Animate Sub-Object Z Axis

Hi all!
I'm trying to animate a pseudo tank, so when it shoots, it's combat tower(where the canon is) goes a bit backward and forward again, to get an effect of recoil. I'm doing that by animating the combat tower Z axis, but when playing the game, the combat tower recoils using the tank's body's Z axis. So if the tank's body is fifty degrees turned and the combat tower is ninety, the combat tower's recoil will be relative to the tank rotation and not it's own. Could someone help me with this please?