Chapter 9: The Battle of Britain: The Prelude, (June–July 1940)
WHEN their offensive against France and the Low Countries ended, the German High Command had no comprehensive plan for a direct assault on the United Kingdom. On 21st May Admiral Raeder, Commander-in-Chief of the German Navy, had raised the subject with Hitler,1 and earlier the leaders of all the fighting services had given some consideration to the question; but no important step was taken until six weeks later. By that time hopes that Great Britain would not fight alone were fading.2 Accordingly, on 2nd July the Führer ordered that plans for an early invasion should be prepared by all three services.3 He was not convinced, however, that their execution would prove necessary.4
On the other hand, an indirect assault on the United Kingdom had been in progress since the beginning of the war. With ten months’ experience of attacks on British trade behind them, the German navy and air force were now presented with a string of Dutch, Belgian and French ports and aerodromes well suited to the work. On the British side the capacity of the Royal Navy to protect convoys had been weakened within the last few weeks by losses at Dunkirk and off Norway, while the Air Staff faced the problem of finding aircraft for anti-invasion reconnaissance without sacrificing convoy-escort and anti-submarine patrols.5 As summer approached, good weather and the arrival of newly built ocean-going submarines further strengthened the German hand. Italy’s declaration of war in early June made the situation still worse from the British point of view. Allied naval and air forces in the Atlantic theatre had already been weakened by steps taken in anticipation of the Italian move, which added twenty large and over a hundred smaller submarines to the enemy’s resources.6
In June, losses to British trade from submarine attack were the heaviest in any month since the beginning of the war.7 The Admiralty were forced to conclude that the navy, lacking bases in Eire and
faced by an enemy well installed in Brittany and Gascony, could not continue to protect the existing convoy-routes through the south-western approaches.8 Towards the end of the month they arranged, therefore, that henceforth inbound traffic, except ships bound for Channel ports from Southampton westwards, should be routed north of Ireland. Outbound traffic would continue to use the southerly routes until the first re-routed inbound convoys reached home waters some weeks later.
In the outcome, growing fears for the safety of shipping threatened by German bombers from northern France led the Admiralty to modify this programme and anticipate its later stages. The southerly routes were not used by ocean convoys after the middle of July; thereafter passage through the English Channel was virtually confined to coasting vessels organised in small local convoys. A provisional plan, whereby inbound ocean convoys were to split up north-west of Ireland so that some of the ships could be taken northabout to the East Coast, was abandoned in favour of a single approach which brought all convoys through the North Channel to the West Coast ports. Thence a northabout link with the East Coast was provided by local convoys from the Mersey and the Clyde.
For the home defences, not merely in their naval aspect but in many other aspects as well, the change had far-reaching consequences. It did much more than merely underline the need for a growing share of such things as anti-aircraft guns and fighter squadrons at the West Coast ports; it also raised further claims which proved very hard to meet. That increased reliance on the West Coast, besides creating new problems of distribution, would place an added burden on the air defences, had long been obvious; less obvious was the extent to which the burden would spread to parts of the defensive structure as yet unready to support its weight. In the first place the defence of the western ports became more urgent, not merely because the enemy could reach them more easily from his new bases, but also because congestion resulting from successful attacks might throw the whole system of ‘turn-round’ and distribution out of gear. That, however, was not all. For the Royal Navy and for Coastal Command the problem of protecting ocean convoys grew more and more acute as U-boat commanders gained experience. It was soon apparent that asdic would not fulfil the hopes previously placed on it, for by surfacing to attack as darkness fell the submarines could escape detection by it while remaining almost invisible to the human eye.9 And similarly the task thrown on the air defences grew more and more onerous as the passage of the months made it increasingly clear that their resources must be used, not only to defend the ports themselves and all the rest of the kingdom, but
also to extend patrols for the protection of shipping to new areas where facilities for aircraft were particularly scanty.10
Yet to a great extent the problem was foreseen before it grew acute. Well before the fall of France, for instance, the defenders were aware that the flanks of the existing system of air defence would be vulnerable if the enemy acquired either aerodromes outside Germany or aircraft of exceptionally long range.* In the early part of 1940 the continuous system ended on the right flank at the Solent, on the left flank at the Firth of Forth. Beyond those points there were only outposts for the defence of Bristol and Scapa Flow. West of Bristol, Fighter Command had not a single aerodrome suitable for modern fighters and radar cover was non-existent or inadequate. In many other places C.H.L. equipments had yet to be installed and C.H. stations were too far apart.11 The Observer Corps system was also incomplete or lacking in some areas, including wide tracts in the west.
