Chapter 23: The Flying Bomb: Part One, 1939–1944
(i)
THE FZG. 76 flying bomb which emerged in 1942 as a rival to the A-4 rocket was not an altogether new conception. Such missiles had been discussed at least as early as the nineteenth century; in the first two decades of the twentieth they were the subject of research in several countries. Before and during the First World War a French artillery officer, René Lorin, advocated bombardment of distant objectives (such as Berlin) with jet-propelled pilotless aircraft stabilised by internal gyroscopes, maintained at a given altitude by barometric means, and guided from piloted aircraft carrying radio-transmitters. Among the forms of propulsion which he considered were a pulse-jet—as afterwards adopted for the German weapon—and, alternatively, a ram-jet giving continuous combustion. As Lorin pointed out, the principle of propulsion by direct reaction was well known to students of mechanics; and he seems to have been more concerned to meet objections founded on the alleged wastefulness of such devices than to counter any which might arise on the score of novelty.*
Though certainly among the first men to conceive, in considerable detail, a jet-propelled pilotless aircraft which anticipated many features of the modern guided missile, Lorin was not alone in his concern with the methods of propulsion which he favoured. In 1907—according to Lorin the year when he himself began work on his project—Victor de Karavodine was granted in Paris a patent for a pulse-jet designed to produce a swift succession of powerful reactions from a combustible mixture fed into it by a low-pressure blower and electrically ignited.† But Karavodine seems to have made no claim for his device as a direct means of propulsion. Although his suggested applications included the working of a turbine, his chief concern was apparently to provide a handy source of power for stationary
* For a popular exposition of Lorin’s views on jet-propulsion and pilotless aircraft, see his pamphlet L’Air et la Vitesse (Paris 1919).
† French Patent No. 374,124. (Specification lodged 9th April 1906; patent granted 10th April 1907.)
machines. A more direct forerunner of the pulse-jet used in the FZG. 76 was that devised some two years later by Georges Marconnet, who described it as particularly applicable to the propulsion of aeroplanes and dirigible balloons.* With this elegant and eminently practical device—the third of a series of six jet-propulsion systems covered by a single patent—Marconnet would seem to have anticipated by some thirty years the principles ultimately applied to the propulsion of the German flying bomb.
After the First World War both pilotless aircraft and jet-propulsion continued to be studied in many parts of the world, though rather as separate issues than as a single subject. Remotely-controlled aircraft driven by orthodox machinery found employment as targets for anti-aircraft gunnery, notably in the United Kingdom. In Germany the use of similar machines for photographic reconnaissance was considered; and such an aircraft was successfully demonstrated at Rechlin in July 1939, though it was never used on active service.1 The application of jet-propulsion to aircraft likewise attracted attention in Germany, as in England. In the early thirties the German inventor Paul Schmidt worked on the problem, and some years later the technical staff of the aero-engine firm of Argus Motorenwerke, under the technical direction of Dr. Fritz Gosslau, devised and produced a pulse-jet of their own. Dr. Gosslau has stated that he then knew nothing of Karavodine or Marconnet, though he afterwards became acquainted with their work and recognised its relevance. After a trial on 13th November 1939, the Argus duct was demonstrated to the German Air Ministry on the last day of that month. As subsequently developed, and with a valve-mechanism designed by Schmidt in place of that first used, it formed the propulsion-unit of the FZG. 76.
But in 1939 the application of the Argus duct to a flying bomb still lay some way ahead. Shortly before the outbreak of war the firm of Argus were invited by the German Air Ministry to submit proposals for a missile with a range of about 350 miles; and for such a range a short-lived pulse-jet would scarcely have been suitable. They suggested a pilotless aircraft propelled by a 600-horse-power piston-engine, or alternatively by a turbo-jet system or a ducted fan.2 The accuracy required for the attacks on purely military targets which were then in view could, however, hardly have been attained by such means. Perhaps partly for that reason—but also because the radio devices needed for control were none too plentiful, and because the spectacular success of the German armies soon seemed to promise rapid victory—the scheme was shelved until, in the early spring of
* French Patent No. 412,478. (Specification—already lodged in Belgium on 17th February 1909, according to the inventor’s declaration—lodged in Paris on 10th February 1910; patent granted 3rd May 1910.)
