The SR-71 Blackbird’s Secret Drone Sibling Flew 4 Missions & Failed Every One

In some ways, the Lockheed D-21 spy drone appears as a program ahead of its time. In other ways, it is a reminder of a pre-digital and pre-satellite world, and a time long before Google Maps’ satellite view existed. The D-21 was an early attempt to replace or complement manned reconnaissance flights over hostile territory following the development of effective Soviet surface-to-air missile defense systems that rendered even high-flying high-Mach aircraft vulnerable.