to nurse this dream, which was mirrored by a German nightmare. On the eve of war, 29 August 1939, Justus Dillgardt, chairman of the Ruhrtalsperenverein organisation responsible for regional water resources, suggested that a succession of bombs exploded sub-aquatically within a hundred feet of the base of his dams, the effects multiplied by the water mass – a scientific phenomenon identified by the British only three years later – might prompt dam collapses. If the Möhne was breached, Dillgardt warned that ‘this entire industrial area … would be completely paralysed … not only would the population of four to five millions be without water, but all mines and coking plants would suddenly cease work owing to lack of industrial water supply’.
Through the early war years, both the Air Staff and British economic warfare researchers sustained enthusiasm for striking at the enemy’s water resources. The Ruhr and its industries accounted for a quarter of the Reich’s entire consumption, much of this derived from the Möhne reservoir. The Air Targets Sub-Committee was told that its destruction would create ‘enormous damage’, affecting hydro-generating stations. The ‘low-lying Ruhr valley would be flooded, so that railways, important bridges, pumping stations and industrial chemical plants would be rendered inoperative’.
In June 1940, amid the crisis of the fall of France, Bomber Command groped for means of striking back at the victorious Nazis. Its senior air staff officer, Gp. Capt. Norman Bottomley, again urged the merit of breaching enemy dams. On 3 July, Portal, then Bomber Command’s C-in-C, wrote to the Air Ministry pinpointing a key target. Surely, he said, ‘the time has arrived when we should make arrangements for the destruction of the Möhne Dam … I am given to understand that almost all the industrial activity of the Ruhr depends upon [it].’ He suggested a possible torpedo attack by Hampden bombers, or high-level bombing attack against the ‘dry’ side of the Möhne’s wall.
But what realistic prospect could there be of such an operation’s success? Throughout the wars of the twentieth century, again and again it was shown that strategy must follow technology, and also required mass, whether in the matter of landing-craft for amphibious operations; radar to negate prime minister Stanley Baldwin’s warning – correct when it was delivered in 1932 – that ‘the bomber will always get through’; or attacks on German dams. It was useless to identify a purpose unless means to fulfil it existed, or might be created, as they certainly could not have been in 1940, when Bomber Command was weak, and Britain’s war effort was focused upon averting defeat.
The weapons available to pursue the airmen’s ambitions remained inadequate in quality as well as quantity. The Hampden bombers mentioned by Portal could carry nothing like heavy enough ordnance to dent, far less breach, the Möhne. A December 1940 study of German bombing of the 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
