The Battle of Peleliu, codenamed Operation Stalemate II by the US military, was fought between the United States and Japan during the Mariana and Palau Islands campaign of World War II, from 15 September to 27 November 1944, on the island of Peleliu.
US Marines of the 1st Marine Division and then soldiers of the US Army's 81st Infantry Division fought to capture an airfield on the small coral island of Peleliu. The battle was part of a larger offensive campaign known as Operation Forager, which ran from June to November 1944 in the Pacific Theater.
Major General William Rupertus, the commander of the 1st Marine Division, predicted that the island would be secured within four days. However, after repeated Imperial Japanese Army defeats in previous island campaigns, Japan had developed new island-defense tactics and well-crafted fortifications, which allowed stiff resistance and extended the battle to more than two months. The heavily-outnumbered Japanese defenders put up such stiff resistance, often by fighting to the death in the Japanese Emperor's name, that the island became known in Japanese as the "Emperor's Island."
In the US, it was a controversial battle because of the island's negligible strategic value and the high casualty rate, which exceeded that of all other amphibious operations during the Pacific War. The National Museum of the Marine Corps called it "the bitterest battle of the war for the Marines".
Background
By 1944, American victories in the Southwest and Central Pacific had brought the war closer to Japan, with American bombers able to strike at the Japanese main islands from air bases secured during the Mariana Islands campaign (June–August 1944). There was disagreement among the U.S. Joint Chiefs over two proposed strategies to defeat the Japanese Empire. The strategy proposed by General Douglas MacArthur called for the recapture of the Philippines, followed by the capture of Okinawa, then an attack on the Japanese home islands. Admiral Chester W. Nimitz favored a more direct strategy of bypassing the Philippines but seizing Okinawa and Taiwan as staging areas to an attack on the Japanese mainland, followed by the future invasion of Japan's southernmost islands. Both strategies included the invasion of Peleliu, but for different reasons.
The 1st Marine Division had already been chosen to make the assault. U.S. President Franklin D. Roosevelt traveled to Pearl Harbor to personally meet both commanders and hear their arguments. MacArthur's strategy was chosen. However, before MacArthur could retake the Philippines, the Palau Islands, specifically Peleliu and Angaur, were to be neutralized and an airfield built to protect MacArthur's left flank.
Preparations
Japanese
By 1944, Peleliu was occupied by about 11,000 Japanese of the 14th Infantry Division, along with a handful of Korean laborers. Colonel Kunio Nakagawa, commander of the division's 2nd Regiment, led the preparations for the island's defense.
After their losses in the Solomons, Gilberts, Marshalls, and Marianas, the Imperial Army assembled a research team to develop new island-defense tactics. They chose to abandon the old strategy of trying to stop the enemy on the beaches, where they would be exposed to naval bombardment. The new tactics would only disrupt the landings at the water's edge and depend on an in-depth defense further inland. Colonel Nakagawa used the rough terrain to his advantage by constructing a system of heavily fortified bunkers, caves, and underground positions, all interlocked in a "honeycomb" system. The traditional "banzai charge" attack was also discontinued as being both wasteful of men and ineffective. These changes would force the Americans into a war of attrition, requiring more resources.
Nakagawa's defenses were centered on Peleliu's highest point, Umurbrogol Mountain, a collection of hills and steep ridges located at the center of Peleliu overlooking a large portion of the island, including the crucial airfield. The Umurbrogol contained some 500 limestone caves, connected by tunnels. Many of these were former mine shafts that were turned into defensive positions. Engineers added sliding armored steel doors with multiple openings to serve both artillery and machine guns. Cave entrances were opened or altered to be slanted as a defense against grenade and flamethrower attacks. The caves and bunkers were connected to a vast tunnel and trench system throughout central Peleliu, which allowed the Japanese to evacuate or reoccupy positions as needed and to take advantage of shrinking interior lines.