1942, the bombing of Lübeck led the Führer to order ‘terror attacks’ on British cities.* In reply to an enquiry the firm were then advised that development of the projected weapon should proceed. The restricted output of radio equipment would still, however, be a bar to its production in large quantities.
Meanwhile the German occupation of northern France had made radio control unnecessary by reducing the range, and consequently the inherent accuracy, required of the missile. Moreover these conditions made it possible to contemplate the use of a relatively cheap and simple jet-propulsion unit. For the flight to southern England from the French coast, a working life of little more than half-an-hour would suffice, and a degree of roughness unacceptable in ordinary aircraft would not matter. The Argus duct—already tentatively applied to powered gliders—thus came into its own when the fortunes of war created the demand for an expendable missile whose virtues were speed, simplicity and cheapness rather than long life or refinement.
(ii)
As long-standing advocates of pilotless flight, and as designers of the propulsion-unit employed for the FZG. 76, the firm of Argus played a big part in the creation of the weapon. They were not, however, its inventors, at least in the accepted sense. The design and manufacture of airframes—as distinct from engines—lay outside their province. The firm of Gerhard Fieseler were called in to do that part of the work; and the prototype was made by Fieseler under the guidance of Robert Lusser. Lusser, a specialist ultimately employed by Fieseler, was in touch with Argus during the early part of 1942, and acknowledged at the end of March that credit for the idea of the flying bomb belonged to the latter firm.3
On 19th June 1942, at a meeting attended by representatives of both firms, Field-Marshal Milch agreed on behalf of the Air Ministry that the highest priority should be given to the development and production of the new missile. According to Dr. Gosslau, who represented Argus, this decision was made on the strength of a verbal description and a rough drawing. Thereafter development proceeded, under the guidance of the Air Ministry, as a joint venture by Argus, Fieseler and Askania, the last firm being responsible for the control-mechanism.
As we have already seen, the missile first flew six months later.† Thereafter a year was expected to elapse before it could be used on active service; but in practice eighteen months were not enough to
* See p. 305.
† See p. 338.
ensure a satisfactory standard of reliability when operations started. As with the A-4 rocket, attempts at large-scale production while development was still in progress led to many difficulties. In the circumstances co-operation between the various firms and agencies connected with the venture was anything but easy.4 Apart from Fieseler, who manufactured prototype airframes and a limited production series needed for experiment and training, and Argus, who made the propulsion-units, the firms of Askania and Walter, concerned respectively with the control mechanism and the launching-ramp, had important parts to play. Other interested parties were the Luftwaffe experimental station adjacent to the rocket establishment at Peenemünde, and the launching regiment training nearby at Zinnowitz.
In the summer of 1943 an Allied bombing attack on the Fieseler works at Kassel had the undesigned effect of holding up delivery of limited production models for some days.5 A consequent check to development at Peenemünde threatened to delay the further programme whereby mass-produced components of the definitive design were to be assembled in quantity at the Volkswagen factory at Fallersleben. Partly in consequence of this setback, but mainly because of the inherent difficulty of settling details of production while frequent modifications were still being made to the design, output from Fallersleben did not begin until late September, less than three months before the date originally fixed for the commencement of the campaign.6
Meanwhile a start was made with launching-sites. Besides two ‘bunkers’ at Siracourt (near Saint-Pol) and Lottinghem (between Boulogne and Saint-Omer), ninety-six open-air sites in Picardy, Artois and Normandy were planned. Each was intended to provide not only for the firing of the missiles from a ramp, but also for their servicing in blast-proof buildings of distinctive shape. Since Flakregiment 155 (W), the unit responsible for operations in the field, had four Abteilugen each comprising two maintenance and supply Batterien and four firing Batterien each capable of manning four positions, simultaneous fire from sixty-four positions was foreseen.
