Contains public sector information licensed under the Open Government Licence v3.0.
The text below is a transcript from images supplied by the Public Records Office of a document, reference code AIR 20/4870.
It is Crown Copyright but licenced as above. This is from the last draft version as amended on 6 May 1945.
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The Observer Corps worked silently, in the isolated places of the countryside and in the back-streets of the town; and what it did was never audible and rarely seen. But another form of defence proclaimed itself melodramatically, noisily and with spectacular effect everywhere, whether in failure or success. If too few of the public had ever heard of the Observer Corps, and fewer still understood the nature and importance of radiolocation, almost every man, woman and child in the country heard and thought it understood the guns. The lofty dark clouds of smoke by day, the starry pillars of fire by night, the neighbouring hellish roar, the distant double thunder – all these became part of the most familiar sounds and sights, sometimes alarming, sometimes comforting, of every citizen, every day and night. The A.A. batteries were in fact like the orchestra in the play.
They were, of course, much more than this. And before recounting the story of the A.A. gunners in this country in the eight months up to May, 1941, it is important for the reader to appreciate at least something of the A.A. problem.
In order to shoot down an aircraft, a shell must be fired so that it bursts very close to that aircraft. The point selected must be one through which the aircraft will pass, and the time at which the shell bursts must be the instant at which the aircraft is at that point in the sky. The gunner, with the aid of suitable instruments, predicts this point and the time at which the aircraft will reach this point. He does this by measuring accurately the present position of the target and computing the rate at which this present position is changing. This may be achieved by measuring the course and speed of the target, calculating the distance the target will travel during the time that the shell takes to get from the gun to the target (time of flight of the shell), and adding this distance to the present position of the target. This will give him a point in the sky through which he predicts the target will fly at a certain time. He lays the guns so that the shell will pass through this point and calculates when to fire the gun so that the target and the shell arrive at this point simultaneously, having set the fuse on the shell so that it functions at the correct time after the shell has been fired.
Two most important facts must now be stressed. Firstly, once the shell has left the gun the gunner can have no influence on it: if the target alters its behaviour during the time of flight it will not pass through the point predicted by the gunners, even if all of them have done their jobs with complete and absolute accuracy. Secondly, a very small error in any one of the operations of prediction may cause the burst to be some considerable distance away from the correct position: For example, supposing an aircraft were travelling at 347 m.p.h. and the speed measured by the gunners were 341 m.p.h. (an error of 6 m.p.h. or about 1.75%) and supposing the time of flight of the shell were 25 seconds, then the shell would burst 220 ft behind the target, and that looks a big miss when you see it in the air. Again, if the fuse is set wrong by one second, it will burst over 500 ft from a target flying at 350 m.p.h. So it will be seen that the most extraordinary accuracy in all stages of prediction and operation must be obtained for A.A. guns to achieve success.
One other point: it concerns the expression “the present position of the target”. A.A. work is complicated by the fact that calculations have to be made in three dimensions, excluding the problem of time which makes a fourth dimension. Thus in order to pinpoint the position of a target in the sky it is necessary to know the bearing (direction) of the target from the gunsite and also any two of the following:
· The height of the target above ground level.
· The range (distance) of the target from the gunsite.
· The angle of elevation of the target from the guns; that is to say, the angle between the horizontal and a line joining the target to the eye of an observer on the ground.
Without this information it is not possible, from one point on the ground, to locate the position of the target in the air. Before the war, the position of the target was located by measuring the bearing and angle of elevation with an instrument called the predictor, and by measuring the height with a heightfinder; both instruments being operated by following the target visually through telescopes on the instruments. It will be seen, then, that in those days the three things used in A.A. gunnery to engage targets were bearing, angle of elevation and height.
In the days before the war there were hardly any attempts made to devise means of engaging aircraft that could not be seen from the ground. Such aircraft are called “unseen targets”, and little was it thought in those days that unseen targets would be the primary targets for A.A. guns during the greater part of the war. But even in the years before the war there were far-sighted spirits who foresaw that London could, and would, be bombed by aircraft that could not be seen from the ground; who foresaw that searchlights, owing to cloud or mist, might not be able to illuminate aircraft sufficiently well for visual following on gunsites; and that bombing from above cloud would be not only practicable, but probable. These people enlisted the help of scientists and set to work to devise a means of organising AA fire against unseen targets.
