellington was very badly off for
engineers, siege artillery and material. Trench works could only be
carried out on a small scale and slowly. Time being usually of great
importance, as in the first two sieges of Badajoz, his technical
advisers endeavoured to shorten sieges by breaching the escarp from a
distance--a new departure--and launching assaults from trenches that had
not reached the covered way. Under these circumstances the direct
attacks on breaches failed several times, with great loss of life.
Wellington in one or two earlier despatches reflected on his engineers
for not establishing their batteries on the crest of the glacis. The
failures are, however, clearly due to attempts to push sieges to a
conclusion without proper preparation.
So much has been written of late years in criticism of the
fortification to what may be called the Vauban period that it is
important to note what were the preparations considered necessary for
a siege at that time (_Journals of Sieges in Spain, 1811 to 1814_).
Sir John Jones summarizes his own experience in Spain and the data
accumulated by practical engineers in former sieges from the time of
Vauban onwards, in the following conclusions: The actual work of
entrenching, sapping, &c., on the front attacked was much the same
whether the fortress contained 5000 or 10,000 men. On the other hand
the guard of the trenches was proportionate to the fighting men inside
the fortress. (The total number of men had of course to be sufficient
to allow three or four complete shifts or "reliefs" for all work and
duties.) Adding a proportion of men for camp and other duties, he
calculates, for the vigorous siege of an ordinary place situated in
open country and containing 5000 men, a corps of 32,080 effectives,
and remarks further that this force would be greatly exhausted after a
month's service. The same place held by 10,000 would call for a
besieging army of 50,830 men (guards and duties increasing, but not
working parties). Thus the besieger should if possible have a
superiority of 7 to 1 if the garrison numbered 5000, 6 to 1 if 10,000
and 5 to 1 if 15,000 and so on. As regards artillery, he should have
as many, and if possible twice as many, guns as those of the defender
on the front of attack, as well as howitzers for sweeping every line
subject to enfilade and mortars for destroying traverses, &c. Later in
the siege, more howitzers and mortars to clear the covered way and
places of arms, and finally, after the covering of the covered way,
fifty additional battering guns would be required. It is apparent from
this that the practical engineers of the day looked upon a siege as a
serious matter, and did not find permanent fortifications wanting in
defensive strength.
Crimea.
During the long peace that followed the Napoleonic wars, one advance was
made in siegecraft. In England in 1824 successful experiments were
carried out in breaching an unseen wall by curved or indirect fire from
howitzers. At Antwerp in 1830 the increasing power and range of
artillery, and especially of howitzers, were used for bombarding
purposes, the breaches there being mostly made by mines. Then came one
of the world's great sieges; that of Sevastopol in 1854-1855 (see
CRIMEAN WAR). The outstanding lesson of Sevastopol is the value of an
active defence; of going out to meet the besieger, with countertrench
and countermine. This lesson has increased in value for us in proportion
to the increased power of the rifle.
In comparing the resistance made behind the earthworks of Sevastopol
with the recorded defences of permanent works, it is essential to
remember that the conditions there were quite abnormal. Sir John Jones
has told us what the relative forces of besiegers and besieged should
be, and the necessary preponderance of artillery for the attack. The
following quotations may be added:
"The siege corps should be sufficiently strong--(1) To invest the
fortress completely, and maintain the investment against all the
efforts of the garrison. (2) If a regular siege is contemplated, to
execute and guard all the siege works required for it. Complete
investment may sometimes be impossible, but experience has repeatedly
shown that the difficulties of a siege are enormously increased if the
garrison are able to draw fresh troops and supplies from outside, and
to rid themselves of their sick and wounded." (Lewis). Again as
regards artillery: "In a regular attack, where every point is gained
inch by inch, it is impossible to succeed without overpowering the
defensive artillery"; and "it is useless to attempt to sap near a
place till its artillery fire is subdued..." (Jones).
These conditions were so far from being fulfilled at Sevastopol that
(a) there was no investment--in fact the Russians came nearer to
investing the Allies; (b) the Russians had the preponderance in guns
almost throughout; (c) the Russian force in and about Sevastopol was
numerically superior to that of the Allies. We must add to this that
Todleben had been able to get rid of most of his civilian population,
and those who remained were chiefly dockyard workmen, able to give
most valuable assistance on the defence works. The circumstances were
therefore exceptionally favourable to an active defence. The weak
point about the extemporized earthworks, which eventually led to the
fall of the place, was the want of good bomb-proof cover near the
parapets.
Franco-German War.
The Franco-German War of 1870 produced no great novelty. The Germans
were not anxious to undertake siege operations when it could be avoided.
