The infantry tank was different from either the "heavy tank" or "breakthrough tank" concepts, although some pre-war multi-turreted heavy machines such as the Soviet T-35 and the German "Neubaufahrzeug" (both taking some of their inspiration from the 1926 Vickers A1E1 Independent – an idea which was abandoned by the War Office in the late 1920s for lack of funding), which were similar, and with similar doctrines for their use. The "Neubaufahrzeug" was considered too slow for Blitzkrieg tactics and fell from favour. German, and to some extent Soviet, wartime doctrine shifted towards faster medium and heavy tanks fighting large multi-tank battles, with the role of the infantry tank in the assault taken by simpler "Sturmgeschütz" self-propelled gun.