T48 Gun Motor Carriage

The T48 57 mm Gun Motor Carriage was a self propelled anti-tank gun produced by Diamond T in 1943 by the United States. It was a 57 mm gun M1 (US production of a British design) mounted on a M3 Half-track. It was built when there was a need for a light, mobile self-propelled gun that could have a high rate of fire and could at least damage, if not knock out most tanks. A total of 962 vehicles were produced from 1943 to 1945. Of these, 652 were provided under Lend-Lease to the Soviet Union and 60 to Britain while the remainder served with US forces. It served during Operation Bagration, Operation Overlord, the invasion of southern France, the Battle of the Bulge and the Western Allied invasion of Germany. . Some of them were converted back to half-tracks.

Originally it had been planned that Britain would receive all of the examples produced, intending to use them in the Western Desert, but by the time they arrived the campaign was over. As a result, the British transferred all the half-tracks to the Soviet Union under the Soviet Aid Programme. The Soviets called it the SU-57

Design
The T48 Gun Motor Carriage was 21 ft long, 7 ft 1 in wide, 7 ft high with a wheelbase of 135.5 in. The suspension consisted of a leaf spring for the wheels and the front tread had Vertical Volute springs. The vehical had a maximum speed of 45 mph. With a fuel capacity of 60 US gallons, it had a range of 150 miles, and was powered by a 128 hp White 160AX, 386 in3, 6 cylinder, petrol engine with a compression ratio of 6:3:1. The power to weight ratio was 15.8 hp/tonne and the vehicle weighed 9.45 tonnes. It also had 6–12 mm of armor, was armed with a single 57 mm Gun M1, and had a crew of three.

Development


The T48 originated from the M3 Gun Motor Carriage in 1942 to meet a British and American requirement for a self-propelled 6-pounder anti-tank gun. The American requirement was dropped later. It was made by emplacing a 57 mm gun M1 – the US production version of the British 6-pounder – in the rear of a M3 Half-track.

Pilot Model
The pilot model was built at the Aberdeen Proving Ground in May 1942. The 57 mm Gun M1 was mounted in the M12 recoil mechanism and installed on a tubular pedastal. The tublar pedastal was soon replaced with a conical structure and was designated the 57 mm gun mount T5. The gun on the pilot model had a traverse of 27.5 degrees in both directions (total of 55 degrees), while having an elevation of +15 to -5 degrees. The short barreled British Mark III 6 pounder gun was installed in the pilot, but the longer barreled 57 mm Gun M1 was specified for the production models. The original travel lock for the recoil mechanism proved to be unsatisfactory, which was replaced by a travel lock on the front hood. The original design had a gun shield from the T44 57 mm Gun Motor Carriage. After the first tests were complete, a new shield was designed with 5/8 inches thick of face-hardened steel on the front and 1/4 inch thick on the sides and top. The shield extended over the crew with a relatively low silhouette of only 90 inches. Because of the experience from the M3 Gun Motor Carriage demountable headlights were mounted to avoid deformation of the hood. The deformation of the hood was caused by the muzzle velocity of the 57 mm gun. The T48 was accepted for production in 1942.

Service history
The British ordered all of the T48s that were produced, intending to use them in the Western Desert Campaign, but by the time they arrived the British had already won the war in the Western Desert and the appearance of the 75 mm gun, and later the Ordnance QF 17-pounder gun, meant that the T48 was surplus to British requirements. As a result, it was almost immediately shipped to the Soviet Union under the terms of the Soviet Aid Programme. Through this programme, the Soviets accepted 650 vehicles, adopting the designation SU-57. A small number were later passed to the Polish People's Army.

Britain accepted 31 converting them back to carriers. The US retained 281 vehicles which were also converted back to M3A1 standard carriers in 1944. They were converted by the Chester Tank Depot.

It served through Operation Dragoon, Operation Overlord, the Battle of the Bulge, Operation Bagration, and the much of the fighting that took place on the Eastern Front. It was retired immediately after the war because the 57 mm gun was no longer effective against most of the tanks that were then in service, making it obsolete.

Operators
 Nazi Germany 🇵🇱 Poland  Soviet Union 🇬🇧 United Kingdom 🇺🇸 United States
 * Wehrmacht units operated small number of T48s captured from UK and the Soviet Union.
 * Polish Army in the East received 15 vehicles operated previously by the Red Army.
 * Red Army operated T48 GMC under designation SU-57.
 * British Army accepted 30 vehicles, later rebuilt as carriers.
 * US Army used T48s rebuilt as M3A1 Half-tracks in 1944. Rebuilt by the Chester Tank Depot.