USSR's potential enemies – the United States and Great Britain, had high-quality air forces with substantial ground-attack experience. The need for a new tracked AA vehicle was apparent. In February 1946, the Design Bureau of Works No. 174 in Omsk and the Research Institute No. 58 in Kaliningrad, Moscow Oblast submitted a joint project for a SPAAG based on the T-34 tank chassis, to be armed with four 37 mm AA guns, to the Technical Council of the Ministry of Transport. However, the project did not proceed due to the desire to concentrate attention on the newest tank chassis available. The Design Bureau of Research Institute No. 58 (NII-58) (formerly known as the Central Artillery Design Bureau, TsAKB), under the supervision of V.G. Grabin, began the development of a twin 57 mm S-68 automatic anti-aircraft gun based on the 57mm S-60 in the spring of 1947. The first S-68 prototype (with ESP-76 diesel-electric drive), was ready in 1948. It was initially mounted on a S-79A four-wheel carriage; that system passed various tests but did not go into production. The final project of the ZSU-57-2 (Ob'yekt 500), armed with twin S-68s and based on a light-weight T-54 tank chassis, was finished in 1948. The first prototype ZSU-57-2 was built in June 1950, the second in December 1950. After official tests, taking place between 27 January and 15 March 1951 in which the vehicle was driven for 1,500 km and 2,000 rounds were fired from its guns, six more prototypes were built for service tests. These prototypes had some improvements included, such as an increased ammunition load (300 rounds), but development stopped again due to the absence of improved S-68A guns. Various updates continued in 1952 and 1953. The service tests, in which two vehicles participated, took place in December 1954. This was due to delays in the development of drives for the S-68 guns. The ZSU-57-2 officially entered service in the Soviet Army on 14 February 1955. Description Overview Based on past experiences with SPAAG designs, Soviet engineers designed a vehicle that used a modified T-54 chassis, with four twin road wheels per side instead of five, and much thinner armour. The vehicle was armed with twin 57 mm S-68 autocannon in a new, large, rotating, open-topped turret. The ZSU-57-2 consists of three compartments: driver's in the front, fighting in the middle and engine-transmission at the rear. The hull is more