The SA-71 was years in research and development, a weapon fielded during the height of the cold war, before it was eventually ousted because of satellite technology.
Borderline space technology itself, it flew so high that pilots had to wear pressurized space suits. Unarmed, the reconnaissance jet flew at three times the speed of sound — but it also suffered a 30 percent crash rate; of the 32 SR-71 built, the U.S. eventually lost more than a third to crashes.
Nonetheless, it maintained its stealth superiority for decades, resisting replacement even against newer technology and newer designs.