10 July 1940-the official first day of the Battle of Britain-witnessed the main assaults by ever-increasing formations of Luftwaffe bombers, escorted by Bf109s and Bf110s. The Thin Blue Line tells the story. RAF Spitfires and Hurricanes endeavoured to repel the Heinkels, Dorniers and Ju88s, frequently with ill-afforded loss in pilots and aircraft.