Bouncing bomb

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The bouncing bomb was a variety of depth charge style 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.

An original Upkeep bouncing bomb at the Imperial War Museum Duxford
An original Upkeep bouncing bomb at the Imperial War Museum Duxford

Barnes Wallis first began to think of producing a bouncing bomb in 1941. He was aware that in the nineteenth century the Royal Navy had observed that cannonballs sometimes bounced on water which increased 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 act as a natural tamping medium, directing the explosion onto the dam, instead of protecting it, and greatly reducing the explosive power required. Current techniques would not allow the placing of a large bomb with the required accuracy. Moreover, the Germans had guarded against attack by torpedo by placing heavy nets upstream of the dams.

Owing to time constraints set by the Royal Air Force, the final version of the bomb had to be different from the initial intention. 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 4 200 kg (9,250 lb) including 3 000 kg (6,600 lb) of Torpex explosive. The choice of Torpex was deliberate: although its brisance is lower than Composition B, the aluminium component in Torpex made the explosive pulse last longer, which was particularly destructive to underwater targets. The bomb was cylindrical in shape, 152 cm (60 inches) in length and 142 cm (56 inches) 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 (18 m or 60 ft) and very precise height, at 386-402 km/h (240-250 mph), 365-457 m (400-500 yards) from the target. On striking the dam the bomb would sink to a prescribed depth of 9.1 m (30 ft) before being detonated by hydrostatic fuse. As a back-up, a chemical time fuse detonated the bomb if the hydrostatic fuse failed.

A de Havilland Mosquito dropping a Highball bouncing bomb at Chesil Beach, Dorset.
A de Havilland Mosquito dropping a Highball bouncing bomb at Chesil Beach, Dorset.

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 was awarded the Victoria Cross. The results of the raid were that out of the six intended targets, four were damaged and two were destroyed. Yet even though the mission was considered a success, the high loss of life in the raid — eight out of 19 planes sent on the raid did not return — 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.

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 a 385 kg (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.

The Soviets also utilized a variant of a bouncing bomb. These were e.g. used in the sinking of the German anti-aircraft cruiser Niobe in Kotka, Finland on July 16, 1944.

[edit] Surviving bombs

All combat Upkeep bombs were disposed of at the end of hostilities. However, concrete-filled bombs were used in test and training drops at Reculver, Kent. Several of these have been recovered in the years since the war and are displayed at various sites:

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