File:Lockheed M-21 with D-21 drone and Boeing 737-300.jpg

Here at the Seattle - Boeing Museum of flight, a genuine CIA M-21 from "Project Oxcart", and the first 737-300, in its launch company colors for US Air. As everyone knows, the SR-71 began life as a CIA program to replace the U-2 with something much faster and much higher flying. When an (NATO named) SA-2 "GUIDELINE" missile shot-down Frances Gary Powers' U-2, someone schemed the D-21, a supersonic drone that would be released by an M-21 at high altitude and high speed, fly high and fast over "denied terrirtory" ie Soviet Union or the People's Republic of China, and bring back the film. I can't remember if the whole drone would be recovered (ala the Ryan Firebee derivatives) or if only the film was expected to be caught in mid-air (ala the Corona film return recon. satellites). In any event, a trial drone launch went very wrong and destroyed both the drone and the launcher. A-12s were single-seat, the second seat being added for the drone controller. Undeniably cool, it was WAY too dangerous, and never went live. Lockheed also pitched an A-12 derivative as the YF-12, a strategic fighter carrying the Eagle missile which would evolve into the AGM-54 Phoenix for the Navy's F-14s. The USAF's SR-71 was the full-boat production endpoint. Two seats because they wanted 2 sets of eyes and brains, vs CIA who had only one seat because it was cheap and they were all about performance. DId CIA have their own SR-71s operating with USAF markings? That's above my pay grade. Did they operate A-12s in parallel? Personally, I doubt it. But I could be wrong. US Air and Southwest were the two launch customers for the model. Lufthansa was the launch customer for the 737-100. Boeing bought this airframe when US Air retired it (based on hours and cycles) and used it to test various theories about the two, fatal, hard-over accidents that have occurred with 737s. Both involved an airplane that suddenly dived into the ground, in spite of the pilots' best efforts. Among other theories tested, this plane was subjected to the "Fat Guy" hypothesis, which suggested that a very over-weight passenger could have damaged the floor of a 737, and thus pulled suddenly on the cables that run from the cockpit to the tail surfaces. No credible weight and shoe-size could be found that would damage a floor. Which is somewhat reassuring, I think. When they'd finished testing the plane, someone suggested the remaining pieces could be given to the museum, and they were.