HE round or not having an HE round at all. Post-war, the UK's Tank Museum credited the US 75mm gun as "America's most important contribution to tank warfare" because of its ability to combine good (for the time) AP and HE performance. They believed that the American observers working with the British before Dunkirk had appreciated the effectiveness of such a dual purpose weapon, and so it was made a prime requirement for US tank production. After experiencing the effectiveness of the American 75 mm tank guns in the infantry support role, the British opted to adopt the American caliber and ammunition by the expedient of boring-out the 6 pounder tank gun to make the Ordnance QF 75 mm. By 1944, this had become the standard British tank gun, equipping the Cromwell tank and Churchill tank for the campaigns in northwest Europe. Variants T6 Experimental anti-aircraft gun based on the M1897 field gun. The barrel was shortened from 36 to 31 calibers, and the Nordenfelt screw breech replaced with the sliding block breech. T7 / M2 Adaptation of the T6 for tank gun role. Used on the early M3 Lee. Barrel length: 31 calibers Muzzle velocity: 588 m/s (1,929 ft/s) with M72 AP shell T8 / M3 Longer derivative of the M2. Equipped American and British vehicles such as the M4 Sherman, the later models of the M3 Lee and the Churchill III/IV (scavenged from Sherman tanks in the North African theatre). The US Army also experimented with mounting the M3 on various wheeled carriages for use as anti-tank gun, but the program was cancelled due to a lack of requirement. Barrel length: 40 calibers Muzzle velocity: 619 m/s (2,031 ft/s) with M72 AP shell M4 The 75 mm aircraft gun M4 is a modification of the M3 gun found in medium tanks. It differs from the M3 gun, only in having a seat for the spline machined in the tube. It was mounted on the M6 mount. T13E1 / M5 A lightweight version of the M3 with a lighter thin-walled barrel and a different recoil mechanism that was used in the Douglas A-26 Invader and the B-25H Mitchell bomber. It uses the same ammunition and has the same ballistics as the M3. M6 A version derived from the T13E1 for the M24 Chaffee. Barrel length: 39 calibres (2,92 m) Muzzle velocity: 619 m/s (2,031 ft/s) with M72 AP shell