with a high velocity, so as to get through the layer of dense air as quickly as possible. In this case the velocity was about 5,000 f.s., or a mile a second.
The gun was made by boring out a ijj-in. naval gun, 56 f.t. long. An inner tube 98-3 ft. long was inserted into the gun, so that 42-3 ft. of it projected from the muzzle, and this projecting portion was covered by a " hoop " or outer layer of steel locked to the muzzle of the original gun. Further, a smooth-bore section of tube, 19-7 ft. long, was attached to the muzzle. This was put on with a screw collar, like the muzzle of the British mountain gun, and was removed for transport. The inner tube was of 21 cm. (8-27 in.) cal., and was thick enough to be bored out to 24 cm. (9-45 in.) and again to 26 cm. (10-24 in.) as it became worn. It was rifled with 64 grooves, uniform twist. The powder-pressure was 19-64 tons per sq. in., which is rather higher than that allowed in ordinary heavy guns. The original breech mechanism was retained. The total weight was 142 tons.
The shell used with the gun, at its original 2i-cm. cal., weighed 264 Ib. It had to be light to obtain the high velocity required.
The object of the smooth-bore section at the muzzle is not very clear; this feature is not embodied in the guns of this type built or designed by other nations. The object of lengthening the muzzle was to increase the range; the object of making the muzzle section de- tachable was to facilitate the transport; and the object of making this section smooth-bored instead of rifled may have been either to reduce friction or to steady the shell after leaving the rifled portion. Being smooth it would naturally wear less than if rifled and would maintain the accuracy of the gun longer.
The recoil mechanism of 2 hydraulic cylinders and one spring pneumatic recuperator cylinder was attached to the bottom of the cradle. To the top of the cradle was attached a counterweight, the 2 sections of which were raised and locked together for the purpose of raising the centre of gravity to such an extent that the gun might be elevated and depressed more easily. The cradle was on central trunnions, so that the gun was balanced without forward preponder- ance. A pit in the ground about 18 ft. deep gave room for recoil.
The elevating mechanism was extremely heavy and unique in design as screw mechanism was not used. Straight racks moved in ways parallel to the inclined lower face of the forward end of the side girders of the mounting; at the lower end they were connected with each other by a heavy shaft to which were attached 2 connecting rods running up to the bottom of the cradle. A 2-speed transmission was provided permitting operation at high or low speed.
The railway carriage body was made up of 2 single web-girders j connected at front and rear by heavy structural steel transoms, and ' reenforced in front by a heavy cast-steel housing for the elevating gear. Owing to the great weight of the 75-mile gun compared to that of its shell the recoil energy was very low, and was considerably less than that of the 15-in. gun.
The dimensions of the gun (without muzzle section) and of the truck were not such as to present any special difficulty in movement by rail. The arrangement for bolting the carriage to the emplace- ment was in 2 main sections, one a base and the other a rotating section. Each section was built up of steel girders and plates. The rotating section was supported on steel balls. At right angles to the direction of the track of the rotating section were 2 girders on the ends of which were key-plates.
The mounting was run on to the emplacement with the rotating section in position and then raised by 4 jacks.
When raised, the bogie-trucks were removed and the rotating section of the emplacement turned through 90 degrees. On lowering the mounting, key-plates fixed under the carriage were fastened to corresponding key-plates on the emplacement. A circular traversing rack of angle and steel pins was bolted to the structural base.
The supposed position of the 75-mile gun was bombarded by the Allies, but it was never hit nor even exactly located.
The guns wore out quickly, owing to the large powder charge employed, and the accuracy soon fell off. The first 21 rounds fired at Paris on March 23 1918 showed that the 50% length zone was about 2 m. and the 50% breadth zone about I m. The fall of the 21 shells fired next day showed an increasing dispersion, and the 6 shells fired on the following day were still more erratic. The gun then stopped firing, and, as was afterwards ascertained, was found to be worn out, and was sent home to be re-bored. Four days later a second gun had been mounted, and the bombardment began again, with similar results as regards accuracy. Altogether the Germans used 7 of these guns, and by Aug. 9, when the Allied advance obliged the Germans to withdraw, all 7 had been re-bored to 24 cm. After the Armistice it was learned that these guns were at Krupps, being re-bored a second time to 26 cm. The 3 guns building at Skoda for the Germans were never finished.