So far as the West of England was concerned the gravest of these shortcomings was the lack of radar stations, for aerodromes of a sort were available, while observer posts, needing no elaborate equipment, could be established fairly quickly. At the time of the Dunkirk withdrawal the Air Ministry adopted an emergency programme designed to meet the most pressing need. They contemplated the early installation of eight new C.H. equipments in the West of England and in Scotland and Northern Ireland, and of fifteen C.H.L. equipments at various places round the coast, from Flamborough Head to Stranraer and Antrim. If possible, all the latter were to be ready by 8th July. In addition, a pool of twelve mobile radar stations was to be made ready to fill gaps or replace equipments knocked out by the enemy. As things turned out, six of the C.H.L. equipments and the same number of C.H. equipments had been added to the chain by the beginning of the second week in July, when the German air force led up to its main offensive of August and September b,^ starting a series of lively attacks on shipping by escorted bombers.12 Map 10 shows the location of radar stations in existence or under construction at that time.
Still earlier, steps had been taken to bring into action a new fighter group in south-west England, thus freeing No. 11 Group for the defence of London and the south-east. This move had been contemplated before the war and plans had been made accordingly.13 Construction of appropriate headquarters at Rudloe, near Bath, began in February 1940; and in July the newly-formed No. 10 Group took control of three sectors with headquarters at Pembrey, in South Wales, Filton, near Bristol, and St. Eval, in Cornwall. A
* See Chapter V.
fourth sector with headquarters at Middle Wallop, on the eastern fringe of Salisbury Plain, remained under No. 11 Group until the beginning of the second week in August. For the present the westward boundary of the area covered by the Observer Corps lay on a line extending roughly from the centre of Lyme Bay to the Gower peninsula; but in the course of the month a new Observer Centre opened at Exeter, and cover was gradually extended further west. Radar stations in the south-west were already reporting to a temporary centre at Plymouth, and continued to do so until the end of July, when a Filter Room opened at Group Headquarters. Appendix 6 shows the organisation of the air defences in the summer.
When No. 10 Group first went into action its commander had four fighter squadrons to divide between his three sectors. But for some months afterwards he continued to lack permanent sector stations and a sufficiency of good aerodromes well placed for his needs. St. Eval, for example, was a Coastal Command station, where his one squadron and sector headquarters were mere ‘lodger units’; Filton was a stop-gap intended to serve only until a permanent station at Colerne was ready. Worse still, as neither radar cover nor Observer Corps cover was yet complete, he could expect only an imperfect picture of enemy movements towards his sectors and across them.
In any case, the creation of No. 10 Group was far from solving the whole problem of defending the western ports, if only because its northern boundary was in South Wales. In the past, North and Central Wales, the Mersey and Northern Ireland had been fairly well protected by the broad mass of the air defences in the east and south; but the barrier had ceased to be effective now that German bombers could get there by crossing or even skirting the thinly-covered south-western counties from new bases in Brittany.
Accordingly, the Air Ministry soon projected yet another fighter group, extending from the south Midlands to the Solway Firth and westwards over Wales and the Irish Sea.14 Before it could go into action the extension of the radar chain up the West Coast must be carried a stage further and the area covered by the Observer Corps must be extended, not merely over the whole of Devonshire and Cornwall for No. 10 Group’s sake, but over western Wales. New aerodromes and sector headquarters were needed, and a complex system of communications had to be created in an area which included wide tracts of desolate country where telephone-lines were scarce. Progress in some of these respects was disappointing. A North-Western Filter Room opened at Preston on 13th August; but the new No. 9 Group was not ready for active operations until December, and took full control of all its sectors only in 1941. Meanwhile the possibility of temporarily extending No. 10 Group’s area northwards was discussed. But in practice the burden continued to rest chiefly on No. 12
Group, although that group promised to be fully occupied with the threat across the North Sea, and on the widely-scattered No. 13 Group. For the defence of Belfast, the Clyde and the North Channel, two squadrons under No. 13 Group moved to Aldergrove and Prestwick, in Northern Ireland and on the Ayrshire coast respectively.
