Towards the end of 1942 a requirement for a tank destroyer to replace the M10 and carry a 90 mm antiaircraft gun was given. The design and development went slowly as other projects received higher priority. It wasn't completed until the end of 1943 and was put into production in 1944.
Declared Standard in June 1944.1
Prototypes were manufactured by Chevrolet Division of the General Motors Corporation.
AP shell had velocity of 2,670 ft/sec, range of 15,600 yards, penetrate 3" at 4,700 yards. The 90 mm gun could fire a 24.1 lb shell at a muzzle velocity of 2,800'/sec.4
The chassis was very similar to the M10A1, but it had the sponson stiffener brackets moved forward to provide more room for the 90 mm ammunition.
An auxiliary generator was installed in the engine compartment with a bracket to hold the trunnions of the slip ring. The electrical installation was modified to accommodate the auxiliary engine and slip ring.
The turret was a new design and had a partial turret basket. There were seats for the gunner (right side1), loader (left side1), and commander that revolved with the turret.
The fixed fire extinguisher cover was changed as was the sub-floor doors.
Tank Destroyer Armament Performance