B Mark III Special (Type 464 Provisioning) was an attack on German dams carried out on 16–17 May 1943 by Royal Air Force No. 617 Squadron, subsequently known as the "Dambusters", using a specially developed "bouncing bomb" invented and developed by Barnes Wallis. The Möhne and Edersee Dams were breached, causing catastrophic flooding of the Ruhr valley and of villages in the Eder valley, while the Sorpe dam sustained only minor damage. The damage was mitigated by rapid repairs by the Germans, with production returning to normal in September..
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