A lifelong scuba diving obsession led Steven Schwankert to the tale of the HMS Poseidon and the startling discovery that the British submarine, which sank off the northeastern coast of China in the 1930s, had been raised by the Chinese in 1972.
That revelation lies at the heart of Schwankert's upcoming book, "The Real Poseidon Adventure: China's Secret Salvage of Britain's Lost Submarine" and an accompanying documentary film chronicling his search for answers about what became of the sunken vessel.
The seven-year transcontinental quest saw frustrations, triumphs and deeply emotional experiences, none more so than bringing together descendants of the Poseidon's crew and sharing with them new information about the submarine's fate.
"I only wish we'd been able to find more relatives.
It feels like we've taken on this incredible responsibility of being custodians of this history," said the 42-year-old Schwankert, an American journalist and diving instructor who has lived in Beijing for more than a decade.
The Poseidon was barely two years old and among the most modern submarines in the British fleet when it arrived at a leased British naval base on Liugong Island, four kilometers (2.5 miles) offshore from the port of Weihai.
While conducting exercises on June 9, 1931, the captain inadvertently turned into a Chinese cargo ship that had altered course in the same direction to avoid hitting the submarine, which was traveling on the surface.
Its hull shattered, the Poseidon sank within four minutes, coming to rest on the sea floor 30 meters (100 feet) below.
Thirty men scrambled out of hatches before it went down, but 26 remained inside, eight in the watertight forward torpedo room.