Captain Nemo's submarine is the Nautilus, an 8-letter word. The Nautilus is a fictional submarine featured in Jules Verne's 1870 novel '20, 000 Leagues Under the Sea'. It was captained by the mysterious Captain Nemo and was powered by electricity. The Nautilus was described as being equipped with advanced technology, including a powerful electric cannon and a diving chamber. It was also capable of traveling underwater for extended periods of time.