UK concluded, a trifle ungrammatically: ‘comparison of the Results … with that obtained by [RAF] General Purpose bombs against similar enemy targets left no doubt as to the inefficiency of our bombs’. GP bombs contained too little explosive, yet until the end of the war Britain’s airmen continued to risk and sacrifice their lives to drop more than half a million of them. The 4,000-lb HC – High-Capacity – bombs introduced in 1941, and known to aircrew as ‘cookies’, were relatively efficient wreckers of urban areas: sixty-eight thousand were dropped in the course of the offensive. They were useless, however, against such huge structures as dams.
It was noted that during the Spanish Civil War, Nationalist forces with direct access to the Ordunte and Burguillo dams had failed in attempts to destroy them, using charges laid by hand. Winston Churchill urged the American people: ‘Give us the tools and we will finish the job.’ Where, now, were to be found tools such as might collapse the enemy’s dams? The Deputy Chief of Air Staff responded to Portal’s proposal to target the Möhne that to breach its concrete mass would require dropping a barrage of a hundred mines on the reservoir side, together with a huge bomb exploded on the ‘dry’ side. ‘The practical difficulties of this method are considered to be insuperable at present.’
The great dams of north-west Germany possess a beauty unusual among industrial artefacts, a majesty enhanced by their settings among hills and woodlands. They were created in the early twentieth century, to meet soaring demand for water from both a rising population and burgeoning regional heavy industries. Work on building the Möhne, then the largest structure of its kind in Europe, began in 1908, part of a construction marathon undertaken by the Kaiserreich in the decade before the First World War. Completed in 1913 at a cost of 23.5 million marks, it was opened by Wilhelm II. The flooding of its reservoir, which eventually held almost five thousand million cubic feet of water, interrupted the Möhne river, which flowed west into the Ruhr.
The new lake, the Möhnesee, displaced seven hundred rural inhabitants of the Sauerland. It became a focus of national pride, and also a tourist attraction. Floatplanes and pleasure craft plied its waters between the wars, as they did likewise on its near neighbour the Sorpetalsperre, constructed between 1926 and 1935 in the Sorpe river valley below the village of Langscheid. A narrow-gauge railway carried more than 300,000 tons of material to what became Europe’s largest construction site, where an earthen embankment was raised around a masonry core. On completion, this rose 226 feet above the river, and was 2,297 feet in length. Its lake held 2,520 million cubic feet of water.
The Eder, forty-five miles south-eastwards in Hesse, was a smaller structure, 157 feet high and 1,312 feet wide, damming the Eder river two miles from the towering old castle of Waldeck to create a reservoir seventeen miles long, holding just over seven thousand million cubic feet of water. It was another pre-World War I project, opened in 1914, and quite unrelated to the Ruhr system. The Nazis stocked all their big reservoirs with quantities of fish, especially pike and carp, as a strategic resource in anticipation of falling sea catches when hostilities began.
The German dams, and especially the Möhne, retained their fascination for British air and economic intelligence officers through the early war years. Many and many were the hours that experts pored over photographs and technical reports about wall thicknesses, surrounding topography, defences. W/Cdr. C.R. Finch-Noyes of the Government Research Department at Shrewsbury examined all available studies and assessments, and on 2 September 1940 reported that if ten tons of explosive could be detonated beneath the Möhne’s wall, ‘there seems a probability that the dam would go’. He suggested that if aircraft flying at 80 mph and very low altitude released a succession of one-ton units close to dams, natural momentum would propel them across the water to the walls, where they would sink, to be detonated by hydrostatic pistols. This was a fascinating notion, because it anticipated – quite unknowingly – Barnes Wallis’s ‘bouncing bomb’, in truth a depth-charge. Finch-Noyes indeed urged that a standard British naval depth-charge might fulfil the requirement. One of his old colleagues, a strange, erratic air pioneer named Noel Pemberton-Billing, suggested that the dam might be attacked using a ‘hydroplane-skimmer’ that would jump over its buoyed net defences.
The Admiralty showed an interest in these proposals, not to attack dams but instead to develop weapons that might destroy targets of its own, enemy warships prominent among them. Some serious research and tests were conducted. On 2 April 1941, a paper authored by Finch-Noyes – ‘Memorandum of proposed Methods of Attacks of Special Enemy Targets’ – highlighting dams, was circulated among service departments. After studying this document, however, Bomber Command’s senior operational staff officer wrote that Finch-Noyes’s ideas must founder because of the immense tonnage of explosive needed to breach a big dam, such as no existing or prospective British aircraft could carry. The project might be of more value to the Royal Navy, he said, because smaller versions of Finch-Noyes’s proposed weapon could be practicable for use against warships.
It is often the case with big ideas, especially scientific ones, that several individuals or institutions grasp the same one independently, sometimes continents apart. Both sides in the most terrible war in history recognised reservoirs as significant industrial targets. In 1940 the Luftwaffe considered attacking the Derwent and Howden dams near Sheffield. The German airmen eventually abandoned consideration of such a strike, for the familiar reason that the dams seemed too large to be breached with existing weapons. It required the advent of a white-haired fifty-five-year-old visionary to empower the Royal Air Force to address a challenge that had vexed and frustrated its leaders since 1938.
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1 WALLIS
If Germany’s dams had been attacked with conventional bombs, rockets or shells, posterity – at least British posterity – might have taken little heed of the story. As it was, the means employed, and the man who devised them, confer enduring fascination. ‘Among special weapons,’ recorded a post-war study of RAF armament by the service’s Air Historical Branch, in language that reflects self-congratulation, ‘the “Dam Buster” must take pride of place … the story of its development and production is an epic in the history of aerial bombs.’
Barnes Wallis was the only ‘boffin’ – to be more accurate, he was an engineer – to achieve membership of Britain’s historic pantheon of World War II, behind Winston Churchill but alongside the Ultra codebreaker Alan Turing and the fighting heroes of the conflict. Until 1951, when Paul Brickhill’s book was published, scarcely anyone knew or remembered anything of Wallis. He had enjoyed some celebrity in the pre-war years, especially in connection with his work on the great airship R100. From 1939 onwards, however, he vanished behind a curtain of official security. He became famous only in the decades that followed, after the release of the film The Dam Busters, in which he was portrayed by Michael Redgrave.
The Wallis legend depicts a genius, seized with a potentially war-winning idea, fighting a lone battle against unimaginative bureaucrats to achieve fulfilment of his conception. The truth was almost entirely the other way around. What was extraordinary about the concept of what became known as the ‘bouncing bomb’ was that in the midst of an existential struggle in which Britain was striving with meagre resources, suffering repeated defeats and setbacks, some of the guiding lights of the war effort, both servicemen and civilians, grasped the potential of Wallis’s fantastic idea, supported its evolution, and within a few short weeks of securing command approval contrived the manufacture of workable examples. Moreover, officialdom proved astonishingly – indeed naïvely – willing to share the inventor’s extravagant hopes for the impact of such an assault upon the Nazi war machine. While scepticism had to be overcome about whether Wallis’s weapons would work and whether resources could be found to construct them, there was much less rigorous analysis of how drastically breaking dams would harm the interests of Hitler – except by Sir Arthur Harris, who had locked himself into a narrative
