An Avro Lancaster makes a 'Dambusters' commemorative flight over Ladybower Reservoir's Derwent Dam
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Ladybower Dam with its staggering 2,000 million gallon water storage capacity, and Howden and Derwent Dams which lie further up the valley were used for six weeks prior to the attacks in 1943 as the practice ground for the bouncing bomb, which was being used to attack the Ruhr Dams, the destruction of which paralysed Germany's industrial heartland during World War 2. The mission had developed out of the bomb itself. The bomb was designed by Sir Barnes Neville Wallis (September 26 1887 - October 30,1979) who was a British scientist, engineer and inventor, and developed into a working device by a team at Vickers. His initial idea was for a 10 ton bomb to be dropped from 40,000 feet (12,200 m), but research showed that without a direct hit a bomb would need to be uncarriably vast to breach a dam. However, a much smaller charge would suffice if it could be exploded directly against the dam wall below the surface of the water. But the major German dams were protected by heavy torpedo netting to prevent such an attack and it was Wallis's breakthrough to see a way past this. A drum-shaped bomb, spinning rapidly and dropped from a sufficiently low altitude at high speed would, for a short distance, skip over the surface of the water in a series of bounces before halting and sinking. An accurate drop could bypass the dam protection and be detonated against the dam with a hydrostatic fuse. After testing and many meetings the idea was adopted on February 26, 1943. The Derwent valley dams were used for practice because of their similarity to those in Germany. The bomb itself was codenamed 'Upkeep'. The dams were to be bombed in May of that year, when water levels would be highest. The operation was given to 5 Group and a new squadron was formed to undertake the mission. Initially called Squadron 'X' it was led by wing Commander Guy Gibson. A further 21 crews were chosen from 5 Group to join the new squadron based at Scampton. The aircraft used were adapted Avro Lancasters dubbed Special Bs; heavy bombers with a crew of 7 -pilot, flight engineer, navigator, bomb aimer, wireless operator, mid-, upper and rear gunners. To reduce weight much of the armour was removed as was the mid-upper turret. The substantial bomb and its unusual shape meant that the bomb doors were removed and the bomb itself hung, in part, below the body of the aircraft. It was mounted in two crutches and before dropping it was spun up to speed by an auxiliary motor. Bombing from 60 feet (18 m) at 240 mph (390 km/h), at a very precise distance from the target, required expert crews, intensive night and low-altitude flying training, and the solutions to two technical problems. The first was to know when the airplane was the correct distance from the target. The two key dams at Moehne and Eder had a tower at each of their ends. A special aiming device (basically a triangle similar to that created by the two towers and an airplane at the correct distance from the dam) showed when to release the bomb. The second problem was to measure the airplane's altitude (the usual barometric altimeters were insufficiently accurate). Two spotlights were mounted under the nose and under the fuselage such that their beams would intersect 60 feet (18 m) from the underside of the plane. At the correct height, the two spots of light would merge into one on the surface of the water. The bombs were delivered to the squadron on May 13, after the final tests on April 29. With promising weather reports the pilots, navigators and bomb aimers were informed of the targets on May 15, the rest of the crews on the following day. The Lancasters were organised into three groups. Formation 1 was to attack the Moehne and after that aircraft still with bombs would attack the Eder. Formation 2 was to attack the Sorpe. The third group was a mobile reserve, it would take off two hours later and bomb as directed, either attacking the main dams or bombing smaller dams at Schwelm, Ennerpe and Dieml. The mission successfully hit the dams, but with considerable losses. In all, of 133 aircrew, 53 had been killed and three bailed out to be made POW's. A plaque on the stone parapet of the dam commemorates the 617 'Dambusters' squadron and The popular 'Dambusters film was made of the event in 1954 (also filmed at Ladybower). The Avro Lancaster seen here made the flight over the Derwent Dam to commemorate the raid.