Battle of Britain
Day and night attacks on London: start of the Blitz

Hitler's "Directive No. 17 – For the conduct of air and sea warfare against England" issued on 1 August 1940, reserved to himself the right to decide on terror attacks as measures of reprisal. Hitler issued a directive that London was not to be bombed save on his sole instruction. In preparation, detailed target plans under the code name Operation Loge for raids on communications, power stations, armaments works and docks in the Port of London were distributed to the Fliegerkorps in July. The port areas were crowded next to residential housing and civilian casualties would be expected, but this would combine military and economic targets with indirect effects on morale. The strategy agreed on 6 August was for raids on military and economic targets in towns and cities to culminate in a major attack on London. In mid-August, raids were made on targets on the outskirts of London.

Luftwaffe doctrine included the possibility of retaliatory attacks on cities, and since 11 May small scale night raids by RAF Bomber Command had frequently bombed residential areas. The Germans assumed this was deliberate, and as the raids increased in frequency and scale the population grew impatient for measures of revenge. On 25 August 1940, 81 bombers of Bomber Command were sent out to raid industrial and commercial targets in Berlin. Clouds prevented accurate identification and the bombs fell across the city, causing some casualties among the civilian population as well as damage to residential areas. Continuing RAF raids on Berlin led to Hitler withdrawing his directive on 30 August, and giving the go-ahead to the planned bombing offensive. On 3 September Göring planned to bomb London daily, with General Albert Kesselring 's enthusiastic support, having received reports the average strength of RAF squadrons was down to five or seven fighters out of twelve and their airfields in the area were out of action. Hitler issued a directive on 5 September to attack cities including London. In his widely publicised speech delivered on 4 September 1940, Hitler condemned the bombing of Berlin and presented the planned attacks on London as reprisals. The first daylight raid was titled Vergeltungsangriff (revenge attack).

On 7 September, a massive series of raids involving nearly four hundred bombers and more than six hundred fighters targeted docks in the East End of London, day and night. The RAF anticipated attacks on airfields and 11 Group rose to meet them, in greater numbers than the Luftwaffe expected. The first official deployment of 12 Group's Leigh-Mallory's Big Wing took twenty minutes to form up, missing its intended target, but encountering another formation of bombers while still climbing. They returned, apologetic about their limited success, and blamed the delay on being scrambled too late.

The German press jubilantly announced that "one great cloud of smoke stretches tonight from the middle of London to the mouth of the Thames." Reports reflected the briefings given to crews before the raids – "Everyone knew about the last cowardly attacks on German cities, and thought about wives, mothers and children. And then came that word 'Vengeance!'" Pilots reported seeing ruined airfields as they flew towards London, appearances which gave intelligence reports the impression of devastated defences. Göring maintained that the RAF was close to defeat, making invasion feasible.

Fighter Command had been at its lowest ebb, short of men and machines, and the break from airfield attacks allowed them to recover. 11 Group had considerable success in breaking up daytime raids. 12 Group repeatedly disobeyed orders and failed to meet requests to protect 11 Group airfields, but their experiments with increasingly large Big Wings had some success. The Luftwaffe began to abandon their morning raids, with attacks on London starting late in the afternoon for fifty-seven consecutive nights.

The most damaging aspect to the Luftwaffe of targeting London was the increased distance. The Bf 109E escorts had a limited fuel capacity resulting in only a 660 km (410-mile) maximum range solely on internal fuel, and when they arrived had only 10 minutes of flying time before turning for home, leaving the bombers undefended by fighter escorts. Its eventual stablemate, the Focke-Wulf Fw 190 A, was flying only in prototype form in mid-1940; the first 28 Fw 190s were not delivered until November 1940. The Fw 190A-1 had a maximum range of 940 km (584 miles) on internal fuel, 40% greater than the Bf 109E. The Messerschmitt Bf 109 E-7 corrected this deficiency by adding a ventral centre-line ordnance rack to take either an SC 250 bomb or a standard 300-litre Luftwaffe drop tank to double the range to 1,325 km (820 mi). The ordnance rack was not retrofitted to earlier Bf 109Es until October 1940.

On 14 September, Hitler chaired a meeting with the OKW staff. Göring was in France directing the decisive battle, so Erhard Milch deputised for him. Hitler asked "Should we call it off altogether?" General Hans Jeschonnek, Luftwaffe Chief of Staff, begged for a last chance to defeat the RAF and for permission to launch attacks on civilian residential areas to cause mass panic. Hitler refused the latter, perhaps unaware of how much damage had already been done to civilian targets. He reserved for himself the power to unleash the terror weapon. Instead, political will was to be broken by destroying the material infrastructure, the weapons industry, and stocks of fuel and food.

On 15 September, two massive waves of German attacks were decisively repulsed by the RAF by deploying every aircraft in 11 Group. Sixty German and twenty-six RAF aircraft were shot down. The action was the climax of the Battle of Britain.

Two days after the German defeat Hitler postponed preparations for the invasion of Britain. Henceforth, in the face of mounting losses in men, aircraft and the lack of adequate replacements, the Luftwaffe completed their gradual shift from daylight bomber raids and continued with nighttime bombing. 15 September is commemorated as Battle of Britain Day.
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