Chastise: The Dambusters Story 1943

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.

In the following month, Collins submitted a report which concluded that if a charge weighing around 7,500 lb was exploded at a depth of thirty feet against the wall of a dam such as the Möhne, it should be capable of achieving a breach. Such a weapon would not require the creation of a new bomber to carry it, but was within the lifting capabilities of the new Avro Lancaster, subject to appropriate modifications. Thus, suddenly, the most intractable obstacle to an attack on Germany’s masonry dams was removed: it seemed feasible – in theory at least – to convey to the target sufficient explosive to destroy it. Credit for the principal scientific achievements that made possible Operation Chastise should rightfully be shared between Collins, who resolved the challenge posed by the physics of destroying a vast man-made structure, and Wallis, who conceived a technique whereby the necessary charge might be laid from the air with the exactitude indispensable to success.

In the late summer of 1942, a situation obtained wherein Barnes Wallis had devised a revolutionary weapon, of which the scientific principles were agreed by most of the experts who studied them to be sound. The Royal Navy was excited about its possibilities for use by the Fleet Air Arm. Widespread scepticism nonetheless persisted, shared by MAP’s David Pye and his deputy, Ben Lockspeiser, about whether the resources could be justified to pursue a speculative technology that could only be used over water, and which demanded superhuman courage and skill from aircrew who would have to launch it against an enemy. Moreover, every aircraft which carried such a bomb would require expensive modification.

Such reservations were fully justified. Lockspeiser wrote to Tizard on 16 June: ‘It is quite impractical and uneconomic to modify our bombers in large numbers for the special purpose of carrying any particular bomb.’ Nonetheless the Admiralty’s enthusiasm, and the uneasy acquiescence of MAP’s AVM Linnell, sufficed to secure a request for Vickers to fit a Wellington twin-engined bomber to carry a prototype Wallis bomb, of which on 22 July an order for twelve examples was placed with the Oxley Engineering Company. On 25 August Wallis attended a meeting at MAP at which arrangements were agreed for a series of trials to be conducted a month later, at Chesil Beach in Dorset.

It is striking to notice, at this stage, two camps in the service ministries and the defence scientific community about the whole project. One faction believed that Wallis’s weapons were fanciful; would never work. The other cherished wildly over-optimistic fantasies concerning their war-winning potential. Fred Winterbotham wrote to the parliamentary secretary at the Ministry of Production on 14 September 1942, speculating about what Wallis’s bombs might achieve: ‘If this new weapon is intelligently used, e.g. for simultaneous attacks on all German capital ships and main hydro-electric power dams, there is little doubt but that Italy could be brought to a complete standstill and that industry in Germany would be so crippled as to have a decisive effect on the duration of the war … To attain this result much preparation and careful planning are clearly required and meanwhile I repeat nothing is being done.’ Here was a manifestation of a British yearning, characteristic of its time and place, for some dramatic stroke that might sidestep battlefield slaughter and bring the war to an early closure. Winterbotham’s note took no heed of the Alpine difficulties in the way of his fantasy, prominent among them that its fulfilment would require hundreds of bombers to be modified to carry Wallis’s weapons. Meanwhile its expectations about what these, or for that matter any, bombs might do to the Axis drifted into fairyland.

That autumn of 1942, the bomb project languished. Oxley Engineering experienced difficulties in constructing the test weapons, and in October Wallis was kept at home for several days by illness. Only on 2 December did he at last board a modified Wellington, piloted by veteran test pilot Mutt Summers – the very same who had parachuted more than a decade earlier from one of the engineer’s less successful prototypes – for a trial of the backspin technology. It worked, though no test bombs were dropped.

Two days later, on the afternoon of the 4th, the Wellington took off for Dorset, where on Chesil Beach a camera crew waited to record the trial bomb-dropping. The first two tests, with non-explosive fillings, resulted in the spheres bursting on impact. When a subsequent succession of droppings took place, Wallis watched from the shore. Outcomes suggested that the technologies for releasing the bomb from an aircraft, and for its subsequent bouncing progress, were viable. Yet repeated collisions with the sea at speeds of over 200 mph imposed enormous stresses on the projectile during its bouncing progress. Half-sized prototypes disintegrated. Their begetter undertook modifications and adaptations, still convinced that the principles of his creation – or rather, his instrument of destruction – were sound.

Following these further developments, Wednesday, 20 January 1943 found Wallis ensconced in Weymouth’s Gloucester Hotel, from which he wrote to Molly: ‘I do wish you could come & share this lovely room. It would be just perfect with you here. If you could come tomorrow by the mid-day train, do … Now we are scheduled to start [tests] at 10 a.m. … so I must go to bed. All my love little sweetheart, and come if you can …’

She came. Almost two decades of marriage had done nothing to cool the couple’s passionate romance. Molly, still only thirty-seven, was now responsible for six children, including a niece and nephew whose parents had been killed in the blitz. This brood was surrendered to their nanny while she set forth for Dorset. On 24 January she wrote to the children from Weymouth about her visit to their father:

… A lovely time it’s been. This morning I drove out with him and the others to the nearest point I was allowed [to the bomb tests] & then I got out and walked back. 8 miles of lovely road, high up with the Downs one side & the sea to other. It was sunny & clear. I did enjoy it. Of course it’s quite mad that they shouldn’t let me watch the proceedings seeing as I’ve lived with it since last February & probably know more about it than anyone save Barnes. But it’s quite true – policemen do bob up and turn you away. I suppose the others would say ‘If that wife why not my wife’ little knowing what a very special wife this one is.

Darling Barnes. You should see him among these admirals and air vice marshals patiently explaining and describing to them & they drinking it all in – or trying to. And he’s so quiet and un-assuming none of them could imagine what pain & labour it’s been. How he’s got up in the middle of the night to go up to the study & work summat out. No wonder he looks drawn and tired. I suppose if he were a self-advertiser he’d have been Sir Barnes in the New Year Honours. Oh well, it’d have been a nuisance. But it’s an exciting life & no mistake.

The contrast seems extraordinarily moving between the private domesticity and indeed passion within the Wallis family, and the devastating public purposes which its principal was pursuing. Some might find it repugnant, in the light of what later befell Upkeep’s victims, but it must never be forgotten that Barnes Wallis’s country was engaged in a war of national survival against one of history’s most evil forces. The engineer was straining every sinew, and all his own astonishing gifts, to assist the Allied cause. During that 24 January trial in Dorset which Molly Barnes was not permitted to witness, one dummy bomb achieved thirteen bounces. Next day, another managed twenty. Wooden test spheres, dropped from between eighty and 145 feet, travelled 1,315 yards across the water. Barnes once wrote down for Molly the closing lines of Tennyson’s ‘Ulysses’, among his favourite poems: ‘One equal temper of heroic hearts,/Made weak by time and fate, but strong in will/To strive, to seek, to find, and not to yield.’

Returning to London, the white-haired evangelist now strode through the corridors of ministries proudly clutching a can of 35mm film, showing his weapon skimming the sea. Eagerly, he awaited authorisation to continue with development of both Upkeep – the dam-bursting version – and Highball, the smaller naval bomb. He chafed for a swift commitment, because for optimum effect an attack on the German dams needed to take place in May, when water levels in the reservoirs were at their maximum height after winter rains and snows.