US planes are equipped with shield generator giving them additional strength. It is a special generator part of which is a cupola glass. So logically the only possible place to mount them is cockpit(numerous pilots have complained about headache but corrup..ehm experts say it is not more unhealthy/dangerous than standing next to microwave or using mobile phone). The protection of cockpit is very weak though. It is able to withstand continuous gunfire of 1 fully-automatic weapon. However, if you manage to hit cupola multiple times at the same moment, some bullets may manage to pentetrate the surface shield, damaging the generator, creating short circuits spreading all over the plane causing huge damage to electronics, interfering with gas tank and ammunition finally creating an explosion...