As Zathros stated, all actual mission deployment of drones was done with B-52. Only first four test launches was made from Blackbird (M-21). Fourth launch ended by accident and the carrier was lost when drone colided with the carrier after its release. Carrier pitched up, front half of the plane separated. One pilot drowned after ejection, because he can not get to his life raft due his injuries. Having opened his helmet visor his suit filled with water. Programe was stoped and drones was modified for B-52.