AHB IIA/1/7 ADGB file folio 23, also

H A Jones, ‘The War in the Air’

Ibid Vol.2 folios 89, 23

‘The War in the Air’ Vol.5 p.159

Home Defence Committee Paper No. 220,

9 Feb 1937

AHB ADGB Vol 2 Folio 89

DPR Committee Paper No 2

DPR Committee Paper No. 2

HCTD S/212

14 May 1937

AHB/IIH1/18

Air Chief Marshal Sir Hugh Dowding: ‘Battle of Britain’ 234

DPR Committee Paper 189

AHB/IIH/93 Encl.1A 19 March 1938

CSSAD 9^th Meeting

CSSAD 23^rd, 27^th, 33^rd Meetings

AHB/IIH1/18

Air Chief Marshal Sir Hugh Dowding ‘Battle of Britain’ 215

CSSAD 26 Nov, 1937

AHB/11H/148 Encl.36

3 July1939

AHB/IIH/240/4/121 FC/S.21197

3 Nov. 1940 Encl.2019 and FC/S.22104

3 Dec. 1940

“The Battle of Britain” 33 etc

AHB/IIA/240/4/126(A)

FC/S.16806 2 Dec. 1939 Encl.19A.

FC/S.22104

The AOC-in-C Fighter Command AA Command’s Despatch Section III Para. 44 et seq.

Ibid 58

AOC-in-C Fighter Command Night Interception Report FC S22104 8 Dec. 1940

Air Chief Marshal Sir Hugh Dowding ‘The Battle of Britain’ p.46

AHB/IIH1/18

Ibid

FIU Report No. 80

FC Operational Instruction No. 90

AHB/IIH1/18

Dowding: Despatch ‘Battle of Britain’ 233

FC/S.15329

28 April 1939

FC/S.16638

10 July 1939

IVA/16

18 Sept. 1940

AHB/IIH1/18 Dowding Despatch “Battle of Britain” 232

S.3867

2 March 1940

CID 283^rd Meeting 29 Oct. 1936

COS (40) 320

4 May 1940

CID 308.A and 319.A

CID 308-A Part II

CID 319-A

AHB/IIH/148

DHO Folder ‘RDF Stations’ also FC Battle Orders, May 1940 D1

AHB/IIH1/18 Dowding: Despatch “The Battle of Britain” 16

AHB/IIE/5

DHO Folder Re-equipment No.2

ADIK 12/1946

FC ORB Dec. 1939

FC/S.18378

AHB/IIH/240/4/122

FC/S.18353 28A

FC ORB

25 Nov 1939

S.3081

AHB/IIE/68

27 Feb 1940

FC/S.18378

CHAPTER 1

BACKGROUND TO THE BATTLE

Attack as the Best Form of Defence

During the war of 1914-1918, the majority of air raids on this country had been made at night.  Sixty-two and a half tons of bombs had been dropped on London killing 670 people and affecting the output of munitions although no factory had been directly hit.  To meet these attacks we were forced by military necessity and public agitation to create an expansive and elaborate system of defences, so that when the Armistice was signed in 1918 we had a home defence establishment of 480 guns, 760 searchlights and 16 fighter squadrons.  It was, nevertheless, not the casualties inflicted by our anti-aircraft artillery or by  fighters co-operating with searchlights that made night raiding a prohibitive form of warfare for the German Air Force.  Enemy attacks ceased because Germany was facing a precarious position on the Western Front the restoration of which demanded all her energy.

Indeed, the difficulties and the uneconomic character of anti-aircraft defence so impressed the air historian that he declared: “the only defence in the air likely to be effective in the long run is an offensive more powerfully sustained than that of the enemy”.

This view still held currency in 1937, for no new developments in night air defence had come about since 1918 either to supersede the system of searchlight aided interception or make it so much more efficient that the chances of direct defence against the night bomber had improved.  “Local defences” it was stated by Air Chief Marshal Sir Hugh Dowding, Chairman of the Home Defence Committee, “however numerous and efficient cannot alone provide an adequate measure of security ….  Offensive action will be ultimately more efficacious in reducing the scale of attack on Great Britain than a vast increase in the number of local defence fighters, though these have a vital part to play, particularly in the initial stages before our counter-offensive has had time to make its effects felt”.  The strength of Fighter Command was accordingly based on the strictest economy of effort relative to the scale of attack it would have to meet[1], and the balance between the offensive and defensive arms of the Metropolitan Air Force was maintained in the proportion of two bombers to one fighter through all the expansion programmes of the rearmament period.

The problem of night defence was affected by this standpoint, for though it was recognised that attacks by night[2] might well be as intense as those by day and that an adequate night defence was imperative, it was held that the preparation of a night defence should not absorb too great a fraction of the whole national effort.

Problem of Continuous and Accurate Location of the Enemy

The problem of air defence is well conceived in three subsidiary but interrelated phases.  Simply stated, these are early detection of the enemy, his continuous and accurate location and, finally, engagement and destruction.  In broad terms, these are the prerequisites of successful interception both by day and by night, with the important difference that by night the limitations of human vision had somehow to be made good.

Late in 1940, a specialised form of night interception involving both airborne and ground radar equipment[3] began to show encouraging results, but until then, searchlights remained the sole means of reducing the limitations of human vision in darkness[4].  It is not a matter of surprise, therefore, that each successive review of the Air Defence of Great Britain emphasised the importance of the searchlights in night defence.  In 1935 it was stated that “without searchlights this operation by night of fighter aircraft and anti-aircraft guns would be severely crippled and interception of the enemy bomber would become a matter of chance”.  In May 1937, the AOC-in-C Fighter Command during the course of a lecture delivered to the Staff College declared that “the disposition of a network of searchlights alone for the time being make night fighting possible save in conditions of exceptional visibility”.

Unfortunately enemy aircraft could neither be continuously nor accurately located by the form of acoustic control upon which the searchlights relied to illuminate their targets.  Sound waves are affected by temperature lapse rate in the atmosphere and by variations of wind speed and direction at different altitudes.  In particular, erroneous calculations were liable to be made owing to the lag in time taken for the sound emitted by an aircraft to reach the sound locator on the ground, a drawback aggravated by the high speeds of modern bombers.  But the difficulties did not end there.  The effective range of the searchlight beam did not exceed 12,000 feet, so that aircraft operating above this height enjoyed immunity for detection.  Indeed, when war came, no beam or combination of beams existed which could secure illuminations above 12,000 feet, so that the successes of searchlights against enemy raiders during June 1940 were short lived.  The enemy quickly rectified his tactical mistake and commenced operating at heights at which attempts to destroy him by searchlight assisted interception were frustrated.

In addition, climatic conditions over this country seriously hampered the workings of searchlights, and it was estimated that there was cloud between 400 and 5,000 feet on over 100 nights during a year.  On moonlit nights, searchlight beams were hardly visible at all.  It was a safe assumption, therefore, that the searchlight would be incapable of illuminating the target on one night in three[5].  Finally, there were tactical difficulties.  It was assessed that a target had to be illuminated for 8 minutes to enable a fighter to close and engage, but nothing in the performance of the searchlight could hold out hope of such a high standard of efficiency.  Evasive action by the enemy and the inherent weaknesses of acoustic control (which the scientists advised “should be relied on to a decreasing extent”) could not both successfully be contended with. 

