Chastise: The Dambusters Story 1943

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.

2

The Boffin and His Bombs (#litres_trial_promo)

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 of his own.

Even had Barnes Wallis failed to secure fame through breaching the dams, he would have deserved notice as a remarkable human being. He was the son of a doctor who practised in London’s humble New Cross area, hampered by having suffered polio. Barnes, born in 1887, attended a minor public school, Christ’s Hospital, only after winning a scholarship. He missed university, and instead became an engineering apprentice at a shipbuilding firm, then in 1913 graduated to working on airship development for the industrial giant Vickers. While he was adequately paid, his finances were chronically strained by his insistence upon aiding other members of his unlucky family. No stranger to pawnbrokers’ shops, he once sold a bicycle to pay for his parents to enjoy a holiday.

When World War I came, Wallis’s repeated attempts to join the army foundered because Vickers reclaimed his services. He served for a few months on airships, with the rank of sub-lieutenant in the Royal Naval Air Service, but retained a lifelong guilt that he had not fought as did most of his contemporaries. In 1922, with the post-war run-down of the armed forces, Vickers abandoned airship production and made Wallis redundant. During the years that followed, somewhat unexpectedly he served as a part-time Territorial Army soldier in an anti-aircraft artillery unit. For a time he studied for an external degree at London University, and was reduced to seeking employment through the scholastic agency Gabbitas Thring, who found work for him as a mathematics teacher at an English school in Switzerland. It was from there, as a bachelor already thirty-five, that he began writing to his seventeen-year-old cousin by marriage, Molly Bloxam, to whom he explained mathematical formulae, then progressed to discussing technical and physics issues that fascinated him. Their correspondence developed into a romance. In that long-ago era before social telephoning, he wrote ten- to twelve-page letters to his beloved, signing himself ‘your affectionate cousin’.

Molly soon pledged her heart to Barnes, but her father was wary of this middle-aged ‘cradle-snatcher’, for a year restricting their correspondence to a letter apiece a fortnight. It was only in April 1925, three years to the day after they met, that they were finally married – to live happily ever after. The Wallises never became rich, but in 1930 they achieved chintzy middle-class comfort in a mock-Tudor suburban home at Effingham in Surrey which eventually hosted the rumpus generated by four noisy children. This largely self-taught polymath rejoined Vickers in the year of his wedding as assistant chief designer, working on the R100, then the largest airship ever built. While labouring at this day job he found time for bell-ringing in the village church and service on the parish council – he was a devout Christian and vegetarian. Until war came he practised Sunday observance, declining even to read a newspaper. A friend wrote of a conversation with Wallis in which he exuberantly expressed his admiration for God: ‘My dear boy, do you realise that the Almighty has arranged a system whereby millions of electric circuits pass up and down a single cord no bigger than my little finger, and each one most beautifully insulated. The spinal cord is an absolute marvel of electronics!’ So deep was Wallis’s attachment to family that for most of his life he subsidised, and indeed supported, first his father, then his grown-up sister and her husband.

All the Wallises were music-lovers, and Barnes played an occasional round of golf on the course adjoining his garden. He proved an ingenious handyman around the house, and an imaginative wood-carver. Though not teetotal, the family drank little, and never succumbed to extravagance. Barnes took a cold bath every morning. For all his devotion to Molly, he could be a stern paterfamilias. ‘We were used to my father isolating himself in his study at the top of the house,’ said his daughter Mary. ‘Always working, often abstracted, he was frequently absent from the daily round of chat, laughter and games which large families enjoy. But when he did join in it was lively and great fun. Even in the darkest days he would burst into cheerful, spontaneously made-up doggerel verse under the name “Spokeshave-on-Spur”, which delighted us all.’ Wallis relaxed discipline on annual family camping and walking holidays. Mary described how, on a Dorset beach, he taught his children to skim flat stones: ‘Mine went plop, plop and sank. His would slide smoothly with six or seven hops and quietly submerge.’ Barnes and Molly, their daughter added, ‘succeeded in protecting us from fear, anxiety, hunger or distress’, a notable achievement for any parents.

