In August 1942, Eichelberger was abruptly sent to the Southwest Pacific Area, where he led American and Australian troops in the bloody Battle of Buna–Gona. In 1944, he had notable victories at Hollandia and the Battle of Biak. As Commanding General of the newly formed Eighth Army, Eichelberger led the invasion of the Southern Philippines clearing the islands of Mindoro, Marinduque, Panay, Negros, Cebu and Bohol. By July 1945, his forces had defeated the Japanese on Mindanao. In August 1945, Eichelberger's Eighth Army began a three-year stint as part of the Occupation of Japan. He retired from the Army at the end of 1948.