SR-71 Blackbird follow-up: A new TERRIFYING Mach 6 spy-drone bomber • The Register
SR-71 Blackbird with D-21B Drone | IPMS/USA Reviews
Lockheed SR-71A Blackbird 61-7958 and D-21 Drone | Warner Ro… | Flickr
GTD-21 TAGBOARD DRONE – Grissom Air Museum
Museum of Flight Reveals Secrets of the SR-71 Blackbird | by Boom Supersonic | Boom Supersonic
Lockheed D-21 - Wikipedia
Chris Bolton Twitterissä: "Thanks to Terry Wu for this. D-21 Drone 501 the complete book of SR-71 blackbird Richard Graham Zenith Press. #501 was the first D-21 drone built. Modified to D21B