It takes a special type of person to serve in a nation’s navy, especially on long voyages that separate men and women from their loved ones, and no service is both loved and hated as that aboard submarines, for very few people ever serve on them on a whim. For one thing, the psychological impact of being trapped for long periods underwater in tight, cramped quarters is more than many people can stand. Also, submarine service is uncharacteristically hazardous; after all, if a surface vessel is sunk, the crew has a reasonable chance of escaping death in lifeboats or being rescued out of the water by another ship. Conversely, if a submarine is badly damaged while submerged, the crew’s chances of survival are at best remote.

Given that there’s such little margin for error in a submersible, many submarine losses remain sources of intrigue and mystery, and during World War II, few sinkings were as controversial as the Surcouf, a Free French submarine that disappeared in the Caribbean in 1942.

When the Surcouf launched in 1929, it was a technological marvel. This wasn’t a conventional submarine at all, but a 3,300-ton, 300-foot-long submersible light cruiser. Armed not just with torpedoes but also a pair of eight-inch guns, the Surcouf had a range of over 10,000 miles and was equipped with a seaplane in a hanger and a prison capable of holding up to 40 prisoners. When it was launched, the submarine looked like something out of the novels of Jules Verne, and many people believed it would make all existing submarines (and many surface warships) obsolete.

On paper, this seemed to be a completely new and potentially lethal form of naval vessel, but in reality, the Surcouf, like other attempts to create such a vessel, had some basic and fundamental flaws. In fact, by the time France found itself at war with Nazi Germany in 1939, the Surcouf was outdated and basically irrelevant.