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Americans, was a longer gun, namely 38 cals., throwing a loo-Ib. shell, and ranged nearly 20,000 yd. with streamline shell. The French had a variety of automobile and tractor-drawn mountings for this gun. One of the latter had a split trail, giving 60 of trav- erse; to transport it, an extra pair of wheels was placed under the point of the trail, and the gun run back so as to divide the weight between the two pairs of wheels. In another form the gun was car- ried on a motor lorry. In 1918 the French used a lo-ton Renault caterpillar tractor with the gun mounted on it for all-round fire. This was a powerful machine with no-H.P. motor. It carried out- riggers which were fixed when the gun fired across the vehicle. One object of putting an all-round mounting on a caterpillar, which itself can be easily turned about, is that when the gun is in a position where it has to stay for days or weeks it is much easier to camouflage a

FIG. 31. 155-mm. G.P.F. on Christie automobile mounting.

mounting which does not have to be shifted to lay the gun. Such a mounting can be sunk in the ground, or a protecting roof can be built over it. At the end of the war a number of St. diamond automobile mountings with electric drive from a power trailer were under order for the 155-mm. gun. An enlarged G.P.F. of 104 more calibre was brought out and used towards the end of the war.

Fig. 31 shows the 155-mm. G.P.F. on Christie automobile mount- ing. This has 8 double-tired wheels with 36" x 6" tires. The two front wheels are fixed, the two rear wheels pivoted for steering. When working as a wheeled carriage, on the road, the two centre pairs of wheels are raised off the ground; when used as a caterpillar, with a " track " round the four wheels on each side, the centre wheels are let down so as to take their share of the load ; the vehicle is then steered by varying the relative speed of the two tracks. The engine (120 H.P., 6-cyl.) drives the front pair of wheels. The total weight with the gun is 17 tons, and the ground pressure 6-1 Ib. per sq. in. The length of the vehicle is 20 ft., or 17 ft. without the gun; the width is 9 ft. 4 in., the height 6 ft. 8 in., and it has 13-in. clearance under. The speed is up to 17 m. an hour on wheels, and up to 12 m.p.h. (or 14}, if breech first) as a caterpillar. Forty gallons of fuel are carried. This vehicle is top wide to pass the British railway load- inj gauge, but is within the limits allowed on the Continent. As it weighs only 17 tons with thegun.it is well adapted for road travelling.

The same gun on an ordinary caterpillar weighs altogether 27^ tons, and its road speed is 5 m. an hour.

A good example of the after-war 6-in. gun is the U.S.A. 1920 model, which is 45 cals. long, M.V. 2,800 f .s. with super-charge, and ^ranges 26,000 yd. with loo-lb. shell. It is stated that a range of '30,000 yd. can be obtained with false cap shell. The gun weighs 79 cwt., and the weight on wheeled carriage is 10-7 tons, so that this gun cannot be transported by horss draught. It can on emergency ba fired from its own wheels, with girdles of linked plates round them to increase the bearing surface, but for continuous fire it requires a platform, or it will probably be used principally on a railway mounting.

A long gun of these characteristics may be looked upon as ap- proaching a limit, both as regards travelling and as regards firing. At about the calibre of 17 cm. begins a class of long guns which re- quires a platform for firing and sub-division for travelling. Both platforms and sub-division may be and frequently are desirable at the 6-in. level, but beyond it there is no choice in the matter so far as wheeled mountings are concerned. At the level of war-time 17-cm. and post-war 15-cm. long guns commences also the class of all- round railway mountings to be described presently.

The provision of platforms formerly caused considerable delay in opening fire; a wooden platform is suitable only for field and medium guns and a concrete platform takes at least a month to set before it is ready to fire from. " Caisson " platforms consist of cellular boxes of iron plate which are sunk into the ground, bolted together on the spot, and filled with concrete or in some cases merely with earth.

Since the concrete is used chiefly to weight the platform, it is not necessary to wait till it has set hard. When the gun is moved to another position, the caisson platform is abandoned, with the ex- ception of the top plate carrying the fittings for the attachment of the gun-mount. During the course of the war these platforms were improved so as to afford support only where required, and so to require less excavation. For this purpose the caissons were made of special shapes, as afterwards described. They were known as " earth-boxes," and in some instances they were not even buried, but erected on the surface of the ground. In some cases the gun or howitzer remains on its travelling wheels for fire, in others it travels in parts and is assembled on the platform.

Tlie German //-cm. (7-in.) Gun. This was a 4O-cal. naval gun, throwing a i4O-lb. shell, M.V. 2,500 f.s., to a range of 30,000 yd. The gun weighed 10-8 tons. Some of these pieces were used on rail- way mountings, others were fitted for road transport. The gun was mounted, in its naval cradle, on a carriage of ordinary field construc- tion, with massive broad-tired steel wheels 6 ft. in diam. The plat- form from which it was fired consisted of five " caissons " or steel boxes, buried in the ground in the form of a cross. The fifth caisson, which bore the pivot, was in the centre of the cross and connected the four arms together. A horizontal framework with a pair of steel girders extended back from the pivot; the gun wheels rested on plates fixed to these girders on either side of the pivot, and the trail abutted against the cross-piece connecting the rear ends of the girders. The whole girder frame, with the gun and carriage, could be revolved about the pivot when it was required to traverse the gun through a large angle; for angles up to 5 each way the carriage could be traversed within the girder frame by shifting the trail along the cross-piece. The rate of fire was one round per minute. The equipment was easily transportable by road in 3 loads, namely, gun on special wagon, carriage, and platform.

This was a powerful long-range gun which could travel by road or rail and could come into action and open fire within 48 hours. The railway mounting for this gun was the same as the platform mounting, and the same horizontal girder frame was used, mounted on a railway truck instead of a caisson platform. The traverse obtainable was 26 degrees.

The French Schneider 22O-mm. (8-66-in.) gun, model 1917, was used in the war with a road-mobile mounting, and has since been mounted on a caterpillar automobile carriage. The gun is 35 cals. long and weighs 9 J tons ; it ranges to 24,500 yd. with a 2OO-lb. stream- line shell, M.V. 2, 580 f.s. It is fitted with double recoil, having both a cradle system (nitrogen recuperator) and an upper-carriage system which recoils against gravity and a buffer.

The road-mobile mounting was sub-divided into two loads, but could be moved as a unit for a short distance. In the firing position the gun, cradle, upper carriage and lower carriage rested on a plat- form (which was permanently fixed to the lower carriage). The platform was pegged down in rear and connected to an earth an- chorage in front. The lower carriage was pivoted to the platform ard could be traversed 25 each way. The weight in action was 25 tons exclusive of the anchorage, and the travelling loads were 16 tons for the carriage and platform unit and 14 for the gun unit.

FIG. 32. French 22O-mi

image.

The gun on caterpillar carriage is shown in fig. 32. The upper car- riage is supported on rollers with springs, and recoils on a slide, so that there is a double system of recoil gear. The upper carriage gives 37 elevation; traversing is effected by turning the whole mounting by means of the caterpillar tracks, which are worked by a lo-H.P. auxiliary motor.

The caterpillar carriage is 26 ft. long, or 35 ft. including the muzzle of the gun in travelling position; the width is 9 ft. and height 10 ft. The road speeds are from \ m. to 5 m. an hour; the low gear is very powerful, and the caterpillar will climb a slope of I in 2. The weight of the gun and carriage is 14 tons, caterpillar 26 tons, total 40 tons. This is too heavy for road bridges, but the weight and dimensions are such as just to admit of its being carried on a French 4O-ton railway .truck. The height and width are in excess of the limits of British railway loading gauge.