In several cases minor fortresses surrendered after a slight
bombardment. In others, after the bombardment failed, the Germans
contented themselves with establishing a blockade or detaching a small
observing force. By far the most interesting siege was that of Belfort
(q.v.). Here Colonel Denfert-Rochereau employed the active defence so
successfully by extemporizing detached redoubts and fortifying outlying
villages, that he obliged the besiegers (who, however, were a small
force at first) to take up an investing line 25 m. long; and succeeded
in holding the village of Danjoutin, 2000 yds. in advance of the
enceinte, for two months after the siege began. He also used indirect
fire, withdrawing guns from the ramparts and placing them in the
ditches, in the open spaces of the town, &c. At Paris the French found
great advantage in placing batteries in inconspicuous positions outside
the forts. Their direct fire guns were at a disadvantage in being fired
through embrasures. These had served their purpose when artillery fire
was very inaccurate, but had now for a long time been recognized by the
best engineers as out of date. The Germans since the siege of Duppel in
1864 had mounted their siege guns on "overbank" carriages; that is, high
carriages which made it possible to fire the guns over the parapet of
the battery without embrasures. The guns in the Paris forts which were
further handicapped by conspicuous parapets and the bad shooting of the
gunners were easily silenced.
At Strassburg indirect fire against escarps was used. The escarp of
Lunette 53 was successfully breached by this method. The breaching
battery was 870 yds. distant, and the shot struck the face of the wall
at an angle (horizontally) of 55 deg., the effect being observed and
reported from the counterscarp. 1000 rounds from 60-pounder guns
sufficed to make a breach 30 yds. wide.
Fig. 71 is a good example of the attack in the late stages. It will be
observed that batteries for mortars and field guns are established in
the captured lunettes. The narrow wet ditch of Lunette 53 was crossed
by a dam of earth and fascines, the headway protected by a parapet or
screen of sandbags.
"Lunette 52 was unrevetted, and its ditch was more than 60 yds. wide,
and 6 to 9 ft. deep.... It was determined to effect the passage by a
cask bridge, for which the casks were furnished by breweries near at
hand.... The formation of the bridge was begun at nightfall. A pioneer
swam across, hauled over a cable, and made it fast to the hedge on the
berm. Four men were stationed in the water, close to the covered way,
the casks were rolled down to them one after the other, and fitted
with saddles, so as to form piers ... these piers were successively
boomed out along the line of the cable.... In two hours the bridge was
finished, and the lunette was entered.... The work had not been
discovered by the besieged, and the formation of lodgments inside the
lunette was already begun, when the noise made by some troops in
passing the bridge attracted attention, and drew a fire which cost the
besiegers about 50 men. A dam was afterwards substituted for the
bridge, as it was repeatedly struck by shells." (_R.E. Professional
Papers_, vol. xix.)
It is curious to realize that this happened at so recent a time. Such
operations would be impossible now, as long as any defending guns
remained in action.
Modern siege warfare.
On the whole it may be said that siegecraft gained practically nothing
from the Franco-German War. The Russo-Turkish war taught less, Plevna
(q.v.) having been defended by field works and attacked by the
old-fashioned methods. For the last ten years of the 19th century
military opinion was quite at a loss as to how the sieges of the future
would work out. As guns and projectiles continued to improve the
"attaque brusquee" proposed by von Sauer had many adherents. It was
thought that a heavy bombardment would paralyse resistance and open the
way for an attack, to be delivered by great numbers and with special
appliances for crossing obstacles. Others thought that the strength of
the defence, as manifested by the Plevna field works, would be greater
than ever when the field works were backed by permanent works, good
communications and the resources of a fortress. One thing was
obvious--namely, that as long as the artillery of the place, of even the
smallest calibres, remained unsubdued, the difficulty of trenchwork and
sapping would be enormously increased, and no one seemed to have formed
a clear conception of how that difficulty was to be met. A lecture
delivered in Germany about 1895 is worth quoting as a fair example of
the vagueness of idea then prevailing: "For the attack, the following is
the actual procedure: Accumulation and preparation of material for
attack before the fortress: advance of attacking artillery, covered by
infantry. Artillery duel. Throwing forward of infantry: destruction of
the capability for defence of the position attacked; when possible by
long-range artillery fire, otherwise by the aid of the engineers.
Occupation of the defensive position. Assault on the inner lines of the
fortress." That seemed quite a simple prescription, but the necessary
drugs were wanting. And even since Port Arthur great uncertainty as to
the future of the attack remains.
[Illustration: From _Textbook of Fortification_, by permission of the
Controller H.M. Stationery Office.