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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, England. It was used in the famous Dambusters raid to attack major dams in Germany's industrial Ruhr Valley during World War II. The mechanical differential analyzer analogue computer used in its design is preserved in New Zealand at MOTAT.

Contents 1 Origins 1.1 Anti-shipping weapon (Highball) 1.2 Anti-dam weapon (Upkeep) 2 Further employment 3 German bouncing bomb 4 Soviet bouncing bomb 5 Surviving bombs 6 See also 7 References 8 External links

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. This peculiarity was used by the artillery of defense of harbors. Vauban had finalized it for the attack of forts.

In April 1942 he published a paper named "Spherical Bomb — Surface Torpedo".

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.

Before and during World War II, the Royal Air Force identified German hydro-electric dams as targets. However, dams were immune to conventional attack because of their size; an immense amount of explosive would be required to breach them because then-current bomb aiming techniques would not allow the placing of a bomb with the required accuracy to avoid the cushioning effect of the water. The other possibility, a torpedo attack, had been foreseen by the Germans, who had guarded against this by placing heavy nets upstream of the dams. Barnes Wallis observed that a larger version of the 'bouncing' anti-ship weapon would skip over the anti-torpedo nets and sink in contact with the dam, where the water would act as a natural tamping medium, directing the explosion on to the dam, instead of protecting it, and greatly reducing the explosive power required.

At the start of 1943 Wallis showed his finished paper "Air Attack on Dams", reporting on the results of experiments including scale models and tests from aircraft.^[1]

Owing to time constraints set by the Royal Air Force, the final version of the anti-dam weapon, codenamed Upkeep (also known as the "Vickers Type 464"), was different from Barnes Wallis's initial intentions, dispensing with the spherical metal shell and the "dimples". 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 height (18 m or 60 ft), speed (386-402 km/h or 240-250 mph), and distance (365-457 m or 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.

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.

Although Operation Cheases 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 by No. 618 Squadron RAF against the German battleship Tirpitz and then against Japanese shipping in the Pacific Theater but the war ended without it being used in conflict.

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 Operation Chastise, 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 found and tested by the Luftwaffe.^{[citation needed]} Designed for use against British shipping, it was given the codename Kurt, and was built at the Luftwaffe Experimental Centre in Travemünde. However, they failed to understand the importance of backspin, and 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.^{[citation needed]}

The Soviets also utilized a bouncing bomb during World War II. These were used in the sinking of the German anti-aircraft cruiser Niobe in Kotka, Finland on 16 July 1944.^{[citation needed]}

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:

• The Imperial War Museum Duxford
• Brookland's Museum in Weybridge, England
• Brenzett Aeronautical Museum, near Romney Marsh.
• The Petwood Hotel, Woodhall Spa, Lincolnshire, was the Officers Mess for 617 Squadron. It has a small museum and a damaged Upkeep bomb on display in the grounds.
• The Spitfire & Hurricane Museum at RAF Manston, Kent.
• The Lincolnshire Aviation Heritage Centre at East Kirkby.
• Dover Castle.
• RAF Lossiemouth - only accessible to the public with prior permission.
• Herne Bay Museum and Gallery.
• A section of a Highball bomb, recovered by the Pembrokeshire Aviation Group, is displayed at Haverfordwest Aerodrome.
• A section of a Highball bomb, recovered by the Royal Navy and local conservation groups from the Fleet in Dorset, is displayed at Abbotsbury Swannery.

• Tallboy bomb
• Skip bombing

• Memories of an apprentice who worked on the bouncing bomb prototypes
• Technical description of the bomb
• Information about Upkeep and test drop video footage
• The special weapons of Barnes Wallis
• Bouncing bombs - History, pictures and videos

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