The T53 90mm Gun Motor Carriage was a design for a combined tank destroyer and self propelled anti-aircraft gun that was rejected after extensive development work had been carried out.
The idea of using the US 90mm anti-aircraft gun in the anti-tank role was at least partly inspired by the successful German use of their famous 88mm gun in that role.
In the summer of 1942 a proposal was put forward to mount a 90mm gun on the chassis of a Medium Tank M4. This design kept the basic layout of the M4, with the engine at the rear, driver at the front and gun in the middle. The idea was approved by the Ordnance Committee in July 1942, with the designation 90mm Gun Motor Carriage T53.
The pilot M4 was built by Chrysler. It was built around a M4A4, a slightly longer version of the M4 powered by a multibank Chrysler engine. The pilot abandoned the original layout, and instead took a rather more complex approach. The multibank engine was removed, and the gun was mounted at the rear. The Continental R975 air-cooled radial engine used in the M4 and M4A1 was mounted in the centre of the vehicle. The drive shaft of this engine was always quite high in the vehicle, and moving the engine forwards meant that the drive shaft had to drop at a steep angle. As a result the transmission and final drive in the nose had to be tilted upwards to match, and an extra piece of armour plate installed to cover the gap this created in the nose of the vehicle.
The gun was carried on a M1A1 mount at the rear of the vehicle. It was partly protected when not in use by side and rear walls that folded at the sponson line to form a firing platform.
The pilot T53 went to the Aberdeen Proving Ground in August 1942. It didn’t perform well in the tests. In the anti-aircraft role it wasn't stable enough for use against high altitude targets. In the tank destroyer role the gun was too far from the centre of gravity, again affecting the stability of the vehicle. The gun was difficult to traverse or elevate when the vehicle was on a slope. The Tank Destroyer Board at Camp Hood tested the T53 next, and also found plenty of faults, including the lack of armour, high silhouette, poor mobility and limited ammo storage room. The Board went as far as recommending that the entire idea of a combined AA and tank destroyer should be cancelled.
Despite these flaws, work continued on the T53. On 27 October 1942 the modified version was designated as the 90mm gun motor carriage T53E1, and production of 500 was authorised, with the potential for another 3,500.
The T53E1 was significantly different to the T53. The engine and gun were swapped around, so the engine returned to its normal position in the rear and the gun was mounted on a platform in the centre of the vehicle. Outriggers were attached to the front and rear bogies on each side to improve the stability when firing. The firing platform was formed by two hinged half-inch armoured plates, mounted on either side of the gun. When moving these would be in the up position to provide some protection, and when the gun was in use they would be lowered to widen the fighting platform.
The protection for the gun crew was improved by adding a gun shield. On the first pilot T53E1 this was made of flat sheets of 0.5in armour, bolted together to form a box that protected the front, sides and top of the gun position. This didn’t perform well in test as the bolts were prone to coming out, and so the second pilot got a shield made up of two semi-circular sheets, one on each side of the gun, but with an open top.
The second T53E1 pilot went to the Antiaircraft Artillery Board at Camp Davis for tests, but despite the changes didn't perform well. The vehicle didn’t carry enough ammo, and its high silhouette made it potentially vulnerable to attack. The Board recommended cancelling the programme, and as the Tank Destroyer Board was no longer interested the project was cancelled on 25 May 1944.
The T53 was developed alongside the T71 90mm Gun Motor Carriage, which entered development in October 1942. This was a more succesful design, and entered service as the M36 90mm Gun Motor Carriage, the most powerful American tank destroyer of the Second World War.