Also known as: nautilus, ノーチラス, ノーチラス号, Eltreum, ヱルトリウム
This Submarine is the home of the protagonists in Fushigi No Umi No Nadia. It is owned and captained by Nemo (Nadia). It was heavily based on the vessel of the same name from Jules Verne's 20,000 Leagues Under the Sea.
It is later revealed that the Nautilus is actually an Atlantean Spacecraft named "Eltreum".