Yet Wallis’s stubborn, spiky eccentricities not infrequently engaged him in quarrels. There was a peculiar episode when Molly met, admired and brought home to Effingham the great birth-control evangelist Marie Stopes. She and Barnes disliked each other on sight, and continued to do so, though her son Harry eventually married the engineer’s daughter Mary. At the outset, Wallis and Stopes argued fiercely over his indulgence and indeed encouragement of Molly’s semi-overt breastfeeding of her baby of the moment, a practice which the visitor deemed barbaric.

Barnes’s favourite domestic relaxation was to read aloud to Molly from Dickens, Hardy or Jane Austen while she mended the children’s clothes. The Wallises were good people, if that is not an inadequate adjective, committed to the virtues of honesty, family and honourable behaviour. This tall, angular figure was also, of course, a workaholic. ‘He was a collision of times,’ observes Richard Morris. ‘In manners and values he was of the 1890s; in aerodynamic possibility, of the 2030s or beyond. He combined confidence, self-pity, vision, regret, hope, loyalty, disdain and ten-score other characteristics.’

To understand Wallis’s wartime experiences it is important to recognise that, while his talents and imagination were remarkable, he was very far from right about everything. All his life he pursued doomed projects with the same manic, obsessive commitment that he brought to those that prospered. Throughout a long association with airships, he failed to perceive that winged aircraft represented the future, writing to a colleague soon after World War I: ‘All my heart is in airships, and I have worked so hard.’ He championed their cause, and especially that of the R100, even after the 1930 incineration of the R101, together with similar disasters in the United States, had laid bare inherent limitations of the lighter-than-air concept.

In 1933 the M.1/30, a prototype torpedo biplane which Wallis designed, broke up in mid-air, though the structural failure was not his fault. Its test pilot, Captain Joe ‘Mutt’ Summers, took to his parachute successfully, but the plane’s observer had a close brush with death when his straps became entangled with the rear machine-gun as the wreck screamed earthwards. The man was fortunate to escape, and to deploy his canopy, before the plane spun into the ground. While Wallis was often applauded for creating the geodetic framework of the Wellesley and Wellington bombers – latticing derived from his wiring system for harnessing the gasbags of airships, which created exceptional fuselage strength – other nations concluded that it was too complex to be cost-effective, and the RAF spurned geodetic frameworks for its later heavy bombers.

Between 1941 and 1943 the foremost brains of Vickers-Armstrong were engaged in creating a new aircraft, christened the Windsor, armed with 20mm cannon, capable of carrying a bomb load of fifteen tons at a speed of 300 mph. Rex Pierson, Barnes Wallis – who held the title of Assistant Chief Designer (Structures) – and supporting teams of engineers and draughtsmen devoted countless hours to this project, which never advanced beyond the prototype stage. The ever-improving performance of the Avro Lancaster, which entered service in 1942, made the Windsor redundant, though work on it continued through 1944.

None of the above is intended to detract from Wallis’s achievements – merely to explain why it was not unreasonable for those in authority to greet with caution his higher flights of imagination. At one time and another of his life, large sums of public money were expended on the development of devices, weapons, and indeed aircraft which failed after he had proclaimed their virtues at Whitehall meetings with the same messianic fervour he deployed in advocating his winners.

Moreover, Wallis was only one among a host of enthusiastic inventors peddling ambitious schemes to the armed forces. Lord Cherwell, the prime minister’s favourite scientist, railroaded into the experimental stage an absurd scheme for frustrating enemy aircraft with barrages of aerial mines. Cherwell likewise promoted a CS – Capital Ship – bomb that was an expensive failure, as were early British AP – Armour-Piercing – bombs. Lord Louis Mountbatten, as director of combined operations, sponsored a scheme for creating aircraft-carriers contrived from ice blocks. Barnes Wallis attempted to persuade the Royal Navy to adopt a smoke-laying glider of his invention. The Americans conducted experiments in fitting incendiary devices to bats, to be dispatched over enemy territory, an abortive operation codenamed X-Ray. Evelyn Waugh’s description, in his satirical war novel Put Out More Flags, of Whitehall recruiting a witch doctor to cast spells on Hitler, did not range far beyond reality. Aircraft designer Norman Boorer said: ‘There were many, many crazy ideas being put forward by all sorts of scientists.’