Problems of Early Detection, Inland Tracking and Height Finding

The Air Defence of Great Britain in the period before September 1939, short of equipment and personnel, and manifestly lacking in quality, demanded complete overhaul.  Late in 1934 the Committee of Imperial Defence therefore formed an Air Defence research Sub-Committee and the Air Ministry established a Committee for the Scientific Survey of Air Defence to undertake this task.  Their work reflects the complex and difficult problem of night defence and shows the numerous directions in which solution was sought.  Searchlights in aircraft, illumination by towed flares, by flares dropping out of bursting anti-aircraft shells, aerial minefields in the enemy’s path, infra-red detection – these were some of the forms of night defence exhaustively debated and carefully tried.  Attention was even paid to an inventor’s claims for his death ray.  Of these possibilities only two were ultimately exploited operationally – the laying of aerial minefields and the airborne searchlight – neither with any marked success.

The main weakness of our defences[6] was the absence of any satisfactory means of early detection.  Happily the principle of radar had been discovered and its practicability conclusively proved at a demonstration at Orfordness early in 1935 and, by March of that year, a Treasury Grant had been obtained for its development.  As a result, our radar stations were in a position by the time war came in September 1939 to detect enemy aircraft at some distance[7], thus giving sufficient warning for both active and passive defence measures to be set in motion before attack developed.  Early warning certainly did much to save Fighter Command from having to resort to the uneconomic tactic of maintaining standing patrols, and in general fighters remained on the ground until required to make an interception.

Early detection was, however, only the initial function of the machinery of defence.  Continuous and accurate location of raiders was also a requirement.  This was possible to seawards by means of the chain of radar stations which covered many of the air approaches to this country from Germany.  Aided by these radar facilities, a system of fighter interception was evolved, carried out by ground controllers in contact with the fighters by radio telephony, the course of our own aircraft being determined by wireless direction finding (D/F) methods.  The system had been far enough developed by November 1937 for Sir Henry Tizard, Chairman of the Committee for the Scientific Survey of Air Defence to say that “interception had now been developed so that in daytime or on clear nights there was a high chance of success at the coast”.

Inland tracking however was carried on by the Observer Corps who depended on a view of the target for accurate location.  In cloudy weather and at night, therefore, enemy aircraft had to be located by sound alone, so that the information furnished by the Observer Corps became too inexact for controlled interceptions to take place.  As Mr. Winston Churchill who had served on the Air Defence Research Sub-Committee wrote to the Secretary of State for Air:  “A weak point in the wonderful development (of radar) is of course that when a raid crosses the coast it leaves radar and we become dependent on the Observer Corps.  This would seem a transition from the middle of the twentieth century to the early stone age.”

In addition to the inaccuracies of overland tracking by night and in cloudy weather, inaccuracies in reading the heights at which enemy aircraft were flying presented a further problem.  Neither the coastal radar stations nor the Observer Corps were able to provide exact heights, and though errors could be compensated for in daytime, it was impossible to compensate for them by night, when interceptions represented as perfectly effected on Operations Room tables were in reality made totally abortive by the great difference in height between the fighter and its target.

Problem of Engagement in Darkness

Inaccurate inland tracking and inaccurate readings of enemy heights were thus the two cardinal defects in our night defence system until the GCI method began to be used early in 1941, and all effort was directed towards overcoming them.  “It was borne in upon me with special force” wrote the AOC-in-C Fighter Command in November 1940, “how hopeless it is to attempt night interceptions against high flying aircraft on the basis of Observer Corps sound plots alone”.  A month later, the AOC-in-C was writing:  “I am convinced that the main obstacle to night interceptions is the lack of accurate tracking inland from the coast, and most important of all, lack of accurate information with regard to the height of the enemy bomber”.

Neither of these defects was eliminated from the night defence system until the early part of 1941, when the application of the radar principle to the special demands of night interception began successfully to be pursued.

Closely linked with the problem of continuous and accurate location was the third problem of interception – engagement and destruction of the enemy.  The best of aircraft and guns would be valueless unless they could be placed within range of the enemy.  We had the Hurricane and the Spitfire, both 8-gun single-seater fighters, but the failure of daytime interception methods at night – owing to the uncertainty of searchlights in illuminating their targets – largely denied to us the use in darkness of the fire power of these aircraft[8].  Indeed the potentialities that seemed to exist in the use of airborne radar equipment for night interception led to the choice of the slower, lesser-armed twin-engined Blenheim as a night fighter, until it was gradually replaced towards the end of 1940 by the faster, more powerfully-armed Beaufighter.  Thus, contrary to original intentions and policy, the development of specialised night fighter formations was proceeding.  “I think” wrote the AOC-in-C Fighter Command in December 1939 “that a division between day and night fighters will soon be forced on us”.  By December 1940 the AOC-in-C Fighter Command was asking for “at least twenty specialised fighter squadrons” to make a success of night interception. 

Gunnery Equipment made to Fire at ‘Seen’ Targets

Anti-aircraft gunnery at night presented a similar paradox, guns being robbed of their full effect so long as no means existed of locating enemy aircraft continuously and accurately.  Practically all gunnery and equipment was designed for visual shooting at ‘seen’ targets both by day and by nights, and some locators were used with guns, a target being tracked by these sound locators for some time to establish its course and speed.  This information was then passed to the guns so that ‘future position’ could be calculated, the fuses set and aim taken.  In all, there was an interval of anything up to a full minute between the pick-up of the target by the sound locators and the arrival of the shell at its destination.  During this time, an aircraft might have moved between four and six miles and, in calculating ‘future position’, it had to be assumed that course and height would remain constant.  This was, in fact, far from the case.  Moreover, at night, Heavy Anti-Aircraft required the illumination of targets by searchlights so that they could be ‘seen’.   Searchlights were therefore deployed with heavy guns round important cities and a system of ‘gun-defended-areas’ (GDA) was accordingly created.  In addition to the drawbacks inherent in location by acoustic method and in location by searchlights whose reliability was always in question, predictors were not designed to accept heights over 25,000 feet and their speed of traverse was limited, so that close targets often moved too fast across the sky to be followed.

Fixed Azimuth System

For the defence of London two lines of sound locators, spaced at intervals of two miles, were sited at right angles to the Thames Estuary on the capital’s eastern flank.  A similar siting of sound locators on its western flank had been carried out.  Each sound locator was connected to the London Gun Operations Room.  It was expected that the two nearest locators would almost simultaneously be able to report the bearing and angle of sight of an approaching enemy machine, while two sound locators from the inner line would be able to supply its speed and direction. Working on this data, the Gun Operations Room was expected to fix the ‘future position’ at which the guns were to engage, the guns making the adjustments necessary to their own position.  This complex organisation for engaging the enemy was called the Fixed Azimuth System.  However when the first big raid on London came (7/8 September), the Fixed Azimuth System broke down completely.  The reasons for the breakdown were threefold: the enemy was flying at greater heights than those at which sound locators could make accurate detections; at times more than one machine was operating between two locators, making it uncertain that both were tracking the same aircraft: and lastly, the assumption that the enemy’s main approach would be up the Thames Estuary was not always fulfilled, many of the raiders passing outside the flanks of the sound locator layout.  Faults in the communications-system did not help to smooth the difficulties, and few of the guns on that day received data on which to engage.  It was therefore decided that guns unable to fire on the Fixed Azimuth System should have a free hand to use any method of control they liked.  A large volume of fire resulted, hailed by the Press as a ‘barrage’, but described by the GOC Anti-Aircraft Command as “largely wild and uncontrolled shooting”.  Results from this were that the public felt better’ upon hearing a big volume of sound, and that any timid German aircrews might have been deterred from pressing home their attacks upon viewing large areas of the sky dotted with shell-bursts.

