Bouncing bomb A bouncing bomb is a bomb designed specifically to bounce to a target across water in a calculated manner to avoid obstacles such as torpedo net s , and to allow both the bomb ' s speed on arrival at the target and the timing of its detonation to be pre - determined , 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 effect similar to the underground detonation of the Grand Slam and Tallboy earthquake bomb s , both of which he also invented . British bouncing bombs . 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 sinking to explode underwater , 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 , and such a weapon would take advantage of the " bubble pulse " effect typical of underwater explosion s , greatly increasing its effectiveness : Wallis ' s paper identified suitable targets as hydro - electric dams " and floating vessels moored in calm waters such as the Norwegian fjords " . 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 , torpedo net s protected them from attack by conventional torpedo es , and a practical means of destroying them had yet to be devised ; and , in 1942 , the British were seeking a means of destroying the German battleship , which posed a threat to Allied shipping in the North Atlantic , had already survived a number of British attempts to destroy it , and for much of the time was being kept safe from attack by being moored in Norwegian fjords , where nonetheless it had the effect of a " fleet in being " . 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 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 , that was then based at Harmondsworth , Middlesex . 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 . " However , the modification of a Vickers Wellington bomber , the design of which Wallis himself had contributed to , 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 . 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 Vickers Armstrongs ] 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 . 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 - named " Upkeep " and " Highball " respectively . 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 . 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 . 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 . 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 . Upkeep . Testing of Upkeep prototypes with inert filling was carried out at Chesil Beach , Dorset , flying from RAF Warmwell in December 1942 , and at Reculver , Kent , flying from RAF Manston in April and May 1943 , at first using a Vickers Wellington bomber . However , the dimensions and weight of the full - size Upkeep were such that it could only be carried by the Avro Lancaster , which was the largest British bomber available at the time , and nonetheless had to undergo considerable modification in order to carry it . In testing , it was found that Upkeep ' s spherical casing would shatter on impact with water , but that the inner cylinder containing the bomb would continue across the surface of the water much as intended . As a result , Upkeep ' s spherical casing was eliminated from the design . Development and testing concluded on 13 May 1943 with the dropping of a live , cylindrical Upkeep bomb out to sea from Broadstairs , Kent , by which time Wallis had specified that the bomb must be dropped at " precisely " above the water and groundspeed , with back - spin at 500 rpm : the bomb " bounced seven times over some 800 yards , sank and detonated " . In the operational version of Upkeep , known by its manufacturer as " Vickers Type 464 " , the explosive charge was Torpex , originally designed for use as a torpedo explosive , 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 depth charge s , 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 . The bomb was held in place in the aircraft by a pair of calipers , or triangulated carrying arms , which swung away from either end of the bomb to release it . 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 . Aiming was by a pair of intersecting spotlight beams , which , when converged on a surface of water , indicated correct height for the aircraft , and 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 chinagraph and string . 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 and 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 . 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 . Highball . In April 1942 , Wallis himself had described his proposed weapon as " essentially a weapon for the Fleet Air Arm " , and this naval aspect was later to be pressed by a minute issued to relevant authorities by British prime minister Winston Churchill , in February 1943 , in which he asked , " Have you given up all plans for doing anything to while she is in Trondheim ? . . . It is a terrible thing that this prize should be waiting and no one be able to think of a way of winning it " . However , Highball was ultimately developed as an RAF weapon for use against various targets , including " Tirpitz " . 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 prototypes specifically for Highball . They were dropped by both the modified Wellington bomber and , at Reculver , by a modified de Havilland Mosquito B Mk IV , one of two assigned to Vickers Armstrongs for the purpose . By early February 1943 , Wallis had come to envisage Highball as " comprising a 500 lb [ 227 kg ] charge in a cylinder contained in a 35 - in [ 89 cm ] sphere with ( an overall weight ) of 950 lb [ 431 kg ] " , and , with modification , the Mosquito could carry two such weapons . 