Have you ever heard of a little application called; "Smashy road"?
I do think I know who stole your tank! Arnold Schwarzenegger. He took it to utah to blow up some shit but unfortunately the local sheriff's department had a little something to say about this. You don't fuck with the terminator though and Arny decided to blow up an entire town. 6 hours and about 400 casualties later, Arny decided it wasn't worth the trouble and gave himself up. Arnold Schwarzenegger, age 74, is currently being held in the utah state prison, in a cell without a window.
I also managed to turn my tank upside down! Drive to the bottom of the map and keep driving against the barrier, boom! Upside-down tank.