The Radar System

The application of the radar principle to anti-aircraft gunnery, and the evolution of GL (Gun Laying), first used in October 1940 after many struggles in the testing stages to obtain a measure of accuracy in reading heights, slowly relieved the problems of gunnery and, most important, no longer made it necessary for the target to be ‘seen’.  An entirely new system of “unseen barrages” was developed with a view to increasing the volume of fire from many guns at once, thus widening the area of the lethal burst.  Guns were re-sited in groups, with a master-site using GL to plot the target and pass information to its satellites each firing independently as the hostile machine entered the barrage belt.

This system was continued until January, 1941, when a change was made, the GL data from that moment being passed back to the Gun Operations Room where predictions were worked out and fire orders issued.

Other Weaknesses in the Night Defences

Although inaccurate tracking and height finding were the cardinal defects in our night defences, other factors contributed towards their comparative failure until the spring of 1941, including a lack of first-class aerodromes, equipped with night-flying facilities; a lack of specialist training in night interception work and difficulties in the maintenance of aircraft and the poorly engineered radar and R/T equipment they carried.  As the AOC-in-C Fighter Command put it: “in nine cases out of ten something would go wrong with the AI set or with the R/T direction finding system or with the communication system before an interception could be made”.  The lack of a suitable aircraft for night interception work was also felt, for though the Beaufighter began to come into service in the Autumn of 1940, it suffered from a great many teething troubles and furthermore, the supply of this type of aircraft was slow.

Indeed, it was not until early in 1941, when some German night raiding had been going on for three or four months, that this type of machine began to operate in anything like effective numbers.

Development of Specialised Night Defences

By the time we had established the GCI system to ensure the accurate measurement of heights and the accurate tracking inland and to seaward of both enemy bomber and intercepting fighter, and by the time other drawbacks had been surmounted, the Germans had begun to withdraw the bulk of their bomber forces eastward for participation in the impending attack on Russia[9].  Thus although we were fast evolving a specialised machinery for night defence, raiding on any serious scale had ceased before it could be tested at its fullest efficiency in 1941[10].

Improvements in our night defences continued throughout 1941.  By November the principle of radar had successfully been applied to the control of searchlights and an apparatus called SLC (Searchlight Control or, more popularly, ‘Elsie’) was coming into use.  It had been well demonstrated that efficient troops could expose their beam directly on an aircraft and maintain illumination even if avoiding action was taken.  A comprehensive drill had therefore been worked out for co-operation between the searchlights and single engined fighters.

The arrival of SLC raised an important issue.  The trend in night fighting had been towards the employment of twin-engined aircraft equipped with AI and operating under GCI control, and the small number of specialised Beaufighter (and earlier Blenheim) squadrons had hitherto constituted the main defence against night raiding.  The GCI system however possessed a limitation in that a controller could direct only one fighter (at most two) at a time towards an interception; a limitation that would most seriously be felt when dealing with the mass attack.[11]  The possibilities of frequent and accurate searchlight illumination of targets by SLC controlled searchlights suggested that the main force of Fighter Command’s single engined fighters could now be brought to bear against large scale raids as had been envisaged at the outbreak of war.

The cessation of important German attacks in the Spring of 1941 however prevented this issue being put to any practical test and both searchlights and the GCI system, therefore, continued to be regarded as essential parts of our night defences.

The Character of Our Defences

Inadequacy of Searchlights

With the exception of the searchlight companies, there was no part of the air defence system that functioned solely by night during the early months of the war.

Throughout the 24 hours, coastal radar stations detected the enemy’s approach, gave instant and early warning to active and passive defences, and tracked his course until he had made landfall. The Observer Corps, likewise working day and night, continued tracking him over land.  The Air Raid Warning procedure remained practically unchanged by day and by night and a single system of communications was in use at all times.  Similarly, until radar methods came to be applied to night defence, no distinction between day and night weapons existed, the daytime technique in interception and gunnery having to suffice at night.  "We relied" said Sir Hugh Dowding, the then AOC-in-C of Fighter Command "upon daytime interception methods, and on searchlights to illuminate and hold the bombers".

But the inadequacies of searchlights had long been in the minds of those responsible for our defences.  In the spring of 1939, the AOC-in-C Fighter Command decided to modernise night flying tactics, taking into consideration the serious shortcomings of searchlights which he ordered to be tried out in a variety of ways.  But the passage of time only served to diminish confidence in the searchlight method and in July 1939 the AOC-in-C Fighter Command was receiving most discouraging reports about the ability of searchlights to pick up and hold high speed targets painted matt black at heights of ten thousand feet and over.  “This gives additional urgency” he said “to the need for pressing on with the new method of night interception”.[12]  Meanwhile the Air Fighting Development Unit, after two months of experiment could only add to the prevailing scepticism about searchlight assisted interception and, on a later occasion, a representative of Anti-Aircraft Command committed himself to the statement that “modern methods of camouflaging night machines were such that it required about nine times as much light to effect illumination visible from the ground as was the case in the last war”.  In addition, difficulties in training aggravated this unpromising situation.

Investigation to Improve the Night Defences

It was not only the inadequacies of searchlights, however, which exercised the minds of those responsible for our defences.  Other deficiencies existed which had been continuously under the investigation of such bodies as the Committee for the Scientific Survey of Air Defence.  Indeed, the shortcomings of night defence caused Sir Hugh Dowding to say that he had “long been apprehensive of the effect of Night attacks, when they should begin, and of the efficiency of our defensive measures”.   So much was the subject to the forefront that in March 1940, Air Vice-Marshal Richard H Peck, then Assistant Chief of the Air Staff (O & I) addressed a minute to the Chief of the Air Staff asking approval for the formation of a committee “to co-ordinate measures for night defence and link up research and development to the stage of practical trial.  There can be no doubt”, he said, “of the magnitude and the urgency of the problem of night interception”.  The Chief of the Air Staff authorised this step and the Committee (called the Night Interception Committee) held its first meeting on 14 March, 1940, under the chairmanship of Air Marshal Peirse, Deputy Chief of the Air Staff, who opened the discussions by stating that “defence against night attack was one of the biggest problems we had to face.  Even if the enemy began by raiding in large numbers by day" he went on, "our good defences would force him to adopt night bombing”.