At the end of the war, the British, French and Italian Govern- ments were each building at least one gun of this type. Few details of them have been published. The Italian gun is of 7-87 in. calibre, 65-6 ft. long. It fires a shell of 231 Ib. with M.V. 4,920 f.s., and ranges 87 m. The greatest height of the trajectory is 25 m. It is stated that the British and French guns are of rather larger calibre, and range further. Both are said to be 104 ft. long, and to be rifled throughout, with no smooth-bore section at the muzzle.
The loo-mile gun is relatively an inaccurate weapon, owing to the variable atmospheric conditions which the shell may encounter during its flight, which was about 3 min. for the German gun. Improvement in this respect is not probable unless it be possible to obtain meteorological reports from high-flying aeroplanes at both ends of the trajectory, or unless a gun of far greater power, firing a shell of at least half a ton, be used. Such a degree of inaccuracy renders the loo-mile gun, as used in the war, nearly useless at any target smaller than a city, and a few shells distributed over such a large area can do little material damage, and can only serve the purpose of annoy- ing or intimidating the civilian population.
American Railway Mountings. The United States had 144 heavy guns on railway mountings in France, including five 14-in. guns. The latter were on sliding mountings of the French type but had central trunnions and no balance springs, and consequently could not be elevated beyond 15 degrees. The U.S. l6-in. howitzer was on a rolling mounting which allowed 5 of traverse each way, but it could not be fired with full traverse at elevations under 40 degrees. Since the war, the United States has been considering the question of substituting mobile railway guns for fixed guns in its coast defences. Such guns require a large arc of fire, usually 180, and a high rate of fire, namely, at least one round a minute; consequently curved-siding mountings would not answer the purpose. It is therefore desired to develop the all-round-fire type of mounting so as to take as heavy a gun as possible, and to open fire as quickly as possible. Guns which are too violent for an all-round truck mounting, such as the 12-in. and over, will have to be let down on to a platform to fire. As it would be difficult to provide permanent platforms in every place where they might be required along the seaboard of the United States, the endeavour is to design temporary platforms which can be laid when required with the least possible delay.
The U.S.A. 12-in. Howitzer on Railway Mounting. This howitzer is 20 cals. long and ranges 22,000 yd. with 7OO-lb. shell. It is on an all-round-fire mounting with 8 outriggers. Instead of being lowered on to the sleepers as in the Armstrong pattern, it is jacked up high enough to insert 6 wooden baulks between the main girder and the rails which are doubled by I-beams, and then let down on to them. The howitzer recoils in a cradle and traverses 360 on a roller ring. This mounting can be used for howitzers up to 12-in. and guns up to the 8-in. inclusive, but not larger, as the size of the roller ring is limited by the loading gauge.
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FIG. 46. U.S. 14-in. g
travelling
position.
The U.S.A. 14-in. Gun on Railway and Platform Mounting. This gun ranges 22 m. at 50 elevation with i,56o-lb. armour-piercing shell, or 292 m. with streamline shell. It is mounted in a cradle with the usual hydro-pneumatic recoil gear; the cradle is on central trunnions so as to balance the gun, and the breech projects so far to the rear that the gun cannot be elevated beyond 15 when fired from the railway. The main girder and bogie trucks are of the ordinary type, allowing a traverse of 2 each way.
This gun is fired from a curved siding, and the mounting then slides back at each shot and has to be hauled forward again. When either the full range or a large arc of fire is required, the main girder, with the gun, is let down on to a platform. This is of simple design, and consists merely of a circular platform plate laid on the ground and held in position by about 60 steel stakes 18 in. long which are driven round it. The platform plate weighs 34 tons ; it is in 2 pieces, bolted together on the spot, and it constitutes the pivot plate and roller ring. The steel stakes take the horizontal thrust of the recoil. The centre of the main girder of the railway mounting rests on the roller ring; the rear end is supported by screw jacks embodied in it, which rest upon circular steel castings laid on the ground. These have to be shifted when the mounting is traversed. It is stated that on sound level ground this platform can be laid in 8 hours, and the gun can be lowered on to it in one hour.
The ig2O-pattern mounting for the 14-in. gun is an improvement on the model just described. It has a top carriage pivoted on the main girder, giving 3| of traverse each way. To prepare the gun for firing, the mounting is jacked up and lowered on to cross baulks as in the 12-in. howitzer mounting. Outriggers are provided in rear to take the horizontal thrust and the mounting is not allowed to slide back on the rails. The steel platform for all-round fire differs from the earlier pattern in that it has a roller path upon which the rollers
