The Battle of the Heligoland Bight was the first "named" air battle of the Second World War, which began the longest air campaign of the war on 3 September 1939, the Defence of the Reich. After the declaration of war, RAF Bomber Command began operations against Nazi Germany but limited their attacks to those targets that were purely military and had little risk of civilian casualties. This largely limited their efforts to attacks on the Kriegsmarine warships in German ports to prevent their use in the Battle of the Atlantic.

The Defence of the Reich is the name given to the strategic defensive aerial campaign fought by the Luftwaffe of Nazi Germany over German-occupied Europe and Germany during World War II. Its aim was to prevent the destruction of German civilians, military and civil industries by the Western Allies. The day and night air battles over Germany during the war involved thousands of aircraft, units and aerial engagements to counter the Allied strategic bombing campaign. The campaign was one of the longest in the history of aerial warfare and with the Battle of the Atlantic and the Allied Blockade of Germany was the longest of the war. The Luftwaffe fighter force defended the airspace of German-occupied territory against attack, first by RAF Bomber Command and then against the United States Army Air Forces (USAAF) in the Combined Bomber Offensive.