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A bouncing bomb is a bomb designed to bounce to a target across water in a calculated manner to avoid obstacles such as , and to allow both the bomb's speed on arrival at the target and the timing of its detonation to be predetermined, in a similar fashion to a regular naval depth charge. The inventor of the first such bomb was the British engineer Barnes Wallis, whose "Upkeep" bouncing bomb was used in the RAF's Operation Chastise of May 1943 to bounce into German dams and explode underwater, with an effect similar to the underground detonation of the later Grand Slam and Tallboy bomb , both of which he also invented.
Barnes Wallis's April 1942 paper "Spherical Bomb – Surface Torpedo" described a method of attack in which a weapon would be bounced across water until it struck its target, then sink to explode under water, much like a depth charge. Bouncing it across the surface would allow it to be aimed directly at its target, while avoiding underwater defences, as well as some above the surface. Such a weapon would take advantage of the "bubble pulse" effect typical of underwater explosions, greatly increasing its effectiveness: Wallis's paper identified suitable targets as Hydroelectricity "and floating vessels moored in calm waters such as the Norwegian ".Sweetman (2002), (Part 1), pp. 107, 113.
Both types of target were already of great interest to the British military when Wallis wrote his paper (which itself was not his first on the subject); German hydro-electric dams had been identified as important bombing targets before the outbreak of World War II, but existing bombs and bombing methods had little effect on them, as protected them from attack by conventional and a practical means of destroying them had yet to be devised. In 1942, the British were seeking a means of destroying the German battleship , which posed a threat to Allied shipping in the North Atlantic and had already survived a number of British attempts to destroy it. During this time, the Tirpitz was being kept safe from attack by being moored in Norwegian fjords, where it had the effect of a "fleet in being".Flower (2002), pp. 10–19, Sweetman (2002), (Part 1), pp. 105–07, and 2002 (Part 2), p. 51. See also German battleship Tirpitz#Operational history. Consequently, Wallis's proposed weapon attracted attention and underwent active testing and development.
On 24 July 1942, a "spectacularly successful" demonstration of such a weapon's potential occurred when a redundant dam at Nant-y-Gro, near Rhayader, in Wales, was destroyed by a Naval mine containing of explosive: this was detonated against the dam's side, underwater, in a test undertaken by A.R. Collins, a scientific officer from the Road Research Laboratory, which was then based at Harmondsworth, Middlesex.Flower (2002), p. 20. See also Solutions and Nant-y-Gro Dam , and video Nant-y-Gro Test (broadband) . The Dambusters (617 Squadron). Retrieved 12 August 2010.
A.R. Collins was among a large number of other people besides Barnes Wallis who made wide-ranging contributions to the development of a bouncing bomb and its method of delivery to a target, to the extent that, in a paper published in 1982, Collins himself made it evident that Wallis "did not play an all-important role in the development of this project and in particular, that very significant contributions were made by, for example, Sir William Glanville, Dr. G. Charlesworth, Dr. A.R. Collins and others of the Road Research Laboratory".Johnson (1998), pp. 29–31, citing Collins, A.R., "The origins and design of the attack on the German dams", in Proceedings – Institution of Civil Engineers. Part 2. Research and theory, 73, 1982. However, the modification of a Vickers Wellington bomber, to the design of which Wallis himself had contributed, for work in early testing of his proposed weapon, has been cited as an example of how Wallis "would have been the first to acknowledge" the contributions of others.Flower (2002), p. 19. Also, in the words of Eric Allwright, who worked in the Drawing Office for Vickers-Armstrongs at the time, "Wallis was trying to do his ordinary job for as well as all this – he was out at the Ministry and down to Fort Halstead and everywhere"; Wallis's pressing of his papers, ideas and ongoing developments on relevant authorities helped ensure that development continued; Wallis was principal designer of the models, prototypes and "live" versions of the weapon; and, perhaps most significantly, it was Wallis who explained the weapon in the final briefing for RAF crews before they set off on Operation Chastise, to use one of his designs in action.Flower (2002), e.g. pp. 30, 42, and Sweetman (2002), (Parts 1 & 2).
A distinctive feature of the weapon, added in the course of development, was back-spin, which improved the height and stability of its flight and its ability to bounce, and helped the weapon to remain in contact with, or at least close proximity to, its target on arrival. Back-spin is a normal feature in the flight of golf balls, owing to the manner in which they are struck by the club, and it is perhaps for this reason that all forms of the weapon which were developed were known generically as "Golf mines", and some of the spherical prototypes featured dimples.
