wheel and an outer broad-tired road wheel of larger diameter, name- ly, 42 in. When the vehicle was run on to the rails, the road wheels were taken off, and the power vehicle and the platform wagon then constituted a unit capable of travelling by rail under their own power. If it was desired to use a locomotive, the platform wagons could be coupled together to form a train, or could be embodied in an ordinary train. However, the power vehicle was not built stoutly enough to be coupled up as part of a train, and when a locomotive was used the power vehicle was carried on a truck.
To mount the howitzer a hole was dug for the caisson platform. The sections of the platform were dismounted from the wagons by screw-jacks and by winches worked from the power vehicle; they were bolted together in position, filled with earth or concrete, and the top plate, with roller ring and pivot, bolted down. A line of rails was then laid across the platform, and the wagon with the upper carriage was brought up on these rails. The ends of the wagon were jacked up, the bogies removed, and the upper carriage lowered through the bottom of the wagon on to its pivot. The howitzer was then lowered into its cradle in the same way.
The Austrian 42-cm. (l6-$-in.) Howitzer. This was designed as a coast-defence weapon in 1914, and must not be confused with the German weapons of the same calibre used in the Belgian sieges of 1914. In 1916 at least one of these Austrian pieces was equipped for transport by rail, and in 1917 a rpad-and-rail travelling equip- ment similar to that of the 15-in. howitzer was built for it.
The howitzer was 15 cals. long and weighed 25-9 tons with the breech mechanism. It was rifled with 84 grooves, uniform twist. It fired a shell weighing one ton, containing 198 Ib. of H.E. in a brass cartridge case. There were 5 charges of frm 64 to 120 Ib., and the extreme range with the 2O-cwt. shell, M.V. 1,380 f.s., was 14,100 yd. There was also a i6-cwt. shell ranging 16,200 yd. In 1918 the Austrians, who favoured heavy shrapnel, were designing a shrapnel for this howitzer, but it was never fired.
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FIG. 39. Austrian 42-cm. howitzer.
The mounting was of the same pattern as that of the 15-in. howit- zer, but heavier. The upper carnage weighed 22-6 tons; there were 2 hydraulic buffers and 2 compressed-air re9uperators, working at a pressure of 60 atmospheres. The howitzer could be fired only between 40 and 70 of elevation; thus the range was shortened by increasing the elevation. Fire at any elevation over 65 is unreliable, as the shell tends to come down base foremost or sideways.
The platform was built up of caissons, and measured 25 ft. by 21 ft. by 4 ft. 6 in. deep. It weighed 57 tons empty. The power vehicle and platform wagons were similar to those used with the 15-in., but the wagons weighed 185 tons, and the heaviest load was 44 tons gross. This equipment was certainly transported by rail, but whether it ever travelled by road is uncertain.
The Krupp 42-cm. (i6-$-in.) Howitzer. A heavy pattern of this piece existed as early as 1911; the light or road-mobile pattern was a surprise brought out by the Germans at the beginning of the war, and intended especially to overpower quickly the resistance of permanent forts in a minimum of time.
The heavy 42-cm. howitzer was transported by rail. It fired several kinds of shell; the heaviest weighed 1 8 cwt. and contained 200 Ib. of explosive; the lightest, which was fitted with a long false point, weighed only 8 cwt. and contained no Ib. of explosive. The extreme range was 15,500 yd. The weight of the howitzer was 25 tons; it was transported by rail, but was not fired from a railway mounting. A portable platform had to be laid for it, and it was mounted by means of a gantry. With carriage and platform, the equipment formed 7 truck-loads of about 25 tons.
The light or road-mobile 42-cm. howitzer weighed about 21 J tons. It was 12 cals. long, rifled with 120 grooves, uniform twist, and had the Krupp wedge breech action. It threw a shell of 15-7 cwt., con- taining 302 Ib. of explosive and ranging 10,300 yd. There was also an 8-cwt. shell as for the heavy 42-cm., which ranged 13,600 yd. This howitzer required 13 heavy steam traction engines to move it by road. The howitzer itself, on special wagon, was drawn by three traction engines, with a fourth in reserve for hills. The cradle formed a second load, and the empty carriage a third; the fourth and fifth loads were the platform, and the sixth was a wagon fitted with a heavy gyn and windlass for mounting the howitzer. This 42-cm.
