Complex sentence: A popular misconception is that these ships were named for the fictional submarine in Jules Verne's 1870 novel "Twenty Thousand Leagues Under the Sea", but "Nautilus" was associated with ships long before Verne imagined his vessel.
Split into simpler sentences: A popular misconception is that these ships were named for the fictional submarine in Jules Verne's 1870 novel "Twenty Thousand Leagues Under the Sea". In fact, "Nautilus" was associated with ships long before Verne imagined his vessel.