to attack "the morale of the enemy's civil population, and in particular, of the industrial workers". Support for this shift came from a minute at the end of March by Churchill's scientific advisor, Lord Cherwell, in which he asserted that losing one's house by bombing seemed to have the greatest impact on civilian morale, which he described as "dehousing". The build up of the 8th Bomber Command was slow and though some small scale raids were made in France during the latter half of 1942, capability to attack Germany was not obtained until 1943. The British resources were also limited. The Western Allies had had to tell the Soviet Union that any idea of opening a second front in Europe in the summer of 1942 was unfeasible. The only thing Churchill had to offer Stalin was a bombing campaign against Germany. This was hard for the RAF to deliver, but it meant that the bombing of Germany could not be abandoned, so Harris would ultimately get the heavy bombers needed. However, by the time of the big raid on Hamburg at the end of July 1943, both air forces needed a significant success to justify their existence. Firebombing research Britain's experience of being bombed in the Blitz had contributed to the RAF's thinking on how to conduct a bombing campaign. It had become clear that incendiaries could inflict much more damage than high explosive bombs. Detailed study of this was carried out by the Research and Experiment unit, RE8, (set up in November 1941). The details of how German houses were constructed were examined and tests were carried out on models to determine how effective an incendiary attack would be. The precise ratio of high explosive bombs and incendiaries was calculated. The high explosive was to blow out windows and make fire fighting dangerous. High explosive bombs with delayed action fuses were included in the mix to further suppress any fire fighting effort. The quantity of incendiaries delivered had to be high enough to totally overwhelm any fire fighting capability, so that a conflagration could become established. The Americans took a high level of interest in the British research on the effect of incendiaries. American expertise and experiments added to the planning of fire bombing raids. Despite belief to the contrary, US aircraft also carried a carefully considered mix of high explosive and incendiary bombs. Large quantities of US-made oil-based