The first intentional air raids on London were mainly aimed at the Port of London, causing severe damage. Late in the afternoon of 7 September, 364 bombers attacked, escorted by 515 fighters. Another 133 bombers attacked that night. Many of the bombs aimed at the docks fell on neighbouring residential areas, killing 436 Londoners and injuring 1,666.
Few anti-aircraft guns had fire-control systems, and the underpowered searchlights were usually ineffective against aircraft at altitudes above 12,000 feet (3,600 m). Even the fortified Cabinet War Rooms, the secret underground bunker hidden under the Treasury to house the government during the war, were vulnerable to a direct hit. Few fighter aircraft were able to operate at night, and ground-based radar was limited. During the first raid, only 92 guns were available to defend London. The city's defences were rapidly reorganised by General Sir Frederick Pile, the Commander-in-Chief of Anti-Aircraft Command, and by 11 September twice as many guns were available, with orders to fire at will. This produced a much more visually impressive barrage that boosted civilian morale and, though it had little physical effect on the raiders, encouraged bomber crews to drop before they were over their target.
During this first phase of the Blitz, raids took place day and night. Between 100 and 200 bombers attacked London every night but one between mid-September and mid-November. Most bombers were German, with some Italian aircraft flying from Belgium. Birmingham and Bristol were attacked on 15 October, and the heaviest attack of the war so far – by 400 bombers and lasting six hours – hit London. The RAF opposed them with 41 fighters but only shot down one Heinkel bomber. By mid-November, the Germans had dropped more than 13,000 tons of high explosive and more than 1 million incendiary bombs for a combat loss of less than 1% (although some aircraft were lost in accidents inherent to night flying and night landing).