Nautilus is the only Navy Ship in The Big Harbour. He has the number 114 on his sides.
He lives at the Naval Yard near the Oceanic Institute. Nautilus was first seen being docked by Theodore and George, when George wanted to be a navy ship too. His second appearance was his starring role, as he was in charge of saving Canso Colossus, the king of super tankers, who was sinking. Theodore and the tugboats seem to look up to him a lot. Besides being one of the sleekest and fastest boats in the Big Harbour, Nautilus also has a big heart and always comes to the aid of any boat. 
Nautilus has the distinctive rounded bow and smooth deck lines of the St. Laurent Class of destroyer escorts which were based at Halifax in the Royal Canadian Navy until the 1990s.
- Season 4 - George and the Navy Ship and Nautilus and the Sinking Ship
- Season 5 - Foduck in Reverse and George and the Flags (cameo)
- Nautilus has a flat round platform on his foredeck where a navy ship's gun turret is usually found. This is likely because many of the model makers and production staff believed a children's show should emphasize peace and not display weaponry.