Despite Wallis’s white hair and the faraway look that was often in his eyes, he was anything but unworldly – indeed, he might be considered a veteran ‘Whitehall warrior’. Over two decades of nurturing and supervising complex projects he had honed skills in haranguing committees; guile in exploiting personal relationships; boldness in bullying companies and institutions to assist him in pursuing his purposes. Like many brilliant men, he existed in a default condition of exasperation towards the failure of others to see things as he did. In 1940, when he was working on modifications to the Vickers Wellington and also on a six-engined ‘Victory’ bomber of his own conception, he wrote to an old World War I colleague: ‘Life is almost unrelieved gloom – worse than 25 years ago, except that this time I can feel that I am doing something useful whereas last war I certainly was not … Tremendously busy – on big developments, which if they had been put in hand two years ago would have won us the war by this time. Too late as usual.’

His ‘Victory’ bomber, claimed Wallis in July 1940, ‘is going to be the instrument which will enable us to bring the war to a quick conclusion’. Since these aircraft would operate at an altitude beyond the reach of German fighters, they could fly ‘at their leisure and in daylight … Irreparable damage could be inflicted on the strategic communications of the German Empire by … ten or twenty machines within the course of a few weeks.’

Here was characteristic Wallis fervour: he deserved full credit for conducting unfunded and unsupported research on the science of destroying large structures from the air, at a time when the RAF was institutionally indifferent to this vital issue. However, Wallis was as wrong as the ‘bomber barons’, and remained so throughout the war, in cherishing exaggerated expectations about what air power might achieve. He was as mistaken as Sir Arthur Harris, though from a different perspective, in believing that the RAF, or indeed the USAAF, could alone defeat Nazism, or even wreck the German economy. This objective was unattainable, regardless of which targeting policy the air forces espoused, or what bombs he might devise for Allied aircraft to carry. Yet Wallis cherished one remarkable idea, that would secure his place in history.

2 GESTATION

Barnes Wallis knew nothing about the Air Staff’s exploration of targeting dams when, early in the war, he himself began studying the vulnerabilities of German power supplies, and explicitly of hydro-electric plants, during spare hours snatched from his ‘proper’ work on a projected high-altitude Wellington, and later the Windsor. He spent months considering the possibility of breaching dams with ten-ton bombs dropped by his own proposed ‘Victory’ aircraft from an altitude of forty thousand feet – three times the operating height of contemporary RAF ‘heavies’. An early enthusiast for his ideas was Gp. Capt. Fred Winterbotham, head of air intelligence at MI6, and a pre-war pioneer of the exploitation of high-altitude aerial photography. He was introduced to Wallis by a mutual friend, City banker Leo D’Erlanger, who had endeared himself to the engineer’s children by once presenting them with a pink gramophone. In February 1940 D’Erlanger brought the air intelligence officer to lunch at Effingham, thinking that Wallis and Winterbotham had common interests. Winterbotham was much taken with the cheerfully bustling Wallis household and its noisy children, the exuberant piano-playing, the obviously blissful partnership of his host and wife Molly.

Winterbotham was something of a charlatan, who played a less important role both in the Second World War and the evolution of Wallis’s schemes than he himself later professed. He was no fool, however, and like many intelligence officers was a keen networker and intriguer. He invited Wallis to lunch at the RAF Club in Piccadilly, and was persuaded by him to lobby the good and great about the Victory bomber, with a wingspan of 160 feet (against the Avro Lancaster’s eventual 102 feet) and its accompanying ‘earthquake’ bomb. Desmond Morton, Winterbotham’s old intelligence colleague, responded to this proposal from his new office in 10 Downing Street on 5 July 1940: ‘My dear Fred … The view held [here] is that such a project as you describe could not come to fruition until 1942, even if then.’ This period was, of course, Britain’s darkest of the Second World War; only by straining every sinew could the Ministry of Aircraft Production create a bare sufficiency of fighters, never mind a speculative giant bomber.