Towards the end of October 1943, part of the first Abteilung of Flakregiment 155 (W) moved to northern France, ostensibly to assist in the final preparation of the launching-sites and make ready for the opening of the campaign in December.7 The bunkers at Siracourt and Lottinghem were still a long way from completion; but according to an estimate made early in November, eighty-eight of the other sites would be ready by the middle of December.8 The hope that operations could begin on that date was, however, belied by facts well known to those responsible for the development and manufacture of the weapon. As we have seen, large-scale production had started only
in late September; and a number of technical shortcomings remained to be overcome before the bombs could be entrusted to units in the field. Moreover the German plan, as it then stood, had radical weaknesses; to understand them, we must return to London and the investigation there in progress.
(iii)
By the end of August 1943, ample evidence had been received in London to suggest that, in words used later by an official chronicler, ‘some form of pilotless aircraft was just as real and immediate a threat as the rocket.9 As early as June a well-placed source had transmitted the report of ‘an air mine with wings’, to be launched by catapult, of which we have already taken notice.* A highly circumstantial report of 12th August confirmed the existence of such a weapon and expressly stated that it was distinct from the A-4 rocket, which our informant referred to by that name.10 On the 30th of the same month a new source, who unfortunately confused the two weapons, gave us the names of Flakregiment 155 (W) and its commander, Colonel Wachtel, stating that the regiment would be deployed in France, about the beginning of November and would man 108 ‘catapults’.11 Soon afterwards brief particulars were received in London of a pilotless aircraft which had landed on the Danish island of Bornholm in the Baltic.12
More important advances in our knowledge of the flying bomb came in the autumn. The briefing of agents in France to investigate constructional work suspected of a connection with ‘secret weapons’ bore fruit towards the end of October, when one of our sources there gave a valuable description of a site at Bois Carré, ten miles northeast of Abbeville.13 Photographs taken by a reconnaissance aircraft a few days later revealed a concrete platform some thirty feet long and twelve feet wide, with its major axis aligned on London; three rectangular buildings, one of which was square; and three buildings shaped like skis laid on their sides.14 Similar though less finished sites had been photographed as early as September; and a review of existing photographs, supplemented by further reconnaissance, soon revealed twenty-nine sites remarkable for the presence of ski-shaped buildings. Reports from agents gave the approximate locations of seventy to eighty more. Existing photographs of Peenemünde were also reviewed, and attention was thereby drawn to the recurrent presence at that station of small aircraft with a wing-span of only
* See p. 346.
about twenty feet.15 These, of course, were flying bombs, though as yet the fact was not established.
A firm link was awaited between the constructions seen in France and activities on the Baltic coast. The ‘ski sites’ might well be—as indeed they were—intended for the ‘catapults’ imputed to Colonel Wachtel; but as yet there was no proof of it. Ultimately the connection was established as the result of a watch which had been kept for many months on a German signals unit and of fresh reconnaissance of Peenemünde. The Luftnachrichten Versuchs Regiment, which specialised in radio beams and radar, was thought likely to assist in the tracking of long-range missiles, and its activities were therefore studied as closely as German security allowed. By October, the 14th Company of the regiment was known to be deployed on the islands of Rugen and Bornholm and on the Baltic coast of Germany as far east as Stolpmünde.16 In the course of the month good evidence was received that the company was tracking flying bombs launched from Peenemünde and also from the neighbourhood of Zinnowitz, where Flakregiment 153 (W) were undergoing training.17 Unfavourable weather made it impossible to follow up this report by photographic reconnaissance until 28th November; but the photographs then taken clinched the matter. They showed at Zinnowitz buildings similar to some of those seen at Bois Carré. Both at Zinnowitz and at Peenemünde ramps were visible, aligned in the direction in which trial shots were known to have been fired; and careful scrutiny revealed on one of the ramps at Peenemünde one of the small aircraft seen in less compromising circumstances on earlier photographs.18 Henceforth it was scarcely possible to doubt that Bois Carré and the other ‘ski sites’ in northern France were intended for launching flying bombs against this country.
