Easy to conceal yet powerful with a massive range, the M5 76mm was adopted by the US from the British. It could penetrate any form of armor, had relative mobility and speed; its only downside was its cost. The AT-76mm owns the same damage as a Flak 88mm.
In 1940, the United States just started to receive its first antitank gun, the 37mm Gun M3. While it fitted the request of the Infantry for light, easy to manhandle anti-tank weapon, Artillery and Ordnance foresaw a need for a more powerful gun. This led to a number of expedient designs, such as adaptations of the 75mm M1897 or towed variants of the 75mm M3.
Late in 1940 the Ordnance Corps started another project - an anti-tank gun based on the 3 inch anti-aircraft gun T9. The barrel of the T9 was combined with breech, recoil system and carriage, all adapted from the 105mm howitzer M2. The pilot of the weapon, named 3 inch Gun T10, was ready by September 1941. Although the subsequent testing revealed minor problems, it was clear that the gun, eventually standardized as M5 on carriage M1, presented major performance improvement over existing designs.
Production began in December 1942. In November 1943 a slightly modified carriage was standardized as M6. In this carriage a flat shield borrowed from the 105 mm howitzer was replaced by a new sloped one. In January 1944 AGF requested to upgrade the guns built with the early carriage M1 to carriage M6; consequently most of the guns that reached the frontline had the M6 carriage.
Large cal. AP shell