After a series of conferences between American, French, and British tank officers, it was decided that two types of tanks should be manufactured in the United States: a heavy model (Mark VIII) and a light machine (Mark I) known as a “whippet.” The heavy tank, which weighs thirty-five tons and carries a crew of one officer and nine men, is armed with two six-pounder rapid-fire guns and six Browning machine-guns, and is capable of a speed of from four and one-half to six miles an hour over ordinary ground. The whippet, named after a breed of small dog used in England for racing, was an adaption of the French Renault tank. It weighs six tons and carries a crew of two men—a driver and a gunner—and over ordinary ground can move at a speed of from seven to eight miles an hour. These, then, were the two types of tanks originally decided upon, but, as will be seen, the programme was considerably altered. When it was decided that the United States should embark on a programme of tank construction, the Ordnance Department had only the haziest instructions to guide it. Owing to the mystery in which the French and British enshrouded the details of their tank construction, all that our Ordnance officers knew about a tank was that it should be able to cross trenches at least six feet wide, that it should be protected with armor-plate approximately five-eighths of an inch thick, and that it should carry one heavy gun and two or three machine-guns. Two experimental machines were laid down and work started on them at once, these models being intended to develop the possibilities of the gas, electric, and steam systems of propulsion as well as to ascertain the relative advantages of very large wheels and a specially articulated form of caterpillar tread.