Most airliners airframes have been adapted to military use. KC-135 Tanker came first, then the 707. KC-10 tanker from the DC-10. 767 airframes as radar aircraft and military tankers in foreign air forces. 747 as E-4 airborne military control center. 737 as the Navy anti-submarine P-8 Poseidon. Lockheed Electra airliner as the Navy P-3 Orion anti-submarine aircraft. Etc.
Good Lord! i didn’t know that.