A graduate of Purdue University, Armstrong studied aeronautical engineering with his college tuition paid for by the U. S. Navy under the Holloway Plan. He became a midshipman in 1949, and a naval aviator the following year. He saw action in the Korean War, flying the Grumman F9F Panther from the aircraft carrier USS Essex. In September 1951, he was hit by anti-aircraft fire while making a low bombing run, and was forced to bail out. After the war, he completed his bachelor's degree at Purdue and became a test pilot at the National Advisory Committee for Aeronautics (NACA) High-Speed Flight Station at Edwards Air Force Base in California. He was the project pilot on Century Series fighters and flew the North American X-15 seven times. He was also a participant in the U. S. Air Force's Man in Space Soonest and X-20 Dyna-Soar human spaceflight programs.