The training of the tank units was based on infantry drill, which is the best means of instilling discipline. This was supplemented, however, by instruction in the use of machine-guns and tank cannon and in the operation and maintenance of gas-engines, the men finally being brought to a point where they were ready to take up technical and tactical tank training at the British and French tank-training centres, to which they were sent as soon as there was accommodation for them. Thousands of men, trained to the limit of the facilities in this country, were held at Gettysburg from April and May until August and September because of the shortage of tanks and the lack of training facilities in France. Not until September, in fact, did any tanks become available for training purposes in the United States, when there arrived five British heavy tanks and several light tanks of American manufacture, thus permitting training to be resumed on a larger scale. When the Armistice was signed, the Tank Corps had a total of 20,212 officers and men, of whom 8,183 were serving in Europe. Shortly before the collapse of Germany preparations had been begun for the great Allied drive planned for the spring of 1919, steps being taken to increase the corps to a point where it could supply tank units for four field armies. The proposed strength for this purpose was 57,940 officers and men, it being planned to have this entire force fully organized, trained, equipped, and in France by the early spring of 1919. The programme of tank construction for the American Army was initiated in February, 1918, but, owing to the extensive arrangements which had to be made with numerous manufacturers for the enormous number of parts required, and to the fact that there existed in the United States little or no accurate data regarding tank construction, the first light tank was not delivered to the Tank Corps in the United States until the following September. Owing to the more complicated mechanism of the heavy tanks, none of them was completed before the signing of the Armistice. The machines used by the American Tank Corps units engaged on the Western Front were supplied by the French and British, no American-built tanks being employed in active fighting during the war. [Illustration: THE AMERICAN WHIPPET TANK.] [Illustration: THE MARK V TANK.] [Illustration: A SQUADRON OF WHIPPET TANKS ADVANCING IN BATTLE FORMATION. _Photograph by Signal Corps, U. S. A._] [Illustration: A SQUADRON OF WHIPPET TANKS PARKED AND CAMOUFLAGED TO CONCEAL THEM FROM ENEMY OBSERVATION. _Photograph by Signal Corps, U. S. A._]