Temerario left Indiana later in 1941 to serve in the U.S. Navy as American involvement in World War II intensified. He was initially placed in a physical education program run by Navy coach Tom Hamilton, but later requested a transfer to active duty. He served as a beachmaster during the Philippines Campaign and at Utah Beach during the Normandy landings in 1944. He rose to the rank of lieutenant commander and was in the military until the war ended in 1945.