Accordingly, on 4th December arrangements were made for photographic reconnaissance of the whole of northern France within 140 miles of London or Portsmouth, in order that no site might be overlooked; and next day attacks on sites already identified were begun by fighter-bombers and light bombers of the Second Tactical Air Force and the United States 9th Air Force.19 Experience soon showed that only a slow rate of destruction could be expected from the use of such aircraft in weather which was equally unpromising for night attacks by the British Bomber Command. British and American authorities agreed therefore that, as an exceptional measure, the heavy bombers of the United States 8th Air Force—whose allotted role in Anglo-American air strategy was to attack the German aircraft industry as a prelude to the forthcoming landing in France—should be used for a weighty attack in daylight on as many of the sites as possible. On 24th December 672 Fortresses attacked 24 sites, dropping more than fourteen hundred tons of
bombs. Altogether more than three thousand tons of bombs were aimed at 52 sites in December;* according to a British estimate, some twenty-one sites were virtually destroyed or seriously damaged, another fifteen probably sustained some damage and six were left untouched. At the remaining ten sites the effects of the bombing could not be assessed.
Captured records show that in December seven sites were in fact destroyed, and that by early January the programme of construction was seriously impeded.20 Perhaps the most important effect of the bombing was, however, to emphasise a major weakness of the German plan. Soon after taking up his appointment in December, General Heinemann, commanding LXV Armee Korps, made a tour of launching-sites. His observations convinced him that their design and the methods adopted for their construction were unsound. The flying-bomb bunkers at Siracourt, Lottinghem and Equeurdreville—like the rocket bunkers at Wizernes and elsewhere—found little favour in his eyes; but these ‘protected’ sites were dear to his superiors, and work on them could not easily be countermanded. As for the ‘ski sites’, they seemed to Heinemann needlessly elaborate and far too vulnerable to air attack. Their distinctive buildings made them easily identifiable, and little had been done to render them less conspicuous by careful use of natural cover. Furthermore, by employing French labour and sometimes even French contractors, those responsible for the work had gone far to ensure that every site was swarming with potential spies. In any case the technical shortcomings of both the rocket and the flying bomb put an early start with either weapon quite beyond the bounds of possibility. In reply to the suggestion that, as the date in December originally projected for the beginning of flying-bomb attacks could not be met, the campaign should start in the middle of January, Heinemann reported that the bomb—though not the rocket, which was causing Dornberger and his technicians endless worry—might possibly be ready in May or June.21
He concluded that the intervening months could be most profitably devoted to a drastic overhaul of arrangements for flying-bomb launching and supply. After early January work on the ‘ski sites’ was continued only as a blind; for practical purposes they were replaced by a new series of launching-sites, less elaborate, less easily visible from the air, and capable of rapid construction from pre-fabricated
* The numbers of sites attacked, and bomb tonnages aimed at them, by the various formations concerned were as follows:
| Sites attacked | Bomb Tonnages | |
| Second Tactical Air Force and 9th Bomber Command | 23 | 1,398 |
| 8th Bomber Command | 24 | 1,472 |
| British Bomber Command | 5 | 346 |
| Totals | 52 | 3,216 |
parts. About a hundred and fifty of these new sites would seem to have been planned; and more than half of them were brought to the verge of completion during the first five months of 1944. At the same time storage depots in caves and tunnels well back from the coast were adopted in place of the eight ‘supply sites’ which the Allies had located, though the latter remained available as alternative accommodation if they should be needed. In the interests of security, access to the new sites was confined to those with special passes; the headquarters of Flakregiment 155 (W) were moved twice within a few months, and for some time its commander was designated by a pseudonym; drastic limitations were placed on leave and the despatch of mail; and French labourers employed at the superseded launching-sites were withdrawn with a stealthiness calculated to foster the impression that the sites were still important. The Germans were fortunate, too, in intercepting a quantity of intelligence material consigned to London and in capturing a number of workers who had hitherto done splendid service in the Allied cause.
