Physics-wise, AddTorque gives a push and lets momentum spin it. Seems to make more sense, for a tank, to turn at a constant speed and only go directly forwards. This is what I use for "tanks":

Quaternion wantFace = Quaternion.LookRotation(target - transform.position);
transform.rotation = Quaternion.RotateTowards(transform.rotation,
    wantFace, 90 * Time.fixedDeltaTime);
// move towards destination at speed (but don't change fall speed):
Vector3 newVel = Vector3.zero;
// only move if we are close to correct angle:
if(Quaternion.Angle(transform.rotation, wantFace)<5) {
  newVel = transform.forward * spd;
}
newVel.y = rigidbody.velocity.y // save gravity
rigidbody.velocity = newVel;

The 90 in rotateTowards is turn speed in degrees/second. The "if angle is close" makes it more robotic-looking. Could easily be a larger angle. For even more fun, go backwards if the angle is past 90 -- gives a cool backup then forwards move.

Also, transform.Translate isn't using rigidbodies -- it's like dragging it in the Inspector. For rigidbody-based movement, you get to use AddForce, and set friction really high. Unless Godzilla is tossing your tanks around, rigidbodies don't seem to get you much.