lol... if only 20mm's were needed to sink ships, then there would be no need for bombers or torpedo planes. The jerries could have saved themselves a shed load of money
You could probably empty your guns into the bridge for the sake of immersion. A fairly common practise for those without some big boom boom slung underneath. (I doubt you'd get any practical value from doing so in game though but you never know, CFS3 had you strafing ships IIRC)