designed for the 6-pounder. The Churchill Marks III and IV, Valentine Mark IX and Crusader Mark III all began to enter service during 1942. The Valentine and Crusader both needed to lose a crew member from the turret. Tanks designed to take the 6-pounder were the troubled Cavalier, the Cromwell and the Centaur. When the Cromwell went into combat in 1944, it was armed with the Ordnance QF 75 mm gun, which was a redesign of the 6-pounder to take US 75 mm ammunition and more useful against general targets. The 6-pounder was also fitted to the AEC Armoured Car Mark II. Although the 6-pounder was kept at least somewhat competitive through the war, the Army started the development of a more powerful weapon in 1942. The aim was to produce a gun with the same general dimensions and weight as the 6-pounder but with improved performance. The first attempt was an 8-pounder of 59 calibre length but this version proved too heavy to be used in the same role as the 6-pounder. A second attempt was made with a shorter 48 calibre barrel but this proved to have only marginally better performance than the 6-pounder and the program was cancelled in January 1943. The 6-pounder was followed into production by the next generation British anti-tank gun, the Ordnance QF 17-pounder, which came into use from February 1943. As a smaller and more manoeuvrable gun, the 6-pounder continued to be used by the British Army for the rest of World War II and for about 20 years afterwards. A 57/42.6 mm squeeze bore adaptor was developed for the gun but was never adopted. The gun was produced in Canada and South Africa, where the Combined Ordnance Factories (COFAC) produced 300. Production US production The idea of manufacturing the 6-pounder in the US was expressed by the US Army Ordnance in February 1941. The US Army still favoured the 37mm Gun M3 and production was planned solely for lend lease. The US version, classified as substitute standard as 57 mm Gun M1, was based on the 6-pounder Mark II, two units of which were received from the UK. Since there was sufficient lathe capacity, the longer barrel could be produced from the start. Production started early in 1942 and continued until 1945. The M1A1 variant used US combat tyres and wheels. The M1A2 introduced the British practice of free traverse, meaning