The Night Interception Committee energetically explored every means of night air defence available or likely to be available, and the record of their deliberations shows that their efforts were directed especially towards the application of radar devices to the problems of night defence,[13] a sign perhaps of their distrust of the weapons immediately at our disposal.  To wait on the production in quantity of new devices and to neglect available resources would never have been justified, particularly as the assumption ‘that Germany may attempt a knock-out blow from the air and that this blow would be delivered with maximum intensity at the moment of declaration of war’ was the one which governed our pre-war policy of air defence.  In view of this assumption, therefore, all the equipment to hand, however unsatisfactory had to be deployed in the air defence of the country.[14]

This deployment of the country’s air defences was carried still further when the threat of a German offensive in the West grew imminent.  The Chiefs of Staff expressed the view that if ever the Germans intended to invade us, an air attack on this country would, in the first instance, probably be aimed at the air force and at the aircraft industry, as a prelude to more ambitious operations.  While they were reasonably satisfied with prospects if such an attack were made by day, they reported that ”our defence against night attack is still far from effective, and while we doubt whether Germany could achieve her aims by night bombardment alone, it must be remembered that our passive defence measures cannot be as effective by night as by day, and morale is more vulnerable during the hours of darkness.”

It was thereupon recommended that every means of air defence should be provided as fast as possible, even if this meant that the production of other equipment, equally important in the long run, were to be retarded.

To discuss the reasons for the unsatisfactory nature of our air defence system, even as late as the summer of 1940, would be profitless, touching as they do upon wider political and economic issues, although concerning night defence, it is worth noting that science had not advanced far enough in the early days of the war to offer those delicate and precise instruments, which alone made night defence effective in the times to come.  New techniques and revolutionary devices had long promised well,[15] but the practical application of an invention demands time.  Unforeseen technical faults and difficulties of production have a habit of cropping up to hinder the progress that in theory seemed so certain.  What is more, once new devices are produced, the training of the large numbers of persons required to operate and maintain them is a lengthy process.  And the reality of factors of this nature is well substantiated by the slowness in perfecting such apparatus as AI, GL, GCI and SLC, and the poor standards of maintenance and frequent mechanical breakdowns occurring in the AI-equipped Beaufighter squadrons when they first came into the fighting line. 

Plans for the Provision of Defences

The successive pre-war reviews of the air defences of Great Britain culminated in the recommendations of the Home Defence Committee of 7^th February, and 15^th May, 1939.  The first of these reviews was accepted at the 346^th Meeting of the Committee of Imperial Defence.  It provided for 1,584 heavy and 1,622 light anti-aircraft guns, some 4,500 searchlights, 1,284 radar sets for the control of guns and searchlights and 24 stations to form the coastal chain (20 having already been approved).  No additions were made to the approved fighter force which remained at 50 squadrons; nor to the balloon barrages which were to contain a London barrage of 450 balloons, and provincial barrages totalling 2,500 balloons.

At the same meeting, the Home Defence Committee was directed to examine a War Office outline of probably future requirements in anti-aircraft guns.  This envisaged a further increase of 1,144 guns or, alternatively, a similar number of UP projectors, an anti-aircraft weapon under development at that time. Such an increase would ensure that the scale of defence for objectives of the highest importance would be up to a 72-gun density.  This conception implied that that number of guns could be brought to bear on any given avenue of approach to a target.  Such an increase would also ensure that the scale of defences in less important areas would be strengthened, though not to the same extent.  The decision reached, however, was that a 36-gun density was a sufficient defence against the weight of attack then considered possible and an increase of 328 guns was recommended in order to obtain this density over all important areas.

Altogether the active defences planned at the outbreak of war included 2,232 heavy anti-aircraft guns (including reserves), about 4,700 searchlights, and 50 squadrons of fighter aircraft.

The broad policy governing the disposition of the fighter squadrons indicated that each sector in Fighter Command should deploy 3 squadrons, 2 of single-engine machines chiefly for day operations and one of twin-engined machines for night work.  The night fighting squadrons were to co-operate with searchlights spaced at intervals of 6,000 yards in the so-called Aircraft Fighting Zones.  Of the Searchlights over 700 were to be of the new 150 cm type distributed among the standard 90 cm projectors in the proportion of 1 - 3.  In important areas however, the searchlights were to be spaced at intervals of 3,500 yards and would co-operate with the anti-aircraft artillery.

These were the plans but they were far from being implemented fully when war broke out.  On September 3^rd 1939 only 695[16] heavy and 253[17] light anti-aircraft guns were in position, 2700[18] searchlights were manned and 34 fighter squadrons were capable of operating against the enemy.  The Aircraft Fighting Zone was incomplete, for there were gaps in the Midlands, and between the Mersey and the Bristol Channel.  Nor did the situation improve rapidly. By December 1939, 20 coastal radar stations were working, but only 7 had high-power transmitting sets and none had the agreed standard receiving set.  Few GL sets had been provided and none for the control of searchlights.  The London balloon barrage was complete but barely 300 balloons were flying in the rest of the country.  In view of these facts, the Chiefs of Staff reported to the War Cabinet, in December 1939, that the defences of the country could not be further weakened, even to provide the Expeditionary Force with additional anti-aircraft defences.

There were slightly more encouraging signs in our fighter defences which disposed 53 squadrons on 12^th November 1939.  Twenty-three of these squadrons were equipped with Blenheim aircraft, but not all of them were available for night fighting.  Four were being used for trade defence duties and 16 of them had not yet been trained to operational standards.  The intention, nevertheless, was to build up a force of 15 twin-engined squadrons for night defence.

Early in 1940, however, alteration in the dispositions of Fighter Command seriously affected the development of its night fighting resources.  Subsequent to a review of fighter strength made by the Air Staff early in January, it was decided to rearm 9 of the existing Blenheim squadrons with single-engined machines, leaving 6 Blenheim squadrons available for night operations, and 4 for trade defence.  Two factors appear to have determined this decision; firstly, the need for increasing fighter strength, with an eye to commitments in France; secondly, the relative scarcity of Blenheim aircraft.  There were 36 Blenheim squadrons in the service at this date, but the current rate of their production would be insufficient to maintain them at full strength as well as provide the aircraft necessary for training on this type.

Thus by the beginning of April, 1940, only 6 Blenheim squadrons remained in Fighter Command, the four trade defence squadrons having been transferred to Coastal Command in January.  And since these 6 Blenheim squadrons[19] were the only ones specialising in night fighting, and assisting in the development of interception with AI, only the single-seater fighters were available in some sectors.  These single-seater fighters, many of them Hurricanes, were able, as events proved, to participate successfully in the night battle when the searchlights offered them illuminated targets, but unfortunately, after an initial but transitory victory, their opportunities dwindled.  New evasive tactics by the enemy and recourse to the conduct of operations at heights beyond the reach of their beam, frustrated the searchlights.  The total number of sorties they made between August 1^st and November 1^st of 1940 was indeed much smaller in relation to their numbers than the total number of sorties carried out by the Blenheim squadrons.  The explanation was that the Commander-in-Chief, Fighter Command, was during that period compelled to keep the exigencies of the day-battles in the forefront of his mind, and that he did not favour the employment of single seater squadrons by night, especially when they had been so severely taxed during daylight.

The German Minelaying Campaign by Night

(Winter 1939 to Spring 1940)

Problems of Intercepting Minelaying Aircraft

While our poor night defences were still the subject of research and discussion, the German Air Force began to put to test what forces we could then command, in the opening phase of their operations, which consisted of an attack on our seaborne trade, especially of an extensive minelaying campaign carried on by night.  This minelaying campaign was concentrated mainly along East Coast waters, particularly in the Thames Estuary, off Harwich and in the Estuary of the Humber.  There is, however, no record of any success achieved by our night defences against the mine-layer.  The shortcomings of radar in detecting low-flying aircraft deprived us of adequate raid intelligence, and without accurate plotting, controlled interception becomes a fortuitous business, promising little more chance of destroying the raider in darkness than a system of free-lance fighter patrols.  The difficulties of engaging the enemy either by gun-fire or searchlights when he was at low altitudes over the water made counter-measures hard to devise.  Although CHL Radar equipment[20] had been sited to provide low cover in areas in which the mine-layer operated, its efficiency at the time was not all that might have been desired and, furthermore, coverage was by no means complete.

