For four long months during the summer of 1940, the RAF and the German Luftwaffe fought an epic battle in the blue skies and over the green fields of south east England. The Battle of Britain was the first major battle to be fought entirely in the air. It was the largest and most sustained bombing campaign yet attempted and the first real test of the strategic bombing theories that had emerged since the First World War. For more than sixty years the story of the Battle of Britain has been the story of an unprepared nation winning against overwhelming odds, a tale of heroism, of a handful of plucky pilots and of the battle winning Spitfire aircraft. Scientists, historians and veterans reveal that in fact Britain was far from unprepared. What were the secret systems and tactics which forced the Germans to withdraw from battle and led them to postpone and then cancel, their plans for invasion?