Project Mercury also excluded civilian NASA X-15 pilot Neil Armstrong, though he had been selected by the US Air Force in 1958 for its Man In Space Soonest program, which was replaced by Mercury. Although Armstrong had been a combat-experienced NAP during the Korean War, he left active duty in 1952. Armstrong became NASA's first civilian astronaut in 1962 when he was selected for NASA's second group, and became the first man on the Moon in 1969. It was further stipulated that candidates should be between 25 and 40 years old, no taller than , and hold a college degree in a
Neil Armstrong Armstrong's engineering ability. Milt Thompson said he was "the most technically capable of the early X-15 pilots". Bill Dana said Armstrong "had a mind that absorbed things like a sponge". Those who flew for the Air Force tended to have a different opinion, especially people like Chuck Yeager and Pete Knight, who did not have engineering degrees. Knight said that pilot-engineers flew in a way that was "more mechanical than it is flying", and gave this as the reason why some pilot-engineers got into trouble: their flying skills did not come naturally. Armstrong made seven flights in the X-15 between