Interesting as I recently learned the 747 was originally designed for the USAF as a freighter. The military applications of this load system seem very logical to outweigh the practicality of it back in that time. Juan Trippe may have mothballed the initial intent for the aircraft with Pan Am money yet one customer in later years had Boeing pull this old design plan out. Just speculation.
This is an often repeated fact, but it is a bit off. Boeing competed against Lockheed for the CX-HLS contract, which Lockheed won with the C-5.
The Boeing airplane looked like a C-5 with a conventional tail. If you google "Boeing CX-HLS" you will find plenty of drawings and models.
The 747 took technology, but not the airframe itself, from Boeing's CX work.
Later Boeing did shop the 747-400F to the USAF as the "C-33", which confuses the issue. But when metal was cut for the first 747 it was a 100% civilian airframe.