The RussianTango-class submarines (Project 641B Som [Catfish]) were the successors to the Foxtrot-class submarine based in the Black Sea and Northern Fleet areas. The first of the class was completed in 1972 at Gorky. A total of 18 were built in two slightly different versions. The later type was several metres longer than the first possibly because of installation of ASW missile equipment.
The bow sonar installations appear to be similar to those fitted into Soviet nuclear attack submarines. The propulsion plant was the same as the last subgroup of the Foxtrot-class submarine. The Tango class had far more battery capacity, far higher than previous conventional submarine class in the Soviet Navy. As a result, pressure hull volume increased. This allowed an underwater endurance in excess of a week before snorkeling was required.
Coupled with new armament and sensor fit, the Tango class were ideal for ambush operations against Western nuclear submarines at natural chokepoints.
Because of its all-hull rubber coating, the sub class was nicknamed "rezinka" [rubber]
Construction of this class has now stopped. One unit remains in the Black Sea Fleet but it may have been decommissioned since 2010.