Wallis was still faced with the problem of placing his hypothetical explosive charge against the wet face of the dam. It has been known since the dawn of artillery that cannon balls could be ricocheted off the surface of the sea and this technique had been used for years to extend the range of black powder guns. Although German physicists in the early 1900?s had identified and quantified the physics of bouncing solid objects off water it was not until Barnes Wallis turned his formidable intellect to the problem that it was proved back spin greatly extended the range of this ricocheting projectiles. Wallis by careful experimentation proved the “Magnus effect” whereby the spinning object is effectively given aerodynamic lift and the number of bounces thereby increased.
Wallis obtained consent to use the testing facilities of the National Physical Laboratory to test out his theories in more detail having carried out initial experiments in his back garden using his daughters marbles as projectiles, fired from a home made slingshot across tin baths of water. Over a period he experimented with projectiles made of wood, aluminium, steel and lead with a view to obtaining the optimum weight, size, design speed and bounce distance on the balls to maximise the skip technique. At this stage all of Wallis’s experiments had been carried using a spherical projectile.
In August 1942 he attended a meeting at Vickers House in London and at this meeting he was able to convince the Ministry of Aircraft Production that the concept of skipping a bomb onto the dam face was feasible. The spinning bomb skipped better than an un-spinning weapon and the backspin that was imparted had the secondary benefit that when the projectile hit the dam face it ricocheted away but the remaining back spin drew the bomb back onto the dam face where it sank and would be exploded by a hydrostatic pistol of the same type used on depth charges. Tests were approved.
On December 4th 1942 a Wellington Bomber flown by Captain Mutt Summers, Vickers chief test pilot arrived over Chesil Beach in Dorset and having lined up carefully with cameras on the beach made its run and dropped the bomb. Unfortunately the bomb disintegrated when it struck the water. By December 9th a new casing had been manufactured and reinforced but this bomb also disintegrated. Tests continued with bombs being dropped and Wallis rowing out in a boat at low tide to inspect the casings. With each test modifications were carried out to the casings and trials continued on January 9th 1943 and the 23rd of the month resulting in a skip of 13 times and on the 10th January a bomb skipped 20 times before finally sinking. Finally on February 5th it had proved possible to skip the bomb for over 1300 yards and for it to generally remain intact at the end.
Whilst this work was progressing Wallis completed a further report entitled “Air Attack on Dams” and submitted it to several Air Ministry and political figures. On January 28th he showed the films of the Chesil Beach tests to a gathering of high ranking staff from the Air Ministry and Ministry of Aircraft Production. The Royal Navy expressed considerable interest with a view to using the weapon against the German battleship Tirpitz and in fact by the end of January an order for 250 weapons was placed on behalf of the Royal Navy who were impressed with the potential of the weapon. Wallis however still felt that the best use for his weapons was against the German dams and proposed therefore that the dams weapon, now codenamed “Upkeep” and the Royal Navy anti-ship weapon, now codenamed “Highball” be developed together. He was concerned that in the event the Royal Navy used the weapon against ships the technology would be made available to Germans and the element of surprise lost.
Wallis had also been working on a smaller version “Baseball” which he was planning to fire at warships from motor torpedo boats. The whole family of bombs were given the codename “Golfmine”.
On February 13th 1943 Air Chief Marshall Arthur Harris was briefed on the dams proposal by Group Captain S C Elsworthy. Doubts however still existed about the feasibility of using upkeep against the dams and Harris who had a strong dislike of any dissipation of effort from the bombing of Germany was not at all keen on the idea. Other operational factors were now coming into play and it was realised that for the dam breaking operation to have the maximum effect it should be carried out when the reservoirs were at their fullest and this would also maximise the effect of the weapons themselves. That was in May and to give the necessary time for crew training, production and provision of all the necessary equipment and planning, a decision on the operation needed to be made by February 15th if it was to occur in 1943.
Air Vice Marshall Robert Saundby a colleague of many years of Harris’ formally re-presented the plan to Harris. He explained that an up rated bomb of 10,000lbs would be needed for the operation and a specially modified Lancaster would be needed to carry it. He further explained that a specially trained Lancaster Squadron would need to be relieved of its normal bombing duties for two to three weeks beforehand to carry out the required training. It was planned at this stage bombing in full moonlight using radio altimeters which were much more sensitive that the usual barometric models normally used. The report was returned by Sir Arthur with a handwritten note stating “this is tripe of the wildest description. There are so many if and buts and there is not the smallest chance of it working”.
The following day a meeting was held at the Air Ministry attended by Wallis and Mutt Summers where it was decided to proceed with the construction of one upkeep bomb and to modify one Lancaster with the required dropping equipment. Harris was informed but was not impressed.
Sir Ralph Cochrane, commanding officer of No 5 Group (and therefore the man who would be responsible for carrying out the operation if it went ahead) was convinced that he plan would work and he arranged a further meeting between Wallis and Harris. Harris remained strongly against the plan but agreed to watch film of the drops at Chesil Beach and following the film agreed to the conversion of three Lancasters for further development work. The following day Wallis was “hauled over the coals” by the Chairman of Vickers Armstrong, Sir Charles Craven. Having come under some considerable pressure from the Air Ministry he advised Wallis that he must stop “making a nuisance of himself” and drop the whole idea. Wallis offered to resign but continue working on the project over the next couple of days. At the Air Ministry however, things were moving quite rapidly. Two days later he was asked to attend a conference at the Ministry of Aircraft production where it was explained that the Chief of Air Staff now wanted every effort to be made on the development of the aircraft and bombs so that the project could go ahead no later than May 26th when it was estimated that the water levels in the dams would fall to low for the best results.
This sudden change in policy faced Wallis with a new problem. Time was now extremely short for the development and production of the bomb, the modification of the aircraft and the training of the crews.
Avro were given the task of modifying the bomb bays of the Lancasters, strengthening the fuselage and building and fitting the frame mechanism to hold the bomb in place. Additionally a Ford V8 engine had to be fitted in the fuselage to spin the bomb up to speed. All that said, the problems were all now practical and the operation could proceed.