Nelma (Project 1851 (X-Ray))

Project 1851 Nelma (NATO: X-Ray) is a Soviet nuclear-powered deep-sea special-purpose submarine designed by the Volna bureau (later Malakhit) and built by the Leningrad Admiralty Shipyard. Operated by the GRU's Main Directorate of Deep-Sea Research (GUGI), these "deep-sea nuclear stations" are used for seabed espionage, research, rescue of crews from sunken submarines and recovery of objects from the seabed, and are carried to the operating area by a mother submarine. The lead boat AS-23 was commissioned in 1986 and retired in 1997; two enlarged Project 18511 Paltus boats, AS-21 (1991) and AS-35 (1995), remain active. Project 1851 displaces about 1,000 t submerged, is 40 m long, has a crew of six and can operate at depths of around 1,000 m.