Before the war many officers in the RAF Bomber Command believed that Germany could be defeated by bombing alone and would not have to be invaded. The bombing of Germany, however, proved to be far more difficult than expected. In a daylight raid on Wilhelmshaven in 1939 German fighter planes directed by radar shot down half the force of twenty-four Wellington bombers. After this the RAF decided to keep to night-time bombing.

The RAF planes were at first to bomb important industrial targets such as factories and railways. But accurate navigation and bombing was difficult at night and this led to the bombers aiming simply at the centre of towns. Photographs taken by high-flying aircraft after raids showed that night bombers were often not even hitting the right towns. At the end of 1941 it was clear that only one bomber in three was getting within 8 km of its target and in the vital Ruhr industrial area, the main British bombing target, only one in ten. Air Marshal Harris became C- in-C (Commander-in-Chief) of Bomber Command in 1942, when critics were saying that the RAF bombing offensive was failing. He disagreed and forcefully demanded more of the big four-engined bombers, which were appearing by then. He believed that if bombs were showered on Germany she would collapse. How this would happen was not clear; most probably by breaking the spirit of Germans by destroying their homes (officially termed 'de-housing'). Factories were a target but, for Harris, not as important as the workers who worked in them. Churchill also believed in this 'area' or 'terror' bombing. Many raids were sent to the Ruhr industrial region, but often failed to hit their targets.

More effective methods gradually came into use. The Pathfinder Force was made up of handpicked crews who marked the targets for the main bomber forces and the routes to them. For this purpose they used the excellent, fast, light bomber, the Mosquito. And in 1943 the Pathfinders obtained the 'Oboe' device for accurate target marking. These markers could be seen through light cloud, industrial haze and searchlight glare. The Ruhr, which had earlier been saved by these factors, suffered widespread devastation in forty-three main attacks during March- July 1943. In an attack by the 'Dambusters' in May 1943 special 'bouncing' bombs broke two of the Ruhr dams. But the third dam held and the damage caused by floodwater was less than expected. Eight bombers, nearly half the squadron, were lost.