Popular Science Monthly 



715 



How the caterpillar crosses a trench. It noses its way down and up, following the contour of 

 the ground. It is steered by the rear wheels or by making one caterpillar go faster than the other 



imaginary wheel of the same diameter. 

 Only that portion of the assumed wheel 

 in contact with the ground acts as the 

 lever and it is this portion that is repro- 

 duced in the front end of a caterpillar belt. 



Why Don't the Tanks Stick in the Mud? 



This large area of the belts in contact 

 with the ground, as shown in the accom- 

 panying sketches, also brings out the in- 

 herent property of the caterpillar which 

 has made it possible for the tanks to 

 traverse soft, muddy ground — the large 

 bearing area of the caterpillar shoes. With 

 the caterpillars thirt%^ inches wide and with 

 about fifteen or twenty feet of length in 

 contact with the earth at any time, the 

 pressure on the ground is said to be less 

 than three pounds to the square inch. 

 This is a great deal less than that exerted 

 by a horse or a two-hundred-pound man. 

 This large supporting area explains why 

 the tanks do not sink down and become 

 mired in places where an ordinary wheeled 

 armored motor car would be hopelessly 

 buried down to the hubs. 



The tanks are of various sizes and designs, 

 each later model being an improvement 

 over its predecessors. The first ones had a 

 maximum speed of from six to eight miles 

 an hour. This was too slow, and the 

 Germans soon found a way to destroy 

 them. Before a tank could get back to 

 shelter after a raid, the German observers 

 were able to wireless its position to their 

 artillery which promptly dropped shells on 

 on it. The latest tanks are lighter than their 

 predecessors, have gasoline engines of over 

 five-hundred horsepower and travel at the 

 remarkable speed of eighteen miles an hour! 



Although varying in size and details. 



all tanks have the common characteristic 

 of being divided into three main compart- 

 ments between the two side caterpillar 

 frames. The first is the observation com- 

 partment in which the driver and his 

 helper are perched high above the ground 

 to direct the movements of the huge steel 

 beast. In the middle is the ammunition 

 room from which the guns carried in the 

 two side turrets are fed. At the rear is the 

 engine room. From two to four gasoline 

 engines are used, these driving the rear 

 axle and its integral sprockets over which 

 the caterpillars run. The latter run over 

 an idler pulley or sprockets at the extreme 

 front ends and are supported by means of 

 rollers attached to the upper portion of 

 the frame on each side when passing over 

 the top. This movement of the caterpillar 

 belts is exactly analogous to that of the 

 ordinary- variety of garden insect with the 

 same name which similarly lays down his 

 own track by humping his back continu-. 

 ously and regardless of the land surface. 



How the Tanks Are Guided 



The tanks are steered by a pair of small 

 ordinar>' wheels at the rear. These are 

 supported in a piv^ot on a frame extended 

 from the rear. They are merely for steering, 

 and support none of the weight of the tank 

 except when bridging wide trenches or 

 dips in the surface. Steering can also be 

 accomplished by making one caterpillar 

 go faster than the other by manipulating 

 clutches on the driving mechanism. 



The tanks have been developed entirely 

 by the British Admiralty, the idea of using 

 the large round end of the caterpillar being 

 credited to E. H. Tennyson D' Eyncourt, 

 Director of Naval Construction. 