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 . However , one prototype with an altered design of casing strengthened by steel plate , but empty of either inert filling or explosive , was dropped on 30 April , and emerged " quite undamaged " . Further testing of two examples of this prototype on 2 May , now with inert filling , was successful with regard to their ability to bounce across the surface of the water as intended , though , on inspection , both were found to be dented . 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 . This series of tests , on 9 and 10 May , was hampered by a number of errors : buoys intended to mark a point from the " 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 incorrect ] jigs for setting up the [ caliper ] arms " . Effects were that the prototypes hit their target too fast , and too hard , and that two aircraft failed to release their prototypes , one of which then fell while the aircraft concerned 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 " . With this in mind , 618 Squadron had been formed on 1 April 1943 at RAF Skitten , near Wick , in north - eastern Scotland , to undertake what was intended to be " Operation Servant " , in which " Tirpitz " would be attacked with Highball bouncing bombs . 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 : nonetheless , 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 " , which in practice meant the abandonment of Operation Servant . Core personnel of 618 Squadron were retained , however , and these continued to be involved in the development of Highball . Demonstrations of progress with Highball occurred in testing between 15 and 17 May 1944 . By this time " Courbet " had been used as part of a Gooseberry breakwater for the D - Day landings , and , a veteran of World War I , was used as its replacement , also moored in Loch Striven . With crew on board HMS " Malaya " , inert Highball prototypes fitted with hydrostatic pistols were aimed at the ship and released , successfully striking the ship , and one punched a hole in the ship ' s side . On 17 May , for the first time , prototypes were released in pairs , only one second apart . By the end of May 1944 , problems with releasing Highball had been resolved , as had problems with aiming , which required a different method to that for Upkeep , and were resolved by Wallis ' s design of a ring aperture sight fixed to a flying helmet . Highball itself was now a sphere with flattened poles , 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 overall weight was , of which was Torpex . However , Highball was never used in action . On 12 November 1944 , its primary target , " Tirpitz " , was capsized by Lancasters from 9 Squadron and 617 Squadron in Operation Catechism , using Tallboy bomb s : these were also developed by Wallis , independently of his work on bouncing bombs . Other potential targets were considered , both during Highball ' s development and later , including ships of the Italian navy , canals , dry docks , submarine pen s , and railway tunnels – for which testing took place , in 1943 – but , while the Italian navy ceased to be an enemy from 3 September 1943 , the remainder were dismissed , in effect , as impracticable . In January 1945 , a Douglas A - 26 Invader of the USAAF was adapted at the Vickers ' experimental facility at Foxwarren , near Cobham , Surrey , 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 an 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 at A - 26C - 25 - DT Invader " 43 - 22644 " on Water Range 60 , causing loss of the rear fuselage and a fatal crash on 28 April 1945 . Baseball . As well as the two types listed above , a smaller weapon for use by MTB s was proposed by the Admiralty in December 1942 . Known as Baseball , this would be a tube - launched weapon weighing , of which half would be explosive , and with an anticipated range of . Surviving examples . Inert prototypes of both Upkeep and Highball that were dropped at Reculver have been recovered and these , along with a number of other examples , are displayed at various sites : In 2010 , a diving project in Loch Striven successfully located " at least eight " Highball prototypes , under more than of water . There are plans to recover some of these prototypes , for conservation and restoration at Brooklands Museum . German bouncing bomb . After Operation Chastise , German forces discovered an Upkeep bomb intact . This was in the wreckage of the Lancaster commanded by Flt Lt Barlow , which had struck high tension cable s at Haldern , near Rees , Germany , and crashed : since the bomb had not been released , and the aircraft had crashed on land , none of the detonation devices had fired . Subsequently , a version of Upkeep , code - named " Kurt " or " Emil " , was built at the Luftwaffe ' s " Erprobungsstelle " , or " test site " , on Germany ' s Baltic coast at Travemünde . However , the importance of back - spin was not understood , and , dropped in trials by a Focke - Wulf 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 . Re - creating the bouncing bomb . In 2011 , a project was initiated to re - create a Dambusters raid . Buffalo Airways was selected as the company to fly the mission , with their own plane and pilots . Buffalo would drop a re - created ' Upkeep ' bouncing bomb from their DC - 4 . The project was documented in the documentary television show Dambusters Fly Again in Canada and Australia , in the UK , and the Nova episode Bombing Hitler ' s Dams in the US . It involved dropping a replica dummy bomb , and blowing up a replica dam . The filming of the documentary was itself documented as part of the Ice Pilots NWT reality series , that follows Buffalo Airways , in season 3 episode 2 " Dambusters " .