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.
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. crête 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 Siting of trenches. 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.
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| 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.
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| Fig. 80. |
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| Fig. 81. |
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| Fig. 82. |
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| Fig. 83. |
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.
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.
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 Trenches. 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.
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 112 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.
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| From Mil. Engineering: Field Defences (1908), by permission of the Controller H. M. Stationery Office. |
| Fig. 84. |
The addition of a loophole of sandbags on the top for concealment (called head-cover), gives increased protection, but at the cost of greater prominence for the parapet (fig. 85). Overhead cover can only be provided in fire trenches by giving the parapet still greater height and it is not usually done. Portions of the trench not used for firing can, however, be given splinter-proof protection by putting over them branches or bundles, covered with a few inches of earth: or by boards, or sheets of corrugated iron if they can be had. A better plan when time permits is to provide cover trenches immediately behind and communicating with the fire trench.
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| From Mil. Engineering: Field Defences, by permission of the Controller H. M. Stationery Office. |
| Fig. 85. |
The question of redoubts has been a vexed one for years; partly they were thought to be unnecessary in view of the resisting power of a line of trenches, but chiefly because the redoubt was always imagined as one of the older type, with a high conspicuous parapet. Of course a redoubt of such a nature would Redoubts. be readily identified and made untenable. But the idea of a redoubt does not necessarily imply command. Its object is that it shall be capable of all-round defence. There can be no doubt that as there is always a possibility of lines being pierced somewhere, it is desirable, unless the whole line is to be thrown into confusion and forced back, to have some point at which the defenders can maintain themselves. This is not possible unless at such points there is provision for defence towards both flanks and rear, that is to say, when there are redoubts, which can hold on after certain portions of the line have been lost and thereby can localize the enemy’s success and simplify
