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Operation Chastise was the official name for attacks carried out by Royal Air Force No. 617 Squadron - subsequently known as the Dambusters - on German dams on May 16/17, 1943, using a specially developed "bouncing bomb" invented and developed by Barnes Wallis. The Möhne and Eder dams were breached, causing catastrophic flooding of the Ruhr valley, but the Sorpe dam sustained only minor damage.
Prior to World War II, the British Air Ministry had identified Germany's heavily industrialized Ruhr Valley, and especially its dams, as important strategic targets: in addition to providing hydro-electric power they also supplied drinking water and water for the canal transport system. The methods used to attack the dams had been carefully worked out. Calculations indicated that repeated air strikes with large bombs could be effective, but required a degree of accuracy which Bomber Command had been unable to attain in the face of enemy defences.
The mission grew out of a concept for a bomb designed by Barnes Wallis and developed by his team at Vickers. Wallis was an aircraft designer who had worked on both the Vickers Wellesley and Vickers Wellington bombers. While working on aircraft he had also begun work on a bomb designed specifically with dam-destruction in mind.
Wallis' initial idea was to drop a 10-tonne bomb from an altitude of about 40,000 feet (12,200 meters). This idea was part of the earthquake bomb concept. However, at that time no bomber aircraft was capable of flying at that altitude with such a heavy payload.
The operation was given to No. 5 Group RAF which formed a new squadron to undertake the mission, initially called Squadron 'X' (its assignment had outstripped the bureaucracy responsible for naming squadrons). Led by Wing Commander Guy Gibson, a veteran of over 170 bombing missions, 21 bomber crews were chosen from the Group to join the new squadron based at RAF Scampton, about five miles north of Lincoln, Lincolnshire.
The targets selected were the two key dams upstream from the Ruhr industrial area, the Möhne Dam and the Sorpe Dam, with the Eder Dam on the Eder River, which feeds into the Weser, as a secondary target. While the loss of hydroelectric power was important, the loss of water supply to industry, cities, and canals would have greater effect. Also, there was the potential for devastating flooding if the dams broke.
The aircraft were modified Avro Lancaster Mk IIIs, known as B Mark III Special (Type 464 Provisioning).[1] To reduce weight, much of the internal armor was removed, as was the mid-upper machine gun turret. The size of the bomb with its unusual shape meant that the bomb-bay doors had to be removed, and the bomb itself hung, in part, below the fuselage of the aircraft. It was mounted on two crutches, and before dropping it was spun up to speed by an auxiliary motor.
Bombing from an altitude of 60 feet (18 meters), at an air speed of 240 mph (390 km/h), and at a pre-selected distance from the target called for expert crews. Intensive nighttime and low-altitude flight training began.
There were also technical problems to solve, the first one being to determine when the aircraft was at optimum distance from its target. Both the Möhne and Eder Dams had towers at each end. A special targeting device with two prongs, making the same angle as the two towers at the correct distance from the dam, showed when to release the bomb.
The second problem was determining the aircraft's altitude (barometric altimeters then in use lacked sufficient accuracy). Two spotlights were mounted, one under the aircraft's nose and the other under the fuselage, so that at the correct height their light beams would converge on the surface of the water. The crews practised at the Eyebrook Reservoir in Leicestershire / Rutland, at the Abberton Reservoir near Colchester, at the Derwent Reservoir, Derbyshire, and at the Fleet Lagoon, Chesil Beach, Dorset. The bomb/mine itself was first tested at the Elan Valley Reservoirs
The bombs were delivered to the squadron on May 13, after the final tests on April 29. At 1800 on Saturday 15 May, at a meeting in Whitworth's house, Gibson and Wallis briefed four key aircrew: Maudslay and Young, the two flight commanders, Hopgood, who would act as Gibson's deputy at the Möhne, and Flt Lt Bob Hay, the squadron bombing leader. The rest of the crews were told at a series of briefings the following day, which began with a briefing of pilots, navigators and bomb aimers at about midday.
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