To a great extent these measures fulfilled their purpose. Between 1st January and 12th June 1944, the superseded ‘ski sites’ attracted a further twenty thousand tons of bombs—or rather more than the Germans had aimed at London during the eight months of the ‘Blitz’,—while the ‘modified’ sites which replaced them went unscathed.22 The bunkers and other underground workings at Watten, Wizernes, Sottevast, Equeurdreville (otherwise called Martinvast), Mimoyecques, Siracourt and Lottinghem—none of which Heinemann meant to use for launching flying bombs or rockets if he could help it—drew another eight thousand tons.* And, as we shall see presently, in due course the ‘supply sites’ also attracted attention which their place in the German system no longer warranted.† But the Allied effort was perhaps not altogether wasted. Despite his timely abandonment of the ‘ski sites’ and distaste for bunkers, Heinemann might doubtless still have used them if we had not bombed them.
The existence of the new series of launching-sites was vaguely reported by agents in February, but was not established until late in April, when air photographs revealed the first of them at the village of Belhamelin, in the neighbourhood of Cherbourg.23 During the next fortnight another nineteen were discovered, and by 12th June the number identified had risen to sixty-six.
By the middle of May there was thus a strong, if superficial, case
* As we have seen in Chapter 22, the first four were planned originally as rocket sites, though Watten was later earmarked as a liquefaction plant and Equeurdreville as a flying-bomb site. Mimoyecques was intended to house a multi-barrelled long-range gun which never emerged from the experimental stage, while Siracourt and Lottinghem were designed from the start as flying-bomb sites.
† For a summary of the Anglo-American air effort against the various classes of site up to 12th June 1944, see Appendix 44.
for diverting to the ‘modified’ sites the bomber effort hitherto expended on the ‘ski sites’. But the times were not propitious for acceptance of such a programme by air commanders bent on the offensive, and perhaps inclined to grudge the many sorties already devoted to the older sites. In the first place the ‘modified’ sites were not attractive targets. Small, well camouflaged, and offering few good aiming-points, they threatened to be hard to damage. Secondly, the menace they presented was not everywhere so deeply felt as that arising earlier from the ‘ski sites’. A member of Leigh-Mallory’s staff may have misinterpreted his chief’s views, but spoke presumably for at least some of his colleagues, when he countered a warning from his less sanguine counterpart at Hill’s headquarters with the formal response that ‘the Allied Expeditionary Air Force attaches little importance to the new sites.24 Finally, by this time the landing in Normandy was only a few weeks away, so that any proposal calling for diversion of part of the Allied air effort from tasks essential to the success of that all-important venture merited jealous scrutiny. A month earlier the British Chiefs of Staff had exercised their right to intervene in the control of the Allied air forces by the Supreme Commander ‘should their requirements for the security of the British Isles not be fully met’, by asking General Eisenhower to ensure that everything possible was done to damage ‘ski sites’ and the installations known to the Germans as ‘bunkers’ and to us as ‘large sites’.25 Thereupon both the Tactical Air Forces and the United States 8th Air Force had notably increased their effort against those objectives. On the eve of the landing, ought they to be asked to devote a comparable effort to the ‘modified’ sites, with all their disadvantages as targets?
