Most historians agree that the very nature of the Battle of Britain changed on 7 September, with a shift away from the direct attack on Fighter Command's airfields and the factories which produced its aircraft. The change in targeting was driven by Goring and supported by Kesselring, who felt that the anti-airfield campaign had run its course, and that Fighter Command was finished. But Sperrle protested strongly, believing that Fighter Command probably still had a thousand aircraft left, and wished to continue to scourge the No.11 Group airfields. He was overruled.
But it would be a mistake to see the targeting of London as necessarily marking a fundamental change in direction by the Luftwaffe. The aim was still the destruction of Fighter Command, and the targeting of London merely represented a switch to a target which the Germans felt was most likely to draw the RAF's fighters into the air, where they could be destroyed. It was, in the words of one German officer, the 'only target that Fighter Command would give everything to defend.' That, at least, was Goring's theory, although it did also mark an opportunity for vengeance following Bomber Command's raid on Berlin on 25 August. And London was a vitally important target. It was Europe's largest city, and was the capital city of a nation whose capital was of unparalleled importance. It was the centre of Britain's economy, a major industrial and port city, the seat of government and the home of the King. Small wonder that it was a tempting target.
But just as Goring had rethought his battle plans, so too did Dowding adjust his tactical thinking, and restructured his forces. By coincidence, as the new phase of the Battle began, Dowding's reclassification of his squadrons came into effect. Thereafter, the frontline squadrons in No. 11 Group were categorised as Class A squadrons, as were those units in Nos 10 and 12 Groups which Park might call on to reinforce his Group. Class B squadrons were fully manned and fully established, and were ready to be called into action, but might be lacking in combat experience or be suffering from a degree of fatigue. Finally, Class C squadrons were those which had suffered severe losses, and were being rested and re-equipped. Experienced survivors from these units were taken (as soon as they were ready) to act as replacements for pilots killed or wounded in the higher category units. This cut the link between an individual pilot and his original unit, but ensured that newly formed squadrons would have a core of combat-experienced veterans. Meanwhile, Keith Park instructed his controllers and pilots to henceforth obey altitude orders from Group, without making any personal interpretations of the heights given. He did this to ensure that climbing fighters did not emerge below their targets, but it caused delays and sometimes meant that the RAF fighters fought the escorts instead of the bombers, which often flew slightly lower.
As if to deliberately confuse Fighter Commander, the Luftwaffe began 7 September as it had begun many of the past days, with a handful of reconnaissance sorties, but thereafter, the radar screens remained clear and the plotting tables empty. The long delay seemed ominous. The Air Ministry had already issued an 'Invasion Alert No. 1' (meaning attack imminent) without having previously issued Alert Nos 2 and 3 (attack probable within two and three days, respectively).
History records that the first raid counter was placed on the plotting table at Bentley Priory at 1554, and that within minutes counters representing many hundreds of aircraft were on the table. Goring had launched virtually the full strength of KG 1, KG 2, KG 3, KG 26 and KG 76, together with the Bf 110s of ZG 2 and the Bf 109Es of JG 2, JG 3, JG 51, JG 52, JG 54, I./JG 77 and I./ and II./LG 2. This colossal armada numbered 965 aircraft, stepped up from 4268m to 7010m (14,000ft to 23,000ft) advancing along a 32.2km (20-mile) front. Dowding and Park correctly guessed that only London could be the target of such a vast force, and at 1617 11 fighter squadrons were ordered into the air, with 21 units airborne by 1630. All available fighters raced towards the capital, with no thought of standing guard over their airfields. The RAF fighters were massively out-numbered by the German escorts, but tore into the enemy with great ferocity. The German bombers aimed for the docks, but their bombs fell over a wide area, from Kensington in the west but concentrated in the East End, and doing as much damage to the densely packed terraces of working-men's houses as to the docks, gasworks and power stations that were also hit. The enemy bombers turned around and were all en route home by 1745, albeit with huge gaps in the neat formations.
As the skies above London emptied of aircraft, the fight was taken over by the firemen, who fought the spreading fires with a grim determination. They fought to douse the burning buildings, the wooden-block road surfaces on older streets and even the surface of the River Thames itself (where floating liquid sugar ignited), all the while with the warehouses of paint, oil, explosives and ammunition blowing up in terrifying explosions. But it was not just the obviously dangerous materials that exploded - flour and pepper were equally dangerous, and the conflagration threatened to become self-sustaining as the fire sucked in oxygen from the surrounding streets. Burning debris was tossed into the air like straw, setting new fires wherever it landed. The London Fire Brigade classified a fire requiring 30 pumps as a 'Major' fire, yet in the early evening of 7 September, the Fire Brigade were tackling nine fires which were officially rated as 'Conflagrations', in that they required more than 100 pumps each. The largest was in the Surrey Docks, where the fire was too large to classify, and where it was arbitrarily rated as a 300-appliance fire.
At about 2010, the next wave of 318 German bombers began to pour down tons of incendiaries. 306 civilians died in the bombing, and 1337 more were seriously injured in the City, with 142 more killed in the suburbs. An enormous pall of smoke hung over the capital, and the fires burned on.
The first day cost Fighter Command dear, with the loss of 15 Spitfires (and four pilots) and 17 Hurricanes (with seven pilots). But the Luftwaffe lost 38 aircraft, including 14 Bf 109s. The balance of attrition was not very different from that suffered during the past weeks, although this changed as the campaign wore on, and the onslaught on London soon became much more costly to the attacker than to the defenders. And the blitz against London lasted long after the Battle ended, bleeding the Luftwaffe white in the process. The attacks continued on 76 consecutive nights, with only a single exception. This was 2 November, when the weather was too poor to allow the German bombers to operate. Perhaps most crucially, the Fighter Command airfields, and the Chain Home stations were given precious respite by the switch in targeting. Even the pilots themselves were rested when not actually in the air over London. Squadrons spent whole days without coming to readiness, and there was even time for newly arrived pilots to be taken on training and familiarisation sorties -luxuries which would have been unthinkable only days before. And, as in the phrase popularly used at the time, 'London could take it'. Dowding was relieved by the switch in targeting, commenting that 'The nearness of London to German airfields will lose them the war.' Churchill put it in typically over-blown fashion. 'London is like some huge prehistoric animal, capable of enduring terrific injury, mangled and bleeding from many wounds yet preserving its life and movement.'