The M5 3in gun motor carriage was the first US tank destroyer to carry a heavier gun than the 37mm anti-tank gun, but it was never a popular design and the project was abandoned before production got under way.
In 1941 US Army Ordnance had designed the M6 37mm gun motor carriage, a tank destroyer that carried the standard 37mm anti-tank gun of the day on the back of a 3/4 ton truck chassis. 5,380 of these vehicles were produced between April and October 1942, but by then it was clear that the 37mm anti-tank gun was obsolete.
Work began on a series of designs for tank destroyers with heavier guns. The first to get underway was the T1 3in Gun Motor Carriage. This mounted a 3in anti-tank gun on a chassis based on the Cleveland Tractor Co high speed tractor, an aircraft towing vehicle used by the USAAF. Work began at the end of 1940, and the T1 was standardized in November 1941 as the M5 3in gun motor carriage.
The M5 was powered by a 160hp Hercules diesel engine. The 3in gun was mounted at the back of the vehicle, with an open gun shield. There was no crew platform, and the crew operated the gun from the ground behind the vehicle.
The resulting vehicle was disliked by Brigadier-General Andrew Bruce, commander of the Tank Destroyer force. He refused to accept the M5 for his tank destroyer battalions, and instead wanted the M3 75mm Gun Motor Carriage, which was based on a half-track personnel carrier. Although work on this project only began in June 1941 it was standardized in October 1941 and was much more popular than the M5. As a result the M5 programme was cancelled before the start of series production.