Nonetheless, through Winterbotham again, Wallis secured an audience with Lord Beaverbrook, Minister of Aircraft Production, at which he pressed his Victory project. The gnome-like tycoon seemed more interested in persuading his visitor to travel to America to explore pressurised aircraft cabins, but their meeting yielded one positive result: it enabled Wallis to secure access to the government research facility at the former Road Research Laboratory at Harmondsworth, just west of London, together with the Building Research Station near Watford in Hertfordshire.

In August 1940 Wallis began tests related to the projected deep-penetration bomb, for which he was also admitted to the wind tunnel at Teddington’s National Physical Laboratory. In retrospect it seems astonishing, and yet also a triumph of official imagination, that even while Britain faced its darkest days, and Fighter Command was challenging the Luftwaffe against odds, a ‘boffin’ was able to undertake such futuristic research almost literally on the ground beneath which the Battle of Britain was being fought. From October onwards Wallis attended a series of meetings with the Ministry of Aircraft Production’s Air Vice-Marshal Francis Linnell, Controller of Research and Development, and Dr David Pye, the MAP’s director of scientific research, together with his deputy Ben Lockspeiser. The last, especially, would play a role in the Chastise saga which continued until the day the operation was launched.

In November the RRL’s Dr Norman Davey began construction of a 1:50 scale model of the Möhne, across a small stream in secluded woodland at the BRS in Hertfordshire. This project reflected the interest not merely of Wallis, but of the RAF’s most senior officers, who had identified the dam as a target. At the same period Wallis was granted access to the Air Ministry’s 1939 research on the Möhne, emphasising the fact that he and the uniformed planners had been thinking along parallel lines. This made Wallis all the more irritated that so many bureaucratic obstacles were placed in the way of what seemed to him an obvious war-winner. In November 1940 also, he wrote a testy note to AVM Arthur Tedder, then serving at the MAP: ‘As a result of the continuing opposition that we have met, it has been necessary to resort to these laborious and long-winded experiments, in order to prove that what I suggested last July [destroying targets with deep-penetration bombs] can in reality be done.’

Norman Davey’s team employed technical data on the Möhne dam’s construction published at the time of its opening in 1913, though the Watford modellers somewhat distorted their own outcome by treating metres as yards in the scaling exercise. Hundreds of thousands of hand-cast mortar blocks were made and laid in the freezing conditions that prevailed through that winter. The model was completed on 22 January 1941, and explosive tests began a few days later. The first results of these were felt by nearby ‘Dig for Victory’ vegetable allotment-holders, who found their plots at Garston suddenly flooded by an inexplicable onrush of water. This also bewildered the BRS testers, because while their dam was damaged by successive explosions, it was not completely breached.

In March 1941 Wallis circulated a long paper entitled ‘A Note on Methods of Attacking the Axis Powers’, in which he wrote about water and coal seams as targets. Such natural resources, he observed, had the great merit that they could not be moved or dispersed: ‘If their destruction or paralysis can be accomplished, THEY OFFER A MEANS OF RENDERING THE ENEMY UTTERLY INCAPABLE OF CONTINUING TO PROSECUTE THE WAR.’ He distributed a hundred copies of this paper, with its extravagant predictions, to his aviation contacts – several journalists received it, together with four Americans and Frederick Lindemann, soon to become Lord Cherwell. Wallis’s daughter later remarked on her father’s carelessness about security: ‘I can hear him now, describing to a friend some interesting feature of his work, laughing, “Frightfully secret, my dear fellow.”’

W/Cdr. Sydney Bufton, an officer with operational experience over Germany who had recently become deputy director of Bomber Operations at the Air Ministry, was sufficiently interested to visit Wallis in his office at Burhill Golf Club, near Weybridge, where the design team found a wartime home after the Vickers plant was bombed. A dams sub-committee was formed at the Ministry of Aircraft Production, which in the following month discussed the Möhne as an important target. Initial calculations suggested that a bomb weighing twelve tons would be required to destroy it.