Similarly, a third new group was clearly needed to bridge the gap between No. 13 Group’s left flank on the Firth of Forth and its outlying squadrons stationed at Wick for the defence of Scapa Flow. During the spring and summer of 1940 the Air Ministry pushed on, therefore, with plans for the development of bases suitable for modern fighters in Caithness, the Orkneys and the Shetlands, and of the other facilities which would be needed to weld all the defences north of Dundee into a coherent whole.15 In August, a new No. 14 Group (succeeding to a designation previously used in France) began to form at Inverness. But some months elapsed before it was able to assume control of the Wick sector and of a new sector with headquarters at Dyce, near Aberdeen.
The formation of new fighter groups and sectors, the lengthening and strengthening of the radar chain, and extension of the area covered by the Observer Corps, were all important steps towards the ideal of a ‘fighter umbrella’ protecting the whole kingdom. But much more was needed. Apart from the parallel need for balloon-barrages, anti-aircraft guns and searchlights in some newly-threatened areas, everything depended on there being enough fighter squadrons to garrison the extended system. Here only modest progress had been made since in March Air Commodore Stevenson, foreseeing the creation of Nos. 10 and 14 Groups, had urged the formation of seven new squadrons without delay and another twenty in the next twelve months.* Having sanctioned three of the new squadrons before being overtaken by the German offensive against France and the Low Countries, the Air Staff were working in May and early June to a programme of sixty squadrons by September.16
When France fell, Air Commodore Stevenson returned to the charge. Calculating that no less than a hundred and twenty home defence squadrons would be needed to achieve security in the circumstances likely to arise in the near future, but recognising that such an enormous increase was quite out of the question, he recommended that ten new squadrons should be formed at once and another ten as soon as possible.17 The output of the fighter factories had improved so much in recent weeks that some such programme might have been feasible had there been no scarcity of pilots. As it was, the supply of trained pilots from the Group Pools or Operational Training Units—itself governed by the output of the Flying Training
* See Chapter V.
Schools—had begun to lag behind the demand created by casualties sustained in France.18 In the circumstances the best that could be done was to add four aircraft to the establishment of each of thirty Hurricane and six Spitfire squadrons, the intention being that they should be flown in an emergency by pilots who would otherwise have been on leave or resting. Fighter Command gained some slight alleviation of its difficulties through the accession in June of sixty-eight pilots hitherto serving in naval air squadrons, of whom ten were withdrawn soon afterwards for service in the Mediterranean. The broad effect of these arrangements, later supplemented by the addition of a number of Dominion and Allied squadrons, was to maintain the strength of the command throughout the summer at the equivalent of about sixty squadrons, including a varying number not fully up to the demands of active operations.19 In actual numbers, Air Chief Marshal Dowding had on 9th July a total of fifty-eight squadrons in various stages of efficiency, besides the Fighter Interception Unit, an experimental night-interception unit which ultimately played a useful part in active operations. Appendix 7 shows where his squadrons were stationed and how they were equipped.
Apart from the foregoing changes, the spring and summer of 1940 were notable for additions to the balloon, searchlight and gun defences. But the full effect of these additions was not felt before the autumn.
We have seen that before hostilities began the scale of balloon defence for the whole country was fixed at 1,450 balloons, that in fact 624 were flown on the first day of the war, and that afterwards unexpected losses forced Balloon Command to conserve its stocks by flying only a proportion of the balloons distributed to squadrons.* Thanks to this policy, by the middle of May 1940, enough balloons were available to meet the pre-war scale.20 Strict economy was, however, still necessary to prevent a recurrence of the crisis. Moreover, as time went on other factors besides the risk of damage in bad weather inclined the Air Staff more and more towards a policy of close-hauling balloons except when the places they guarded were imminently threatened.21 Among them were the danger to growing numbers of British aircraft compelled by the needs of war to cross defended areas, and later the risk of electrical interference with gun-laying radar sets.
