During the Battle of Britain in summer 1940, the Luftwaffe inflicted severe damage to the Royal Air Force, but did not achieve the air superiority that Hitler demanded for the proposed invasion of Britain, which was postponed and then cancelled in December 1940.[74] The Luftwaffe ravaged British cities during The Blitz, but failed to break British morale. Hitler had already ordered preparations to be made for Operation Barbarossa, the invasion of the Soviet Union.