:Directing an aircraft to intercept an enemy target is not much different from directing a ground to air missile to do the same thing and this was being done by Project Nike in the 1950s. Radar fire control and air defense were big areas of development during WW II and it's not surprising that they would be combined in the post war era, especially once the Soviet Union had nuclear weapons. It's my impression that the designers of SAGE quickly realized the potential of digital computers and had very ambitious goals.  How well things actually would have worked in practice, during a mass air attack on the U.S., as opposed to demonstrations involving a few aircraft, is another question. Of course the same debate is playing out today over missile defense.