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684 FIG. 5. Gun-carrying Tank.

48 were made, delivery in France commencing in July 1917. They appear to have been employed as much' for the conveyance of ammunition and stores as for the purpose for which they were designed. In Dec. 1916, also, the design of the " Whippet," the Medium Mark A. tank, (see figs. 6 and 7) was commenced. Of this type 200 machines were produced, delivery in France starting at the end of 1917. It was evolved to be complementary to the heavy tanks and to meet the demand for a speedier, handier machine which could be produced in large numbers. Its main points were its increased speed, nominally 8 m. per

hour on the flat, and an average across-country of 5 m. per hour, and its lightness, one-half that of the Mark I. machine. It was also easier to transport by rail. Each track was driven independently by a four-cylinder 45 H.P. Tylor engine. Trans- mission was by cone clutches to gear boxes of the constant mesh type, giving four speeds forward and one reverse. The design was largely due to Sir W. Tritton. Thus, at the end of 1916, in addition to the first type of heavy tank in the field, measures were in hand to supply a much improved pattern of that ma- chine (Mark IV.) and also a lighter type the " Whippet."

FIG. 6. Medium Mark A. or " Whippet " Tank.