HERE IS THE "LOCKHEED D-21". They built a Drone and placed that as "piggy-back" on to an "SR-71". Here is what Wikipedia says about it: The Lockheed D-21 was an American reconnaissance drone with maximum speed in excess of Mach 3.3 (2,215 mph; 3,564 km/h). The D-21 was initially designed to be launched from the back of a M-21 carrier aircraft, a variant of the Lockheed A-12 aircraft. Development began in October 1962. Originally known by the Lockheed designation Q-12, the drone was intended for reconnaissance deep in enemy airspace.

The D-21 was designed to carry a single high-resolution photographic camera over a preprogrammed path, then release the camera module into the air for retrieval, after which the drone would self-destruct.[1] Following a fatal accident when launched from an M-21, the D-21 was modified to be launched from a Boeing B-52 Stratofortress. Several test flights were made, followed by four unsuccessful operational D-21 flights over the People's Republic of China, and the program was canceled in 1971.