On the evening of 16th-17th May an attack on German dams was carried out by 617 Squadron RAF Bomber Command under the codename Operation Chastise. It used special “bouncing bombs” developed by Barnes Wallis to breach the dams Mohne and Edersee which caused catastrophic flooding of the Ruhr valley and of villages in the Eder Valley. Another dam was targeted, the Sorpe Dam, but this sustained only minor damage. Two hydroelectric power stations were destroyed and several more damaged. An estimated 1,600 civilians, about 600 Germans and 1,000 enslaved labourers, mainly Soviet, were killed by the flooding. The RAF lost 53 aircrew with 3 captured, and 8 aircraft were destroyed.