The T72 76mm Gun Motor Carriage was designed in an attempt to arm the M10 3in GMC with the new M1 76mm gun. The 76mm gun had been developed in an attempt to produce a lighter version of the existing 3in anti-tank gun. The 3in gun was used in some heavy tank designs and in the M18 tank destroyer, but it was considered to be too heavy for use in a medium tank.
The 3in gun weighed 1,990lb and had a total length of 158.1in. The new 76mm M1 weighed only 1,141lb despite being slightly longer, at 163.75in. The two guns used similar ammunition, with the same projectiles but different powder cartridges. A complete APC M62 round for the 3in gun weighed 27.24lb; the equivalent round for the 76mm gun was only 20.77lb. Despite the lighter cartridges the two guns had the same muzzle velocity and armour penetration.
Work on the T72 began in March 1943. It used the chassis of the petrol-powered M10A1, but with a modified version of the turret that had been designed for the T23 medium tank. The T72 used an open topped version of this turret, with thinner armour. More ammunition could be carried, with 27 rounds in the turret bustle and another 72 in sponson racks, almost double the amount that could be carried on the M10.
Two test models were ordered. The conversion was fairly simple and they were delivered to the Aberdeen Proving Ground in April 1943. The T72 was two tons lighter than the M10, and the new turret had more space and better controls. Although the T72 was a successful design, the new T70/ M18 Hellcat, with torsion bar suspension, was considered to be a better mount for the 76mm gun. Work on the T72 was cancelled early in 1944. The new turret was abandoned completely and the Army decided that any future 76mm armed version of the M10 would use the M18 turret.
By this point a better use for the M10 chassis had been found. The T71 mounted a 90mm anti-aircraft gun in a new turret on the chassis of the M10. This design was standardized as the M36, and saw combat in northern Europe in 1944-45.