WATCH: Lost WWII U.S. Navy Sub Found in Southern Thailand

Divers '95% certain' wreck is USS Grenadier, scuttled while under attack by Japanese in April 1943

An American submarine sunk off the coast of Thailand in World War II has been found south of Phuket, a team of technical divers reported this week.

Lying upright, partially covered in fishing nets, on a sandy seabed 83 meters under water about 80 nautical miles south of Phuket, the wreck is said to be the USS Grenadier, which was scuttled while under attack by Japanese aircraft and ships on April 21, 1943.

The four-man team are waiting to get their October 2019 finding verified by the United States Naval History and Heritage Command.

“It is every technical diver’s dream to find a piece of history,” said diver Lance Horowitz. “We train a lot for these challenging dives because we like to explore and find what is not easily accessible. This is our first time making such a discovery, but we are searching for other shipwrecks too.”

Horowitz is part of the team of four technical divers that located the Tambor-class sub last year. They located it with side-scan sonar, which allows them to capture images of the seabed from their private yacht.

Horowitz and team member Ben Reymenants live in Phuket while Benoit Laborie and Jean Luc Rivoire live in Singapore. They took six dives over six months through March of this year to try to identify the submarine.

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

“After six dives on the shipwreck, we are now 95% confident that this is the USS Grenadier,” he said.

The reason for the uncertain 5 percent is the team could not find the sub’s name plaque because the topside outer hull and fairwater has eroded and ripped away by nets and anchors from fishing boats, leaving the pressure hull exposed. They did find an electrical resistor inscribed with the name of a Chicago company that has manufactured parts for more than 90 years and used in navy vessels.

“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. 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,” Rivoire said. “It is a truly powerful feeling.”

The team also found the hatches fully opened, a sign that the boat was sunk deliberately and jibes with historical accounts by survivors.

Divers measured various parts of the sub including the conning tower, hatches and capstans. Those measurements matched identically technical drawings of a Tambor-class vessel, the navy’s first fully successful fleet submarine.

Finding the wreck was an exercise in research and personal interviews in Thailand.

They had searched archives of twelve countries that had World War II-era submarines reported lost and not yet found in the Strait of Malacca. That narrowed it down to three possible subs. The description and dimensions seemed to match the USS Grenadier perfectly.

Reymenants gathered coordinates from various sources, most of them local fishermen who reported often losing nets while trawling. They assumed they were snagged on rocks or reefs.

The team used the side-scan sonar to search the coordinates until they saw the sub’s shape on the sonar screen.

The divers aren’t disclosing the wreck’s precise location because of the frequent looting of historical wrecks for scrap metal. They also are working with relevant government agencies and following their guidelines about war heritage sites.