 The 707-700 was a test aircraft used to study the feasibility of using CFM International CFM56 engines on a 707 airframe and possibly retrofitting existing aircraft with the engine.After testing in 1979, "N707QT", the last commercial 707 airframe, was restored to 707-320C configuration and delivered to the Moroccan Air Force as a tanker aircraft via a "civilian" order.Boeing abandoned the retrofit program, since it felt it would be a threat to the Boeing 757 and Boeing 767 programs.