On Aug. 11, 1966, a fishing boat came upon a badly bruised man floating in the water off Brest, France, clutching an inflatable life raft. He identified himself as Josef Papp, a Hungarian-Canadian engineer, and claimed he had just bailed out of a jet-powered submarine that had crossed the Atlantic in 13 hours.

The media laughed at this, but Papp insisted he had built a cone-shaped sub in his garage that could reach 300 mph using the same principle as a supercavitating torpedo. He even wrote a book, The Fastest Submarine, to answer his critics … but somehow this failed to explain how the sub worked, or why plane tickets to France had been found in his pocket, or why a man matching his description had been seen boarding a plane to France hours earlier.

For what it’s worth, Papp did patent a number of other inventions, including a fuel mixture composed from inert noble gases. So maybe he was telling the truth.