It was decided in November 1942 to devise a larger version of Wallis's weapon for use against dams, and a smaller one for use against ships: these were Code name "Upkeep" and "Highball" respectively.Sweetman (2002), (Part 1), p. 110. A third version, code-named "Baseball", was also planned for use by MTBs or MGBs of the Royal Navy Coastal Forces, but "never saw the light of day"Flower (2002), p. 22. Though each version derived from what was originally envisaged as a spherical bomb, early prototypes for both Upkeep and Highball consisted of a cylindrical bomb within a spherical casing. Development, testing and use of Upkeep and Highball were to be undertaken simultaneously, since it was important to retain the element of surprise: if one were to be used against a target independently, it was feared that German defences for similar targets would be strengthened, rendering the other useless.Flower (2002), p. 22; Sweetman (2002), (Part 1), p. 114. However, Upkeep was developed against a deadline, since its maximum effectiveness depended on target dams being as full as possible from seasonal rainfall, and the latest date for this was set at 26 May 1943.Flower (2002), p. 25. In the event, as this date approached, Highball remained in development, whereas development of Upkeep had completed, and the decision was taken to deploy Upkeep independently.Sweetman (2002), (Part 2), p. 48.
In January 1974, under Britain's "thirty year rule", secret government files for both Upkeep and Highball were released, although technical details of the weapons had been released in 1963.
In the operational version of Upkeep, known by its manufacturer as "Vickers Type 464", the explosive charge was Torpex, originally designed for use in torpedoes, to provide a longer explosive pulse for greater effect against underwater targets; the principal means of detonation was by three hydrostatic pistols, as used in , set to fire at a depth of ; and its overall weight was , of which was Torpex. Provision was also made for "self-destruct" detonation by a fuze, armed automatically as the bomb was dropped from the aircraft, and timed to fire after 90 seconds.Flower (2002), p. 31. Designing the UPKEEP Mine . Royal Air Force Museum. Retrieved 13 August 2010. The bomb was held in place in the aircraft by a large pair of calipers, or triangulated carrying arms, which swung away from either end of the bomb to release it.Flower (2002), p. 31. Diagrams from document produced by Dr Wallis to explain how the bouncing bomb Upkeep worked. The National Archives. Retrieved 10 August 2010. Back-spin was to begin 10 minutes before arriving at a target and was imparted via a belt driven by a Vickers Jassey hydraulic motor mounted forward of the bomb's starboard side. This motor was powered by the hydraulic system normally used by the upper gun turret, which had been removed. Close contact with the dam was necessary to obtain the maximum effectiveness from the explosive.
Height was checked by a pair of intersecting spotlight beams, which, when converging on the surface of the water, indicated the correct height for the aircraft – a method devised for the raid by Ben Lockspeiser of the Minister of Aircraft Production, and distance from the target by a simple, hand-held, triangular device: with one corner held up to the eye, projections on the other two corners would line up with pre-determined points on the target when it was at the correct distance for bomb release. In practice, this could prove awkward to handle, and some aircrews replaced it with their own arrangements, fixed within the aircraft itself, and involving Grease pencil and string.Flower (2002), pp. 35–36.
On the night of 16/17 May 1943, Operation Chastise attacked dams in Germany's Ruhr Valley, using Upkeep. Two dams were breached, causing widespread flooding, damage, and loss of life. The significance of this attack upon the progress of the war is debated. British losses during the operation were heavy; eight of the 19 attacking aircraft failed to return, along with 53 of 113 RAF aircrew.Johnson (1998), p. 31, describes this as "about average losses in bombing raids at that time", but cf. Problems , The Dambusters (617 Squadron). Retrieved 10 August 2010. The breach resulted in the deaths of roughly 1600 civilians, including around 1000 prisoners and slave laborers. Upkeep was not used again operationally. By the time the war ended, the remaining operational Upkeep bombs had started to deteriorate and were dumped into the North Sea without their detonation devices.Flower (2002), p. 62, and Robert Owen, "Operation Guzzle", in Breaching the German Dams Flying into History, RAF Museum, 2008.
From November 1942, development and testing for Highball continued alongside that of Upkeep, including the dropping of prototypes at both Chesil Beach and Reculver. While early prototypes dropped at Chesil Beach in December 1942 were forerunners for both versions of the bomb, those dropped at Chesil Beach in January and February 1943 and at Reculver in April 1943 included Highball prototypes.Sweetman (2002), Part 1, pp. 112, 118. They were dropped by the modified Wellington bomber and at Reculver by a modified de Havilland Mosquito B Mk IV, one of two assigned to Vickers Armstrong for the purpose.Sweetman (2002), Part 1, pp. 114, 118. By early February 1943, Wallis envisaged Highball as "comprising a charge in a cylinder contained in a sphere with (an overall weight) of "; a modified Mosquito could carry two such weapons.Sweetman (2002), Part 1, p. 113.
