Nautilus was the first practical submarine, commissioned by Napoleon and designed by the American inventor Robert Fulton, then living in France. Launched in 1800, it was made of copper sheets over iron ribs, 6.5 m long with a conning tower for observation. It used rudders for vertical and horizontal control — the origins of the diving planes used on all modern submarines — and tanks of compressed air to give the crew of four a submerged endurance of six hours. Underwater, Nautilus was propelled by a four-blade propeller turned by hand. On the surface a folding mast was erected and the vessel was powered by sail.

Nautilus was tested in France in 1800–1801, when Fulton and three mechanics descended to a depth of 8 m using ballast tanks. Nautilus sank a schooner using a towed gunpowder charge that Fulton called a "torpedo" after the electric ray. However, the French were not impressed and stopped Fulton's funding in 1804.

Fulton took Nautilus to the United Kingdom and sank a 300-ton brig in 1805, but the Royal Navy was not interested.

See ships named Nautilus for other ships of this name.