And pilots. The Allies rotated squadrons in and out of combat and sent the experienced and battle-weary off to recuperate at flying schools, teaching the newcomers how to stay alive for the first few hours of combat; the Luftwaffe kept the squadrons in combat until battle-weary meant lost in action. Meant the aces built up huge scores in the Soviet Union and Africa; it meant that their skills weren't passed on; it meant they couldn't maintain their edge.