Text from Wikipedia
Project 122bis (NATO codename Kronstadt class) submarine chasers were a Soviet design which were exported throughout the communist bloc in the 1950s. The first ship, BO-270, was built at Zelenodolsk in 1945-1947 and a total of 227 were built for Soviet Navy (175) and border guard until 1955. As well as this, twenty Project 357 (Libau class) despatch vessels were built on the same hull, but were lightly armed.
Service history
The ships served in 1950s–1960s on all Soviet fleets and flotillas in the Baltic Sea, Black Sea, Caspian Sea, Arctic Ocean and Pacific Ocean as part of Soviet coastal anti-submarine defences. Ships were also given to the Soviet Border Guards and were used actively as border patrol ships. Most of the Soviet sub-chasers were decommissioned between 1958 and 1970, although some were in service until the 1990s as training stations. Thirteen of the decommissioned and disarmed ships were delivered to the DOSAAF Voluntary Society for use as training ships.