A team of experts took five days last week to clear their way into just one small cave with a 7ft opening.
Archaeologists found a set of bones which are believed to be human and will be taken back to Japan for testing.
“They found some bones while they were clearing the entrance of the cave,” Bernadette Carreon, a local journalist, told ABC Radio. “They did not use heavy equipment because they have to make it clear of heavy ordnance. When it’s clear, the archaeologists can go in and start bone collection.”
Marines smoke cigarettes, but keep their weapons close in a blasted landscape of Peleliu Island, Palau during WWII
The attempt to find the bodies has been welcomed in Japan and is part of an effort to end a brutal chapter from the war, in which US marines were pitted against Japanese troops who had set up their defences in the intricate labyrinth of heavily fortified caves and underground bunkers. It is still regarded as one of the harshest conflicts in the history of the marines.
Unlike previous battles in the Pacific, the Japanese did not focus their defence on using suicide charges to prevent the Americans from establishing a beachhead.
Instead, the Japanese forces largely allowed the marines to land but staged their defence from inside the caves.
The Japanese, who had occupied Palau for about 30 years, had spent decades using dynamite and axes to enlarge existing caves on Peleliu and blast out new ones. The caves and their entrances were then heavily camouflaged.
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The US forces expected the battle in September 1944 to last only four or five days. “It will be a hard-fought quickie,” predicted William Rupertus, the US marine commander. It took more than 10 weeks.
More than 1,600 US soldiers were killed during the battle, which ended with the marines blowing up many of the caves, leaving thousands of the enemy trapped inside. Shortly before the Americans finally seized the small island in late November, Col Kunio Nakagawa, the Japanese commander, atoned for his defeat by committing ritual suicide in his post.
About 35 Japanese soldiers remained hiding in the caves until April 1947, more than 18 months after the war officially ended. They were the last troops to surrender.
Keiji Nagai, 93, and Kiyokazu Tsuchida, 95, two of the 35 soldiers who surrendered in 1947, met the Japanese emperor and empress earlier this month to provide an account of the hand-to-hand combat they experienced during the battle. The empress quietly told Mr Nagai: “You went through a lot.”
Authorities began collecting the remains at various locations around the island in 1953, but Japanese authorities say 2,600 soldiers have yet to be found. The bodies are believed to be holed up inside about 200 caves which were deemed dangerous and left sealed to prevent public access. About 450 Japanese soldiers survived the battle and later helped to direct the authorities to the site of graves.
The island of Peleliu (Alamy)
The entire island has become something of a monument to the battle, with unexploded bombs a constant threat to residents and tourists. Following the war, Japan created a peace park which included a Shinto shrine with the inscription “To all countries’ unknown soldiers”.
Officials in Palau have worked closely with Japan to try to recover the remaining bodies and return them to the families of the soldiers. Some representatives of the families of the Japanese soldiers have assisted with the search.
Sachio Kageyama, from a group representing families and fellow soldiers of those who fought on the island, told The Japan Times: “I hope the forthcoming visit by the emperor will pave the way for [further] collection of remains.”
Palau, a remote cluster of islands east of the Philippines with a population of about 21,000, was the scene of heavy fighting during the war. The fierce battle at Peleliu was over an airfield now deemed of questionable strategic value by most historians.
The search for the bodies has also focused on a long-lost mass grave on the western side of the island, close to where the current cave search is being conducted.
US military documents indicating the cemetery’s location were found two years ago at a naval museum in California. The documents included a map created in January 1945 which says “Japanese cemetery” and points to the centre of the island. A separate report from a construction battalion says that logs were placed on the site to prevent people disturbing the graves. US officials reportedly told Palau in 1994 that a mass grave was located near Nakagawa’s grave.
US experts have also been searching Palau’s coral reefs, lagoons and islands for planes that were lost in the conflict. Last year, underwater robots were used to find two warplanes on the ocean floor.