By the winter of 1941/1942 both the British and German strategic bombing campaigns had reached a low ebb. The German offensive, a nine-month period of night bombing known as the Blitz, which had left London and many other British cities heavily damaged, had come to an end in May 1941, when the Luftwaffe had switched its resources to the invasion of the Soviet Union. Thereafter it had confined itself to hit-and-run raids on British coastal towns. Meanwhile, the RAF's night bombing offensive had been shown to be largely ineffective, as revealed by the Butt report in August 1941, and by Christmas the offensive had largely petered out.
When it resumed in March 1942 with the bombing of Lübeck, there was a marked change in effectiveness. New heavy bombers (the Stirling and Halifax, followed by the Manchester and Lancaster), improved navigation (with aids such as Gee and Oboe), new leadership (with the appointment of AVM Harris) and new tactics (the bomber stream, use of incendiaries, and focusing on a single target) all contributed. Not least of these was the switch to area bombing. Prior to this the RAF had attempted to make precision attacks, aiming at individual factories, power stations, even post offices, in multiple strikes across the country; this had been costly and ineffective. In March 1942, and following the Luftwaffe's example they began concentrating a single blow against an area where several worthwhile targets existed, not least the homes and morale of the civilian population living there. These changes resulted in the destruction of Lübeck, and came as a profound shock to the German leadership and population.