The Redoutable (S 611) was the lead ship of her class of ballistic missile submarine in the French Marine Nationale. Commissioned on 1 December 1971, she was the first French SNLE (Sous-marin Nucléaire Lanceur d'Engins, "Device-Launching Nuclear Submarine"). She was fitted with 16 M1 ballistic missiles, delivering 450 kt at 2000 kilometres. In 1974, she was refitted with the M2 missile, and later with the M20, each delivering a one-megatonne warhead at a range over 3000 kilometres. The Redoutable ("formidable" or "fearsome" in French language) was the only ship of her class not to be refitted with the M4 missile.