WWII fighter bullet proof protection I.D.?

[browningautorifle]

I am surmising that armour plate would stop 303 stuff

Practically nothing will stop .50 AP, 20 MM will just take an aircraft apart. And that at 1000M. Yes, it will help to deflect but would only stop .303 for sure. I knew a man that shot at FW and ME 109s with four Inglis .303 from a tail turret and .303 did all but nothing. They'd sit there and look at you. He said when the new "American" turrets came in with two .50s, they'd take a short burst and then back off to max range. He said the junk would just cloud off behind them upon strike...