1,700 f.s.,and ranges over 10,000 yd., while the weight in action is only 19! cwt.
The Russian field gun was considered by many artillerists to be an injudicious combination of ballistic elements, as its i4-J-lb. shrapnel was too light for its very high M.V. of 1,930 f.s. However, it was a fairly efficient shrapnel gun and did well in the first cam- paigns of the war, till trouble in the Russian factories and the de- struction of Putiloff arsenal by fire reduced the output of ammunition and entirely stopped that of shrapnel and time fuzes.
The American Post-war Field Gun. The United States' pre-war field gun was an early pattern of quick-firer by Ehrhardt of Diisseldorf. In 1916 a split-trail equipment was designed, but the American
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FIG. 12. American field gun, 1920.
artillery used the French 75-mm.gun during the war. An American 75-mm. equipment is under trial (1921), the specification for which was originally as follows: Range 15,000 yd. with 15-lb. H.E. shell; split-trail carriage to give 30 traverse and 80 elevation; M.V. 2, 1 75 f.s. ; variable controlled recoil ; smokeless and flashless powder ; weight in action, not more than 32 cwt. The gun has been made and approved; it gives ballistics slightly in excess of those required. The carriage was made, but was found rather too heavy. The split-trail carriage had been intended for a " universal " field carriage to take either the field gun or the field howitzer, and to give 80 of elevation with the latter; this made it heavier than it need have been to take the gun only. A box trail carriage was therefore brought out; this gives only 10 traverse and 45 elevation, but is well within the limits of weight.
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FIG. 13. Holt caterpillar automobile carriage, mounting iO5-mm. howitzer, 1920.
The gun on box trail carriage is shown in fig. 12. It is known as the 75-mm. gun, model 1920. The_ gun is said to weigh only 7-37 cwt., which is remarkably light for its power. It is 42 cals. long, has a horizontal sliding-blork breech action, and has constant recoil (42 in.). It fires a 15-lb. H.E. shell ranging 15,100 yd. with super-charge, which gives a M.V. of 2,175 f-s- With the ordinary charge the M.V. is 1,500 f.s., this low velocity being purposely adopted to save the wear of the gun. The shrapnel is heavier than the H.E. shell, weighing 17 lb., and should be a very efficient projectile with the super-charge, with which its M.V. is about 2,040 f.s. With the or- dinary charge the velocity would probably be too low and the tra- jectory too curved for good bullet-effect. Both the shrapnel and the H.E. shell have a forward centring band. The shrapnel has a clockwork fuze made by the Waltham Watch Co., and the H.E. shell is of the thick-walled class with base percussion fuze.
The cradle trunnions are set far back, giving a forward prepon- derance which is supported by a balance-spring called in America an " equilibrator." This feature is met with in almost all carriages giving high angles of elevation. The carriage traverses on the axle 5 each way. The wheels are only 4 ft. in diam., as against 4 ft. 8 in. in the pre-war equipment; this reduction is necessary to keep the carriage steady in firing without the use of a very long and heavy trail. Solid-rubber tires 35 in. in diam. are fitted, to enable the gun to be drawn at a fast pace behind a motor without injury.
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FIG. 14. Christie automobile carriage.
The main shield of the American field gun is fixed to the trail and traverses with the gun; there is a folding top-shield and a hanging shield under the trail. The gun has the independent line of sight and is sighted with the panorama sight. The Americans graduate their sights in " mils," a mil being the angle subtended by i/iooo of the range, which is about 3-6 minutes. This method, first introduced by the Swiss, afterwards adopted by the French, and now employed by the artillery of almost all nations, is a great improvement on the cumbrous system of degrees and minutes.
During the war an improvised automobile carriage for field guns was made by mounting the gun on a 5-ton Holt caterpillar tractor. This mounting allows of 45 elevation and 28 traverse; it weighs 6 tons complete. The power is the same as that of the 2^-ton tractor, and the highest road speed is 9 m. an hour.
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FIG. 15. German 77-mm. field gun, 1896.
This was followed by the 1921 Holt caterpillar automobile carriage for field gun and field howitzer shown in fig. 13. It is capable of 30 m. an hour on the road an unprecedented speed for a caterpillar as these machines, as hitherto built, are subject to violent vibration and consequent damage when ran at speeds beyond a walking pace. In this case the entire mounting is spring-supported, the drums carrying the caterpillar tracks are rubber-cored and rubber-covered, and rubber is used on the track shoes, track rollers, front idlers, and drive sprockets. The tracks are as light as possible, even the connecting-pins being hollow. The main frame is supported on coil-springs in rear and a plate-spring in front; the latter acts as an equalizer between the two front track drums, so that one track can rise 15 in. higher than the other. Removable shields are carried.
The field gun lies along the top of the carriage when travelling. For firing it is elevated on the cradle trunnions, which are set well to the rear, the resulting forward preponderance being balanced by springs. It is probable that the new pneumatic balance springs will be used, as described below for the 6-in. carriage. Owing to the position of the trunnions, the gun recoils down the rear of the mount-
