The tiny nation of Palau, a remote cluster of islands located east of the Philippines, saw heavy fighting between Japanese and Allied troops during World War II. In September 1944, U.S. and Japanese forces squared off in one of the war’s toughest battles on a narrow coral island called Peleliu. Over 10 weeks of fighting, some 10,000 Japanese forces (along with nearly 1,800 Americans) were killed; the bodies of around 2,600 of the Japanese soldiers were never found. More than 70 years later, investigators are now searching some 200 underground caves in the hopes of locating the lost remains.

One of the costliest battles of World War II began on September 15, 1944, when U.S. Marines landed on Peleliu, a volcanic island in the western Pacific ocean measuring only 6 miles long and 2 miles across. General Douglas MacArthur had pushed for the amphibious attack on the Japanese-controlled island and its airfield in order to diminish the potential threat to future Allied operations in the Pacific. Having learned from past attacks, however, the island’s Japanese defenders took a new strategy. They hunkered down in a vast network of underground caves connected by passageways and tunnels in an attempt to protect themselves from Allied bombardment and bog the enemy down in a protracted conflict that would yield massive casualties.

Though U.S. commanders predicted the battle for Peleliu would last only four or five days, it would stretch on for more than two months, as some 11,000 Japanese troops dug in and defended the island against 28,000 Americans. U.S. forces finally secured the island on November 27, after suffering the highest percentage of casualties of any battle in the Pacific: nearly 1,800 killed and 8,000 more wounded. As it turned out, Peleliu would ultimately prove to have little strategic importance, and would be remembered as one of the most controversial battles of the war.

The Japanese, of course, suffered even more casualties in the Battle of Peleliu. More than 10,000 soldiers were killed, many of them trapped inside their underground bunkers when U.S. forces exploded the caves during the battle. The bodies of some 2,600 Japanese soldiers were never found. In a stunning twist, a group of 35 soldiers survived within the caves of Peleliu, hiding out for some 18 months after the war ended before finally surrendering in April 1947. Two members of this group, both in their 90s, met with Japan’s Emperor Akihito and Empress Michiko last month and described their experience during the battle and its aftermath.

Now, in advance of a planned visit by the emperor and empress to Palau early next month, an international team has been painstakingly searching through some of the 200 long-sealed caves on Peleliu in the hopes of locating the remains of the lost Japanese troops. So far, they have discovered the bodies of six men in a cave located in an area on the island’s western coast known as the promontory.

The remains were found near a heavily fortified concrete bunker containing an anti-gun tank, and search officials believe they belong to the crew that manned the tank. Steve Ballinger, operations director of the non-governmental organization Cleared Ground Demining, told the Australian Broadcasting Corporation that it took a number of days for U.S. forces to capture this heavily fortified location during the Battle of Peleliu. “It’s my understanding that those [bodies] were the crew, perhaps the officer and his men that were manning that gun….[A] number of U.S. soldiers died in that vicinity as well.”

Searchers in the caves have had to proceed with extreme caution, due to the threat of booby traps or unexploded munitions left in the battle’s wake. Ballinger says his team uncovered a number of relics of war during their search around the area where the six bodies were found, including “hand grenades, large projectiles, small arms ammunition and (an) array of explosive remnants of war.” According to Ballinger, Japanese and U.S. anthropologists and archaeologists were allowed to enter the cave where the remains were found, but it has since been resealed, and the bodies of the six soldiers will be repatriated to Japan.