On 11 April 1941, David Pye of the Road Research Laboratory convened a meeting about Wallis’s various advanced weapons concepts with the AAD – Aerial Attack on Dams – Advisory Committee, which was also attended by the great scientific civil servant Sir Henry Tizard. At this it was concluded that the science of Wallis’s ideas about destroying dams seemed sound: the intractable problem persisted, however, of devising a means of delivering to Germany a weapon such as might create the impact that he sought. This was no mere detail, but the core of the issue with which the Vickers engineer and the many technicians associated with his project would wrestle for the next two years.

Their progress was impeded, not by a mindless bureaucracy, but instead by practical difficulties which had to be addressed with severely constrained resources. Wallis scarcely helped his own case by arguing as if he, and he alone, held the key to winning the war. This was a vice to which bigger men were also prone. In September 1941 Churchill rebuked Portal, the chief of air staff, for submitting to him a paper which promised that if Britain built four thousand heavy bombers, the RAF could crush the Nazis within six months, without need for assistance from the other two services.

The prime minister responded in one of his most brilliant memoranda: ‘Everything is being done to create the bombing force on the largest possible scale … I deprecate, however, placing unbounded confidence in the means of attack, and still more expressing that confidence in terms of arithmetic … Even if all the towns of Germany were rendered largely uninhabitable, it does not follow that the military control would be weakened or even that war industry could not be carried on … The Air Staff would make a mistake to put their claim too high … It may well be that German morale will crack, and that our bombing will play a very important part in bringing the result about. But all things are always on the move simultaneously … One has to do the best one can, but he is an unwise man who thinks there is any certain method of winning this war, or indeed any other war between equals in strength. The only plan is to persevere.’

The prime minister would assuredly have said the same wise things to Barnes Wallis, had he been party to the correspondence about his putative wonder-weapons. On 21 May 1941 the engineer received a letter from Sir Henry Tizard, telling him that his ideas for both the Victory bomber and the deep-penetration bomb had been rejected by the Air Staff. Wallis was distraught. His fortunes had reached their lowest wartime ebb.

What followed, albeit painfully slowly in Wallis’s eyes, reflected an important contradiction about the conduct of the Second World War. As a fighting force, man for man, from beginning to end the Wehrmacht showed itself more professionally skilful than either the British or American armies. Yet the Western Allies nonetheless contrived to make better war than did the Axis powers. An important part of the reason for this was that they empowered many of the brightest people in their societies to deploy their talents, with an imagination which the dictatorships never matched. The codebreakers of the US Navy’s Op20G and the US Army’s Arlington Hall, together with Britain’s Bletchley Park, provided conspicuous examples of this phenomenon. So, too, did a host of projects commissioned and undertaken by scientists and engineers on both sides of the Atlantic.

Although Barnes Wallis’s Big Plane, Big Bomb proposals had been formally rejected in May 1941, he nonetheless persuaded the MAP’s David Pye that he should retain access to government facilities, to continue his experiments on the ballistics of dam-breaking. Through that autumn tests continued, to determine the necessary weight of explosives, and the conditions in which they must be detonated, to contrive breaches in huge structures.

It was an elaborately formal age. Many of the papers in what became a mountainous correspondence between Whitehall’s civilian and service departments about the engineer’s infernal machines began as did this one to an under-secretary of state: ‘Sir, I have the honour to state that consideration has again been given recently to the possibility of breaching one or more of the important canals in North West Germany.’ The engineer concerned was referred to ‘as Mr B.N. Wallis of Vickers’. The writer signed himself ‘your obedient servant’.