The German minelaying operations commenced in mid-November of 1939 and three units participated.  According to then available intelligence, these included elements of KG4, KG26 and KG30 under the director of Fliegerkorps IX at Jever,[21] and the Heinkel 115, a seaplane, seemed to be one of the types of aircraft mainly used for this work.  The wreckage of a machine discovered off the East coast during December, 1939, which turned out to be a Heinkel 115 provided evidence that they had been adapted for dropping mines probably of the magnetic type, with a parachute attachment to increase accuracy of laying.  There had also been frequent reports from various sources that float-planes had been seen to alight on the water, and though it was not possible to confirm many of them, there were indications that aircraft capable of landing on water were engaged.  Raids by Fighter Command Blenheims of No. 25 Squadron on the sea-plane base at Borkum at least showed our belief of the time that such attacks might reduce the measure of mine-laying operations by the Germans, while Bomber Command ‘security patrols’ over Sylt and Borkum during the night were begun with a view to hampering them still further.  

Early Attempts at Interception Using AI

Our best hope of intercepting the mine-layer seemed to be with the Blenheim fighters which were experimenting with AI, the airborne radar equipment, and were controlled from those radar sites possessing the necessary R/T facilities for passing instructions to pilots.  Accordingly Fighter Command despatched a signal on November 22^nd to No. 11 Group, to the Radar Flight at Martlesham Heath and to the Radar station at Bawdsey.  It read:

      “German aircraft have been active off the East Coast each evening

      after sunset believed to be minelaying.  Intention is to intercept and

      engage these aircraft to seawards employing AI Blenheim fighters

      operating under the control of Coastal Radar stations having R/T and

      controllers.”

Two Blenheims from Martlesham Heath were to operate under the control of Bawdsey and two Blenheims of No. 25 Squadron were to operate from Manston so soon as R/T control could be established at the radar stations at Dover and Dunkirk.

A further signal from Fighter Command of November 27^th instructed No. 11 Group to send three AI Blenheims of No. 600 Squadron to Manston, where they would fit themselves for night operations against German mine-layers by intensive daylight exercises.

Soon afterwards these operations commenced and, though they continued for about three months, proved abortive.  The defects of early AI equipment and of the ground radar apparatus, the immaturities of a yet undeveloped system of control and of untried night tactics no doubt all contributed towards the failure.  Nevertheless, mechanical limitations could mainly be held responsible, for it was only very much later that radar became effective in operation against aircraft at low altitudes.

However, valuable experience was gained not only about workings of AI in practice and in the matter of a technique of control, but in the evolution of a satisfactory procedure for night interception work of this specialised nature.[22]

Failure of the AI Experiments

The German minelaying campaign grew to become a source of anxiety to the War Cabinet.  Sinkings through mines which in September had amounted to 26,409 tons and in October 29,388 tons rose alarmingly in November to 99,918 tons, in December to 65,000 tons and in January 1940 to 83,217 tons, following the employment of aircraft to lay mines.  It is not possible to assess the number of tons of shipping sunk by air mining alone, since U-boats and E-boats also participated in this work, but it is certainly not possible to doubt the considerable effect of the part played by the German air arm.  Owing to the gravity of the situation, the Chief of the Air Staff recommended that a system of standing patrols should be inaugurated as a measure additional to the attempts at interception with AI Blenheim fighters.  Accordingly No. 11 Group was made responsible for patrolling the coastal area from Folkestone to the No. 12 Group boundary, No. 12 Group were to safeguard their own coastal front using 8-gun fighters if Blenheims were not available and, similarly, No. 13 Group, using Gladiators, Blenheim or 8-gun fighters as available were to watch their coastal front.  These patrols were to be maintained at low altitudes over the most threatened stretches of water.

Efforts to intercept the minelayer were continued well into 1940 but no results were achieved and hopes of success were always slight.  Addressing the Chief of the Air Staff in December, 1939, Sir Henry Tizard, his Scientific Adviser, wrote: “Director of Communications Development and I have been having a discussion about the interception of low flying aircraft at night, and I think you might like to know our conclusions.  We agree that the AI apparatus now being fitted to machines is quite unsuitable for the purpose.  It was not designed to meet these conditions and we do not think you ought to rely on it in the least.”

Summing up the difficulties of CHL interception the AOC-in-C Fighter Command advanced his reasons for the lack of success.  They were:

(a)    Lack of trained controllers.

(b)    Limitations in the R/T facilities available.

(c)    Unless the fighter could be manoeuvred from a point immediately over the CHL station, it could not be observed simultaneously with the enemy aircraft.

(d)    There were gaps in the vertical coverage.

(e)    The range of CHL required to be increased.

(f)      Interception at night required an accuracy of 300 yards, hence the importance of AI and the importance of reducing its minimum range to something like this distance.

(g)    Height indications were unreliable.

In March of 1940 the three AI aircraft of No. 600 Squadron which had been operating under CHL control from Manston were withdrawn and placed at the disposal of their squadron commander.  They had patrolled consistently but abortively, seeking out enemy machines in all sorts of weather in the vicinity of the Thames Estuary; they had practised assiduously by day the method of using AI, but they had failed.  In fact, neither effort nor ardour could overcome the technical weaknesses inherent in the primitive airborne radar equipments of those days, nor the drawbacks in the sets used for ground control.

No. 60 Group ORB July 1940

AHB/IIE/5

SD 264

Ibid

SD 264

AHB/IIH1/18 Dowding: Despatch para. 75 etc

SD 264

Pile: Despatch I paras 5 et seq.

Ibid 5, 7

Ibid 48

S.3984 Night Interception Committee 7^th Meeting 16 June 1940

HCTD/S.321 Air Scientific Intelligence Report No.6, 28 June 1940,

AHB/IIE/77/6

No. 80 Wing ORB

No. 80 Wing ORB

AHB/IIE28/1

CHAPTER 2

BACKGROUND TO THE BATTLE

The Functioning of the Defences

Raid Intelligence

Before considering an early phase of German night operations against land targets which began in June, 1940, it is essential to examine the functioning of the air defences available to us at the time particularly to examine the means whereby raid intelligence was obtained and distributed to the various parts of the defensive network, for it was against the background of this raid intelligence that a specialised system of night defence later began to take its place.

Radar was the foundation of our raid intelligence organisation, making both early detection and accurate and continuous location of an enemy possible, at least to seaward.  In July, 1940 our coastal radar chain consisted of 30 CH stations and 30 CHL stations, the CH stations being capable of detecting enemy raids at long range and the CHL stations capable of detecting low-flying raids.  These stations were disposed round the coast between Scapa Flow and Strumble Head in Pembrokeshire.  At the beginning of the war, Fighter Command had not only been in operational control of the radar-chain but had also been responsible for the training of operators, while experimental and research work, as well as equipment and maintenance, had come under the Director of Communications Development at the Air Ministry.  Such a division of authority had not proved satisfactory and in February 1940, No. 60 Signals Group had been formed in Fighter Command to take over the technical and administrative control of the radar chain.  This Group although placed directly under the Air Ministry for technical supervision came under the operational control of Fighter Command, an arrangement which left the Director of Communications Development free to concentrate on the immense programme of research and development that had been planned.  This division of authority continued throughout the whole period of the German air offensive.

