Bouncing Bomb - British Bouncing Bombs

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 explosions, 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 nets protected them from attack by conventional torpedoes, 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 Tirpitz, 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. kg 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 279 pounds (127 kg) 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 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.