Lockheed D-21

The Lockheed D‑21 was a pioneering supersonic reconnaissance drone developed in the late 1960s by Lockheed Corporation for the United States Air Force. Born from the abortive M‑21 carrier aircraft concept, the D‑21 was launched from a modified A‑12 or later from a B‑52 bomber, reaching speeds above Mach 3 and cruising at altitudes of 90,000 feet. Its sleek, cigar‑shaped fuselage housed a single Pratt & Whitney J58 turbo‑ramjet engine, providing the thrust needed for sustained hypersonic flight. Guidance relied on an inertial navigation system supplemented by terrain‑contour matching, while a sophisticated optical‑camera payload captured high‑resolution imagery of hostile territory. Only 30 airframes were built, and the program suffered several high‑profile failures, but the D‑21 demonstrated that unmanned platforms could survive the extreme thermal and aerodynamic loads of Mach‑3+ flight. The aircraft’s legacy lives on in modern high‑speed UAVs such as the MQ‑9 Reaper’s “Uav‑21” concepts and in the continued development of hypersonic reconnaissance concepts. The D‑21 remains a milestone that proved the feasibility of autonomous, high‑altitude, high‑speed intelligence gathering, influencing both military doctrine and aerospace engineering. Its impact can be traced to today’s hypersonic cruise missiles and experimental aircraft such as the SR‑72, confirming the D‑21’s enduring relevance.

Lockheed Corporation

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