From the £2,000 budget then allocated to Wallis’s activities by the MAP, money was found to buy from Birmingham City Council a small dam at Nant-y-Gro in Powys, North Wales, rendered redundant by the construction of a larger replacement. A key figure in the experiments that followed was Arthur Collins, a scientific officer in Harmondsworth’s ‘Concrete Section’, who made a breakthrough. For years it had been assumed, not least by Barnes Wallis, that an enormous explosive charge would be necessary to destroy a dam such as the Möhne. Yet experiments convinced Collins, who in turn persuaded Wallis, that a relatively small charge might achieve a wholly disproportionate result if it was detonated sub-aqueously and close to the target, using a timer or a hydrostatic pistol: it could thus harness the power of the water mass to channel the force of the blast. Here was the phenomenon identified as a threat back in 1939 by the German official responsible for his country’s north-western dams. Both Collins and Wallis became increasingly fascinated by the physics of explosions, and especially by the scope for harnessing the power of water, and indeed of earth, dramatically to increase the impact of underwater or underground explosions – the ‘conservation of suspended energy’ that would eventually make possible Operation Chastise.

In the course of 1941 and 1942, Wallis pursued enquiries about Germany’s dams through patent agents in Chancery Lane, and about hydro-electric control mechanisms via an engineering firm in Kilmarnock. In April 1942 – Holy Week, as it happened – experiments assisted by his children, using marbles projected into an old galvanised washtub on the terrace outside his home at Effingham, shifted his attention from deep-penetration ‘earthquake’ charges towards the notion of much smaller spherical bombs, bowled – in cricketing parlance – or ricocheted – to use Wallis’s original choice of word – towards German dam walls. Here, he was thinking in a fashion not dissimilar from Finch-Noyes and Pemberton-Billing. He envisaged two related, but different weapons: a larger model for attacking dams, later codenamed ‘Upkeep’, as it will hereafter for convenience be called; and a smaller version, to be codenamed ‘Highball’, for use against shipping.

Sir Charles Craven, a former Royal Navy submarine officer who was now chairman of Vickers, did not explicitly bar Wallis’s spare-time work on futuristic weapons. He emphasised, however, that it must not interfere with the engineer’s day job, developing the Windsor bomber. In post-war evidence to the Royal Commission on Awards to Inventors, Wallis stated that ‘the inception of the [bouncing bomb] was the result of private experiment and work outside the scope of his normal employment and that this work was carried out against the wishes of his employers’. He subsequently expanded on this theme, saying that ‘had he not persisted in his efforts to interest the authorities in the face of continued discouragement and even contrary to the wishes of his own Directors, the attack on the dams would never have been made’. In the narrative that follows, it should not be forgotten that, until the last stage of the development of Wallis’s revolutionary weapons, his work on them represented, in the stern view of his employers, a spare-time indulgence.

3 FIRST BOUNCES

In the late spring of 1942, Barnes Wallis reported to the MAP and the Air Ministry that he believed he could overcome a critical problem – accurately to deliver a charge from a fast-moving bomber against a target protected with anti-torpedo nets – by bouncing a bomb across the water in the fashion he had explored with marbles on his terrace at Effingham. Moreover, a century and a half earlier Vice-Admiral Horatio Nelson and his fellow Royal Navy commanders had shown the way, exploiting the technique of bouncing cannonballs across the sea to pummel French warships. At the end of May, Wallis set off with his secretary, former British ladies’ rowing champion Amy Gentry, for Silvermere Lake near Cobham to test the potential of using a catapult, much more sophisticated than a child’s toy, to bounce small projectiles down a test tank. In the course of these experiments they found that, if a golf-ball-sized object was backspun on release, it would ‘ricochet’ far more vigorously. Vickers’ experimental manager George Edwards, a keen cricketer, later claimed credit for this idea, but the evidence suggests that Wallis developed it himself, and merely had later conversations about it with Edwards.

The eventual form of Upkeep was that of a large, cylindrical naval depth-charge. Until late April 1943, however, Wallis envisaged its shape as almost or absolutely spherical, the huge canister containing the charge being encased in an outer shell of wood. It was also at times described as a mine, which became part of its cover story in official correspondence and later news coverage. Since legend, however, knows the dam-busting weapon as a bomb, that is how it will continue to be described in this narrative.

