We need not here discuss the role of the defenders' artillery in
replying to that of the enemy and playing on the attack; nor for the
moment consider how far the defence of the trenches while under
artillery fire can be made easier by overhead cover. The main question
is--what is, in view of the nature of the attack, the best disposition
of lines of trench; and do they require the addition of redoubts?
The most important point, with the object of protection, is that the
trenches must not be conspicuous; this is the best defence against
artillery. With the object of resistance by their own fire they must
have a good view, or, as it is generally described, no _dead ground_ in
front of them. For this purpose 300 or 400 yds. may be enough if the
ground is even and affords no cover.
This necessity for invisibility, together with the shallowness of the
zone that suffices for producing a decisive fire effect, has of late
years very much affected the choice of ground for a line of trenches.
Siting of trenches.
For a defensive position on high ground, it was usually laid down
until the South African War that a line of trenches should be on the
"military crest" (Fr. _crete militaire_), _i.e._ the highest point on
the hill from which the whole of the slopes in front can be seen. Thus
in the three sections of ground shown in fig. 79 it would be at a, b
and c respectively. The simplicity of this prescription made it
attractive and it came to be rather abused in the text-books. There
were, even before the improvements in artillery, objections to it,
because on most slopes the military crest would be found at very
different elevations on different parts of the line, so that by a
strict adherence to the rule some of the trenches would be placed near
the top of the hill, and some in dangerous isolation near the bottom.
Moreover a rounded hill has no military crest.
[Illustration: FIG. 79.]
Further, we have to consider nowadays not only the position of the
fire-trenches, but those of supports, reserves and artillery, and the
whole question is extremely difficult.
For instance, considering the sections alone, as if they did not vary
along the line, the positions at _a_ and _b_, fig. 79, are bad because
they are on the sky-line and therefore a good mark for artillery. That
at _b_ is especially bad because the slope in front is so steep that
the defenders would have to expose themselves very much to fire down
it, and the artillery fire against them can be kept up until the very
last moment. The position _c_ has the advantage of not being on the
sky-line, but the position of the supports in rear is exposed.
[Illustration: FIG. 80.]
Such a position as that at _d_, fig. 80, is good, but protected or
concealed communications must be made for the supports coming from _e_
over the brow of the hill.
[Illustration: FIG. 81.]
Another possible position for the infantry line is at _f_, fig. 81,
with the guns on the high ground behind. They might easily be quite
concealed from the enemy's artillery. The drawback is that no
retirement up the exposed slope would be possible for them, except at
night. The fire from _f_ will be _grazing_, which will be a great
advantage as compared with the _plunging_ fire that would be obtained
from a position up the hill.
It is idle, however, to give more than the most cursory consideration
to sections of imaginary positions. It is only by actual practice on
the ground that skill can be attained in laying out positions, and
only a trained soldier with a good eye can succeed in it. Briefly, the
advantages of view and position given by high ground must be paid for
in some degree by exposure to the enemy's artillery; and at least as
much consideration--possibly as much labour--must be given to
communications with the fire-trenches as to the trenches themselves.
Irregular ground simplifies the question of concealment but also gives
cover to the enemy's approach. The lie of the ground will itself
dictate the position of the trenches, subject to the predispositions
of the responsible officer. On flat featureless ground the general
trace of the trenches should be irregular. This makes a more difficult
target for artillery, and affords a certain amount of cross and
flanking fire, which is a very great advantage. Great care should,
however, be taken not to expose the trenches to oblique or enfilade
fire; or at least to protect them, if so exposed, by traversing.
[Illustration: FIG. 82.]
Trenches.
Concealment of trenches is generally attempted by covering the freshly
turned earth of the small parapet with sods, leafy branches or grass.
In this connexion it should be remembered that after a day or two cut
leaves and grass wither and may become conspicuous against a green
surface. Where the ground is so even that a good view of the
foreground is possible from the surface level, the trench may be made
without a parapet; but this entails great labour in removing and
disposing of the excavated earth. A common device is to conceal the
parapet as well as possible and to make a dummy trench some distance
away to draw fire.
Besides the direct concealment of trenches, care must be taken that
the site is not conspicuous. Thus a trench should not be placed along
the meeting line of two different kinds of cultivation, or along the
edge of a belt of heather on a hill-side, or where a difference of
gradient is sharply defined; or where any conspicuous landmark would
help the enemy's artillery to get the range.
[Illustration: FIG. 83.]
Trenches are broadly distinguished as "fire trenches" and "cover
trenches," according as they are for the firing line or supporting
troops. The following simple types are taken from the 1908 edition of
_Military Engineering_ (part 1): "Field Defences."
Fig. 82 is the most common form of fire trench, in which labour is
saved by equalizing trench and parapet. This would take 1-1/2 to 2
hours in ordinary soil. Fig. 83 shows the same trench improved by 2 or
3 hours' more work. Fig. 84 shows a fire trench without parapet, with
cover trench and communication.
[Illustration: From _Mil. Engineering: Field Defences_ (1908), by
permission of the Controller H. M. Stationery Office.