Lend Lease Tank Destroyer

The Ordnance Department of the US Army agreed to produce a copy of the British 57 mm QF 6-pounder for Lend Lease aid. This gun was also installed in the new tank destroyer. The decision was officially made on April 15th, 1942. The new tank destroyer was indexed GMC T48.

It did not take a long time to build this vehicle in the workshops of the Aberdeen Proving Grounds owing to its simplicity. A prototype was ready by the end of May. Interestingly enough, it did not use the American variant of the 57 mm M1 gun with a 50-caliber barrel, but an early British Mk.III. It had a shorter barrel (43 calibers) but with thicker walls, which made it heavier than the M1. The gun was equipped with an M12 recoil brake and installed in the front of the fighting compartment on a cylindrical pedestal (soon replaced with a conical one). The design reused the upper part of the M1 carriage. The whole design was indexed 57 mm Gun Mount T5. It offered a much larger traverse than the 75 mm Gun Mount M3 used on the GMC M3: 55 degrees vs 40. The elevation range was smaller: from -5 to +15 degrees. No auxiliary armament was provided.

As a result of experience gained on the GMC M3, the T48 did not use the stock gun shield from the very beginning. Initially it used a gun shield from the GMC T44, the failed prototype of a 57 mm gun carriage on the chassis of a Ford 4x4 truck. After the first trials it was replaced with a new special gun shield that protected the crew not only from the front, but partially from the sides and the top. The front of the shield was 15.9 mm thick and the rest of the plates were 6.35 mm thick.

The design of the gun mount and shield reduced the height of the GMC T48 by 36 cm compared to the M3: from 2.49 to 2.13 meters. This made the vehicle easier to hide on the battlefield and more likely to survive an encounter with enemy tanks.

The layout of the fighting compartment changed a little compared to the GMC M3. The M3 carried some of its 75 mm rounds in the pedestal and some under the floor of the fighting compartment. The T48 had its ammunition in the rear, between the fuel tanks. After learning from trials of the GMC M3, the T48 had easily removable headlights, as they could be damaged by the shockwave of firing the gun at low elevation. The crew consisted of five men: the commander, gunner, loader, driver, and his assistant.

The GMC T48 was not initially built for use by the US Army. It was meant exclusively for use by America's allies. Production was set up at the Diamond T Motor Company in December of 1942. 50 vehicles were delivered by the end of the year and 912 more by May of 1943. The full production run totalled 962 vehicles. Production vehicles used the 57 mm M1 gun with a full 50 caliber barrel.

The British ordered 680 GMC T48s. They planned to use them in North Africa, but the first batch arrived only in the summer of 1943 when the remaining Axis forced in Tunisia had already surrendered. The British did not consider the GMC T48 suitable for the European theatre. Only 30 vehicles were accepted into service after modification (in part, installation of the Wireless Set No.19). The British T48s never saw combat. They were eventually converted into APCs. The same fate awaited the 282 unissued vehicles that remained in the US. All of them (with the exception of one) were converted into APCs at the Chester Tank Depot in 1944.

The 650 vehicles rejected by the British quickly found new owners. They were delivered to the USSR as a part of Lend Lease aid. 241 vehicles arrived by the start of 1944, 223 more in the first half of 1944, and the remained in the second half of 1944. The Red Army referred to them by the index SU-57.

The SU-57 primarily went to light SPG brigades. Seven such brigades were formed in February of 1944. Three of them (16th, 19th, and 22nd) were issued SU-57s, the rest got SU-76Ms. The latter was considered the primary type of vehicle for these brigades and the SU-57 was only a backup. These brigades were formed from tank brigades and inherited their support units (AA machine gun company, command company, technical company, medical platoon). The motorized rifle battalion was exchanged for an SMG battalion without fire support. The main units of the brigades consisted of three SPG battalions (each composed of four 5-gun batteries and one commander's tank). The brigade numbered a total of 1144 personnel, 60 SPGs, 5 tanks (3 battalion commanders and two in the HQ signals platoon), 3 APCs (in the HQ company recon platoon), and 151 cars.

All three of the SU-57 brigades formed in the Moscow Military District and were included in the 1st Ukrainian Front in July of 1944. The 16th brigade went to the 3rd Guards Tank Army, the 19th to the 1st Guards Tank Army, and the 22nd to the 4th Tank Army. These brigades took part in the Lvov-Sandomierz Offensive, in which the 16th received the battle honour of Przemyśl and the 22nd received the Order of the Red Banner. The 19th brigade along with the entire 1st Guards Tank Army was pulled into into the reserve in September and transferred to the 1st Belorussian Front in November. It took part in the liberation of Pomorye. On March 17th 1945 the brigade achieved Guards status and received a new number: 70. The two other brigades took part in the Berlin and Prague Offensive Operations. The commander of the 1st Guards Tank Army Colonel General M.E. Katukov was not kind to this tank destroyer in his report to the Main Tank and Automotive Directorate dated October 15th 1944: "The 57 mm SPG brigade was used as a screen in directions of likely tank attacks. These SPGs are too bulky and their guns are ineffective."

The SU-57 was also issued to independent motorcycle regiments and battalions. Here they were seen as a potential replacement for towed anti-tank guns. The TO&E attached an anti-tank artillery battalion composed of twelve 45 mm or 57 mm guns to each independent regiment and four guns to each independent battalion. The SU-57 arrived as a replacement for the 57 mm guns. The composition of any battalion could be mixed. For instance, the 4th Independent Motorcycle Regiment had ten SU-57s and four 76 mm ZIS-3 guns before the start of the Iași-Chișinău Operation in August of 1944. Each of the three tank corps of the 2nd Tank Army of the 1st Belorussian Front had four SU-57s in their motorcycle battalions during the Lublin-Brest Operation. The aforementioned 1st Guards Tank Army had the 6th Guards Motorcycle Regiment (12 SU-57s) and 16th Guards Motorcycle Regiment (6 SU-57s) among its units.

When formation of three medium SPG brigades armed with SU-100 tank destroyers began in December of 1944, their reconnaissance companies were supposed to include three SU-76 SPGs. Two of the brigades (the 207th and 209th) received SU-57s instead. Finally, a new TO&E of a Guards Heavy Independent Tank Brigade was introduced in early 1945. Its reconnaissance companies included three SU-57s. This is the only case when the SU-57 was included as a first choice and not as a replacement for a SU-76 or towed gun.

The Red Army had written off 212 SU-57s by June 1st, 1945. Not all were lost. 15 were transferred to the Polish Army. Out of the 438 remaining SPGs 271 were in front line units, 90 in military districts, and 77 in repairs.

The only Soviet ally to use the SU-57 was Poland. 15 SPGs were transferred to the Wojsko Polskie on March 10th, 1944. 13 of them were initially included in the 4th company of the 1st Reconnaissance Battalion, but this company was turned into the 7th Independent SPG Battalion (Dywizjon Artylerii Pancernej) on April 7th. The unit was composed of an HQ platoon, three 4-gun batteries, a supply section, a repair section, a quartermaster section, and a medical section. In addition to 13 SPGs, the battalion had one BA-64 armoured car, 19 unarmoured cars, and 4 motorcycles. The battalion was used to guard the 1st Polish Army HQ in August-October of 1944 and then fought as a part of the 1st Infantry Division. In January of 1945 the battalion fought alongside the 1st Independent Cavalry Brigade and then the 1st Reconnaissance Battalion as of February of 1945. The SPGs fought in Germany and returned to Poland with five SU-57s. The battalion was disbanded on November 13th and the SPGs were handed over to internal security forces. They were converted into APCs and used in fighting against the Ukrainian Insurgent Army.