howitzer was fired from its wheels, and was the heaviest wheeled equipment ever built. It could not be fired from the bare ground; it used a portable platform under the wheels and a trail abutment. It was fired only between 40 and 60 of elevation. The carriage had a ring cradle with hydro-pneumatic recoil gear, giving 6 ft. of recoil, which was mounted on central trunnions on the lower car- riage. The massive steel-disc wheels were provided with girdles. The platform was a steel casting in one piece, and extended under the wheels only. The trail abutment consisted of steel caissons or boxes, bolted together to form a curved caisson 7 ft. from front to rear, 10 ft. 6 in. wide, and 5 ft. deep. The caisson was shaped to form a step in front, which supported the point of the trail and formed an abutment behind it. This caisson was sunk into the ground behind the howitzer. A pinion on the point of the trail engaged with a rack on the abutment, and the piece was traversed by turning the pinion. The downward blow on firing was divided between the steel plat- form and the caisson under the trail. The caisson was made wide enough to allow about 60 of traverse.
The road-mobile 42-cm. howitzer fulfilled its strategic purpose well. The essence of the German plan of campaign was speed; they wanted a powerful siege howitzer which could be brought into action in the first few days of the war and which must therefore be inde- pendent of the railways in case these were found to be partly de- stroyed or otherwise unavailable. They therefore built a " super- heavy " short-range weapon just within the limits of weight for transportation by main roads, and capable of opening fire in a few hours without waiting for a permanent platform to be built.
It will be noted that the German 42-cm. howitzer is less powerful both as regards range and weight of shell than the Austrian 42-cm. already described, which piece also is claimed to be transportable by road, and it seems probable that the Austrian rather than the German pattern will be adopted in future construction.
Railway Mountings. These are of great importance where the country is covered with a close network of railways. Irrespective of the great loo-mile guns, ordinary heavy guns on mobile railway mountings range about 18 m., so that numerous positions are avail- able for them within range of any desired target. Taking London as an instance, a circle with i8-m. radius drawn from Charing Cross passes through Redhill, Weybridge, Watford, Hatfield, Epping, Dartford, and Oxted, and crosses no less than 29 railway lines.
Railway mountings are of two main types: the all-round mount- ing, with which the gun can fire in any direction from its truck; and the curved siding, or gun-spur mounting. With the latter the gun is layed for direction by running the gun-truck along the curve till it points in the direction of the target. A variant of the second type is that in which the gun can fire from the truck only in the di- rection of the rails, while for all-round fire it is lowered on to a specially laid platform, and becomes a non-mobile gun.
The present tendency is to develop the all-round railway mount- ing. This has the advantage that the gun can be fired from any point on the railway; it can follow up the troops during mobile warfare or it can shift from day to day during non-mobile warfare, opening fire from fresh places. The curved-siding mounting takes time to prepare, and then ties the gun down to one position, unless alterna- tive spurs are laid. It makes the fire slow, especially with mountings that run back along the track at every shot. Moreover, the curved siding and the track leading up to it are difficult to conceal. On this account the Germans, at the beginning of the war, used the perma- nent platform type, in spite of its immobility. They had no satis- factory all-round railway mountings, and, since they objected to the curved siding, they used to build a temporary line to a permanent gun-platform laid in a wood or other place suitable for concealment. Having mounted the gun, they took up the temporary line and removed all traces of it.
The main difficulty in designing a railway gun-mounting is to keep its height and width within the limits allowed by the railway loading gauge. The British loading gauge is 13 ft. I in. above rails in centre and 10 ft. II in. at sides; the width allowed is 8 ft. 6 in. on some lines and 9 ft. on others. The Continental loading gauge is approximately 14 ft. high and 10 ft. wide. Since the platform of the lowest commercial truck in use is 3 ft. 9 in. above the rails, this leaves little headroom available for a gun and mounting. There is practically no limit to the length permissible, as the girders constituting the mounting itself are carried on 2 or 4 bogies; nor to the weight, as railway bridges are quite strong enough to carry 15-in. gun-mountings. Neither is there any limit to the downward stress on the rails caused by firing, provided that it is taken by a sufficient number of wheels or a large enough bearing-area of plat- form. Some makers, however, require an extra set of rails laid, or even 2 extra sets (6 rails in all) for their heaviest mountings to fire from. These extra rails are especially necessary w-ith those mount- ings in which the gun does not recoil on its carriage but the whole truck slides back along the rails on firing and has to be run up again after every shot; the recoil is absorbed by friction along the rails.
Experience shows that the track resists the downward pressure due to firing so long as this is within 3 kgm. per sq. cm., or 42 Ib. per sq. in., on the ballast under the sleepers; that is, the resistance depends on the area of the sleepers. When the firing stress is locally high, owing to its being borne by some 12 baulks under the centre of the mounting instead of by 32 or more bogie wheels at the ends, the