In any case, the fact that there were now enough balloons to meet
* See Chapter 5.
the pre-war scale did not mean that all squadrons had their full complement; for since the beginning of the war the number of squadrons had increased. Apart from a short-lived demand for barrages at French ports used by the Expeditionary Force, new barrages had been authorised at several places, including a number of fleet anchorages and harbours. Again, some existing barrages had been made larger. By April 1940, such additions and extensions, with an increased allocation for training and the creation of a mobile barrage suitable for swift deployment at any point which might be newly threatened, had already added some six hundred balloons to Balloon Command’s establishment without adding a single balloon to its real strength.22
After the fall of France the barrages at French ports were no longer necessary, but other needs became acute. In particular, more or larger barrages were urgently needed at the western ports; at the same time there was a growing demand for balloons flown from waterborne moorings as a deterrent to minelaying aircraft. Air Chief Marshal Dowding was ready with concrete proposals to deal with this situation. Besides providing an average of ten waterborne balloons at each of fourteen estuaries to meet the second need, he contemplated new barrages, with an aggregate establishment of 112 balloons, at Pembroke, Falmouth, Ardeer and Yeovil, and the addition of 96 balloons to existing barrages at Liverpool, Runcorn, Manchester, Bristol, Hull and in South Wales. The projected scale would thus rise from 2,027 balloons to 2,375. Clearly, therefore, the authorised establishment of Balloon Command was due for revision. To cover an estimated requirement of at least forty balloons at Belfast while providing a margin for further demands and unforeseen contingencies, the Air Staff accordingly fixed at the end of July a new figure of 2,600 balloons.23 Production, which had amounted to only 212 balloons in September 1939, and 148 in October, had been roughly trebled since that time, largely by the erection of new plant, and was expected to reach the satisfactory figure of 1,200 a month within the next three months.24 Meanwhile fifty-two squadrons, with an aggregate strength of 1,466 balloons towards their nominal establishment of 1,865, were actually deployed and another two were working up. Their deployment is shown in Appendix 8.
To meet new demands for anti-aircraft artillery was much harder. When France fell, General Pile held only 1,204 heavy and 581 light anti-aircraft weapons towards his approved scales of 2,232 and 1,860 respectively.25 Intake amounted during the next five weeks to 124 heavy and 182 light guns, but about two-fifths of the former and a quarter of the latter had to be allotted to training and to places abroad, including some of those now threatened by Italian intervention. Thus on 28th July the United Kingdom still had only about
one-half of the heavy and less than one-third of the light anti-aircraft weapons considered necessary before the German occupation of the European seaboard.26
This was a grave shortcoming. Strong defences for aircraft factories were deemed essential; it was desirable that aerodromes should be well defended; and the western ports, a number of naval bases and many industrial areas also had strong claims. On the other hand there was no prospect, as there was where balloons were concerned, that the production problem would soon be solved. For the moment all that could be done was to allot more guns to aircraft factories, aerodromes and other specially important or vulnerable targets, mainly at the cost of temporarily depleting the defences of London and other towns.27 The disposition of the guns in July is given in Appendix 9. As an additional deterrent to low-flying aircraft a number of aircraft factories were furnished with an easily-made ‘parachute-and-cable’ device consisting of a linear arrangement of rockets to which light steel cables were attached. Searchlights were more plentiful, nearly four thousand being available towards the pre-war scale of 4,128, though here again there was a strong case for increasing a figure calculated to meet a situation much more favourable than that which now existed.
To sum up, the air defences reached the crucial summer of 1940 with a fighter force which its Commander-in-Chief and the Air Staff were at one in thinking uncomfortably small; an early-warning and reporting system tolerably near completion in the south and east, but notably deficient in the west and parts of Scotland; a marked but scarcely acute shortage of balloons; and a grave shortage of antiaircraft artillery and of the new devices needed to counter the night-bomber and enable the guns to engage unseen targets with success. Perhaps most serious of all so far as the immediate outlook was concerned, the fighter force, having overcome the worst of its deficiencies of equipment through the great effort made by the aircraft industry, was now threatened with an equally disturbing shortage of trained pilots. Such was the inevitable outcome of the change from a peace to a war footing and of the casualties sustained in France.