Wallis told Fred Winterbotham that he saw every reason to believe that the new weapon’s destructive principles would prove as applicable to enemy shipping as to dams, locks and suchlike. Thus, on 22 April 1942 Winterbotham accompanied the engineer to discuss the project with Professor Pat Blackett, the exceptionally enlightened physicist who was scientific adviser to the Admiralty. Blackett, in turn, lobbied Tizard, who despite his opposition to Wallis’s big-bomb project a year earlier was now sufficiently excited to visit him at Burhill on the 23rd. Tizard thereafter supported Wallis’s request for access to two experimental ship tanks at the National Physical Laboratory at Teddington, where he began tests in June which continued over twenty-two days, at intervals until September. If the pace of progress appears slow, it must be remembered that Britain was still conducting its war effort on desperately short commons, while Wallis was earning his bread working on the Windsor bomber.

Although the Royal Navy was perhaps Britain’s most successful armed service of the war, the Fleet Air Arm was its least impressive branch. Despite the much-trumpeted success of a November 1940 torpedo attack on Italian capital ships in their anchorage at Taranto, carried out by antiquated Swordfish biplanes, thereafter British naval aircraft enjoyed few successes. Churchill more than once acidly enquired why the Japanese seemed much better at torpedo-bombing than was Britain’s senior service. Admirals were thus immediately attracted to a new technology which might make the Fleet Air Arm less ineffectual. For months after Wallis’s ‘bouncing bomb’ was first mooted, the RAF sustained institutional scepticism; sailors did more than airmen to keep the concept alive.

Tizard himself attended some tests at Teddington, as did Rear-Admiral Edward de Faye Renouf, a former torpedo specialist who was now the Admiralty’s director of special weapons. Renouf and several of his staff watched a demonstration in which a two-inch sphere was catapulted down a tank, bouncing along the water until it struck the side of a wax model battleship and rolled down beneath its hull. The admiral, a gifted officer recently recovered from a nervous breakdown after a succession of terrifying experiences while commanding a cruiser squadron in the Mediterranean, urged Sir Charles Craven of Vickers to give priority to Wallis’s weapons research. Renouf envisaged a projectile that might be released from the new twin-engined Mosquito light bomber.

That month, May 1942, Wallis produced a new paper incorporating all this research, entitled ‘Spherical Bomb, Surface Torpedo’. His thinking still focused entirely on round weapons, described in a note from Winterbotham to the Ministry of Production as ‘rota-mines’. Wallis’s paper cited earlier work by a German scientist, and also showed that for a bomb to get close enough to a dam to enable the principle of ‘Conservation of Suspended Energy’ to work, it needed to impact upon the water almost horizontally, at an angle of incidence of less than seven degrees, which meant that it must be dropped from an aircraft flying very low indeed: at that time, 150–250 feet seemed appropriate. Wallis envisaged its release from a range of around twelve hundred yards, to allow time for the attacking pilot to turn away and escape before flying headlong over the target and its defences. Not until months later was a requirement accepted for the aircraft to carry its bomb much closer, and thereafter to overfly the objective.

In a further demonstration of the validity of Churchill’s observation that ‘All things are always on the move simultaneously,’ at the Road Research Laboratory Arthur Collins had meanwhile been conducting a succession of tests on two 1:10 scale models of the Nant-y-Gro dam. On 10 May 1942 Wallis and his wife Molly travelled to Wales with Collins’s team to witness experiments on the full-sized dam. These established that if an explosion took place at any significant distance from its wall, the blast was too weak to precipitate a fracture. Collins wrote: ‘A solution to the problem was, however, found almost by chance shortly afterwards.’ His team needed to remove one of the damaged scale models at Harmondsworth, and used a contact charge to shift the concrete. The result was devastation, on a scale unmatched by any ‘near-miss’.

Further tests confirmed the result, and on 16 July Wallis received an invitation to attend a full-scale demonstration a week later. He was nettled by the short notice, and warned a little pompously that he was working under such pressure – presumably on the Windsor bomber – that he would probably be unable to get away. Nonetheless, he was present at Nant-y-Gro when, on the 24th, army engineers blew a 279-lb charge of which the effects were filmed with high-speed cameras brought to North Wales from the Royal Aircraft Establishment at Farnborough. The test explosion proved a triumph, blasting a breach in a masonry construct that was, for practical purposes, a small-scale version of a German dam.