The Foxtrot class was the NATO reporting name of a class of diesel-electric patrol submarines that were built in the Soviet Union. The Soviet designation of this class was Project 641. The Foxtrot-class group of submarines became the most successful of the Soviet post-World War 2 diesel-electric attack submarine offerings. The design saw construction from the period spanning 1957 to 1983 and were in service from 1958 until as recently as 2014 with foreign navies. Seventy-five total boats made up the class and these served the Soviet/Russian navies as well as the naval services of Cuba, Libya, India, Poland and Ukraine.

The boats displaced 1952 tons when surfaced and 2475 tons when submerged. Overall length was 91,3 m with a beam of 7,5 m and a draught down to 5 m. Power was served through 3 diesel units of 2,000 horsepower output and 3 Electric motors. Power was sent to 3 shafts. A single auxiliary motor was also carried. Performance included a maximum surfaced speed of 16,8 knots and a maximum submerged speed of 16 knots. Range was out to 30,000 nautical miles giving the Foxtrot-class excellent reach. It could stay submerged for up to five days. Its crew numbered seventy-seven. Armament was 10 torpedo tubes with six located at the bow and four at the stern. Twenty-two torpedo reloads were carried.

The Foxtrot-class was a regular component of all four Soviet Navy fleets and represented one of the more important boat groups of the Cold War years. Relatively fast and powerful, they showcased the Soviet commitment to an effective underwater attack force rivaled by few world powers of the period - this prior to the shift to all-nuclear-powered types. The Russian Navy retired its last Foxtrots between 1995 and 2000; units were scrapped and disposed of for museum purposes.

Submarine B-9 laid down on 26 December 1964 at the Shipyard No.196, Leningrad (yard No.816), launched on 31 March 1965, commissioned on 30 November 1965.

18 July 1991 transferred from Northern Fleet to the Black Sea Fleet.

Submarine B-9 was decommissioned and excluded from the lists of the Black Sea Fleet on 17 July 1997 and scrapped.