There was, however, another class of objective, whose destruction promised—though uncertainly—to disrupt the enemy’s plans at a cheaper rate. The purpose of the eight so-called ‘supply sites’ which the Allies had discovered in northern France had never been established; but their situation and their construction at the same time as the ‘ski sites’ suggested that they might be intended for the storage and servicing of flying bombs. As we now know, when firing from the ‘ski sites’ was envisaged the Germans had indeed assigned that role to them. If the enemy still meant to use them, now that he had apparently abandoned the ‘ski sites’ in favour of the ‘modified’ sites, attacks on them should provide a simple answer to the Allied problem. Accordingly, on 16th May the Chiefs of Staff invited the Air Ministry to ‘examine and report on the desirability of attacking supply sites rather than the new-type pilotless-aircraft sites’.26
In fact, of course, the enemy no longer meant to use the ‘supply sites’, at any rate while the caves and tunnels which replaced them remained at his disposal. The Air Ministry could not know this;
what they did know was that no connection had ever been traced between the ‘supply sites’ and the ‘modified’ sites, and that even the association of the former with the ‘ski sites’ was conjectural. They suggested, therefore, a trial attack to test the enemy’s response. If closely followed by reconnaissance, it might do something to reveal the purpose of the sites.27
In the outcome United States bombers made two attacks on a selected site at Beauvoir, where they dropped close on 300 tons of bombs. Gaps were torn in the railway line that served the place; and twelve days after the first attack it was noticed that the enemy had done nothing to repair them. Nor were there any indications at other ‘supply sites’ that the Germans were moving in supplies.
Meanwhile the ‘modified’ sites had gone unmolested except for an unsuccessful experimental attack by fighter-bombers on 27th May; and no further attempt was made to interfere with them during the short time that elapsed before the Germans used them. At Hill’s headquarters, and perhaps in certain sections of the Air Ministry, the omission caused some disappointment; but the decision was broadly justified by subsequent events. Supply was indeed General Heinemann’s weak link, though the proper method of assailing it had not yet been discovered.
(iv)
In order to trace the evolution of plans for the direct defence of the United Kingdom against flying bombs, we must now return to December 1943.
Early in that month the Chiefs of Staff decided that, while the attacks on ‘ski sites’ which were just beginning might do much to reduce the danger from such missiles, measures of direct defence must also be studied. With their approval the Air Staff therefore furnished Air Chief Marshal Leigh-Mallory with an appreciation of the threat from pilotless aircraft and accompanied it by instructions ‘to consider, in consultation with the GOC-in-C, Anti-Aircraft Command, counter-measures possible with the resources at his disposal and to prepare plans accordingly.28 Leigh-Mallory gave corresponding instructions to Air Marshal Hill, as the officer directly responsible for air defence.
Thereupon Hill, in consultation with General Pile, produced an ‘outline plan’ which he submitted to Leigh-Mallory in the middle of the month.29 Observing that, despite the absence of a pilot who could be killed or incapacitated, the missiles would presumably be vulnerable to the same forms of attack as were used against ordinary aircraft, he recommended that fighters, guns, searchlights and balloons
should all be used, and should be deployed in such a manner as to avoid causing mutual interference. At the same time he pointed out that the bombs—which were said to move at anything from 250 to 420 miles an hour—might well prove too fast for his fighters, and would in any case make difficult targets for anti-aircraft gunners. He asked, therefore, that the offensive against ‘ski sites’ should be vigorously maintained, and that he should be kept informed of the progress made by two committees which were examining the chances of countering the missiles by radio-jamming or electro-magnetic interference. In the event, as we have seen, the offensive against ‘ski sites’ was offset by the building of the ‘modified’ sites; while the measures considered by the two committees proved either inapplicable or impractical.
After further consultation with Pile, Hill followed early in the New Year with a detailed plan, which Leigh-Mallory approved and remitted to higher authority. But meanwhile the success of the offensive against ‘ski sites’ had made it probable that attacks with flying bombs would not begin until the Allied landing in Normandy was close at hand. Early in February the Chiefs of Staff asked, therefore, for a new plan designed to reconcile defensive needs with full provision for the support of the Expeditionary Force. In the meantime Hill and Pile were authorised to proceed with certain administrative arrangements envisaged in the existing plan.
