Bouncing bomb

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The bouncing bomb was a kind of bomb designed by Barnes Wallis of Vickers-Armstrong at Brooklands, Surrey. It was used in the famous Dambusters raid to attack major dams in Germany's industrial Ruhr Valley during World War II.

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Barnes Wallis first began to think of producing a bouncing bomb in 1941. He was aware that in the 19th century the Royal Navy had bounced cannonballs on water to increase their range. Initially his work on the device was to attack battleships. The bomb could be released away from the ships; the bomb would skip over anti-torpedo defences, and when it struck would roll down the hull to below the waterline, where a battleship would be least protected. An additional advantage was that the bomb could contain a much greater quantity of explosive than a torpedo. This version of the bomb, which was sphere-shaped and dimpled like a golf-ball, was codenamed Highball and was developed to be dropped from a modified de Havilland Mosquito that could carry two of the weapons.

The dam targets were largely immune to conventional attack because of their size. An immense amount of explosive would be required to breach them, and the cushioning effect of the water meant that a near miss would be ineffective. However a bomb placed right by the dam would be effective because the water would direct the explosion onto the dam, instead of protecting it, and greatly reduce the explosive power required. Current techniques would not allow the placing of a large bomb with that much accuracy. The Germans had guarded against attack by torpedo by placing nets upstream of the dams.

Due to time constraints set by the Royal Air Force, the final version of the bomb had to be different than initially intended. Barnes Wallis had to forgo the spherical metal shell and the "dimples". This new version was codenamed Upkeep. Referred-to as a "mine" and officially termed the "Upkeep store", it weighed 9,250 lb including 6,600 lb of RDX explosive. It was cylindrical in shape, 60 in length and 56 in diameter. The bomb was designed to be spun backwards at high velocity (500 rpm) before being released. It then literally bounced over the water (avoiding the torpedo nets) in the same way that a spinning stone will skip. However, to achieve this effect the bomb had to be released from a very low (60 ft) and very precise height, at 240-250 mph, 400-500 ft from the target. On striking the dam the bomb would sink to a prescribed depth of 30 ft before being detonated by hydrostatic fuze. A time fuze detonated the bomb if the hydrostatic fuze failed.

The bombs were successfully deployed using the Avro Lancasters of No. 617 Squadron RAF in Operation Chastise (the Dambusters Raid). The raid, on the night of 16/17 May 1943, was led by Wing Commander Guy Gibson, for which he won the Victoria Cross. The results of the raid were that out of the 6 intended targets, 4 were damaged and 2 were destroyed. Yet even though the mission was considered a success, the high loss of life in the raid prompted the Upkeep bomb project to be discontinued. Highball was to have been used in the Pacific Theatre but the war ended before it could be implemented.

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Both Upkeep and Highball remained Official Secrets until January 1974, when (along with the documents revealing the Ultra secret) the files were released under Britain's "thirty year rule".

After the raid the Germans discovered an Upkeep bomb that had failed to explode lying in some woods and subsequently an 850 pound version of the bouncing bomb was also attempted by the Luftwaffe. Designed for use against British shipping, it was given the codename Kurt, and was built at the Luftwaffe Experimental Centre in Travemünde. In trials, dropped by an Fw 190 it proved to be dangerous to the delivering planes as the bomb matched the speed at which it was dropped. Attempts to rectify this with booster rockets were ultimately a failure, and the project was discontinued in 1944.

All combat bombs were disposed of after the war. But a number of concrete-filled Upkeep bombs that were used for testing and training have been recovered and are on display in several museums.

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