by Animats 5 hours ago
That was also said about the B-707, which was supposed to have some parts commonality with their KC-135 Stratotanker built for the USAF. But as development progressed, the airliner and the tanker diverged.
The B-747 went through a similar process. Boeing was proposing a big cargo aircraft to the USAF (the CX-HLS), but that was never built. Lockheed got the C-5 contract instead, which satisfied the USAF's need for a really big cargo plane. So the B-747 was built as a commercial plane, mostly to Pan Am's requirements.
Military-civilian commonality was mostly wishful thinking at the management levels, as it turned out.
The Lockheed L-100 Hercules does exist and is apparently a civilian C-130
It still does happen though, so not totally wishful thinking - but it seems to go the other way, commercial to miliary e.g. like the KC-30A tanker which are converted from standard commercial A330-200s (and as I understand the new version will be from A330neos).
The 707 was redesigned with a wider fuselage to carry the number of passengers the airlines wanted.