Nautilus is the fictional submarine belonging to Captain Nemo featured in Jules Verne's novels Twenty Thousand Leagues Under the Sea (1870) and The Mysterious Island (1874). Verne named the Nautilus after Robert Fulton's real-life submarine Nautilus (1800). For the design of the Nautilus Verne was inspired by the French Navy submarine Plongeur, a model of which he had seen at the 1867 Exposition Universelle, three years before writing his novel.

Nautilus is described by Verne as "a masterpiece containing masterpieces". It is designed and commanded by Captain Nemo. Electricity provided by sodium/mercury batteries (with the sodium provided by extraction from seawater) is the craft's primary power source for propulsion and other services. The energy needed to extract the sodium is provided by coal mined from the sea floor.

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