We see them in our mind's eye spitting fire as they crossed No Man's Land, amid the smoke and dust of bursting shells. Keeping steadily on their courses they dived into huge craters made by exploding shells; stretched themselves across trenches, brushed trees and boulders aside, and kept steadily on their courses. German wire entanglements were as so many pieces of string before their huge frames. Nothing deterred them. They moved forward into the face of the enemy, reaching the first line of German trenches. There the soulless devices sat complacently astride the trenches, and turning their guns along the ditches swept them in both directions. THE TANK DEFIES ALL OBSTACLES. The tanks which were introduced by the English, move along on revolving platforms, so to speak. These platforms enable the tank to overcome all obstacles as the caterpillar tread is curved up in the arc of a huge circle at the front which gives the vehicle its wonderful tractive powers. This large curvature acts as a huge wheel with a tremendously long leverage equal to the radius of the circlet or the spokes of the imaginary wheel of the same diameter. Only that portion of the assumed wheel which would come in contact with the ground acts as the lever, and it is just this portion that is reproduced in the front end of a caterpillar belt. Although varying in size and details, all tanks have the common characteristic of being divided into three main compartments between the two side caterpillar frames. The first is the observation compartment 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 or four gasoline engines are used--these driving the rear axle and its integral sprockets over which the caterpillars run. The latter run 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 continuously and regardless of the land surface. The tanks are steered by a pair of small ordinary wheels at the rear. These are supported in a pivot 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 be accomplished by making one caterpillar go faster than the other by manipulating clutches on the driving mechanism. TANK'S "CATERPILLAR" FEATURE.