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 was designed to replace the earlier Zulu class, which suffered from structural weaknesses and harmonic vibration problems that limited its operational depth and submerged speed. The first Foxtrot keel was laid down in 1957 and commissioned in 1958 and the last was completed in 1983. A total of 58 were built for the Soviet Navy at the Sudomekh division of the Admiralty Shipyard (now Admiralty Wharves), St. Petersburg. Additional hulls were built for other countries.