At first sight the underlying causes of the last difficulty may not be apparent. It may be thought that the shortage of pilots must have been foreseen and hence ought not to have occurred. But even if the first assumption were sound, the second would not necessarily follow from it. The immediate causes of the shortage were unexpectedly heavy losses and accelerated expansion of the fighter force to meet
the novel situation arising from the French collapse. But the roots of the problem went much deeper. On account of the time factor, the difficulties experienced in 1940 could have been avoided only by a big expansion of the Air Ministry’s facilities for training and recruitment at a stage when war was far from certain; and probably no amount of foresight would have enabled the Air Staff to persuade a peacetime government to sanction such a step before the Munich crisis. Nor could they have made sure in time of peace that recruits of the right sort would be found. The standard set by the Royal Air Force for its fighter pilots demanded that they should be well and recently trained, in excellent physical condition and at the peak of their young manhood. To ensure that an ample reserve of men satisfying these conditions should be ready at a moment chosen by the enemy, the Air Ministry would have had, in the first place, to find and train them; secondly, to keep them in training after they had qualified; and thirdly, to replenish the reservoir at frequent intervals in order to replace pilots who grew too old or could no longer be counted on for other reasons. The system of short-service commissions, on which the air force relied for a high proportion of its peacetime strength, went some way to ease the problem, but could have provided a sufficient reserve of young fighter pilots with recent experience only if the number on the active list at any one time had been raised to a higher figure than in fact the peacetime service could absorb. The Royal Auxiliary Air Force, although intended to provide a second line of Territorial squadrons rather than a reserve of pilots to replace casualties in the Regular squadrons, also helped to make the air force more elastic. But its scope was limited both by the size of peacetime votes and by the number of suitable candidates who could be induced to join. In view of these difficulties it is not surprising that the Air Ministry did not solve a riddle inherent in the peacetime structure of the service.
Thus, at least as soon as fighting began in France, the leaders of the air force had reason to fear that a well-timed blow by the enemy might find them with dangerously few fighter pilots. On the other hand, they had the satisfaction of feeling that quality had not been sacrificed to a vain attempt to achieve mere bulk. Their aim had been to build a fighter force not only as well-equipped as possible, but trained to an exceptional standard of efficiency; and they saw no reason to suppose that they had missed their mark. Well-schooled in a system which gave wide scope to personal initiative, intensely proud of their machines and at the peak of their physical resources, the young Hurricane and Spitfire pilots were confident of their ability to do all that was expected of them, and much more. Those who had fought at Dunkirk and elsewhere knew that they had fought well; and if it is now clear that numerically they had not always been
as successful as they thought, their conviction that they could fly and shoot at least as skilfully as their opponents was none the less well-founded. They believed that they could meet the coming blow; before long they would have an opportunity of seeing whether they were right.
By the end of May a large part of the German air force was already based in Holland, Belgium and northern France, preparing to support the army in its drive towards the Seine. Before the completion of the withdrawal from Dunkirk, and while air operations were still in progress on both sides of the Somme, a part of the bomber force was turned southwards against objectives remote from the main front. On the first two days of June, German bombers attacked towns and centres of communication in the valley of the Rhone and southern France. Next day they made a sharp attack on the outskirts of Paris. Clearly the main object of these raids was to support the army by delaying the arrival of reinforcements in northern France; but inclusion among the targets attacked of oil refineries and aircraft factories seemed to mark a shift towards the ‘strategic’ conception of air warfare. Consequently a raid on London in the near future appeared not at all unlikely.
On June 5th the German army began its final thrust towards Paris and the lower Seine. Within a few hours a new stage of the air war opened not, indeed, with a raid on London, but with a scattered attack on many parts of the United Kingdom. That night and the next, small numbers of bombers flew over the country, interrupting sleep and causing the sirens to sound over a wide area, but otherwise doing little harm. Most of the bombs they dropped were aimed at aerodromes, but some fell harmlessly in open country.
In London and at Stanmore the small scale and wide distribution of these raids, and of others which followed later in the month, aroused much speculation. At least one government department suspected that they were a rehearsal for the dropping of parachutists as a prelude to invasion.28 Another and better founded theory was that the German air force was trying out methods of navigation which would enable its crews to find their targets in conditions of weather and visibility otherwise prohibitive. There was no doubt that, by taking bearings and cross-bearings on a series of German medium-frequency radio-beacons, each transmitting a characteristic signal capable of being changed from time to time in the interests of security, aircraft on their way to raid this country could fix their positions well enough to make the finding of a prominent landmark
fairly simple. But Dr. R. V. Jones, a physicist introduced to the intelligence branch of the Air Ministry for the special purpose of studying enemy weapons and methods, suspected something more.29 A document recovered from a German bomber brought down in March had mentioned a ‘KNICKEBEIN beacon’ described as operating on a certain bearing from darkness until dawn. Later the wreckage of another aircraft, belonging to the same unit as the first, had yielded a diary in which was written the same word KNICKEBEIN—an evident code-word roughly translatable as ‘googly’. A third item of intelligence connected the word with a town in western Germany and a geographical reference corresponding to the neighbourhood of a manufacturing centre in the Midlands.
