The Battle of the Beams was a period early in the Second World War when bombers of the German Air Force (Luftwaffe) used a number of increasingly accurate systems of radio navigation, developed by Johannes Plendl, for night bombing in the United Kingdom. British "scientific intelligence" at the Air Ministry fought back with a variety of their own increasingly effective means, involving jamming and distortion of the radio waves. The period ended when the Germans moved their bomber forces to the East in May 1941, in preparation for the attack on the Soviet Union.