Also, you can't just break a single piece of armor off. I'd make the armor intrinsic to the vehicle, and increase the DR: unless you have something that's made to penetrate tank armor, you can't penetrate it reliably...

Furthermore, its machine guns are too light... give them static modifiers to damage, and increase the rate of fire. I'd also boost the main cannon to at least 6d6 +mod damage. Most likely at least 10d6, since it can probably blast through a 2-in iron door.