American self propelled artillery developed on its own terms, especially tank destroyers. After a series of experiments, American tank destroyers became very similar to their own tanks. As a rule they were based on tank chassis, but had thinner armour and higher mobility. The first such vehicle was the GMC M10, which made its debut in March of 1943. Its replacement, the M36, appeared on the battlefield a year and a half later. This was the best of American tank destroyers. Like the Soviet SU-100 its career spanned more than a decade. The last conflict it took part in was the Yugoslavian Civil War in the 1990s.
Attempt at improvement
It just so happened that development of the GMC M10 started to cross paths with the Medium Tank T20, a prospective medium tank that was supposed to replace the Medium Tank M4. This had to do with the armament first and foremost. Both vehicles were developed with a 76 mm gun based on the 3" AA gun in mind. One of the prospective weapons for the T20 was the T12 gun, later standardized as the M7.
This coincidence in armament is no surprise. Both the GMC M10 and Medium Tank T20 were developed by the Tank-automotive Center that was organized in Detroit in 1942. The TAC was headed by Joseph Colby and included a number of engineers who used to work for the Ordnance Department. Most of these were military men, and Colby himself retired with the rank of Brigadier.