Once the day fighters had saved Britain from invasion, it fell to the night fighters to save her cities from destruction. At the beginning, interception by night proved virtually impossible, particularly, as the German bombers carried out their raids in cloudy weather. Soon, however, the navigator was presented with a mysterious little black box, which turned out to be the parent of airborne radar and the key to aerial tactics. This made a major contribution to the war in the skies, first protecting the British cities from the incessant raids of 1940 and later enabling the bombers to carry out their vital operations over Germany. `Jimmy' Rawnsley, crewed with gunner `Cats-eyes' Cunningham were among the first to use this new technology when it was introduced to the Blenheim they were flying and went on to become one of the RAF's leading night fighter crews, destroying over 20 enemy aircraft.