Such scraps of evidence led Dr. Jones to suspect the Germans of planning something far more dangerous than a mere array of beacons. He feared that they were experimenting with a system of directional radio beams capable of being made to intersect over a given spot. Such beams could be used to guide the pilot of an aircraft equipped to receive their signals to an unseen target and let him know when he had reached it. If the Germans succeeded in perfecting such a system their bombers might be able to find our towns with considerable accuracy on the darkest nights, and perhaps in weather which would hamstring the defences.
At first, many of Dr. Jones’s colleagues doubted whether such a device was feasible. Some scientists argued, for example, that a radio wave of the postulated frequency could not possibly be made to bend round the earth from Germany so much as to be receivable in a bomber over England. But Jones persisted. At least he could show that, although his hypothesis might not be sound, its implications, if it should prove so, were serious enough to make failure to test it inexcusable. Ultimately the matter was discussed on 6th June at a meeting over which the Prime Minister presided. Nine days later prisoners of war, who had hitherto been reticent, at last made admissions which went some way to confirm the existence of the beams; and on 18th June an organisation was created under the Air Ministry to investigate signals on the suspected frequency, both from a specially-fitted van and from an Anson aircraft.
The German raids were resumed that night, when the first bomb dropped on Greater London fell at Addington. They continued on a small scale throughout the rest of the month. On its second flight the Anson found firm evidence that a radio beam crossed the English coast at the mouth of the Humber on a bearing consistent with the theory. After Dr. Jones had expressed the opinion, on 28th June, that the device would enable the Germans to ‘place an aircraft within 400 yards over a point in this country’, further discussions were held, in which Mr. Churchill again took an active part. The sequel was the
formation in July of No. 80 Wing, commanded by Wing-Commander E. B. Addison, a signals expert, for the purpose of taking measures designed to counter a variety of German aids to navigation. Under Wing-Commander Addison’s direction arrangements were made both to jam KNICKEBEIN and to re-radiate transmissions from the medium-frequency beacons in such a way that bomber-crews would be presented with an embarrassing choice of apparently authentic signals. In the interests of security and in view of its dependence on sources of information with which operational commanders were not directly concerned, No. 80 Wing worked under the immediate control of the Air Ministry, but kept in close touch with the operations room of Fighter Command at Stanmore. There it was represented by liaison officers who also controlled the working of our own radio transmitters so that they should help the enemy as little as possible.
Thus on balance the June raids were a poor investment for the German air force. In the course of the month thirteen aerodromes, sixteen industrial plants and fourteen port areas were bombed, but the bombing was nowhere heavy enough to do lasting damage.30 The heaviest casualties caused by a single attack occurred at Cambridge, where nine people were killed on the night of the 18th. A few German bomber units gained experience of night-flying over the United Kingdom, but at the heavy cost of compromising one of their most important aids. Begun at a time when the British Government was called upon to decide how far the few fighter squadrons left in France after the withdrawal of the Air Component should be reinforced, the raids were of too minor a character to bear heavily on that issue; and such effect as they may have had upon it was scarcely calculated to advance the German cause.31 Moreover, their immediate cost in aircraft lost was fairly heavy. Either because they underestimated the defences or because their navigational researches required it, German pilots flew too low for safety. Of twenty-two night combats between German bombers and British fighters in June, five occurred at altitudes below 9,000 feet and only three above 12,000 feet. The average height of the bombers was probably about 10,000 feet. Consequently the imperfections of the defences were minimised. In the absence of the airborne radar and improved gun-laying devices with which he and General Pile were still experimenting, Dowding relied on searchlights to supplement the ordinary methods of interception used in daylight.32 At such low altitudes the searchlight crews, although handicapped by old-fashioned sound-locators, proved capable of holding and illuminating their targets quite well, even on moonlit nights. In the course of the night raids eleven bombers were brought down. German losses for the month also included a minelaying seaplane and a reconnaissance aircraft of bomber type.33
These results were flattering to the defences. They were not a
