BEIJING (AP).- 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.

In a daring move, the eight popped the hatch and attempted to surface using a Davis lung, an early forerunner of scuba gear that included a store of pure oxygen and a kind of canvas brake to prevent rising too quickly. Led by Petty Officer Patrick Willis, six of them made it to the surface, the first-ever such escape in the history of submarining.

That led to a shift in standard navy procedure from waiting for rescue to immediately seeking escape, along with the later development of escape chambers to allow surfacing without suffering from the bends caused by a too-rapid ascent.

The Poseidon tragedy received wide publicity at the time, in part because of the court martial of the captain, Lt. Cmdr. Bernard Galpin, who was found culpable. A feature film was made about the events. But the accident was afterward consigned to history, eclipsed by the ensuing drama of World War II and dogged by a stigma surrounding naval deaths during peacetime.

Schwankert and documentary makers Arthur and Luther Jones sought to fill in gaps in the story both at Weihai and Britain's naval archives. The book and film are fleshed out by discussions with descendants, two of whom later travel to the site of the sinking to lay a wreath and search for a memorial to the men who died.

It was in 2006, about a year into the project, that Schwankert first came across references online that the Chinese had raised the sub. He tracked down an account of the salvage operation in a 2002 Chinese naval magazine.

As the project evolved, a key question emerged: Why had China opted to salvage the sub? Naval convention frowns upon such secret operations.

Although Schwankert never definitively answers the question, it wasn't for lack of trying.

He attempted several times to interview the two engineers in charge of the 1972 operation, finally seeking to meet them under the pretext of presenting gifts from Poseidon descendants. Each time he was rebuffed.

His research prompted Britain's Defense Ministry to ask China for details. Chinese authorities confirmed the salvage operation but said poor record-keeping and the passage of time had left no additional information.

Schwankert considers a number of possible motives, including recycling the steel hull or studying the submarine's construction. But he believes it most likely that China wanted to test salvage techniques at a time when its navy was preparing to launch a modern submarine fleet.

Schwankert happened on the story of the Poseidon while researching the possibility of diving wrecks from the 1894-1895 Sino-Japanese War.

"I feel absolutely, stupidly lucky for stumbling on it," he said.

That 2005 discovery prompted him to contact longtime friend Arthur Jones, who was attracted as much by the subject matter as by Schwankert's enthusiasm, as witnessed on an early visit to Weihai.

"The idea of a personal obsession — that really drew me in," Jones said by phone from his home in Shanghai.

Along with documenting Schwankert's quest for answers, the film uses footage from the 1930s. Poignant moments show descendants watching old newsreels of the events, including David Clarke seeing footage for the first time of his grandfather, survivor Reginald Clarke, receiving a medal.

"You can really see how those events continue to have ramifications over people's lives," said Jones, who hopes to begin showing the documentary, "The Poseidon Project," at festivals later this year.

The book and film come at a time when China is beginning to rediscover its naval history, as illustrated by the extensive publicity given to the ongoing excavation of the almost 2,000-year-old Nanhai One merchant vessel.

"The discoveries in the next five years will be mind-blowing, something like the discovery of the terracotta warriors but at sea," Schwankert said.

"The Real Poseidon Adventure: China's Secret Salvage of Britain's Lost Submarine" is due out in 2013 from Hong Kong University Press.




Copyright 2012 The Associated Press.