The ring of detached forts.
The distance of detached forts from the place depends on the range of
the siege artillery and the distance at which it can usually be
established from the forts, and is variously given by different
continental writers at from 4 to 9 km. (4500 to 10,000 yds.). The
bombarding range of siege howitzers with heavy shells is considered to
be about 8000 yds., and if it is possible for them to be emplaced within
say 2000 yds. of the forts, this would give a minimum distance of 6000
yds. from the forts to the body of the place. Some writers extend the
minimum distance to 7 km., or nearly 8000 yds. In practice, however, it
must happen that the position of the forts is determined to a very large
extent by the lie of the ground. Thus some good positions for forts may
be found within 4000 or 5000 yds. of the place, and no others suitable
on the same front within 15,000 yds. In that case the question of
expense might necessitate choosing the nearer positions. Some examples
of the actual distances of existing forts have already been given.
Others, more recent, are, at Bucharest 7-10 km., Lyons 8-10(1/2),
Copenhagen 7-8 and Paris 14-17. _Strategic pivots_ are in a different
category from other fortresses. While not necessarily protected from
bombardment, they may yet have one or two forts thrown out from 9 to 12
km., to get advantage of ground. Such are Langres, Epinal and Belfort.
_The Enceinte._--The desirability of this is almost universally
allowed; but often it is more as a concession to tradition than for
any solid reason. The idea is that behind the line of forts, which is
the main defensive position, any favourable points that exist should
be provisionally fortified to assist in a "step-by-step" defence: and
behind these again the body of the place should be surrounded by a
last line of defence, so that the garrison may resist to the last
moment. It may be remarked that apart from the additional expense of
an enceinte, such a position would not, under modern conditions, be
the most favourable for the last stages of a defence. Again, there is
the difficulty that it is practically impossible to shut in a large
modern town by a continuous enceinte. It has been proposed to
construct the enceinte in sections in front of the salient portions of
the place. This system of course abandons several of the chief
advantages claimed for an enceinte.
In actual practice enceintes have been constructed since 1870 in
France and other countries, consisting of a simple wall 10 or 12 ft.
high with a banquette and loopholes at intervals. This of course can
only be looked upon as a measure of police. For war purposes, in face
of modern artillery, it is a _reductio ad absurdum_.
_The Safety Armament._--If the bulk of the artillery is to be placed
in positions prepared on the outbreak of war, it is considered very
necessary that a few heavy long-range guns should be permanently in
position ready at any moment to keep an enemy at a distance, forcing
him to open his first batteries at long range and checking the advance
of his investment line. Such guns would naturally be in secure
positions inside the forts, and if they are to be worked from such
positions they must have armour to shield them from the concentrated
fire of the numerous field artillery that a besieger could bring to
bear from the first.
The question of artillery positions.
Artillery outside the forts constitutes the most important part of the
defence, and there is room for much discussion as to whether it should
have positions prepared for it beforehand or should be placed in
positions selected as the attack develops itself. On the one hand the
preparation of the positions beforehand, which in many cases means the
use of armour and concrete, increases very largely the initial expense
of the defence, and ties the defender somewhat in the special
dispositions that become desirable once the attack has taken shape.
Moreover, such expenditure must be incurred on all the fronts of the
fortress, whereas the results would only be realized on the front or
fronts actually attacked. On the other hand much time and labour are
involved in emplacing heavy and medium artillery with extemporized
protection, and this becomes a serious consideration when one remembers
how much work of all kinds is necessary in preparing a fortress against
attack. Again, to avoid the danger of a successful attack on the
intervals between the forts before their defences have been fully
completed, the fire of the guns in the intermediate positions might be
urgently required. The solution in any given case would no doubt depend
on the importance of the place. In most cases a certain amount of
compromise will come in, some preparation being made for batteries,
without their being completed. Armoured batteries of whatever kind must
in any case be prepared in peace time. It should not be overlooked that
as, whatever theories may exist about successive lines of defence, the
onus of the defence will now lie on the fort line, just as it formerly
did on the enceintes, so that line should be fully prepared, and should
not have to commence its fight in a position of inequality.
[Illustration: From Brialmont's _Progres de la defense des etats et de
la fortification permanente depuis Vauban_, by permission of M. le
Commandant G. Meeus.