Foxtrot-class Hunter-Killer Submarine

The Project 641 Foxtrot-class was a class of diesel-electric patrol submarines that were built in the Soviet Union.

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 fifty-eight 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.

The Foxtrot-class was comparable in performance and armament to most contemporary designs. However, its three screws made it noisier than most Western designs. Moreover, the Foxtrot-class was one of the last designs introduced before the adoption of the teardrop hull, which offered much better underwater performance. Also, although the Foxtrot was larger than a Zulu-class submarine, the Foxtrot class had two of its three decks dedicated to batteries. This gave it an underwater endurance of ten days, but the weight of the batteries made the Foxtrot's average speed a slow 2 knots at its maximum submerged time capability. Due to the batteries taking up two decks, onboard conditions were crowded with space being relatively small even when compared to older submarines such as the much older American Balao-class submarine. The Foxtrot-class was completely obsolete by the time the last submarine was launched. The Russian Navy retired its last Foxtrots between 1995 and 2000, units were scrapped and disposed of for museum purposes. During the division of the Soviet Black Sea Fleet, in 1997 one Foxtrot-class submarine (later renamed as Zaporizhzhia) was passed to Ukraine as it was not operational since 1991. The ship never effectively served in the Ukrainian Navy and was under repair. In 2005 Ukrainian Ministry of Defence wanted to sell it, but was unsuccessful. Following successful post-repair trials in June 2013, it was recognized as operational.