Two hydroelectric power stations were destroyed and several more damaged. Factories and mines were also damaged and destroyed. An estimated 1, civilians — about Germans and 1, enslaved labourers , mainly Soviet — were killed by the flooding.
Despite rapid repairs by the Germans, production did not return to normal until September. The RAF lost 56 aircrew, with 53 dead and 3 captured, amid losses of 8 aircraft.
Before the Second World War , the British Air Ministry had identified the industrialised Ruhr Valley , especially its dams, as important strategic targets. Calculations indicated that attacks with large bombs could be effective but required a degree of accuracy which RAF Bomber Command had been unable to attain when attacking a well-defended target. A one-off surprise attack might succeed but the RAF lacked a weapon suitable for the task.
The mission grew out of a concept for a bomb designed by Barnes Wallis , assistant chief designer at Vickers. At first, Wallis wanted to drop a long-ton 22, lb; 10, kg bomb from an altitude of about 40, ft 12, m , part of the earthquake bomb concept. No bomber aircraft was capable of flying at such an altitude or of carrying such a heavy bomb and although Wallis proposed the six-engined Victory Bomber for this purpose this was rejected. Wallis devised a 9, lb 4, kg bomb more accurately, a mine in the shape of a cylinder, equivalent to a very large depth charge armed with a hydrostatic fuse, designed to be given a backspin of rpm.
Initially the backspin was intended to increase the range of the mine but it was later realized that it would cause the mine, after submerging, to run down the side of the dam towards its base, thus maximising the explosive effect against the dam.
