The SR-71 is a 60's era aircraft. First flight in 64. Its predecessor, the A-12, flew in 62 with construction starting in Sept. 1960. Prior to that these aircraft were a series of paper designs beginning in the late 50's. Early versions of the J-58 were run in the late 50's, but these early engines were not flown in A-12/SR-71; substantial rework was needed to sustain mach 3.