USS Triton became the first submarine to circumnavigate the globe while submerged for most of the voyage.
The U.S. Navy nuclear-powered radar picket submarine completed Operation Sandblast in 1960. It departed New London, Connecticut, on 16 February and returned there on 10 May, following a route broadly based on Ferdinand Magellan’s first circumnavigation. Triton travelled about 36,000 nautical miles and remained submerged except for scheduled operational necessities.
The voyage demonstrated the endurance and navigational capability of nuclear propulsion. Triton was commanded by Captain Edward L. Beach Jr., who later described the mission in the book Around the World Submerged.
USS Nautilus is sometimes given as the answer because it made historic Arctic voyages, including the first under-ice trip to the North Pole. Triton’s distinction is different: it completed the first submerged circumnavigation of Earth.