The Observer Corps

The next source of raid intelligence was the Observer Corps.  In July 1940 the Corps consisted of a Headquarters located at Fighter Command and five areas, (Southern, Midland, Northern, Scottish and Western), with their headquarters at Uxbridge, Grantham, Catterick, Edinburgh and Gloucester respectively.  These contained 33 Observer Groups, each with a Centre, to which the posts, situated for the most part at vantage points in the open country, telephoned plots of enemy aircraft.

The main lack of coverage, like that of the searchlight zones, was in the south-west, and in Wales.  The Welsh coastal area was almost entirely unprovided with observer posts and, though this weakness was not felt while the Germans were still based in their own country, it was a serious gap now that they could approach Liverpool by flying over Wales from bases in Normandy.  In the south-west a new Observer Group with its Centre at Exeter had been formed, but it did not commence operations until July.

Thus we had as sources of raid intelligence the radar chain, plotting to seaward and the Observer Corps organisation plotting inland.  So long as the aircraft was visible, Observer Corps plotting was adequate.  When however, they had to rely on plotting by sound, as at night, or under conditions of cloud, the tracks produced were too inaccurate for controlled interception.  This weakness, already remarked upon, did not however reduce the value of Observer Corps plotting to another part of the defence organisation, the Air Raid Warning System.

Air Raid Warnings

The issue of raid warnings was the business of an Air Raid Warning Officer[23] who worked in the Command operations Room with a view of the Plotting Table on which tracks of enemy raids were displayed and on which the whole country was shown in outline, divided into 130 ‘warning areas’.  When a raid was judged to be within 20 minutes of warning area, the raid warning officer would send a preliminary warning to the area threatened through one of his 3 telephone operators, connected with the trunk exchanges in London, Liverpool and Glasgow.  This warning was immediately retransmitted to the warning area, where it was distributed to the police and to the fire and ARP services.  This was known as the ‘Air Raid Messages – Yellow’.  At night there was also a ‘Purple’ warning, which was a signal for the dowsing of exposed lights in factories, marshalling yards and docks.  The sirens warned the public only when the Air Raid Warning Officer saw clearly that a district was threatened with attack, and this was done upon receipt from him of the ‘Air Raid Message – Red’.  The ‘Air Raid Message – White’ signified that the raiders had passed and again the sirens told the public with their long, sustained blast.  Fighter Command Headquarters was also in contact with certain broadcasting stations which were warned to cease transmitting so that the enemy would be afforded no navigational assistance.

While the Air Raid Warning System employed the raid intelligence provided by Radar and the Observer Corps to keep the passive defences informed of approaching attack, this same intelligence had to be employed by fighters, guns and searchlights through more complicated methods.

Plots of enemy aircraft approaching the coast were passed from radar stations to the Filter Room at Fighter Command, where it was the duty of the officer responsible to evolve a track of the raid.  A second function of importance to be performed at Fighter Command was the identification of the raid, and decision had to be taken whether the track being plotted was friendly or hostile.  This problem of recognition was always difficult, notably during the early hours of the morning when our own bombers were returning from raids and enemy aircraft were still over the country.  But on the successful designation of raids as hostile or friendly depended the saving of fighter effort and the avoidance of false air raid alarms.  The IFF[24] device helped to minimise errors in identification, but it was not fully efficient at that time, and it was necessary to attach liaison officers from Bomber and Coastal Commands to Fighter Command who in direct contact with their own Operations Rooms, were able to assist identification from up to date information about the movements of their aircraft.

Plotting

Radar plots, giving position, height and numbers of approaching formations, having been filtered and the track of a raid as it moved on were passed (‘told’) by the Filter Room staff to the plotters around the table in the Operations Rooms both at Command and at the Fighter Groups.  From the Groups these plots were told by multiphone amplifier to Sector Operations Rooms.  Sometimes both radar and coastal Observer Centres might be plotting raids simultaneously until they made landfall, but once out of the orbit of the radar stations, raids would then be plotted by the Observer Corps only.

Observer Centres had direct telephone lines to Fighter Groups and to some sectors but not to Fighter Command Headquarters.  The procedure for the transfer of plotting from Radar stations to the Observer Corps was that a ‘sea teller’ in the Group Operations Room passed to Observer Corps Centres details of aircraft detected by radar and likely to enter their area.  The Centres then warned individual posts of the approach of such aircraft and the posts, picking them up would send back to the Centres their identity, position and course.  Frequently identity had already been established by the time the Observer Corps had taken over plotting.  Observer Centres ‘told’ all hostile or doubtful raids to the appropriate fighter groups and sectors and the group re-transmitted these plots to the Command Operations Room.  The aim of the system was, therefore, to ensure that all possible information about enemy movements would simultaneously be displayed in Sector and Group Operations Rooms and on the Command plotting table.

The Machinery of Interception

The assembly, analysis and transmission of raid intelligence fell heavily upon the Filter Room and Operations Room staffs both at Command and at the Groups.  To have sub-divided tactical control after the same fashion would have been to overstrain their resources.  In the words of Air Chief Marshal Lord Dowding: "It appeared to me quite impossible to centralise control at Command Headquarters, and even Group Commanders would be too busy during heavy fighting to concern themselves with details of interception.  The system was that the Command should be responsible for the identification of approaching formations and for the allotment of enemy raids to Groups where any doubt existed.  Group Commanders decided which sectors should meet any specified raid and the strength of the fighter force that should be employed.  Sector Commanders detailed the strength of the fighter units to be employed and operated the machinery of interception.” 

The functions of the Sector Operations Room and the Sector Controller were therefore particularly important in the defences, for not only would the Sector Controller be directing fighters towards their targets (or vectoring them as it was commonly called), he would have to watch their movements closely in relation to those of the enemy in order to make the changes of course necessary to effect an interception.  He would also have to keep fighters away from Gun Defended Areas or make sure that the batteries were aware of the presence of friendly aircraft.  At night, in addition to the raid intelligence made available to him through the normal channels, he would receive information from the searchlight liaison officer in his Operations Room concerning the position of enemy aircraft.

By night, the Sector Controller laboured under many serious difficulties, the most serious of which was that the plots laid on his table were often as much as four minutes old, and often older, making the accuracy which controlled interception at night demanded impossible to achieve.  By day when a pilot could see his target up to distances of 20 miles, depending upon visibility, such inaccuracies could be allowed for and result in successful interceptions.  At night however, without searchlight illumination of the raider, the fighter had to be brought to within 300 yards of the enemy before he could see it, so that the technical of controlled interception used successfully by day proved ineffective.

