The vast majority of the current U.S. tree is made up of prototypes that never saw any real production or combat. A lot of the German mediums are prototypes, the tier 9 and tier 10 heavies are prototypes, and so is most of the top of the German artillery line. Even some of the turret and gun combinations on some of the tanks were prototypes.
The entire game is made up of fantasy combinations and prototypes for the most part, with fantasy armor ratings and all sorts of crap like that.
It's a fun game, but if you're looking for realism and historical based vehicles and the like, you'll be sorely disappointed.