During the Second World War, Operation Chastise was a specialized strategic bombing operation carried out by 617 Squadron of the Royal Air Force. It was directed against German dams that provided water and power to dams in the Ruhr. 617 Squadron was created for the mission, under Wing Commander Guy Gibson. They trained in intense secrecy, not even Gibson knowing the exact target, and then having the targets held to a minimum number of officers. Operational security was extreme because the Germans could easily install countermeasures of balloon-supported cables, metal nets, or low-level anti-aircraft artillery.
Barnes Wallis, who designed the Vickers Wellingto, originally proposed to attack dams with extremely large penetrating "earthquake bombs", which indeed were used later in the war. At the time, however, no available aircraft could lift them. Arthur Harris, head of RAF Bomber Command, resisted the proposal, calling it "Tripe of the wildest description". He commented that the revolving mine would tear itself from the bomb bay and destroy the aircraft carrying it. He also said "The war will be over before it works - and it never will". Harris did not want to loose any of his precious Lancaster bombers on a "wild goose chase" that stood little chance of success. He knew from previous attacks just how venerable his bombers were.
Chief of the Air Staff, Air Chief Marshal Sir Charles Portal, was impressed with Wallis' test results, ordering Harris to provide three Lancasters: "If you want to win the war; bust the dams".  Wallis, to bring the bombload within the capacity of available aircraft, developed a "bouncing bomb", code-named Upkeep, which would, delivered at a precise speed and altitude, 60 feet (18.29m) and a speed 220 mph (354 km/h), skip over the lake formed by the dam, and then sink such that its force was delivered, through incompressible water, to the dame. No other weapon available at the time could damage the massive structure of dams.
Nineteen modified Avro Lancaster bombers carried out the attack during the night of 16/17 May 1943, successfully breaching the Mohne and Eder dams, but failing with attacks on two others, the Sorpe and Schwelme. Wing Commander Gibson repeatedly flew over the Mohne and Eder dams to draw fire away from the attacking aircraft and was subsequently awarded the Victoria Cross for his gallantry. Thirty-two other members of the Squadron were also decorated but a total of eight aircraft and their crews were lost during the night.
The raid did cause significant problems to German industry, but was not as devastating as had been hoped. Albert Speer wrote "employing just a few bombers…came close to a success which would have been greater than anything they had achieved hitherto with a commitment of thousands of bombers." His efforts to get the Luftwaffe to undertake similar attacks of Russian hydroelectric plants was unsuccessful.