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476 natural crest. Immediately beside the main wire is a continuous infantry parapet, which has at frequent intervals concrete shelters for machine-guns as well as infantry. On the natural crest, a central structure of concrete and armour contains the commanding officer's observation post and two machine-guns in cupolas for the direct

FIG. 2. Plan of a Metz Feste. References. 01, 02, main infantry works; 03, 04, flank portions of infantry positions organized as " redoubts"; bi, b2, etc., armoured batteries (bs, dummy); al, a.2, etc. war barracks, fi, (2 etc. artillery observatories; hi, h2 etc. coun- terscarp casemates, caponnieres and the like for flanking perimeter wire or ditch wire; ki, k2, etc., infantry observatories (armoured); m, m, parapet sentry posts ; cf, C2 etc. concrete shelters for infantry on duty; i, entrance blockhouse^

sweeping of the foreground, and towards the flanks two somewhat 'similar structures house each a 75-mm. Q.F. gun, its observation post, and the observation post of one of the mam armament batter- ies mentioned below. Just behind the crest are two large battle-

batteries," was destined to survive and multiply in the World War. The rear defence of the inner system is provided by the rear por- tion of the perimeter trench, with its concrete machine-gun shelters and its wire.

The most marked characteristic of this design is the fact that the interior space of the " group" is organized principally for step- by-step close-defence, whereas it is utilized in a Feste for battery sites. The middle foreground is under the fire of two quick-firing guns in cupolas, but the author of the system evidently does not trust to these organs overmuch, for he arranges that they shall be fired into and destroyed by the main-armament guns if captured. The essential element of the first stage of close-defence is the machine-gun detachments in the front trench, which are housed under concrete till the moment of action. The second stage, which begins when the assault has broken into the front trench, is a com- bination of counter-attack from the great shelters behind the crest with machine-gun fire from the central crest cupolas; to facilitate this counter-attack, the back of the front trench is smoothed to glacis-form. When all this is lost, the inner system with its " infan- try batteries " sited well down the reverse slope, has still to be car- ried before the main-armainent or traditore batteries can be reached, and the machine-gun cupolas of the keep not only cooperate in this third stage, but (with the blockhouses attended to earlier) make it difficult for the enemy to make a lodgment even in the fourth and last stage. In all stages after the first, the curved fire of the trench- mortar battery plays a part. In this respect, and in the free use of machine-guns and local counter-attack, de Mondesir's fortifica- tion anticipated by ten years or more the trench-warfare methods that developed in the World War.

The above outline account of applications, practical and theoretical, of the new " group " principle requires the addition of a few details as to the principal constituent elements of such works, the counter- scarp casemate or caponniere for low-flanking of a ditch, the main- armament or safety-armament battery made up of cupolas (as dis- tinct from the cupolas themselves), and the traditore battery.

The Austrian counterscarp casemate, illustrated in fig. 4, is con- structionally a simple example. Under the counterscarp wall, on the further side of the ditch, facing the salient angle of the work, a chamber is formed with embrasures for rifle, machine-gun or light- artillery fire along the two adjacent ditch lengths. In this case armour is used for the embrasures, each gun-room (K K) having two very light guns or pompoms. B is a living room for the squads assigned to the defence, A a latrine, St a stairway leading to P, a concrete tunnel under the ditch which communicates with the body of the work.

Fig. 5 shows a counterscarp casemate of more advanced type. It is amongst the most modern examples of such structures, form- ing part of a 1914 work at Metz. It fires in one direction only. The inner portion of its mass is in ordinary, the outer in reinforced con- crete, and the total thickness is 3 metres. Fire is arranged in two tiers, for rifles, and for machine-guns, and one embrasure (the safest) is allotted to a searchlight. The details are worthy of close attention. The top of the wall is formed as an overhang, under which the fronts pi the fighting chambers are recessed. This gives enhanced protection from fire, and also from the risk of grenades

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.FiG. 3. Section of infantry work 01 of fig. 2, on line a-b.

shelters in concrete for counter-attack infantry. Then, well back, comes an inner system forming a still flatter " lens." This contains the main armament batteries, the traditore element, and the infantry keep. Its front wire traverses the whole interior of the group, leav- ing the crest elements and counter-attack shelters outside it, and resting its flanks on the infantry parapet, the junction being sealed by blockhouses. Within this wire, which is protected frontally by several " infantry batteries," i.e. loopholed steel screens or pent- houses for riflemen, lie, towards the flanks, two batteries of main armament artillery in cupolas and one or two " Bourges casemates " genuine traditore batteries which can only fire to the flank and rear and are heavily protected and masked towards the front. Cen- trally placed between the artillery positions is the infantry keep, in this case as in the German the basis unit. It is four-sided and has a deep wired ditch which is flanked not by counterscarp casemates, but by two low caponnieres springing from the base of the escarp at the diagonal angles. In the concrete of this keep are the war bar- racks of the whole garrison, observation cupolas, and at least two machine-gun cupolas which are in fact the essential defence of the keep. Embryonic counter-mine systems are provided at the salients of the keep. Behind the keep is a battery for small short-range mortars a novelty which, unlike the present writer's " infantry

being thrown in by an assailant overhead. At the foot of the wall is a pit which lowers the floor of the ditch so far that the assailant in the ditch cannot reach the embrasure. This pit also serves to take debris that might otherwise mask the fire of the lower tier. A gal- lery formed in the mass of the counterscarp connects the casemates of the different angles.

An example of the modern counterscarp is shown in fig. 6 from another Metz work. Here it will be noticed that, for defence and also for ventilation, the gallery possesses a loophole. Over this is a grille to prevent the placing of scaling-ladders and the upper part of the counterscarp wall is formed to a peculiar section which gives a minimum foothold to an assailant scrambling down, and presents an unfavourable striking angle to all projectiles.

The Mass for it is a mass rather than a wall is 7 metres thick for 7 metres of height. The communication tunnel between such a gallery and the body of the work (fig. 7) gives 2 metres of (ordinary and reinforced) concrete protection besides that afforded by the earth of the ditch floor.

Some designers, owing to the risk of the backs of counterscarp chambers and galleries being breached by mining, or the communi- cating tunnel destroyed from above or below, prefer to keep the ditch between the enemy and the flanking organ. In this case a