Obstacles.
The escarp is falling into disfavour, on account of the great expense of
a revetment that can withstand breaching fire. A counterscarp of very
solid construction is generally used. It is low and gives cover to a
wire entanglement in the ditch. This may be supplemented by a steel
unclimbable fence, and by entanglements or thorn plantations on the
covered way and the lower slopes of the parapet. Entanglements are
attached to steel posts bedded in concrete. The upper parts of
revetments and the foundations of walls are protected against the action
of shells, that falling steeply might act as mines to overturn them, by
thick aprons of large stones. Fig. 54 shows most of these dispositions.
Search-lights.
Electric search-lights are now used in all important works and
batteries. They are usually placed in disappearing cupolas. They are of
great value for discovering working parties at night, and lighting up
the foreground during an attack; and since only the projector need be
exposed, they are not very vulnerable. Their value, however, must not be
over-estimated. The most powerful search-light can in no way compare
with daylight as an illuminant, and, like all other mechanical
contrivances, they have certain marked drawbacks in war. They may give
rise to a false confidence; an important light may fail at a critical
moment; and in foggy weather they are useless.
Armour.
The use of armour (see also ARMOUR-PLATES) for coast batteries followed
closely upon its employment for ships, for those were the days of short
ranges and close fighting, and it seemed natural not to leave the
battery in a position of inferiority to the ship in the matter of
protection. In England the coast battery for a generation after the
Crimean War was a combination of masonry and iron; and in 1860 Brialmont
employed armoured turrets at Antwerp in the forts which commanded the
Scheldt. For land defence purposes, however, engineers were very slow to
adopt armour. Apart from all questions of difficulty of manufacture,
expense, &c., the idea was that sea and land fronts were radically
different. It was pointed out that a ship gun, fired from an unsteady
platform, had not enough accuracy to strike repeated blows on the same
spot; so that a shield which was strong enough to resist a single shot
would give complete protection. A battery on a land front, on the other
hand, was exposed to an accurate fire from guns which could strike
successive blows on the same spot, and break down the resistance of the
strongest shield. But in time continental opinion gradually began to
turn in favour of iron protection. Practical types of disappearing and
revolving cupolas were produced, and many engineers were influenced in
their favour by the effect of the big high-explosive shell. Eventually
it was argued that, after all, the object of fortification is not to
obtain a resisting power without limit, but to put the men and guns of a
work in an advantageous position to defend themselves as long as
possible against a superior force; and that from this point of view
armour cannot but add strength to defensive works.
[Illustration: From Deguise's _La Fortification permanente_, by
permission of J. Polleunis.