The ZSU-57-2 Ob'yekt 500 is a Soviet self-propelled anti-aircraft gun (SPAAG), armed with two 57 mm autocannons. 'ZSU' stands for Zenitnaya Samokhodnaya Ustanovka (), meaning "anti-aircraft self-propelled mount", '57' stands for the bore of the armament in millimetres and '2' stands for the number of gun barrels. It was the first Soviet mass-produced tracked SPAAG after World War II. In the USSR, it had the unofficial nickname Sparka (), meaning "twin mount," referring to the twin autocannon with which the vehicle is armed.
Development history Origins During World War II, ground-attack aircraft emerged as a significant threat to mechanized units on the move. Conventional towed anti-aircraft artillery (AAA), as well as vehicle Mounted smaller machine guns like the ones found on the ZiS-12 were an inadequate response under such conditions owing to the time needed to bring anti-aircraft machine guns into action. This experience made it clear that an anti-aircraft tracked vehicle, armed with small-bore autocannons or heavy machine guns, was needed. Vehicles such as the German Wirbelwind and specialized variants of the US M3 Half-track had been used to good effect in the final battles of World War II, both by the Germans, the US and nations which had received the M3 through Lend-Lease.
In 1942, Soviet engineers developed the T-60-3. The vehicle, based on the T-60 light tank chassis, was armed with two 12.7 mm DShK heavy machine guns; but the prototype did not go into production because of flaws in the design. The SU-72 SPAAG and several other experimental vehicles based on the T-60 or T-70 light tank chassis and armed with 37 mm autocannon were also tested in 1942–1943. The ZSU-37 was based on the chassis of the SU-76M self-propelled gun (SPG) and armed with one 37 mm 61K anti-aircraft autocannon in an open-top rotating armoured turret. The vehicle entered production in February 1945 and was in small-scale production until 1948.
After World War II it became clear that the firepower of a single 37 mm AA gun was insufficient to destroy the high-speed, low-altitude targets, which airplanes started to become at the time. SPAAGs based on light tank chassis had poor maneuverability in difficult terrain, slow off-road speed and insufficient range in comparison with medium tanks and SPGs. Thus the ZSU-37s were retired from service by the end of the 1940s.
ZSU-57-2 prototypes For several years after World War II there were no new SPAAG models in the USSR except for the BTR-152A (which were armed with two or four 14.5mm KPV heavy machine guns, designated ZTPU-4) and the BTR-40A (ZTPU-2) wheeled SPAAGs. Two of the 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 (932 miles) 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. With the Warsaw Pact, all Russian allied countries were given a number of the ZSU-57-2.
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 in order to not overwork the inbuild V-54 4-stroke diesel V12 engine of the T-54. 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 spacious in comparison with the T-54 because of the thinner armour and has different locations for some equipment. The general layout, with transverse mounting of the engine, is the same.
Driver's compartment The driver's compartment is located on the left hand side of the front of the hull. The driver's seat is moved forward and to the left in comparison with its location in the T-54. The compartment is equipped with a single-piece hatch cover opening to the left and two periscopic vision devices. One of them can be replaced by the TVN-1 infrared vision device which is operated together with the infrared headlamp (active night vision), which is mounted on the right track board. A fire-fighting equipment signal panel and a spare parts case are also located in the driver's compartment.
Turret The open-topped box-type welded turret has a ball-bearing race ring 1850 mm in diameter. The turret rear can be removed, which makes replacement of the guns easier. The turret can be covered in the travelling position by a tarpaulin which has 16 plexiglass windows.
To aim the guns, base data such as the target's speed, direction and range must be entered into the sighting system by the sight adjuster, who sits to the left of the guns at the rear of the turret. The target's speed and direction is determined by visual estimation, while range can also be estimated visually or with the rangefinder. The upper front of the turret has two small ports with armoured covers meant for collimators of the sight.
To fire the guns, the breeches must first be opened. The left and right loaders, located in the forward part of the turret on both sides of the main armament, load clips into the magazines of their respective weapons. The loaders' travel seats should be stowed in clamps on the turret sides before opening fire. The gunner, seated on the left hand side in the middle of the turret, aims ("lays") the gun and opens fire using an electric trigger, which fires both barrels, or two-foot pedals, which can fire either barrel independently. If manual mechanical backup gunlaying is used instead of electro-hydraulic drive, three crew members instead of two should work with the sight. The commander, who sits on the right hand side in the middle of the turret, lays the gun in azimuth, the gunner in elevation and the sight adjuster enters data into the sight. The loaders feed clips into the twin autocannon manually as needed, similar to the Bofors 40mm.
