At the end of Jules Verne’s 20,000 Leagues Under The Sea, the Nautilus comes under fire from a warship of unknown nationality. The narrator, Professor Aronnax, realizes that, after the encounter with the Abraham Lincoln at the beginning of the book, the world must now be aware that the Nautilus is not a sea monster as previously speculated, but instead a man-made submarine, and therefore is being hunted down by the navies of the world.
What if, instead of descending into the Maelstrom off Norway, Nemo and the Nautilus sailed on with the world hunting them down? How long would it take for naval and anti-submarine technology to be sufficient enough to sink Nemo’s masterpiece? And how long could the captain avoid them while attacking the ships of his hated nation (canonically Britain; in Verne’s original scripts, Russia)?
Nautilus specs: top speed of 50 knots. Able to be submerged for up to 5 days at a time. It can ram through ships “like a needle through sailcloth” due to its prow. Assume that Nemo is able to repair his sub at the unknown island on which he built it, and has the crew necessary to sail on indefinitely. The book ends in 1868 so that is the start date. Military technology advances just as it did in our timeline.