reliable foretaste of what might happen if more concentrated night attacks were made in the near future by bombers flying higher. In that case airborne radar, new equipment for gun-laying and searchlight control, and other devices still in embryo would be badly needed. If they were not yet ready, it was because priority had necessarily been given to early-warning radar, the watchdog of the defences at all hours.* For the moment, however, Dowding judged, quite rightly, that a big daylight offensive was the first important trial he would have to face. Meanwhile the night raids provided useful experience for both the air defences and the Civil Defence services. Perhaps not least important, they made the practice of routine precautions familiar to many citizens, while providing a good test of the public warning system. The authorities soon found that the existing practice, whereby the sirens were sounded in all areas even remotely threatened by hostile aircraft, resulted in much needless loss of sleep and played into the enemy’s hands by allowing a handful of bombers to keep most of the country under warning.34 Moreover, the frequent sounding of sirens in places where no bombs were dropped seemed likely to rob the warning of significance. Towards the end of the month, therefore, a new policy was tried. Henceforth a distinction was drawn between the probability of attack and its bare possibility. Greater discretion was exercised in the issue of public warnings, and more use was made of precautionary messages whereby the Civil Defence services in a locality only remotely threatened could be warned for action without sounding the sirens. The policy entailed some risk: on the night of the 26th, for example, when it was first applied, Cardiff was bombed though the sirens had not sounded; but on balance the new system was a great improvement on the old and served the public interest better.
At an early stage in their discussion of invasion plans the German High Command acknowledged that they could not conquer the United Kingdom without first defeating the Royal Air Force. In his first invasion directive of 2nd July the German Chancellor expressed the view that a landing in England was possible if air superiority could be achieved, and called upon the Luftwaffe to calculate the chances of achieving it.35 Ten days later a more detailed appreciation laid down the principle that control of the air over the landing area and the sea approaches to it was essential to atone for naval weakness, and that in consequence no crossing could be made until the
* See Chapter II.
Royal Air Force had been robbed of the power to intervene effectively.36 A further directive issued on 16th July gave the air arm the huge task of preventing all air attacks on the invading forces, destroying coast defences covering the landing points, breaking the initial resistance of the British land forces and annihilating reserves behind the front.37 Although the British Army was known to be in difficult straits after its heavy losses of equipment in France, it was expected to fight fiercely, so that the final clauses of this instruction alone were clearly a tall order.
Accordingly, the chief concern of the Luftwaffe in early July was to prepare itself for these responsibilities, or at least for such of them as seemed to its leaders likely to arise in practice. At the close of the campaign in France a number of units went back to Germany to rest and re-equip. During the next few weeks large numbers of captured aerodromes in France, Belgium and Holland were made ready, stocks of bombs and fuel were built up, and widespread preparations were made for the great air blow which was either to render an opposed landing in England possible, or make it unnecessary by forcing the defenders to give up. Recognising that the Royal Air Force was not likely to succumb in the day or two allowed in earlier cases, the German Air Staff proposed, with remarkable self-confidence, to devote four days to the subjugation of the fighter defences south of a line from London to Gloucester, and four weeks to the conquest of the air force as a whole.38 Besides directly attacking the ground organisation on which the Royal Air Force depended, they intended to compel our squadrons to consume their resources in defending shipping, ports and aircraft factories.39 By this means they hoped to prevent rapid replacement of equipment destroyed on the ground and in air combat without abandoning their attempt to sever our supply lines. The air battle proper would begin in August, so that a landing could follow early in September, when good weather for the trip across the Channel might be expected.
Ultimately some amendment of this programme became necessary. Meanwhile the High Command allotted responsibility for the main attack to the two air fleets which had supported the German armies so successfully in France and the Low Countries. Luftflotte s, whose units were based in northern Germany, Holland, Belgium and France north of the Seine, would be concerned mainly with the area east of a line from Le Havre through Selsey Bill to the Midlands; Luftflotte 3, based in western France, would deal similarly with objectives west and north-west of that line. (See Map 11.) Each Luftflotte was to attack shipping off its own stretch of coast. Diversionary attacks, intended to draw off part of the defences from the south, would be made on north-east England, south-east Scotland and shipping in adjacent waters by Luftflotte 5 from Norwegian and Danish
bases. Field-Marshals Kesselring and Sperrle, commanding Luftflotten 2 and 3 respectively, were perhaps the ablest and certainly the most experienced operational commanders in the German air force. Besides their work in France and the Low Countries, the former had commanded Luftflotte i in Poland; the latter had commanded the Kondor Legion in Spain in 1936 and 1937, thus furnishing the German Air Staff with new foundations for its strategic doctrine.
