Air Offensive, Europe Campaign 4 July 1942 to 5 June 1944) Pre-war doctrine had held that waves of bombers hitting enemy cities would cause mass panic and the rapid collapse of the enemy. As a result, the Royal Air Force had built up a large strategic bomber force. By way of contrast, Nazi German air force doctrine was almost totally dedicated to supporting the army. Therefore, German bombers were smaller than their British equivalents, and Germany never developed a fully successful four engined heavy bomber equivalent to the Lancaster or B-17, with only the similarly sized Heinkel He 177 placed into production and made operational for such duties with the Luftwaffe in the later war years.
The main concentration of German raids on British cities was from September 7, 1940 until May 10, 1941 in the most famous air battle of all time, known as the Battle of Britain. Facing odds of four against one the RAF held off the mighty Luftwaffe forcing Hermann Wilhelm Göring to withdraw his forces and more importantly indefinitely postpone invasion plans. This proved the first major turning point of the War. After that most of the strength of the Luftwaffe was diverted to the war against the Soviet Union leaving German cities vulnerable to British and later American air bombings. As a result of the victory, Great Britain was used by U.S and other Allied forces as a base from which to begin the D-Day landings in June 1944 and the liberation of Nazi-occupied Western Europe.
From 1942 onwards, the efforts of Bomber Command were supplemented by the Eighth Air Force of the United States Army Air Forces, U.S. Army Air Forces units being deployed to England to join the assault on mainland Europe on July 4, 1942. Bomber Command raided by night and the US forces by day.