Barnes Wallis was 53 years old when WWII started. He had a gentle, slightly absent-minded face, as if he was always pre-occupied with scientific figures, which he probably was since he was an aircraft designer, so people were surprised to learn that he was not just a genius, but also extremely persistent. He had worked for Vickers since before WWI and he had designed the most successful British dirigible and the Wellington bomber, as well as was currently designing its successor, the Warwick bomber.

However, Wallis was fascinated by bombs. At that time, British bombs were both weak and extremely inaccurate because the budget for bomb production and research had been tiny during the interwar years. Production of new bombs had only started in 1938, so there were very few new bombs when the war started and none were larger than 500 lbs. Both the Treasury and the upper levels of the Air Force were against the development of larger bombs partially because they would require larger planes, so the RAF only placed orders for 1,000 lb bombs six months after the war started. Wallis felt that this approach was mistaken because well-designed factories and dams would only be scratched by small bombs, so he began to consider how to make more powerful bombs and the planes to carry them.

His day job was dealing with problems related to the Warwick’s tail so he did all of his research during his lunch hour and evenings, instead of spending time with his family. He quickly decided that coal mines were too deep to be seriously damaged by bombs while oil fields were too far away. However, Germany’s three huge dams in the Ruhr Valley, the Moehne, the Eder, and the Sorpe, were worthwhile targets because they controlled the levels of the waterways that carried the endless flow of barges to the foundries in the Ruhr Valley. Destroying these dams would not only deprive the foundries of both power and water, but also wreck the roads, bridges, and railways that formed the transportation network that supplied the German military machine with tanks, guns and planes. 500 lb bombs were essentially useless against these dams since the base of the Moehne was 112 feet thick and it was 130 feet high, while the Eder was even bigger.

These dams were so massive that not even 1,000lb bombs would be powerful enough but through his research, Wallis found that when a bomb was dropped in water the shockwave greatly magnified the power of the bomb. His first design was for a ten ton bomb but since no bomber existed that could transport it he had to consider whether it was possible to design a more powerful plane. The advantage of such a bomb was that even if it missed, the resulting shockwave would most likely destroy the target or shatter its foundation.

When Wallis presented his designs to people in the RAF and the Ministry of Aircraft Production shortly after Dunkirk, the usual reaction was skepticism and/or derision, but Air Vice Marshal Arthur Tedder was interested although he had little influence at the time. The decision-makers in the RAF were naturally pre-occupied with the practical demands of preparing for a German invasion and thus had little time or patience for revolutionary yet still theoretical ideas. Wallis survived an interview with the famously short-tempered Lord Beaverbrook, the Minister for Aircraft Production, and convinced him to consider diverting vital resources to developing two ton and six ton bombs that could be carried by existing bombers. The Blitz had started by this time so bombing experts were interested in the idea of hitting Germany back.

However, when Tedder was assigned to be the head of the RAF in the Middle East Wallis lost his strongest supporter and he learned that the key decision-makers in the British government did not understand his calculations, so they would prefer to rely on dropping many little bombs rather than a handful of huge bombs. Instead of giving up in frustration, he spent several months preparing a book long ‘note’ explaining in great detail his theories  in a manner that could be understood by laymen and then sent the ‘note’ to roughly seventy influential men in science, politics and the military. The mass market mailing approach produced results and he finally attracted the attention of the Ministry of Aircraft Production, which resulted in him making presentations to a series of committees.

A side effect of the German bombing of English factories was that the people in charge of production had seen firsthand that 250lb or 500lb bombs, no matter how many, were still relatively ineffective since factories could be repaired and operational almost immediately after being bombed. He won permission to conduct tests on scale models but he found that in reality a 30 ton bomb would be required, which even he realized was impossible. Wallis seemed to have reached an impasse until he remembered watching his children skipping stones. He tested the basic theory in a tub outside his house and determined that presuming that he could figure out how to control the dropping of a bomb so that it skipped correctly and impacted the dam, a bomb of only 9,500lb would do the job.

Now all he had to do was convince the officials in Whitehall that he was not a crackpot. Fortunately, Professor Patrick Blackett, head of an operational research branch, was interested in the idea and arranged for more advanced testing in a huge ship-testing tank hundreds of feet long. It took until mid-1942 to figure out that the missile needed to be shaped like a chubby barrel and dropped with a certain amount of backspin to ensure that it stayed on the same axis through its skips. Unfortunately, solving the physical problems proved to be easier than persuading those officials with decision-making power to understand the potential of his theories. Wallis hit a polite, respectful, but unmoving wall until a chance encounter with a key official to discuss a different idea won him permission to build a half dozen prototypes. He only needed the first two to fine tune the process and he had not used all six before he gave a presentation to a room full of admirals, who were not that interested in dams, but were bursting with excitement, as much as senior admirals can be, at the prospect of putting the Tirpitz out of their misery.

After a great deal of behind the scenes maneuvering, Churchill decided that the dams would be the first target. The decision came down in February 1943 and the mission had to launch in May to cause the greatest possible damage, so it was a tight deadline. However, eight days later the project was cancelled, so Wallis sank two airtight glass containers in the giant tank, and persuaded a trusting young woman to go in one of them and film the bomb smashing the other container. He then braved a meeting with Air Marshal Bomber Harris, Chief of Bomber Command, that produced a Lancaster bomber for testing. It was fortunate that he did so because Harris’ pressure probably played an important role in pushing through against the entrenched bureaucracy, who despised the nonsense about the dams. With Harris behind him, the project was restarted and the race was on to produce working versions of the bombs in time for the mission.

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