Make a short mission with one of each tank, be gunner, and hit the other tank. When the crew leaves the tank and you have killed them, go to the other tank at look at the damage done.
In my last test it hit the T-100 in the tracks, crew abandon the vehicle, I shoot them. Then I got to the damaged T-100. I target my own M2A1 and hit it in the tracks, crew leaves again...