Did you know, that it's actually effortless to get a tank out of Fort Zancudo? You don't have to be level 70 and have 1.5 million in the bank, or get some level 20 to lend you a Cargobob, and attempt to steal one from the Fort.
In fact, did you know, that they actually drive straight out the front gate, and are docile once they leave the base? Giving you a free tank to jack for only one star? I just found this out today when trying to Cargobob a tank out of Fort Zancudo to go after a guy on a tank rampage.
They will only drive out of the base, when you don't have any stars, even a level 3 can get a tank from the base! I had no idea. (O_O')