The Lockheed D-21 was one of the most ambitious spy aircraft ever conceived—a pilotless reconnaissance drone designed to fly faster than Mach 3, cruise at the edge of space, penetrate the world’s most heavily defended airspace, and photograph China’s secret nuclear facilities without risking a single American pilot. Born in the aftermath of the U-2 incident that brought down Francis Gary Powers, the D-21 represented the cutting edge of Cold War technology, combining Blackbird-inspired stealth, extreme speed, and revolutionary unmanned flight. But turning that vision into reality proved far more dangerous than anyone expected. A catastrophic midair collision claimed the life of a test crewman, repeated operational missions ended in bizarre failures, priceless intelligence sank to the bottom of the Pacific, and one of the world’s most advanced drones ultimately crashed inside enemy territo

Source: The Mach 3 Ghost That Simply Vanished