In 1941 he was called to United States Marine Corps service as a combat instructor at the Marine Corps Base Quantico in Virginia. He was later deployed to the South Pacific, where his fluency in the Japanese language allowed him to understand spoken orders from the Japanese and to confuse Japanese soldiers with false orders of his own. He became the first to raise the American flag on Bougainville Island in the Landings at Cape Torokina in November 1943. Less than a week later he lost his left leg when a tank he was commanding was attacked after taking out six machine gun nests. He was awarded the Navy Cross for his heroism in this battle, and the Purple Heart for being injured while serving.