Gymnote (S655) was an experimental submarine of the French Navy. She was a trials submarine for submarine-launched ballistic missiles (SLBM) and powered by diesel electric engines. She is named in honour of Gymnote, the world's first all-electric submarine built in France in the late 19th century.

The French planned a nuclear propelled submarine in the late 1950s and laid down a hull (no Q244). Because France had not developed uranium enrichment facilities at the time, the planned power plant was to be a heavy water reactor, which could utilize natural uranium. But French engineers were unable to produce a reactor small enough to fit into the submarine, which led to the project being canceled in 1959.^[1]

In the early 1960s the French government decided to develop an independent nuclear deterrent based on SLBM's. Hull Q244 was redesigned as a trials submarine with diesel-electric propulsion and four missile tubes in an extended casing. Re-designated Q251 and christened Gymnote, she was commissioned in 1966 and fired the first M-1 missile in 1968. The M-1 missile was subsequently deployed aboard the Redoutable-class submarines. She was extensively rebuilt in 1977-79 to enable trials of the new M-4 missile. In the 1980s, as part of a general re-numbering of the French submarine fleet, Gymnote was re-designated S655.

Gymnote was decommissioned in 1986.

• List of submarines of France

• Gardiner, Robert, ed. (1995). Conway's All the World's Fighting Ships 1947–1995. London: Conway Maritime. ISBN 0-85177-605-1. OCLC 34284130. Also published as Gardiner, Robert; Chumbley, Stephen; Budzbon, Przemysław (1995). Conway's All the World's Fighting Ships 1947–1995. Annapolis, MD: Naval Institute Press. ISBN 1-55750-132-7. OCLC 34267261.