produced during the entire conflict, compared to over 4,400 French and over 2,500 British tanks of various kinds. Nonetheless, World War I saw the first tank-versus-tank battle, during the Second Battle of Villers-Bretonneux in April 1918, when a group of three German A7V tanks engaged a group of three British Mark IV tanks which they met accidentally. After the final German spring offensives of 21 March to 18 July 1918, the Entente deployed tanks en masse at the Battle of Soissons (18 to 22 July 1918) and Battle of Amiens (August 1918), which ended the stalemate imposed by trench warfare on the Western Front, and thus effectively ended the war. Tactically, deployment plans for armour during the war typically placed a strong emphasis on direct support for infantry. The tank's main tasks were seen as crushing barbed-wire and destroying machine-gun nests, facilitating the advance of foot soldiers. Theoretical debate largely focused on the question of whether to use a "swarm" of light tanks for this, or a limited number of potent heavy vehicles. Though in the Battle of Cambrai a large concentration of British heavy tanks effected a breakthrough, it was not exploited by armour. The manoeuvrability of the tank should at least in theory regain armies the ability to flank enemy lines. In practice, tank warfare during most of World War I was hampered by the technical immaturity of the new weapon system, limiting speed, operational range, and reliability, and a lack of effective armoured tactics. Strategic use of tanks developed only slowly during and immediately after World War I, partly due to these technical limits but also due to the prestige role traditionally accorded to horse-mounted cavalry. An exception, on paper, was the Plan 1919 of the British Army's Colonel J. F. C. Fuller, who envisaged using the expected vast increase in armour production during 1919 to execute deep strategic penetrations by mechanised forces consisting of tanks and infantry carried by trucks, supported by aeroplanes, to paralyse the enemy command-structure. Following the First World War, the technical and doctrinal aspects of armoured warfare became more sophisticated and diverged into multiple schools of doctrinal thought. Interwar period 1920s During the 1920s, a very limited number of tanks were produced. There were however, important theoretical and technical developments. Various British and French commanders who had contributed to the origin of the tank, such as Jean Baptiste Eugène Estienne, B. H.