Served in the Air Force from 1950 to 1958, fighting in the Korean War then serving as a test pilot and flight instructor. In early 1959, he volunteered for the NASA space program and flew on the second Mercury spaceflight, the Liberty Bell 7. He also flew on the Gemini 3 mission in March 1965, becoming the first American to fly into space twice. He was killed in the Apollo 1 fire.