The original model of 1915 was altered in 1917 to take a bare charge, owing to shortage of brass for cartridge cases; this involved the use of an obturating breech mechanism and added 55 Ib. to the weight. The ballistics remained as before.
The 155-mm. howitzer is transported on its own wheels with a limber fitted for horse draught, or may be limbered up to a tractor. It travels in the extreme recoil position to distribute the weight. The weight in action of the 1917 pattern is 3-3 tons, and the weight with limber 3-7 tons, so that it is sufficiently mobile to accompany troops. It can if desired be divided into two units weighing 2-5 tons for the howitzer and 2-6 tons for the empty carriage. It was used by both the French and the Americans as part of the divisional artillery.
The U.S.A. 155-mm. (6-l-in.) howitzer, 1920 model, is 24} cals. long, and fires a 95-lb. shell, M.V. 1,850 f.s., ranging 16,000 yd. The carriage has a plain trail, and gives 65 elevation and 10 traverse on the axle. It has hydro-pneumatic controlled recoil gear. A split- trail carriage giving 60 traverse is also being tried. This piece is an example of the changes made in howitzer equipments since 1914. The 6-in. howitzer of that date was some 12 cals. long, M.V. 950 f.s. ; the modern howitzer is twice as long and has double the muzzle velocity and double the range, and would formerly have been classed as a gun.
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FIG. 28. German 15-cm. howitzer, long pattern, 1913.
The German 15-cm. (5'9-in.) howitzer, 1902 pattern, was a light horse-drawn weapon weighing only 44 cwt. in action. It fired a 95-lb. shell and ranged 7,000 yd. It was II cals. long, of ordinary Krupp pattern with variable recoil, and the carriage gave elevation up to 65 in order to obtain a steep angle of descent at short ranges.
formerly by a pair of compression springs set forward of the cradle trunnions. The action of these is not very satisfactory, as if the thrust of the spring is sufficient to support the gun at a high elevation, when the spring is fully extended, then it is excessive at a low eleva- tion. Telescopic springs were used in the Krupp mountings to give a more uniform thrust. But these balance springs are now being superseded by compressed-air " equilibrators." This device, in principle, was used in the French Rimailho howitzer; in its present form it was first brought out in the British Armstrong railway mountings, and has since been adopted for caterpillar mountings. It consists of two steel tubes fitting one into the other, the outside ends of the tubes being closed. The telescopic vessel thus formed is filled with compressed air, which tends to force the tubes apart. It is prevented from escaping by a double packing, with a recess beween the two packings which is filled with grease, constituting a " grease seal." The compressed air gives a more regular thrust than a spring, and can be connected to the cradle with suitable leverage so as to balance the gun at every elevation. The gun can then be elevated and depressed by the handwheel with comparatively slight effort. When the compressed-air equilibrator is used in the heavy railway mountings described later, the construction is slightly different ; the telescopic vessel is filled with oil or glycerine instead of air, and is connected by a tube to a reservoir of compressed air so that the air has no access to the packings. The reservoir is of such a size relatively to the cubic contents of the equilibrator as to give the desired variation of thrust at different elevations. This gear is known as the " hydro-pneumatic balance spring."
The 1913 pattern gave somewhat better ballistics; this had rear trunnions and balance spring, and was locals, long; it had an air recuperator. This was superseded by an improved pattern, 17 cals. long, giving M.V. of 1,270 f.s. and a range of 9, yd. with 95-lb. shell. This howitzer fired without a platform, using mats under the wheels in soft ground. It weighed about 61 cwt. in action, and was easily transportable. Though inferior in power to the French 155- mm., it was an excellent weapon, and was the principal piece em- ployed by the Germans in trench warfare, besides being mobile.
Heavy Guns and Howitzers. The 6-in. Gun. The authorities of all the military nations concur in considering this gun as one of the most important types used in land as well as in naval warfare. The
FIG. 29. British 6-in. gun, Mark XIX., 1916.
pattern developed in the latter part of the war throws a shell of ipo Ib., containing 12 Ib. of H.E., a distance of 15 m. The shell, while not too heavy for transport or handling, is powerful enough to do great damage to buildings, bridges, and similar targets, and it is practically impossible to build cover proof against it without re- course to armour plates or masses of concrete.
At the beginning of the war the British had no 6-in. mobile guns. The Mark VII. 6-in. was taken from coast defence and mounted on a simple carriage with traction-engine wheels. On firing, the carriage ran back up inclined planes, and ran forward again into position. This gun ranged only 17,700 yd. In 1916 a later pattern, Mark XIX., was mounted on the 8-in. howitzer carriage, with cradle and buffer (fig. 29), which much increased its rate of fire. The 6-in. Mark XI. naval gun, a much more powerful weapon, was on a railway mount similar to those described below.
The Germans, in addition to old-model siege guns, had a 15-cm. naval gun, 40 cals. long, mounted with its naval ring cradle and short-recoil buffers on a heavy-wheeled carriage. This was re- placed towards the end of the war by the 1916 pattern, 43 cals.
FIG. 30. French 155-mm. G.P.F., 1916.
long, which had a maximum elevation of 42andrangeof 25,000 yd. There were two patterns; in the lighter the weight of the gun unit in travelling was 6j tons, that of the carriage unit 5} tons. In action the gun and carriage weighed gj to 10 tons according to mark. Beds were provided for soft ground.
The French, after using up the 6-in. de Bange guns of their fortresses on various mountings, old and new, and bringing in naval and other guns of 14, 14-5, 15-5 and 16 cm., adopted as standard the design of Colonel Filloux known as the 155-mm. (6-l-in.) G.P.F. (grande puissance Filloux). This gun, which was also used by the
