Incidentally the A-12 (basically a single seat SR-71) was adapted into the M-21 that carried a D-21 drone. This was a failure though, and the Chinese now have

Incidentally the A-12 (basically a single seat SR-71) was adapted into the M-21 that carried a D-21 drone. This was a failure though, and the Chinese now have a wreck of a D-21 in one of their museums.