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.
The version of the bomb required to destroy the dams was codenamed Upkeep. Referred-to as a "mine" and officially termed the "Upkeep store", it weighed 9,250lb including 6,600lb of RDX explosive. It was cylindrical in shape, 60in in length and 56in in diameter. The bomb was designed to be spun backwards at high velocity (500rpm) 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 (60ft) and very precise height, at 240-250mph, 400-500ft from the target. On striking the dam the bomb sank to a prescribed 30ft depth before being detonated by hydrostatic fuse. A time fuse detonated the bomb if the hydrostatic fuse 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. Because of the high loss of life in the raid, and for other reasons, the Upkeep bomb project was discontinued. Highball was to have been used in the Pacific Theatre but the war ended before it could be used.
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 Travemnde. 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.
How the bomb worked
