Yep, it's an M-21 Blackbird carrying a D-21 recon drone. Only 3 were ever built (following the production of the A-12), and they were designed to fire the D-21 drone into Russian airspace since Russia and the United States had signed a treaty to banned MANNED flights over each other's land. Hence, the D-21 was used as an UNMANNED version of the SR-71 (same engine and all). The plane was cancelled when a D-21 collided with the M-21 it had just been launched from, killing the crew.
Your go, Mike Rotch.