Colonel John Blashford-Snell discovered the half-submerged, cast-iron wreck off the coast of Panama while searching for ancient ruins.

She was built in 1864 by a visionary craftsman, Julius Kroehl, for the Union forces during the American Civil War. But the boat, called Explorer, was never used in the conflict and was subsequently taken to Panama where she was used to harvest pearls.

She was ideal for this purpose because of a unique lock-out system, identical to the one in the Nautilus from Verne’s book, published in 1870.

The lock-out system is a reversible air-lock that enables submariners to leave the vessel, harvest pearls from the sea-bed, then return to the submarine. Like Explorer, Nautilus was also used to gather items from the seabed.

Colonel Blashford-Snell, who runs the Dorset-based Scientific Exploration Society, said: “I had been told about the sub 20 years ago and it was described as a Japanese mini-sub. I was then told that in fact it was just a boiler, so I didn’t worry about it. Then recently I was on an exploration in the area looking for ancient ruins and forts. I was contacted by a maritime museum in Canada who knew we were in the area and asked if we could examine the vessel.”

When Colonel Blashford-Snell and his team dived to examine the wreck they discovered that it was much older than previously thought.

He explained: “It was quite an experience because we had an expert with us who said it was much earlier than we had thought and in fact dated from the American Civil War. It had a conning tower and I felt as if Captain Nemo should be in it at the controls.”

The submarine, which measures 36ft by 10ft, was lying in under 10ft of water off Isla San Telmo, an island in an archipelago known as The Pearl Islands, since being abandoned after three years in the pearl industry. Her crew all died from what was described then as a “fever”, but what was more likely to have been the bends after they regularly submerged to about 100ft to work.

Manned submarine techology was just developing when Verne was writing the novel in which Captain Nemo and his crew travel the world’s oceans.

Colonel Blashford-Snell, 67, added: “What made it ideal for the pearl trade was its lock-out system, which meant people could get out of it, gather up pearls then return to the submarine. I realised it was identical to the system used in Nautilus. In the book it mentions that Nautilus was first spotted in 1866, just two years after the Explorer was built.

“And 1864 was significant in another way because it was the year of the first sinking of a ship, USS Housatonic, by a submersible, the hand-cranked CSS Hunley.” Wyn Davies, a maritime historian, said: “If Jules Verne was researching the relatively new world of submersible vessels he would probably have heard of the Explorer’s lock-out system. Submarine inventors were keen to sell their products so there would have been none of today ’s secrecy and technologies would have been keenly scrutinised on both sides of the Atlantic. As far as I’m aware, the Explorer had the world’s first lock-out system and its uniqueness might have stimulated Verne’s imagination.”

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