 Internally they were coated with layers of "Linatex" and the cockpit bulkhead was fireproofed with a thick panel of asbestos.On all the German fighters and bombers, the fuel tanks were self-sealing, and although capable of sealing leaks from enemy rounds, this could not prevent possibly fatal damage being inflicted by the "De Wilde" incendiary round which was being used by the RAF.A much more serious issue for the Luftwaffe's single-engined fighter force during the Battle was the Bf 109E's limited fuel "capacity" as originally designed.