Another of the Sector Controller’s difficulties was the limitation placed upon him by the D/F ‘fixing’ method of tracking fighters.   By day when formations were operating, their position could be fixed by a signal automatically transmitted by one aircraft in the formation for 13 seconds in each minute, which was picked up by two or three D/F stations set up in the sector for the purpose.  These D/F stations would pass their readings by telephone to the ‘triangulating’ room at the Sector, and the resulting ‘cut’ would indicate the position of the formation.  In this manner large formations of aircraft could be tracked.  At night however when formation flying was not possible (at least in any numbers), the D/F fixing method only permitted the Sector Controller to keep track of individual machines.[25]  Thus by night the simultaneous control of only a small number of night fighters was possible in any one period.

Apart from the method of control by the D/F fixing system, fighters at night were placed on patrol lines marked out either by ground flares or by searchlight marker beacons, in the hope that they would be able to intercept approaching raiders by general indications of enemy positions transmitted to them by the Sector Controller.[26]

Co-operation between Fighter Command and AA Command

These were thus the limitations under which our night defences laboured in the summer of 1940 and although measures were in hand to overcome them, the process of doing so was slow.  Limitations similarly existed with the guns and searchlights and new equipment was also being developed for increasing the efficiency of Anti-Aircraft Command whose problems were not unlike those confronting Fighter Command.  Both depended on accurate data of the enemy’s movements for the effective operations of their own defensive machinery, and as has been emphasised, the degree of accuracy demanded for night interception and for the operation of guns and searchlights by night was extremely high.  Faced with largely identical problems, the joint working of Anti-Aircraft Command and of Fighter Command became imperative, particularly if the difficulties inherent in the night defence problem were successfully to be met.  The fact that the headquarters of both Commands stood in the grounds of the same country house[27] perhaps best symbolises the close relationship existing between them.

     At the beginning of war there were 7 AA divisions:

     1^st – The Metropolitan area of London

     2^nd – Northern East Anglia, East Midlands, Humber

     3^rd – Solway Firth, Scotland, Northern Ireland

     4^th – N.W. England, West Midlands, North Wales

     5^th – South Wales, S.W. and Southern England

     6^th – S.E. England and Southern East Anglia

     7^th – N.E. England

At the end of 1940, the General Officer Commanding felt the necessity for much reorganisation in order to relieve the burdens on the existing Command and Divisions, and also to achieve a closer co-ordination of boundaries with Fighter Command.  Five new Divisions were therefore created:

     8^th – covering the south coast as far as Bournemouth

     9^th – South Wales

    10^th – the West Midlands and Central Wales

    12^th – Clyde, Solway Firth and Northern Ireland

In addition, to ease the supervision of this organisation, three AA Corps were created:

1.     AA Corps in the south (Nos. 1, 5, 6, 8, 9 Divisions

2.     AA Corps in the Midlands (Nos. 2, 4, 10, and 11 Divisions)

3.     AA Corps in the North (Nos. 3, 7, and 12 Divisions)

Thus No I AA Corps Area corresponded with that of Nos. 10 and 11 (Fighter) Groups, No. 2 AA Corps area corresponded with that of Nos. 9 and 12 (Fighter) Groups, and No. 3 AA Corps area corresponded with that of Nos. 13 and 14 (Fighter) Groups.

Within these broad, co-operative arrangements was a further disposition of particular importance for night defence, by which each fighter sector was allotted a number of searchlight companies, usually forming a brigade, which worked in conjunction with the night fighters operating in the sector.

Heavy guns[28] and searchlights were controlled from Gun and Sector Operations rooms.  The same raid intelligence was available at a gun operations room as at sector operations rooms, through the anti-aircraft liaison staffs that were stationed at all operations rooms throughout Fighter Command.  There was also a counterwise flow of raid intelligence from gun and searchlight detachments to their respective operations rooms, which, in turn, ‘told’ to group and sector operations rooms.

Each gun operations room controlled a gun area, providing individual sites, to which it was connected by direct telephone lines, with information about all aircraft in the vicinity.  In addition, it actually controlled fire against unseen targets, and acted as an exchange for transmitting gunnery data from gun site to gun site.

Searchlights, at this date, were controlled by searchlight control officers stationed at sector operations rooms.  There were direct telephone communications between sectors and searchlight company headquarters; thence, intelligence was passed to searchlight sections, and to individual detachments.

Such then were the methods adopted by Anti-Aircraft Command for the control of its operations at the time when night bombing of land targets by the German Air Force first commenced.

The Role of the German Air Force before the Night Battle

A feature of the German air offensives in Poland, in Norway and in the West was the concentration upon battlefield operations.  While the battles in the West were in progress, even long range bomber units stationed in Southern Norway and North-west Germany, away from the fighting areas, were not directed against targets in England.  Such night attacks as were executed were aimed, firstly, at protecting the right flank of the advancing armies by means of an extensive minelaying campaign along the coasts of Holland, Belgium and North-eastern France and, secondly, by a similar campaign in the Southern Flanders Bight and in the Straits of Dover, aimed at impeding the movement of Allied shipping, especially during the evacuation of Dunkirk.  In the early days of June, this type of activity was continued, minelaying aircraft frequently visiting the Coasts of south-east and southern England and dropping mines near the many small harbours between Ramsgate and Portsmouth.  Here again the aim was to hinder the passage of shipping, weaken communications between England and France, and thus indirectly assist the armies assailing the line of the Somme.

During the first week in June, however, small bombing and reconnaissance raids against England by night commenced.  At first the majority of these sorties were confined to the coastal counties in the East and South East, but as more units were brought into operation and as the Germans took over more airfields along the French seaboard, these sorties were extended towards the West of England and as early as the end of June, methodical reconnaissance of the route from the Bristol Channel to Merseyside was begun, while the industrial Midlands also became the subject of attention.

This preliminary phase of armed reconnaissance came to an end about the middle of August and there began a series of night attacks of mounting intensity.  The restricted operations undertaken by the German Air Force during June and July can be explained by the necessity for a period for redeployment and re-equipment following the battles in France when many losses had been incurred and many aircraft had been worn out by continuous flying.  This strategic redeployment was completed by the end of July about six weeks after the fighting in France had ceased and in the disposition of forces, Luftflotte 2 under Generalfeldmarshal Kesselring covered Holland, Belgium and Northern France, while Luftflotte 3 under Generalfeldmarshal Sperrle covered Western and Southern France.  Luftflotte 5 under General Oberst Stumpf covered Norway and Denmark.  The plan was for Luftflotten 2 and 3 to secure air superiority over Southern England while Luftflotte 5 was to engage our defences in the North.

