What is this white-tail, short upper deck 747 I just saw?
All factory freighter 747s have short upper-decks, that includes the -400F and -8F. Some don't, but those are converted from passenger 747s that had the stretched upper-deck.

It could have been a 747-400F contracted by the military, plenty of those come in all-white, such as N404KZ:


source

I don't know on what basis the military prefers contractors over C-5s, etc., but an example of a civilian 747 contracted by the Air Mobility Command that crashed is National Airlines Flight 102.