Ewbank joined the U.S. Navy in 1943 as American involvement in World War II intensified. He was assigned for training to Naval Station Great Lakes near Chicago, where Paul Brown, a former classmate who succeeded him as Miami's starting quarterback, was coaching the base football team. Brown had become a successful high school coach in Ohio before being named head football coach at Ohio State University in 1941. At Great Lakes, Ewbank was an assistant to Brown on the football team and coached the basketball team.