It also depends on where you hit them. An A20 has lots of empty space inside, especially in AH where the gunner seats aren't manned. A 20 mm hole in the aluminum wall would only add ventilation without affecting maneuverability. The weakest parts in almost any plane would be the engine area and pilot, when looking at real warbirds. Debrody, I was with the group to see the Brewster IRL closely while it was restored. We found a bullethole in the rear and it looked as if the bullet had travelled through the empty space inside the plane until hitting the cast iron back rest armor, breaking it into two pieces. That was the biggest single damage in the whole fuselage, the crashing being caused by engine hits. Makes me wonder how the WW2 pilots could fatally hit anything without the self aiming armament we have today. The aluminum walls are just one step further from the canvas of WW1 planes, mostly there only for added aerodynamics.
