Bouncing bomb

Vickers Type 464 code name: Upkeep store
Upkeep bouncing bomb at the Imperial War Museum Duxford
Type	Conventional (depth charge)
Place of origin	United Kingdom
Service history
In service	May 16/17 May 1943 (Operation Chastise)[1]
Used by	No. 617 Squadron RAF
Wars	World War II
Production history
Designer	Barnes Wallis
Designed	April 1942
Manufacturer	Vickers-Armstrongs
Produced	February 1943
Number built	120 (62 inert and 58 HE filled); 19 used operationally
Variants	Highball spherical bouncing bomb, concrete training bombs
Specifications
Weight	4195 kg (9,250 pounds)[2]
Length	60 inches (152 cm)
Width	56 inches (142 cm )
Muzzle velocity	240-250 mph (386-402 km/h) 500 rpm backward spin[3][4]
Effective range	400-500 yards (365-457 m)
Filling	Torpex
Filling weight	6,600 pounds (2,990 kg)[2]
Detonation mechanism	hydrostatic fuze (depth of 30 ft),[4] with backup chemical time fuze.

A bouncing bomb is a bomb designed specifically to bounce to a target such as across water to avoid torpedo nets. Unlike skip bombing,^[5] which uses conventional bombs as during the March 1943 Battle of the Bismarck Sea, the British, Germans, and Soviets developed World War II bombs specifically for bouncing to targets and then exploding. The inventor of this technique was the British engineer Barnes Wallis. His Upkeep bouncing bomb was used in the May 1943 British Operation Chastise to bounce into dams and explode underwater with similar effect to the underground detonation of the earth quake bomb (e.g., Grand Slam bomb and Tallboy bomb), which he also invented.

British bouncing bombs

Animation of a bouncing bomb path over torpedo nets into a dam

Barnes Wallis's April 1942 paper Spherical Bomb — Surface Torpedo described the attack on a battleship by bouncing a weapon on the surface of the water, striking the ship, and then dropping to explode at a depth where the hull is less protected. Exploding these weapons underneath a target's hull also took advantage of the bubble pulse phenomenon typical of underwater explosions, greatly increasing their effectiveness.

'Highball' bomb

The prototype's spherical design with dimples gave way to a smooth spherical bomb codenamed Highball developed to be dropped from a modified de Havilland Mosquito that could carry two of the bombs. The diameter was 35 inches (890 mm), designed with a charge weight of 600 lb (272 kg) of Torpex and an all-up weight of 950 lb (431 kg). The mechanical differential analyzer analogue computer allegedly used during design is preserved in New Zealand at MOTAT.^{[citation needed]} In December 1942, full-scale test drops of the spherical design began at Chesil Beach using a modified Vickers Wellington. ^{[6] [7]}

At the start of 1943, Wallis' paper Air Attack on Dams reported the results of scale model experiments and aircraft drops.^[8]

In January 1945, a USAAF A-26B Invader was adapted at the Vickers experimental facility at Foxwarren to carry two Highball inert weapons almost completely enclosed in the bomb bay, using parts from a Mosquito conversion. After brief flight testing in the UK, the kit was sent to Wright Field and installed in an A-26C Invader. 25 inert Highball weapons, renamed 'Speedee' bombs, were also sent for use in the USAAF trials. Drop tests were carried out over the sea near Eglin AFB, Florida, but the programme was abandoned after the bomb bounced back at the A-26 causing loss of the rear fuselage and fatal crash on 28 April 1945.^[9][10]

'Upkeep' bomb

Möhne dam after Operation Chastise

The operational British bouncing bomb was officially code named Upkeep store^{[citation needed]} and was known by the manufacturers as Vickers Type 464. The cylindrical bomb used Torpex ("torpedo explosive") to provide a longer explosive pulse for greater effect against underwater targets. Testing of the bouncing bomb was done at Reculver, Kent. During this time, Barnes Wallis lived at the Mill House, Chislet.^[11] In May 1943, Operation Chastise attacked dams in Germany's Ruhr Valley -- two were breached causing damage variously described as "catastrophic" or "with limited effect".^[12] The British losses during the operation were heavy (8 of the 19 attacking aircraft did not return), and although plans were made to use the weapon to attack other dams, it was not used again operationally. In January 1974 under Britain's "thirty year rule", the files for both Upkeep and Highball (along with Ultra files) were released, although technical details of the weapons had been released in 1963.

Surviving bombs

Inert development bouncing bomb on display at Abbotsbury Swannery on the Fleet Lagoon behind Chesil Beach.

All remaining combat Upkeep bombs were disposed of prior to the end of hostilities, as their condition had started to deteriorate.^[13] However, concrete-filled bombs used in test and training drops at Reculver, Kent have been recovered and are displayed at various sites:

• Dover Castle.
• Imperial War Museum Duxford
• Brooklands Museum in Weybridge
• Herne Bay Museum and Gallery.
• Brenzett Aeronautical Museum on Romney Marsh.
• Spitfire & Hurricane Museum at RAF Manston, Kent.
• Lincolnshire Aviation Heritage Centre, East Kirkby.
• Haverfordwest Aerodrome displays a section of a Highball bomb
• Abbotsbury Swannery displays a section of a Highball bomb
• RAF Lossiemouth - only accessible to the public with prior permission.
• The Petwood Hotel museum, Woodhall Spa, Lincolnshire, displays a damaged Upkeep bomb.
• Newark Air Museum displays an Upkeep test piece bomb^[14]

German bouncing bomb

After Operation Chastise, German forces discovered in some woods, an Upkeep bomb that had failed to explode. Subsequently, a 385 kg (850 pound) version of the bouncing bomb, codename Kurt, was built at the Luftwaffe Experimental Centre in Travemünde.^[7] However, the importance of backspin was not understood, 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.^[15]

Soviet bouncing bomb

Soviet forces are reputed to have used two bouncing bombs during the attack that sunk the World War II German anti-aircraft cruiser Niobe in Kotka, Finland on 16 July 1944.^{[citation needed]} No development details are known for this device, and it may have been a skip bombing incident.

External links

• Test film of both Upkeep and Highball bouncing bombs including US A-26 Invader test drops
• The bouncing bombs - History, pictures and videos.
• Barnes Wallis Memorial Trust http://www.barneswallistrust.org/

Notes

References

• Flower, Stephen. (2002). A Hell Of A Bomb. Tempus. ISBN 075242386X
• Flower, Stephen. (2004). Barnes Wallis' bombs : Tallboy, Dambuster & Grand Slam. Tempus. ISBN 0752429876 (Hardback edition of 'A Hell of a Bomb')
• Gardner, Robert. (2006). From Bouncing Bombs To Concorde. Sutton Publishing. ISBN 0750943890
• Johnsen, Frederick A. (1999). Douglas A-26 Invader (Warbird Tech Series Vol.22). Minnesota: Specialty Press Publishers. pp. 85-90. ISBN 1580070167.
• Morpurgo, Jack Eric. (1981). Barnes Wallis : A Biography. Ian Allan ISBN 0711011192
• Simons, Graham M. (1990). Mosquito: The Original Multi-Role Aircraft. Arms & Armour. ISBN 0853689954
• Sweetman, John. (1999) The Dambusters Raid. Cassell. ISBN 0304351733