I've seen in various movies and books where a machine gunner will attempt to disable a tank. In particular a Tom Clancy book (forgot which one, but it involved Korea). Also, in the movie Fury during the first battle a machine gun seems to engage the tanks (though maybe they were just trying to hit the tank commander or the troops behind the tanks). Is this an actual effective tactic? Is the idea to disable certain systems (periscope, radio, etc.) or simply make the commanders job more difficult by "buttoning up"? Can machine guns achieve penetration in certain areas of the tank?