 The Messerschmitt Bf 109 E-3 received extra armour in late 1939, and this was supplemented with a 10 mm thick armoured plate behind the pilot's head during and after the Battle of France.Behind the fuel tank, an 8 mm armoured plate was placed in the fuselage protecting the tank and the pilot from attacks from behind.By July 1940, more efficient de Havilland and Rotol constant speed propellers had begun replacing two-pitch propellers on front line RAF fighters.