Project TAGBOARD was a CIA program using a variant of the A-12 spy plane called the M-21. M stood for Mothership because the plane carried the D-21 (Daughter ship) drone. When mated the full ship was designated MD-21. Both were predecessors to the SR-71 blackbird. Interestingly the D-21 drone was originally designated as the Q-12.
Very interesting four minute video narrated by Kelly Johnson including footage of an MD-21 breakup at mach 3. Both the pilot and the LCO survived the mach 3 breakup/ejection but the LCO died when his spacesuit took on water after parachuting into the ocean due to being punctured during the ejection. The pilot was recued. https://www.youtube.com/watch?v=GMyC2urCl_4