The German Air Force was in fact for the first time to be called upon to act, not in concert with the Army, but by itself.  Alone it had the responsibility of creating those conditions which could enable the Army to undertake the invasion of these islands.  This primary aim, as is known, had to be modified owing to the Luftwaffe’s failure to achieve air superiority over Southern England.  New and modified aims were therefore set forth, said to be “economic war from the air, subjection of civilian morale to heavy strain and lastly, reprisals[29] for British raids on German towns”, and these new aims were to be achieved by mass bombardment at night.[30]

Note: Some material for this section has been derived from German sources, especially a lecture by a Hauptmann Bechtle on ‘The Air Offensive against Britain’, delivered in Berlin in April, 1944.  Hauptmann Bechtle’s sources of information are given as:

     GAF General Staff/8^th Abteilung (Historical Archives)

     GAF General Staff/6^th Abteilung (Quarter Master General’s Dept)

     GAF Operations Staff/1c – Intelligence, HQ Luftflotte 3

While preparations for large scale attacks were proceeding, the enemy no doubt felt that his bomber pilots should familiarise themselves with the conditions of night flying over England, while to test the strength of the defences, specific targets were occasionally attacked with fair accuracy.  Furthermore, such attacks, though of a minor character, served as good propaganda material for consumption at home and around them, colourful stories of blows upon the last enemy, England, could be built.  But it is conceivable, also, that the chief purpose of these night flights was to test out several radio aids to navigation and blind-bombing devices that the enemy was suspected of developing.[31]

The German Night Flying Organisation

     By contrast with our own night flying airfields[32] the German Air Force had many magnificent bases from which to operate both in Germany itself and later in the occupied territories.  In Germany, the expropriation of land for the Air Force involved compensation to private owners or the sacrifice of farmland and forest valuable to the State.  Such restraints as applied to the acquisition of land in their own country however did not apply in the countries the Germans had come to dominate.  Moreover, a vast reserve of labour was available in prisoners of war, demobilised soldiers and unemployed civilians, and the Germans did not fail to make the utmost use of the resources they had acquired.  The number of acres lost to cultivation, though colossal, did not matter and German airfields began to sprawl across western Europe in numbers sufficient for an Air force of considerably greater first line strength than that of the Luftwaffe.

In Germany, Denmark and Holland, airfields which did not possess grass surfaces usually had a capital layout of runways, special servicing tarmacs and three or four dispersal areas adjacent to the landing-ground, with aircraft shelters close together.  Special branch railway lines serviced the airfield.  In France and Belgium, airfields covered much wider areas, dispersal being at some great distance from the landing-ground.  A single runway was originally provided at most of them but the construction of a second and even a third runway was generally put in hand without delay.  Up to the autumn of 1940, these runways, with concrete surfaces, measured 1500 yards in length and 40 yards in width.

Night flying airfields possessed an elaborate and varied system of aids.  Non-visual aids consisted mainly of radio beacons giving out particular signals at intervals, thus enabling the aircraft to take bearings and even cross bearings so as to ‘fix’ its position.  The characteristic emitted by these beacons and their respective positions would be known to crews before taking off so that the problems of navigating by night were considerably simplified.  In addition, the German Air Force possessed a well-developed system of Regional Control for the assistance of machines making lengthy flights.  Provided with a list of the wireless call signs employed by the controls for the various areas over which a flight was being made, an aircraft was in small danger of losing itself and could at any time call for information or help.  The Regional Control system existed also at airfields, so that an aircraft could always call an airfield on the medium frequency band (300-600 kc/s)[33] and ask for homing or for such help as a damaged machine might require in landing.  The Lorenz blind-landing equipment was a common installation at German airfields and was always available to aircraft coming down in doubtful weather, while the so-called ZZ procedure for landing under the strict instructions of an airfield controller who directed the operation from frequent wireless D/F fixes and bearings obtained from transmissions by the aircraft was also used.

Numerous visual aids to night navigation and landing also existed including a system of ‘visual Lorenz’ for use in conditions of low cloud or ground mist.  This consisted of a long line of lights leading up to the boundaries of the airfield intersected at right angles by two or three shorter lines of lights.  These points of intersection told the pilot his exact distance from the main runway, thus enabling him to regulate his height as he came in to land.  Flashing beacons (Blinkfeuer), usually white, signalled two letter characteristics denoting the airfield in whose vicinity they were situated.  Thus the characteristics B/X might have stood for Bordeaux while the characteristics O/B might have stood for Orleans-Bricy.  Rotating Light Beacons (Leichtes Leuchtfeuer) were in different colours, each colour representing the region or sector in which they were located.  Searchlights (Flugsicherungs-scheinwerfer) also played their part in ensuring the safety of German aircraft by night and one light of almost every battery was detailed to act as pointer towards the aerodrome.  The other aids to night flying included a well laid on flare path, boundary lights and the usual obstruction lights.

Captured documents and observations by RAF crews suggested also that a complex of about 75 Visual Navigational Beacons existed in North-west Germany, the Low Countries and France, usually on the same sites as the high powered Radio Beacons.  These Visual Navigational Beacons, showing certain recognition signals, were used by German crews on night operations for ascertaining their positions either when setting out or returning from operations.

It will thus be seen that in addition to a system of blind bombing and radio navigational aids, the German Air Force had begun to establish a highly efficient night flying organisation as soon as they took possession of airfields in the occupied countries, an organisation which was working well by the time they had decided to undertake full-scale night attacks against this country in the summer of 1940.

Note:  Information for the compilation of this section about GAF night flying organisation comes from AP1928 (October, 1941).

Enemy Blind Bombing and Navigational Aids

Evidence concerning the use of radio navigational aids by the German Air Force had been accumulating slowly during the spring of 1940 and it appeared that during March a document salvaged from an aircraft of KG26 made mention of ‘a Knickebein beacon’ operating at 315° from darkness until 0600hrs.  One or two other such beacons were also mentioned.  At that stage little could be done and further developments had to be awaited.  Later, a diary was picked up from another aircraft of KG26 in which it was stated that the author had taken ranges on Knickebein in collapsible boats.  Prisoners had been interrogated but had attempted to be misleading in their replies.  Nevertheless it began to be clear that a beam was sent on short waves and that it was almost a kilometre wide.  Intelligence sources were then suddenly able to add to this slight and laboriously garnered information by providing the phrase ‘Knickebein Kleves is at 53/24 N 1° West’, which indicated the neighbourhood of Nottingham.  It seemed possible, therefore, that an aeroplane flying over the Nottingham area had found a ‘cut’ or intersection of beams at that point.

On 15^th June, however, interrogation of a prisoner had produced the story that they had set up a very high powered beacon and that they flew in a beam, but that they had so far not been able to use it against targets in this country as they had not been able to obtain a sufficient divergence of base to get a good ‘cut’.  A high degree of navigational accuracy was apparently possible by this means, alleged to be within about 4 square kilometres.  Investigation on our side had led to the discovery of two such high powered beacons, but their exact use had not then been determined.

At an emergency meeting to discuss the implications of this situation, the Night Interception Committee recommended among other steps to be taken:

(1)    That a flight of aircraft fitted with Lorenz equipment should be formed to obtain further information about German beams.

(2)    That a jamming system should be evolved.

Our Air Scientific Intelligence subsequently discovered that the German blind bombing technique had been developed ‘almost beyond what we had thought possible.’  It was considered that the German Air Force, using a revolutionary method, could ‘place an aircraft within 400 yards over a point in this country’.  So serious was the threat that a meeting was immediately convened at No.10 Downing Street, with the Prime Minister himself presiding, to discuss the situation and the possible counter measures.

Organisation of Counter Measures

Meanwhile an organisation had been set up on 18^th June 1940 under the Deputy Director of Signals ‘Y’ to investigate German beam type transmissions on 31.5 mc/s, these signals having been detected by our Wireless Intelligence service, and the last days of June were passed in carrying out investigations with a mobile van fitted with the necessary wireless equipment.  Investigation flights in an Anson aircraft were also carried out and, during the second of these, it was established that a German beam crossed the English coast at the mouth of the Humber on a bearing which indicated that its source was near Cleve.