Armament
The twin S-68s are recoil-operated and weigh 4,500 kg. Their construction was based on two 57 mm S-60 AA autocannons. The guns have a recoil of between 325 and 370 mm. The individual weapons cannot be swapped from one side to the other as they are mirror images. Each air-cooled gun barrel is 4365 mm long (76.6 calibers) and is fitted with a muzzle brake. They can be elevated or depressed between −5° and +85° at a speed of between 0.3° and 20° per second, the turret can traverse 360° at a speed of between 0.2° and 36° per second. Drive is from a direct current electric motor and universal hydraulic speed gears (a manual mechanical drive is also provided in case of electrohydraulic failure; with the use of mechanical drive, elevation speed is 4.5° per second and the turret traverse speed is 4° per second).
The guns firing together are capable of firing up to 210–240 fragmentation and armour-piercing tracer (AP-T) shells per minute, with a practical rate of fire of between 100 and 140 rounds per minute, which gives a fire time of 2–3 minutes before running out of ammo. Muzzle velocity is 1,000 m/s. Each clip has 4 rounds, each of which weighs 6.6 kg; the charge in each round consists of 1.2 kg of 11/7 nitrocellulose powder, a projectile weighs 2.8 kg. Maximum horizontal range is 12 km / 7 miles (with an effective range against ground targets of up to 4 km / 2.5 miles. Maximum vertical range is 8.8 km / 28,871 ft with a maximum effective vertical range of 4.5 km / 14,750 ft). Fragmentation rounds have a safety-destructor which activates between 12 and 16 seconds after being fired to ensure the shells will not fall back to ground, so the maximum slant range of anti-aircraft fire is 6.5–7 km / 4-4.3 miles. BR-281 armour-piercing rounds are able to penetrate 110 mm armour at 500 m or 70 mm armour at 2,000 m (at 90° impact angle).
The S-68 autocannon was the most powerful AA gun installed on SPAAGs at that time. According to the statistical data of the Air Defence Research Institute No. 2, a direct hit of a single 57 mm shell could destroy a contemporary jet aircraft. In order to shoot down a jet bomber of the Canberra type, an average of 1.7 hits were deemed necessary.
The vehicle carries 300 rounds, and the ammunition is stowed as follows: 176 rounds in clips inside the turret, 72 rounds in clips in the hull front, and 52 separate (unclipped) rounds in special compartments under the turret floor. Armour-piercing rounds in clips are placed in the rear part of the turret to the left and right of the guns. Empty shell cases and clips are removed via a conveyor belt through a special port in the turret rear into an external metal wire basket on the back of the turret.
Armour protection The ZSU-57-2's armour is welded rolled steel sufficient to protect the vehicle from 7.62mm armour-piercing bullets at 250 meters.
Armour thickness is as follows: Hull front: (upper) – 13.5 mm; (lower) – 15 mm; at 60 degrees upper Hull sides: (upper) – 15 mm; (lower) – 13.5 mm Hull rear: 8 – 10.6 mm at 45 degrees Hull roof: 15 mm Hull bottom: 13.5 mm Turret sides: 13.5 mm Gun mantlet: 15 mm Turret roof: open
Maneuverability The ZSU-57-2 has a maximum road speed of 50 kilometres per hour (31 miles per hour), which is reduced to around 30 km/h off-road(19 mph). The vehicle has better acceleration compared with the T-54 because of its better power-to-weight ratio (18.6 hp per tonne). It has an operational range of 420 km(261 miles) on roads and 320 km(199 miles) across country. The vehicle can cross 0.8 m high vertical obstacles, 2.7 m wide trenches, ford 1.4 m deep water obstacles and climb 30° gradients.
The ZSU-57-2 uses the same engine as the T-54. It is a water-cooled V-54 4-stroke diesel V12 engine with a displacement of 38.88 litres, which develops 520 hp (388 kW) at 2,000 rpm. The engine itself weighs 895 kg. Fuel capacity is 830 litres carried in three fuel tanks inside the hull (640 L total) and two external fuel tanks on the right fender each of 95 L; fuel capacity was increased in comparison with the T-54. External rear-mounted supplemental fuel tanks can increase the road range to 595 km (370 miles).