The WWII Borfors (Idk if that is spelled right) and the Flakverling 1 or 2 hit ANY vehicle. It usually 1 hit kills a T90. That is even better than the Pak-40.

I don't know If this is a bug or not, because these two anti-aircraft guns both are cheaper, faster rate of fire, they rotate fully around, and a LOT more damage than the anti-tank guns. The two AAs put the Pak-40 and the M1 on the side of the streets with no jobs... ._.