The divers have sent photos and other evidence from six dives they made from October 2019 to March this year to the United States Naval History and Heritage Command for verification that they have found the USS Grenadier, one of 52 American submarines lost during the conflict.
The 1,475-ton, 307-foot long Grenadier was scuttled by its crew after bombs from a Japanese plane almost sent them to a watery grave.
All 76 of its personnel survived the bombing and sinking, but their agony to follow would be prolonged.
After being taken prisoner, they were tortured, beaten and nearly starved by their Japanese captors for more than two years, and four did not survive that ordeal.
The wreck lies 270 feet underwater somewhere in the Strait of Malacca, about 92 miles south of Phuket, Thailand.
We’re pretty confident that it is the USS Grenadier
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, Thailand.
Mr Reymenants was one of the divers who took part in the dramatic rescue of a dozen boys and their football coach who got trapped in a cave in northern Thailand two years ago.
The Belgian has been researching possible locations for shipwrecks for many years, Mr Horowitz said in an interview, and Mr Rivoire had a suitable boat to explore the leads he found.
Mr Reymenants would ask fishermen if there were any odd spots where they had lost nets, and then the team 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 try to work out which lost vessel it could be, and then dived again.
“And so we went back looking for clues, nameplate, but we couldn’t find any of those,” recalled Mr 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 that it is the USS Grenadier.”
The Grenadier left Pearl Harbour on February 4 1942, on its initial war patrol.
Its first five missions took it to Japanese home waters, the Formosa shipping lanes, the southwest Pacific, the South China Sea and the Japanese-occupied Dutch East Indies (now Indonesia).
It sank six ships and damaged two.
It sailed on March 20 1943, from Fremantle, Australia, on its sixth patrol, to the Malacca Strait and north into the Andaman Sea.
The commanding officer, Lieutenant Commander John A. Fitzgerald, recorded what happened there in a report written after being freed from a Japanese prisoner-of-war camp 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.
When it surfaced after 13 hours it was clear the Grenadier was too crippled to flee or fight.
Codebooks and sensitive equipment were destroyed as preparations were made to scuttle the submarine.
The crew abandoned ship and an hour later were hauled aboard an armed merchant ship, which took them to Penang on the Malayan Peninsula.
