ARMORED TRACTORS. As the re sult of experiments conducted in November 1915, at Fort Sill, under the direction of the Field Artillery Board, with caterpillar tractors as motive power for field artillery, and other experiments conducted both at Fort Sill and the Rock Island Arsenal with motor trucks as transports for the same arm of the service, the United States Army has its newest Field Ar tillery regiment moved by motor power com pletely. Thus it would appear that the United States was in the lead in establishing practical applications to military use of American com mercial engines; and that when the editor of the Field Artillery Journal wrote the caption beneath a photograph of a tractor ((Artillery Horse of the Future" he was nearer to the truth than such glimpses into the future usu ally are.
The American built caterpillar tractors, heavily armored, made their appearance from behind the British lines in the battle of the Somme and were revealed as armored motor cars capable of advancing over the rough ter rain resulting from the terrific bombardment by high-powered explosive shells. The car or tractor resembles an enormous armadillo. The crew is protected by varying numbers of arm ored plates, any one of which is impervious to machine gun or rifle fire as well as shrapnel bullets. It is asserted that only a direct hit from a gun of large caliber could put one of these monsters out of action. The car com pletes the work of the artillery bombardment on the enemy trenches before the infantry ad vances. Its chief work on the Somme front was to locate the German machine gunners and blow them out of their positions so that they could not mow down the advancing infantry. This done, the infantry could occupy the aban doned enemy positions with comparative ease.
The completed car, as employed by the Brit ish, is made simply by enlarging the platform on the tractor so that it extends over most of the machinery and furnishes room for machine guns and their crews and by covering the whole with a tortoise shell of steel armor.
The machine has a fore wheel which is used only for guiding purposes. No weight rests on this wheel and it could be removed altogether without causing the frame of the tractor to dip more than a few inches. The weight is
carried on the two caterpillars. These consist of two belts with corrugated surfaces, on the inside of each of which are two lines of steel rails, jointed in short sections and operated by sprocket wheels. As the endless belt turns with the progression of the machine the for ward sprocket wheel lays down the track and the rear one picks it up again.
Each of the caterpillars is under independent control and by starting one while the other is motionless the entire machine can be turned in its own length — a characteristic which would account for some of the strange manoeu vres which led observers to describe the ((tanks') as wallowing about, seating houses and pawing the debris under their belliess and so on.
The pressure on the ground under the cater pillar — the string of steel plates seven feet long and two feet wide on which the entire weight of the machine is supported—is less than that caused by the foot of a horse or even of a man. And owing to the construction and location of the engines, the centre of gravity of the whole machine is near the back of the caterpillar and not more than 18 inches off the ground. For this reason the machine can roll along without danger of tipping over on an almost incredible slope and it can run consid erably more than half its length forward over a chasm without any support at all.
When it moves across a trench the front wheel, on which normally no weight rests, crosses first. The forward end of the cater pillar would then move forward over the open part of the trench and the machine be sup ported by the rear of the caterpillar, where most of the weight was concentrated, on one side with the guide wheel forward to act as a steadier in front. Then by the time the rear part of the caterpillar had reached the edge of the trench the forward part would already be across and there would be very little displace ment of the machine. In this way the machine could cross a trench almost as wide as the ground length of the caterpillar.