become the standard for most succeeding tanks across the world even to this day. The FT was the most numerous tank of the war; over 3,000 were made by late 1918. Germany Germany fielded very few tanks during World War I, and started development only after encountering British tanks on the Somme. The A7V, the only type made, was introduced in March 1918 with just 20 being produced during the war. The first tank versus tank action took place on 24 April 1918 at the Second Battle of Villers-Bretonneux, France, when three British Mark IVs met three German A7Vs. Captured British Mk IVs formed the bulk of Germany's tank forces during World War I; about 35 were in service at any one time. Plans to expand the tank programme were under way when the War ended. Other nations The United States Tank Corps used tanks supplied by France and Great Britain during World War I. Production of American-built tanks had just begun when the War came to an end. Italy also manufactured two Fiat 2000s towards the end of the war, too late to see service. Russia independently built and trialed two prototypes early in the War; the tracked, two-man Vezdekhod and the huge Lebedenko, but neither went into production. A tracked self-propelled gun was also designed but not produced. Although tank tactics developed rapidly during the war, piecemeal deployments, mechanical problems, and poor mobility limited the military significance of the tank in World War I, and the tank did not fulfil its promise of rendering trench warfare obsolete. Nonetheless, it was clear to military thinkers on both sides that tanks in some way could have a significant role in future conflicts. Interwar period In the interwar period tanks underwent further mechanical development. In terms of tactics, J.F.C. Fuller's doctrine of spearhead attacks with massed tank formations was the basis for work by Heinz Guderian in Germany, Percy Hobart in Britain, Adna R. Chaffee, Jr., in the US, Charles de Gaulle in France, and Mikhail Tukhachevsky in the USSR. Liddell Hart held a more moderate view that all arms – cavalry, infantry and artillery – should be mechanized and work together. The British formed the all-arms Experimental Mechanized Force to test the use of tanks with supporting forces. In the Second World War only Germany would initially put the theory into practice on a large scale, and it was their