Divers believe they have found the wreck of a US Navy submarine lost 77 years ago in Southeast Asia during World War II.
The team have sent photos and other evidence from six dives made from October 2019 to March this year to the United States Naval History and Heritage Command for verification they have found the USS Grenadier, one of 52 American submarines lost during the conflict.
The 1,475-ton, 93-metre long Grenadier was scuttled by its crew after bombs from a Japanese plane almost sent them to a watery grave.
All 76 personnel survived but their agony to follow would be prolonged.
After being taken prisoner, they were tortured, beaten and nearly starved by the Japanese for more than two years, and four did not survive.
The wreck lies 82 meters underwater in the Strait of Malacca, about 150 kilometres south of Phuket, Thailand.
It was discovered by Singapore-based Jean Luc Rivoire and Benoit Laborie of France, and Australian Lance Horowitz and Belgian Ben Reymenants, who live in Phuket.
Reymenants was one of the divers who took part in the dramatic rescue of a dozen boys and their soccer coach trapped in a cave in northern Thailand two years ago.
The Belgian has been researching locations for shipwrecks for years, Horowitz said, and Rivoire had a suitable boat to explore the leads he found.
Reymenants would ask fishermen if there were any odd spots where they'd lost nets and then they would use side-looking sonar to scan the sea floor for distinct shapes.
When they dived to look at one promising object, it was a lot bigger than expected, so they dug back into the archives to figure out which lost vessel it could be, and dived again.
"And so we went back looking for clues, nameplate, but we couldn't find any of those," recalled Horowitz.
"And in the end, we took very precise measurements of the submarine and compared those with the naval records. And they're exactly, as per the drawings, the exact same size. So we're pretty confident."
The Navy command's Underwater Archaeology Branch on average receives two to three such requests a year from searchers like the Grenadier divers, said its head, Dr Robert Neyland.
"A complete review, analysis and documentation may take two months to a year to complete," he said.
The Grenadier left Pearl Harbor on February 4, 1942, on its initial war patrol.
It sailed on March 20, 1943, from Fremantle, Australia, on its sixth patrol, to the Malacca Strait and north into the Andaman Sea.
Commanding officer John A. Fitzgerald recorded what happened there in a report written after being freed in 1945.
On the night of April 20, the submarine glimpsed two small freighters and set course to intercept them the next morning, sailing on the surface for speed.
In the morning, a plane was sighted; an immediate crash dive was ordered but the ship did not descend far enough, fast enough.
Blasts from two bombs battered the sub; key parts of the vessel were mangled; power and lights were lost and a fire broke out.
All hands desperately worked to fix what they could as Fitzgerald ordered the ship to stay on the sea floor.
When it surfaced after 13 hours it was clear the Grenadier was too crippled to flee or fight.