Doing some of my airplane learning, I have come across a point many times that the engines for the Boeing 747 (at least partially) came from Boeing's competitor to the C-5 Galaxy. What was this plane that Boeing had made to compete with the C-5?
In 1964 the US Air Force awarded study contracts for a new cargo aircraft to Boeing, Douglas and Lockheed. The aircraft was called CX-HLS. ( cargo experimental - heavy logistics system)
Lockheed won with the C-5A design. Boeing's design was never built but would have looked like this:
source: Widebody Aircraft Chronology
Source: Boeing archives
Boeing called the aircraft CX-HLS( Cargo Experimental - Heavy Logistics System). It never entered production though.
The below image is of a scaled down model of the CX-HLS.
Details about the CX-HLS can be found here