[lentulusgracchus]

The Boeing 720 saw some limited civilian use but airlines wanted the longer 707 for extra passenger capacity so the 720 was used mostly by the military for refueling and other missions (RC-135, VIP etc.)

Are you sure about that? (I do remember vaguely seeing something about former Boeing 720's in military service.) With a different airframe, the Boeing 720 should have had a separate military designation to distinguish it from military C-135's and VC-135's and their recon/EW kin.

[saganite]

Apparently I’m not sure about that. The 707 lineage is a little more complicated than I thought. Ignore anything I said on the subject!