In tests at Reculver in the middle of April 1943, it was found that Highball's spherical casing suffered similar damage to that of Upkeep. A prototype with an altered design of casing strengthened by steel plate, but empty of inert filling or explosive, was dropped on 30 April and emerged "quite undamaged".Sweetman (2002), Part 1, p. 118. In further testing on 2 May, two examples of this prototype with inert filling, bounced across the surface of the water as intended, though both were found to be dented.Sweetman (2002), Part 1, p. 119.
Further testing was carried out by three modified Mosquitoes flying from RAF Turnberry, north of Girvan, on the west coast of Scotland, against a target ship, the former French battleship , which had been moored for the purpose in Loch Striven.Sweetman (2002), Part 2, p. 52. RAF Turnberry occupied the site of Turnberry golf resort. This series of tests, on 9 and 10 May, was hampered by a number of errors: intended to mark a point from Courbet, where the prototypes were to be dropped, were found to be too close to the ship by , and, according to Wallis, other errors were due to "Variations in dimensions of prototypes after filling and dimensionally jigs for setting up the caliper arms".Sweetman (2002), Part 2, pp. 52–53. Because of these errors, the prototypes hit the target too fast and too hard. Two aircraft failed to release their prototypes, one of which then fell off while the aircraft was turning for a second attempt.
It was under such circumstances that Upkeep came to be deployed independently of Highball. In addition to continuing problems in testing Highball, it had been observed at the end of March 1943 that "At best aircrews would need two months' special training".Sweetman (2002), Part 1, p. 115. With this in mind, 618 Squadron had been formed on 1 April 1943 at RAF Skitten, near Wick, in northeastern Scotland, to undertake "Operation Servant", in which Tirpitz would be attacked with Highball bouncing bombs.Sweetman (2002), Part 2, pp. 48–49. On 18 April it was recommended that Operation Servant should be undertaken before the end of June, since 618 Squadron could not be held back for this purpose indefinitely. It was not until early September 1943 that, in view of continuing problems with both Highball and its release mechanism, most of 618 Squadron was "released for other duties". This in practice meant the abandonment of Operation Servant.Sweetman (2002), Part 2, pp. 54, 57. Core personnel of 618 Squadron were retained and these continued work on the development of Highball.Flower (2002), p. 78.
Testing between 15 and 17 May 1944 showed progress with Highball. By this time Courbet had been designated for use as a Gooseberry breakwater for the invasion of Normandy, so the old battleship , then in reserve, was used instead (also moored in Loch Striven). With crew on board Malaya, bombers dropped inert Highball prototypes fitted with hydrostatic pistols, aiming at the ship. They struck the ship, and at least two punched a hole in the ship's side. On 17 May, for the first time, Highball prototypes were released in pairs, only one second apart.Flower (2002), pp. 78–79.
By the end of May 1944, problems with releasing Highball had been resolved as had problems with aiming. Aiming Highball required a different method from Upkeep; the problem was solved by Wallis's design of a ring aperture sight fixed to a flying helmet.Flower (2002), pp. 78–80. Highball was now a sphere with flattened , and the explosive charge was Torpex, enclosed in a cylinder, as in Upkeep; detonation was by a single hydrostatic pistol, set to fire at a depth of , and its weight was , of which was Torpex.
Highball was never used operationally: on 12 November 1944, in Operation Catechism, Lancasters with sank its primary target, Tirpitz. Other potential targets had been considered during Highball's development and later. These included the ships of the Regia Marina, canals, dry docks, , and railway tunnels (for which testing took place in 1943). But Italy surrendered in September 1943, and the other target ideas were dismissed as impracticable.Flower (2002), e.g. pp. 66–67, 72–76. On 3 September 1943, an armistice was signed between Italy and the Allies.
In January 1945, at the Vickers experimental facility at Foxwarren, near Cobham, Surrey, a Douglas A-26 Invader medium bomber of the USAAF was adapted to carry two Highballs 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, Ohio, and installed in a A-26C Invader. Twenty-five inert Highballs, renamed "Speedee" bombs, were also sent for use in the USAAF trials. Drop tests were carried out over Choctawhatchee Bay near Eglin Field, Florida, but the programme was abandoned after the bomb bounced back in a drop on Water Range 60, causing loss of the rear fuselage and a fatal crash on 28 April 1945.Flower (2002), pp. 87–88. Also Gardner (2006), Johnsen (1999), and Douglas A-26C breaks apart in mid-air testing a bouncing bomb at YouTube. Retrieved 11 December 2010.
In 2010, a diving project in Loch Striven successfully located several Highball prototypes, under around of water. In July 2017, two Highballs were successfully recovered BBC News – Divers recover World War Two Highball Bomb. Retrieved 22 July 2017. from Loch Striven in a joint operation by teams from East Cheshire Sub-Aqua Club and the Royal Navy. One is now displayed at the de Havilland Aircraft Museum and the other arrived at Brooklands Museum in late 2019 after undergoing conservation at the Mary Rose Trust.
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