the more suitable. We should, therefore, ensure that an adequate effort is devoted to this objective before considering the possibility of an attack upon the Eder.’ He added in a covering note: ‘I feel a lot of time would be wasted if we go to the lengths of making a minute examination of all possible targets.’
Intelligence was a fundamental weakness of Britain’s strategic air offensive. Bomber Command’s decisions about targets were often made on the basis of their accessibility or vulnerability to attack, which had earlier in the war prompted an emphasis on relatively easily-located coastal objectives. Before an operation, immense effort was expended upon fixing routes, providing electronic aids and counter-measures, deciding bomb and fuel loads, and nominating diversionary landing fields. By contrast, examination of targets’ economic significance was often as superficial as post-attack damage assessment. In planning for Chastise, the Möhne and the Eder were prioritised because both were masonry structures, and thus most likely to succumb to Wallis’s bombs. Yet while the Möhne was a hub of the Ruhr industrial water system, the Eder was unrelated to it. At an early stage of the war, the Ministry of Economic Warfare’s experts had concluded that if the Möhne and the nearby Sorpe could both be breached, the effect on Ruhr water supplies might well be catastrophic. If only one was destroyed, however, stated the MEW, the Nazis could probably contain the threat to Ruhr industrial activity.
The Sorpe was an immensely thick earthen dam, which sloped steeply on the reservoir side in a fashion which ensured that a mine which was bounced up its lake towards the wall must roll away backwards on impact. On 18 March an Air Ministry ad hoc Chastise committee, chaired by Bottomley, agreed that the Sorpe’s construction thus ruled it out as a target. It was also decided that a strike with Highballs, carried by Mosquitoes of the RAF’s Coastal Command, should be attempted more or less simultaneously against Tirpitz or another German battleship in the Norwegian fjords. Bottomley reported to the chiefs of staff, outlining progress: ‘the speed with which [Highball and Upkeep] have been developed has been so high and the time available to complete them before the required date is so short, that there is a considerable element of gamble’.
A fierce division of opinion about scheduling now emerged between the RAF and the Royal Navy. The airmen had become committed to attacking the dams before the end of May. The sailors, however, recognised that the first use of bouncing bombs, whether Upkeeps or Highballs, could also prove the last, because the Germans would adopt counter-measures to protect vulnerable watery targets. Thus, the navy wanted Chastise deferred until Coastal Command was ready to attack German warships with Highballs, an operation codenamed Servant. It was acknowledged that the tri-service chiefs of staff might have to be asked to arbitrate on this knotty issue.
The airmen meanwhile reached an irrational compromise about the Sorpe dam, such as was typical of the entire bomber offensive. While acknowledging that it was unsuitable as an objective for bouncing bombs, it was restored to the target list because of its agreed strategic importance. Wallis thought that four or five of his Upkeeps might breach it without being bounced. He cited the precedent of the 1864 natural collapse of the Dale Dyke dam near Sheffield, which destroyed six hundred homes and killed at least 240 people. An earth dam with a concrete core, he claimed, would become ‘practically self-destroying if a substantial leak can be established within the water-tight core’.
This may have sounded persuasive, but it was in fact ill-founded: since the Dale Dyke dam had a clay rather than a cement core, it was not comparable with the Sorpe. The planners eventually decided that the Wallis bombs used against the Sorpe must be dropped following a lateral, overland approach, without backspin, to sink and explode on time fuses rather than by pressure upon a hydrostatic pistol. It seems remarkable that Wallis or anyone else supposed that Upkeeps would thus achieve their purpose-designed ballistic effect any more than might any other explosive charge of similar size – in other words, a conventional bomb. It is hard not to suspect that the engineer asserted the plausibility of destroying the Sorpe because he feared that if he did not do so, the entire commitment to Chastise would once more be thrust into doubt because of that dam’s strategic centrality.
On 25 March another meeting of the Air Ministry committee, attended by an array of brass representing both the Royal Navy and the RAF, including Saundby from Bomber Command, was told that construction of the ‘Type 464 Provisioning’ Lancaster variants was proceeding on schedule. Sixteen Mosquitoes were also being readied to carry Highball. Forty inert Upkeeps had been constructed for test purposes.
Two important, related tactical decisions were made. The first was that moonlight would be essential, to enable crews to drop their weapons with the necessary accuracy. Normal Bomber Command ‘ops’ did not take place under such conditions, which made aircraft of Harris’s Main Force easy prey for night-fighters, responsible for almost three-quarters of Luftwaffe ‘kills’ of British bombers. Thus, the Chastise attackers would fly all the way to their targets at very low level, below the German radar threshold, where they would be hard for fighters to spot or engage. The principal menaces to the Lancasters’ survival would be light flak – anti-aircraft gunfire – and such physical hazards as power lines.
Even as these issues were being thrashed out, at High Wycombe Harris made the only significant decision with which he, as a declared Chastise sceptic, was entrusted: which aircrew should fly the operation? The C-in-C determined that they should be drawn from 5 Group, an elite formation that he himself had commanded earlier in the war. He instructed its new AOC, Ralph Cochrane, that instead of diverting a line squadron to attack the dams he should form a new, special one. He also identified the officer who should lead it.
2 GIBSON
And so to Wing-Commander Guy Penrose Gibson, the man with the dog; the short, sad twenty-four-year-old with the brilliant smile who became a national hero. At the Air Ministry meeting of 15 February Saundby, newly promoted to become Harris’s deputy, asserted that ‘two weeks would provide sufficient time in which to train crews for this operation’ – which said more about his own and his chief’s insouciant attitude to Chastise than about their understanding of the supreme challenge their fliers were about to be invited to undertake. For years the vexed debate about an air attack on Germany’s dams had focused upon means – devising weapons that might make possible such a stroke. Now, however, the spotlight shifted: towards the very young men, still unknowing two months before they took off, who would be called upon to fulfil the vision of Barnes Wallis.
Gibson was about to go on leave to Cornwall, after receiving a second DSO for his distinguished tenure commanding 106 Squadron, when on the afternoon of 14 March 1943 he was summoned to Grantham to see 5 Group’s chilly, clever new AOC. The Hon. Ralph Cochrane, by common consent Harris’s outstanding subordinate, was an autocrat possessed of better manners and more imagination than his superior at High Wycombe, especially about means of attacking Germany from the air. He was a scion of a smart Scottish family – his father was an army officer turned Unionist politician, ennobled in 1919. Ralph, one of five children, entered the Royal Naval College, Osborne, aged thirteen in 1908, the year in which the Wright brothers made their first flights in Europe.
While flying airships on convoy escort duty during the First World War, he met Barnes Wallis. Cochrane once tried to sink a German submarine by dropping four 8-lb bombs on it, without convincing either himself or the enemy of the efficacy of air power. He was still an airship man when he encountered Sir Hugh ‘Boom’ Trenchard, wartime commander of the Royal Flying Corps and founding father of the RAF. ‘Young man,’ said Trenchard, ‘you’re wasting your time. Go and learn to fly an aeroplane.’ Within a few years, Cochrane was serving as a flight commander in Iraq, where Arthur Harris was converting Vernon troop-carriers into bombers on his own initiative, and experimenting with the prone position for bomb-aiming. In 1937 Cochrane became a founding chief of staff for New Zealand’s air force. By 1943 he was recognised as one of the RAF’s ablest senior officers, described by a navigator in one of his squadrons, later the offensive’s official historian, as ‘a ruthless martinet’.
A bewildered Gibson was