By the third week in July dispositions for the battle were substantially complete. Thereupon the units concerned were ordered to assume ‘full readiness’, although detailed plans for their employment had still to be perfected.40 Between them Luftflotten 2 and 3 had at their disposal some 1,130 long-range bombers; about 320 dive-bombers; roughly 800 single-engined and 250 twin-engined fighters; 60 to 70 long-range reconnaissance aircraft (besides a number of long-range earmarked for armed reconnaissance of ports and shipping); and some 90 short-range reconnaissance machines.*41 The last were of no value for the initial air assault, but would be needed for the close support of any troops which might ultimately land in Britain. Luftflotte 5, under General Stumpff, had available for use against the United Kingdom and its shipping some 130 long-range bombers, 30 to 40 twin-engined fighters and about 50 long-range reconnaissance aircraft.42 Normally about two-thirds of the bombers in each Luftflotte were expected to be serviceable at one time, the remainder being grounded for inspection and minor repairs; but the proportion would tend to rise in quiet periods and fall after a few days of active use. Generally the serviceability of the fighter units was somewhat higher; some units, for example, had had nearly all their aircraft serviceable in the closing stages of the French campaign, when they were working on extended communications and had been busy for several weeks. In broad terms, the two Luftflotten responsible for the main assault were capable of putting into the air rather less than 800 long-range bombers and 250 dive-bombers supported by about 820 fighters.43
As for the opposition they must expect, the German Air Staff put
* More precisely, the figures on 20th July were:
|LUFTFLOTTEN 2 and 3|
In addition, Luftflotten 2 and 3 disposed of some 90 short-range reconnaissance machines and Luftflotte 5 of 84 single-engined fighters for local defence.
Fighter Command’s strength at fifty squadrons of single-engined fighters, or a total of 900 first-line aircraft, excluding the twin-engined Blenheims. Of these they expected about 675 to be serviceable on a given day.44 In fact, Air Chief Marshal Dowding had forty-eight such squadrons ready for action on 9th July and four more forming or re-equipping; but the first figure included two Defiant squadrons of limited value for day fighting. His six Blenheim squadrons, like the Fighter Interception Unit, were now primarily night fighters—a fact known to the Germans—although for certain minor tasks they might still be used in daylight. Towards his authorised establishment of 1,450 pilots Dowding had 1,253.45 Reckoning his squadrons at their normal tactical strength of twelve machines apiece, he could not count on putting more than some 600 day fighters into action at one time, even in the unlikely event of his committing all his day squadrons simultaneously. Theoretically the number would rise to 700 or more if pilots could be found to man the additional machines attached to certain squadrons.46 Map 12 shows how these forces were disposed. As for Dowding’s other resources, the German Air Staff rightly thought the number of antiaircraft guns in the United Kingdom far from adequate; and in fact there were still fewer light guns than they supposed.47 They regarded the searchlight defences with a respect attributable to their recent performance against night-bombers, but attached little importance to the balloon defences in view of their limited altitude and their susceptibility to damage in bad weather.48
In most respects, then, the German appreciation of the defences was not too wide of the mark. But in one respect the Luftwaffe miscalculated badly. Although aware of the existence of the radar chain, if not of its extent, they thought so little of its effectiveness that their formal survey made no mention of it.49 From the British standpoint, on the other hand, it seemed likely to be the crucial weapon. Dowding and his subordinate commanders could have no doubt that success or failure would turn largely on their ability to distinguish between main and subsidiary attacks. Where the speed of the enemy’s advance was reckoned in hundreds of miles an hour instead of ones or tens, the time left for decision would be very short; and only the information furnished by the radar chain could help them to decide swiftly and correctly. If the oracle spoke clearly and was understood, they might win with their six or seven hundred fighters; if it failed them or they mistook its message, then defeat was almost certain.