Following the 1939 aerial Battle of the Heligoland Bight, Royal Air Force (RAF) attacks shifted to the cover of darkness, initiating the Defence of the Reich campaign. By mid-1940, "Generalmajor" (Brigadier General) Josef Kammhuber had established a night air defense system dubbed the Kammhuber Line. It consisted of a series of control sectors equipped with radars and searchlights and an associated night fighter. Each sector named a "Himmelbett" (canopy bed) would direct the night fighter into visual range with target bombers. In 1941, the Luftwaffe started equipping night fighters with airborne radar such as the "Lichtenstein" radar. This airborne radar did not come into general use until early 1942. Frank became an ace after downing his 5th victim, Armstrong Whitworth Whitley, "Z6505", MH-F, No. 51 Squadron RAF. Sergeant J. C. W. King and his crew were captured.