Wire may be used as a _high_ or _low entanglement_ or as a fence or
trip wire or concealed obstacle. The usual form of high wire
entanglement consists of several rows of stout stakes 4 or 5 ft. long,
driven firmly into the ground about 6 ft. apart, and connected
horizontally and diagonally with barbed wire.
[Illustration: FIG. 94.--Crows' Feet.]
[Illustration: FIG. 95.--Plan and section of Trous-de-loup.]
_Palisades_ are still used, and need no description. They were
formerly often made bullet-proof, but this is no longer possible.
_Fraises_ are seldom heard of now, though they may appear occasionally
in a modified form. They were much used in connexion with deep
ditches, and are palisades placed so as to project horizontally from
the escarp, or sloping forward in the bottom of the ditch. _Military
pits_ both _deep_ and _shallow_ (the latter, shown in fig. 95, called
_trous de loup_) are not so much used as formerly, because the
obstacle is hardly worth the labour expended on it. Both, however,
were employed in the Russo-Japanese War. _Crows' feet_, formerly much
used as a defence against cavalry, are practically obsolete. They
consisted of four iron spikes joined together at their bases in such a
manner that however they were thrown down one point would always be
pointing upwards (fig. 94). _Chevaux-de-frise_ (q.v.) were formerly a
much-used type of obstacle.
The best obstacle is that which can be made to fulfil a given object
with the least expenditure of time and labour. From this point of view
barbed wire is far the best. One of its greatest advantages is that it
gives no cover whatever to the enemy.
_Fougasses_ have always for convenience been classed as obstacles. A
fougasse is a charge of powder buried at the bottom of a sloping pit.
Over the powder is a wooden shield, 3 or 4 in. thick, and over the
shield a quantity of stones are piled. The illustration, fig. 96,
gives a clear idea of the arrangement. A fougasse of this form,
charged with 80 lb. of powder, will throw 5 tons of stones over a
surface 160 yds. long by 120 wide. They may be fired by powder hose,
fuze or electricity. Their actual effect is very often a matter of
chance, but the moral effect is usually considerable.
_Dams_ are most effective obstacles, when circumstances allow of their
use. They are constructed by military engineers as small temporary
dams would be in civil works.
Illumination.
A most important question, especially in connexion with obstacles, is
that of lighting up the foreground at night. Portable electric
searchlights are most valuable, especially for detecting the enemy's
movements at some distance; but their use will naturally always be
restricted. Star shells and parachute lights fired from guns are not
of much use for the immediate foreground, and do not burn very long.
They were formerly chiefly of use in siege works, to light up an
enemy's working parties. Germany has introduced lightballs fired from
pistols, which will probably have a considerable future.
Various civilian forms of _flare-light_ would be very useful to
illuminate obstacles, but cannot well be carried in the field.
_Bonfires_ are very useful when material is available. They require
careful treatment, _e.g._ they must be so arranged that they can be
lighted instantaneously (they may be lighted automatically, by means
of a trip wire and a fuze); they must give a bright light at once
(this can be ensured with shavings or straw sprinkled with petroleum);
they must be firmly built so that the enemy cannot destroy them
easily; and if possible there should be a screen arranged behind them
so that they may not light up the defence as well as the attack.
Blockhouses.
Blockhouses are familiar to the public from the part they played in
the South African War of 1899-1902. In the old-fashioned permanent
fortification they were used as keeps in such positions as re-entering
places of arms and built of masonry. Stone blockhouses have long been
used in the Balkans for frontier outposts; they are sometimes built
cruciform, so as to get some flanking defence. In the form of
bullet-proof log-cabins they have played a great part in warfare
between pioneer settlers and savages.
[Illustration: From _Mil. Engineering_, by permission of the
Controller H.M. Stationery Office.