The outcome was a scheme of limited scope, whereby the two commanders sought to offset the danger from the much-mauled ‘ski sites’ mainly with weapons which could be spared from Operation OVERLORD, and some of which would be held in a reserve created at the expense of the defences assigned to embarkation areas and the like. The OVERLORD/DIVER plan, as it was called—these being the respective code-words for the landing in Europe and attack by flying bombs—was submitted to Leigh-Mallory towards the end of February, was then approved in turn by the Supreme Commander and the Chiefs of Staff, and on 4th March was sent on Hill’s authority to formations which might one day have to give effect to it. The plan assigned the leading role to fighters. Whenever an attack seemed imminent in daylight, standing patrols for the defence of London would be flown at 12,000 feet off the coast between Beachy Head and Dover, over the coast between Newhaven and Dover, and over Kent and Sussex between Hayward’s Heath and Ashford. When an attack began, further aircraft would patrol the same lines at 6,000 feet. In darkness, fighters under various forms of radar control would be reinforced, if necessary, by more fighters controlled by sector-stations. Additional security for London would be provided by 192 heavy and 246 (later 192) light anti-aircraft guns and 480 balloons. To reduce the risk that their radar equipment might be jammed, the heavy guns would be
sited in folds and hollows of the North Downs; the light guns would be deployed mainly on searchlight sites and would have the assistance of about 200 searchlights specially earmarked for the task. The balloons would fly from the belt of high ground between Cobham (Kent) and Limpsfield, and were expected to remain permanently airborne.
The plan provided also for the defence of Bristol and the important area round the Solent. At neither place were standing patrols thought necessary in view of the relatively long warning which could be expected before the missiles reached their targets; but fighters would be held ready to intercept in the normal way. In addition, Bristol would be defended up to the time of the Allied landing in Normandy by 96 heavy and 36 light anti-aircraft guns, the latter assisted by searchlights already present. In the neighbourhood of the Solent the big deployment of heavy and light anti-aircraft guns already contemplated in connection with OVERLORD would suffice, with a few additional searchlights, to meet the threat from flying bombs. In all three areas, the plan rested on the correct assumption that radar stations and Royal Observer Corps posts would be able to track the missiles, and furthermore to distinguish them—respectively by ‘track behaviour’ and by the noise they made—from ordinary aircraft.
The OVERLORD/DIVER plan was designed to meet such an offensive as the enemy might be capable of launching from ‘ski sites’ left intact by Allied bombing. That it did not match the effort of which the ‘modified’ sites proved capable was not the fault of Hill, who subsequently met the problems thus created with an energy and power of decision which earned him a high reputation. But if the plan was a reasonable insurance against the dangers predicted by the Air Ministry in March and April, it fell short of providing that margin against unforeseen contingencies which its author, in common with every prudent commander, would have sought if his choice had been unfettered. As compared with the earlier plan it provided, for example, only 288 heavy and 282 light anti-aircraft guns instead of 528 and 804 respectively.* Moreover, as Hill prophetically observed, the gunners would face a particularly awkward problem if the
* The respective figures were as follows:
| Original Plan | OVERLORD/DIVER Plan | |||
| H.A.A. | L.A.A. | H.A.A. | L.A.A. | |
| London | 400 | 346 | 192 | 246 * |
| Bristol | 96 | 216 | 96 † | 36 † |
| Solent | 32 | 242 | – | – |
| 528 | 804 | 288 | 282 | |
* Reduced by D-day to 192.
† To be withdrawn by D-day.
missiles flew at 3,000 feet or so, instead of the 6,000 or 7,000 feet predicted, and at one time contemplated by the enemy.
With this plan in their files the formations under Hill’s control awaited as March gave place to April, April to May, and May to June, the offensive which Heinemann and Wachtel were working against time to mount.
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