launch a program to replace the ZSU-57. The ZSU-37-2 and -23-4 were the products of the attempt, and the ZSU-23-4 Shilka would see widespread service in various countries. Production history Although the vehicle entered service in 1955 and in the same year the No. 174 Works located in Omsk began producing the hulls and turrets, the first vehicles were completed in 1957 after the first 249 57 mm twin S-68 guns were produced by the Artillery Works No. 946 located in Krasnoyarsk. A total of 5,300 of these weapons were produced by the end of the 1950s. The hulls and turrets were produced by No. 174 Works where the final assembly also took place while the Krasnoyarsk Works, belonging to the Ministry of Heavy Engineering, participated in some production stages. The ZSU-57-2 remained in production until 1960 when the No. 174 Works stopped producing the hulls and turrets for ZSU-57-2. More than 2,023 ZSU-57-2s were produced in Soviet Union. 250 ZSU-57-2 SPAAGs based on the Chinese Type 59 (a copy of the Soviet T-54A) tank chassis were produced under license in North Korea. The turrets were bought from the USSR and delivered between 1968 and 1977. Since the production of the ZSU-57-2 turrets ended in 1960 the turrets that North Korea bought must have come from decommissioned Soviet ZSU-57-2s. The turrets were ordered in 1967. Service history Former USSR The ZSU-57-2 officially entered service with the Soviet Army in 1955. The first vehicles began replacing BTR-40A's and BTR-152A's in the anti-aircraft batteries of tank regiments in 1957. It was first shown publicly during the military parade in Moscow on 7 November 1958. Initially, tank regiments had a single battery equipped with four SPAAGs, later increased to two batteries, each equipped with four SPAAGs. The vehicle was also used by some motor rifle regiments (which in the 1960s had one battery equipped with four SPAAGs or, more likely, with six 23 mm ZU-23 towed twin AA guns). The anti-aircraft performance of the ZSU-57-2, however, was quickly found to be unsatisfactory and, because of rapid air force development, the vehicle was deemed obsolete by the early 1960s. ZSU-57-2s were gradually replaced by radar-guided ZSU-23-4 Shilkas from the beginning of 1965. Towards the end of the 1960s, a frequent configuration was one battery of an AA battalion in a tank regiment equipped with ZSU-23-4s and another battery equipped with ZSU-57-2s. Unpopular in the