Captain Nemo's Nautilus was cool right from the start--when Jules Verne published 20,000 Leagues Under the Sea in 1872, the undersea vessel immediately captured the public's imagination. Even when submarines became an actual reality within a generation, Nemo's sub still maintained a warm spot in the hearts of science fiction fans everywhere.
So when Walt Disney planned to make a live-action movie version of the novel in 1954, he and his special effects guys had quite a task. They had to come up with a design for the Nautilus that looked advanced enough to be believable, but also still looked to be a product of the Victorian Era. It had to at least come close to the wonderful vehicle that had been residing in everyone's imagination for 80 years.
Designer Harper Goff proved to be up to the task. The Nautilus in Disney's film looks exactly right. Thus it becomes the anchor point upon which was added a literate script, a wonderful performance by James Mason as Nemo, and an absolutely terrific fight with that giant squid.
Thus the Nautilus jumped into first place as the single coolest make-believe submarine ever. Though both the Seaview and the Proteus eventually scored high in pure coolness as well, neither of them really came close to Nemo's fantastic Victorian-Age submersible.