I got a cool way to get army vehicles such as a Patriot, a Rhino and a Barracks without cheats and with a little police intense action.

First you have to own the Abandoned airport in Verdant Meadows which is in the desert near Bone County. Then you must locate the Military base which is right beside your airport to the east. Get a fast vehicle and go around the sides of the military base until you reach a little fence that you can break through with your car. Once you enter the base you will recive 5 wanted stars so make it quick and grab whichever army vehicle you want. make your way out of the base the same way you came in and go back to the abandoned airport and put the vehicle in the big hangar. then go inside your little house and save your game. When your done saving your wanted stars will be gone and you can do it again. It takes a while but its worth it when your drivin downtown los Santos in a friggin Tank. or its cool in 2 player mode to raid the military base and stel some crap.