Chastise: The Dambusters Story 1943. Max Hastings

him with a dramatic challenge. At breakneck speed he must convert his theoretical concept into a viable bomb, while work was simultaneously rushed forward on building the modified Lancasters. Avro, the plane’s manufacturers, agreed to fit the necessary electrical release gear, along with strongpoints where the bomb doors must be removed, and hydraulic power for backspin pulleys. Vickers would meanwhile make protruding retainer arms for the Upkeeps, to be attached to the strongpoints; a rotational driving mechanism; and the bombs themselves. All the latter work would be carried out at Weybridge, with Avro dispatching a team to work on the Vickers site. Wallis promised to provide working drawings of the latest version of Upkeep within ten days. Craven expressed concern about whether a revolutionary weapon of such size could be machined within the necessary time-frame.

      Before the final decision, some minor obstacles had to be swept away. By coincidence Combined Operations, then headed by the frisky Lord Louis Mountbatten, was proposing an attack on the Möhne, which Mountbatten described as ‘one of the great strategic targets’. Special Operations Executive also suggested an assault by parachute saboteurs. Both bodies’ proposals were now quashed, fortunately for those who might have been charged with implementing them, in favour of what was designated Wallis’s ‘rolling bomb’. It would be the RAF which destroyed the dams of north-west Germany. Or nobody.

3

       Command and Controversy

      1 TARGETS

      At the end of February 1943, more than six years after the RAF first discussed the feasibility of attacking Germany’s dams, and over three years since the war began, air chiefs and engineers embarked upon a ten-week dash to launch the operation that was shortly thereafter codenamed Chastise. The strategic planning – above all, about target priorities – took place within the Air Ministry. This was gall and wormwood to Sir Arthur Harris, who regarded his own headquarters staff as the only proper people to arbitrate on such matters.

Wallis, in a paper headed ‘Air Attack on Dams’ that had been circulated to a range of interested parties on the secret list back in January, identified six plausible targets – the Möhne, Eder, Sorpe, Lister, Ennepe and Henne – of which the reservoirs held a combined total of almost nine thousand million cubic feet of water, while seven other, smaller dams retained just 423 million. Breaching the Möhne alone, he promised, would cause ‘a disaster of the first magnitude’ extending to the lower reaches of the Ruhr. He appears to have intended this judgement to describe solely the industrial consequences, and to have given no consideration one way or another to the inevitable human cost among civilians caught in the path of the intended deluges, whom air-raid shelters would avail little. Thereafter, to a remarkable degree the Air Ministry made its Chastise targeting decisions on the basis of the assessment advanced by Wallis, a professional engineer but an amateur analyst of Ruhr industries.

      From the Directorate of Bomber Operations, Gp. Capt. Syd Bufton* wrote to AVM Norman Bottomley, Portal’s deputy, urging the primacy of the Möhne over the Eder – also mentioned by Wallis: ‘The former is much more important, and tactically 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’