Sometimes I think the people who designed these kinds of saucer crafts actually believed in extra-terrestrial UFOs and were on a mission to try and duplicate what they envisioned their technology would be.
Or, our government has witnessed said technology and tried to recreate/reverse-engineer it? Makes you wonder why they would build something like this just on a without a valid reason behind doing so.
The US government seems to be quite ready to try out a lot of fringe stuff if it provides military applications (see http://en.wikipedia.org/wiki/Stargate_Project). They may as well just have gotten their inspiration from the general flying saucer hype.
I think far more likely, they thought "Saucer? How would that even fly? But wait, what if it was spinning really fast? Hmm... let me get my slide rule...".