In 1958, he was selected for the U.S. Air Force's Man In Space Soonest program. In November 1960, Armstrong was chosen as part of the pilot consultant group for the X-20 Dyna-Soar, a military space plane under development by Boeing for the U.S. Air Force, and on March 15, 1962, he was selected by the U.S. Air Force as one of seven pilot-engineers who would fly the space plane when it got off the design board.[41]
In the months after the announcement that applications were being sought for the second group of NASA astronauts, Armstrong became more and more excited about the prospects of both the Apollo program and of investigating a new aeronautical environment. Armstrong's astronaut application arrived about a week past the June 1, 1962, deadline. Dick Day, with whom Armstrong had worked closely at Edwards, saw the late arrival of the application and slipped it into the pile before anyone noticed.[42] At Brooks Air Force Base at the end of June, Armstrong underwent a medical exam that many of the applicants described as painful and at times seemingly pointless.[43]
Deke Slayton called Armstrong on September 13, 1962, and asked whether he would be interested in joining the NASA Astronaut Corps as part of what the press dubbed "the New Nine"; without hesitation, Armstrong said yes. The selections were kept secret until three days later, although newspaper reports had been circulating since earlier that year that he would be selected as the "first civilian astronaut."[44] Armstrong was one of two civilian pilots selected for the second group; the other was Elliot See, also a former naval aviator.[45] See was scheduled to command Gemini 9, but died in a T-38 crash in 1966 that also took the life of crewmate Charles Bassett. Armstrong was the first American civilian in space, but the first civilian was Valentina Tereshkova of the Soviet Union, nearly three years earlier. A textile worker and amateur parachutist, she was aboard Vostok 6 when it launched on June 16, 1963.[46]