HTMS Sattakut

The wreck's final resting angle is contested off Koh Tao's west coast: most accounts describe it upright on the sand, one instead on its starboard side; either way, the wheelhouse rises to about 18 metres and the hull runs down to a 30-metre seabed. Most dives start on the superstructure and work along the deck toward the bow and stern, where two Bofors 40mm anti-aircraft guns are still mounted, exactly as they were when she was in active service. Fusiliers move over the hull in loose schools, yellowtail barracuda circle at range, and a resident giant grouper works the same stretch of deck most divers describe passing. Moray eels and lionfish sit in the crevices between compartments; blue-spotted stingrays and the occasional Jenkins whipray rest on the sand around the base.

Divers trained for overhead environments can drop through one of several open hatches and follow the corridors inside, torch and reel out, past portholes that still let outside light filter through the hull. Everyone else stays on the exterior, which alone covers the wreck's full depth range and holds the same guns, coral growth and fish life visible from the outside. The standard boat trip pairs the wreck with the calmer Hin Pee Wee reef 30 metres away, usually reef first, wreck second, so the dive opens gently before the steel comes into view.

HTMS Sattakut's draw is a genuine WWII combat record: a decommissioned Royal Thai Navy vessel, deliberately sunk to give Koh Tao's Advanced-level divers something beyond a training tank. Local dive schools run their PADI and SSI Wreck Diver courses on this specific hull, so repeat divers treat it as a working wreck: one diver reported doing it around fifty times and still returning to it.

Visibility swings harder here than a single advertised range suggests: divers have described the same week as near-zero on one dive and the clearest they had seen the site on another, sometimes shifting from bow to stern within a single dive.

She was built as USS LCI(L)-739, a Landing Craft Infantry launched at Commercial Iron Works in Portland, Oregon, on 27 February 1944 and commissioned into the US Navy a week later1. Reclassified twice during her wartime service, first as gunboat LCI(G)-739 in December 1944 and then as mortar-support vessel LCI(M)-739 the following April, she earned three battle stars: the Western Caroline Islands and Palau campaign in late 1944, Iwo Jima in early 1945, and the Okinawa Gunto operation that ran through to June 19451.

After the war she passed to the Royal Thai Navy and was renamed HTMS Sattakut, hull number 742, entering Thai service around 1946 or 1947, sources differ on the exact year though her identity and WWII record are not in dispute. She served for years afterward before being set aside for a new role: on 18 June 2011 the Department of Marine and Coastal Resources sank her near Koh Tao as a deliberate artificial reef1. The first attempt, in rough weather, left her lying on her side; a salvage team righted her and moved her to her current position near the Hin Pee Wee reef in early August 2011. Her final resting angle is disputed, upright on the sand versus her starboard side, but her hull, wheelhouse, portholes and both Bofors 40mm anti-aircraft guns remain intact and colonised by coral, sponge and reef fish.

She is not to be confused with two other Thai Navy wrecks that sometimes surface in the same searches: an uncorroborated "HTMS Suphairin" or "HTMS Hanhak Sattru," and "HTMS Hanhak Sattru 312," a separate wreck a Koh Tao operator lists under its own page.

Crystal Dive and Big Blue Diving each teach their own wreck course on this hull, so divers can train for the interior and not just book the exterior dive. A torch is worth carrying even if you stay outside: several compartments are visible through the portholes and open hatches without going in. Nitrox extends useful bottom time across the working depth, and a reel, line and knife belong on anyone planning to go inside.

The vessel was cleared of fuel and hazardous material before scuttling, so treat the coral and sponge growth on the hull as living reef and leave it undisturbed; hold your position near the structure with buoyancy control, never a handhold.