The SR-71 should be on this list. <2 years from idea to one of the most remarkable aircraft ever built. Also quite fast :)
Look at the defense allocations for basic research into hypersonic capable materials to prove that they are still years away the most basic deployment and once the research is done, there is no supply base to make the materials (FA8650-20-S-5003)
How many aircraft today can fly horizontally over 2,000 mph?
". . . maybe."
It may have been fast 50 years ago?