The USS Grenadier, one of 52 US Navy submarines lost during WW2, has been claimed as found by a technical-diving team at a depth of 83m off the coast of Thailand.

The Tambor-class Grenadier (SS-210), regarded as the navy’s first fully successful fleet submarine, was pursuing two Japanese ships off Phuket when it was damaged by an enemy aircraft on 21 April, 1943.

After 15 hours’ frantic repair work on the seabed the crew managed to get the submarine back to the surface, but the damaged engines couldn’t move it. Seeing vessels in the distance, they decided to scuttle Grenadier to stop it falling into enemy hands.

The 76 men waited to be picked up by a Japanese armed merchant ship – and ended up spending the rest of the war in prison camps in Japan, where four of them died.

The four well-established technical divers, from France, Belgium and New Zealand, had launched an expedition to check various marks gathered mainly from fishermen, using side-scan sonar from their Singapore-registered yacht.

They located the wreck some 80 nautical miles south of Phuket in October last year, and explored it using closed-circuit rebreathers and DPVs. The submarine sat upright on sand, partially covered by fishing nets and with its hatches fully open, consistent with having been sunk deliberately.

There was no nameplate, however.

“The topside skin of the submarine has been eroded and probably torn off by the nets and anchors of fishing-boats, leaving the pressure-hull exposed,” said one of the dive-team, Ben Reymenants. But the divers did find a resistor marked with the name of a Chicago-based company that has been making electrical parts for naval vessels for more than 90 years.

“After six dives on the shipwreck, we are now 95% confident that this is the USS Grenadier,” said Reymenants’ colleague Lance Horowitz.

The team has decided to release the news now, even though they are still waiting for their identification to be verified by the US Naval History & Heritage Command.

“It is every technical diver’s dream to find a piece of history – we train a lot for these challenging dives because we like to explore and find what is not easily accessible,” said Horowitz who, like Reymenants, lives in Phuket. The others, Jean Luc Rivoire and Benoit Laborie, are based in Singapore. “This is our first time making such a discovery but we are searching for other shipwrecks too.

“We could not dive into the site straight away because of bad weather conditions and strong currents. It requires a fair amount of planning. Some of the risks when diving 80m deep on a wreck with low visibility are entanglement or not finding the line back to our boat at the surface and drifting away in the current while still having to do long decompression stops.”

The team followed their dives by scouring the archives of 12 countries that might have had unaccounted-for submarines in the Strait of Malacca. Of the three possibilities, the wreck seemed a perfect match for the USS Grenadier’s description and dimensions, including details such as the conning-tower, hatches and capstans.

The divers have not disclosed the wreck’s location and say they are co-operating with relevant government agencies and following guidelines on war heritage sites. They plan further dives to explore the guns, torpedo-tubes and periscopes.

“We hope to definitively identify it, bring some closure and honour the memories of the war heroes who served on this ship,” said Reyemants.

The four divers have been diving for many years around the world in deepwater sites and challenging environments such as caves in Florida and South-east Asia.

“It is thrilling, when you arrive at the bottom of the ocean in the middle of nowhere and you start to distinguish the massive silhouette,” said Rivoire.

“It then comes to mind the history attached to it and being lucky enough to be the first one to approach the submarine since it sank more than 75 years ago. It is a truly powerful feeling.”