It must be remembered that all this took place sometime before the war started, and that Radiolocation had hardly been heard of in those days, and that the only equipment in existence that could attempt to locate the position of an unseen target was the Sound Locator. This instrument, even if it could have been made to operate with absolute accuracy, was not able to pin-point the position of an aircraft in the sky. It could merely measure a line to the aircraft; it could not determine how far along this line the aircraft actually was. In other words, it could measure the bearing and the angle of elevation to the target, but could not measure either the range or the height of the target. However, two sound locators at different places on the ground could each measure a line to the target, and the point of intersection of these two lines would be roughly the location of the target in the sky. It was along these lines that the scientists and gunners worked for the defence of London against the night bomber.
A line of sound locators was laid out along the eastern and southern approaches to London; a second similar line of sound locators was deployed nearer to London. Inside the second, an imaginary barrage line was drawn, and the data required for the guns to be able to put shells up at any point on this barrage line were calculated and printed in a book for each gunsite. The idea was that two sound locators in the first line would plot the position and time that an enemy bomber crossed the first line, and two sound locators in the second line would do the same when it crossed the second line. By that means the course and speed of the target could be measured; the point and time that the bomber would cross the barrage line could be calculated. This point and time would be broadcast to the gunsites, and a barrage would be put up at that point by all guns in range. That was the idea, and a most elaborate system of automatic calculating machines and communications was designed and installed. The design of them bore the hallmarks of a genius although they were necessarily extremely complex and not infallible.
During the first nine months of the war when there was practically no air activity over this country, and even during the three months of terrific daylight raiding when the Battle of Britain was won, few of the public clearly foresaw the new menace: the bomber that could be seen neither from the ground nor by the pilots of night fighters in the air. But in September, 1940, as we have seen, the storm burst. London’s great and complex system of AA defence was put to the test and it failed of its complete purpose, though it did much to prevent accurate bombing. It failed because sound location could not take on a large number of aircraft; because it could not operate with the noise of guns firing and shells bursting; because the whole system was too complex, too centralized and too inaccurate. Some new science that did not depend on sound was required to enable the gunners to determine continuously the position of unseen targets, and so to enable fire to be brought to bear on them as if they were being followed visually through telescopes. The only science that could fulfill this requirement was Radiolocation.
At the end of 1939 and up to the late summer of 1940 AA Command began to receive a few – but only a very few – radiolocation instruments. They were called GL (gun laying) sets. These instruments were designed to provide early warning of the approach of enemy aircraft to gunsites. They also enabled the visual instruments on the site to be put on to the target at maximum visibility range, and finally the height of the target to be measured at the earliest possible moment. It is obvious that a target can be followed visually through a telescope at very much greater range than with the naked eye. But in order to lay the telescope so that the target can be picked up in the telescope’s field of view, it is necessary for it to be directed approximately in the right direction. In pre-war days this was done by first detecting the target with the naked eye and then directing the telescope on to it. The object of the GL was to direct the telescope on to the target when the aircraft was still too far away to be seen with the naked eye, but not too far to be seen through a high-powered telescope.
The GL measured the bearing (not very accurately) and the range (extremely accurately) of the target from the gunsite. It could not measure either the angle of elevation or the height of the target, so that by itself the GL could not determine the actual point in the sky of the target. Of course it was never originally intended that it should do this. It was always assumed that the target would be seen visually through telescopes so that the angle of elevation could be measured which, combined with the range measured by the GL and the bearing measured visually, would enable the point in the sky of the target to be continuously determined.
In December 1939 and through to the summer of 1940, AA Command received their first GL Mk. I. By August they had a few in operation – but only a very, very few; by September there were just about enough to equip half the London gunsites. But when night raids on London began in earnest at the beginning of September, the GL sets were no use unless the searchlights illuminated the bombers, and still London relied on the system previously described, for its defence against the unseen bomber. When this system was found to be unsuccessful, the GOC-in-C, AA Command called in all the scientists he could lay his hands on and told them that some means had got to be found – and found immediately – for using the GL Mk. I to locate the position of the unseen targets so that reasonably accurate fire could be put up against them. He gave the scientists just one day to get the answer.
No one who was in London on the first night of the great barrage as it was described, will forget it quickly. The courage which its great noise instilled into the hearts of all Londoners spread throughout the country like the beacons which were lit for the Armada. And that great display of gunfire took place less than 24 hours after the scientists had received their orders from the GOC-in-C, AA Command. It was not true to say that the scientists had got theanswer to the problem, but they had got an answer. The GL was used to obtain the bearing and range to the target, and a sound locator was deployed in each site to measure a rough angle of elevation. Thus a rough height was obtained, and the position of the target located approximately. With such crude means, the fire could not be expected to be other than pretty inaccurate, but it did serve as a great morale-raiser for the people and it also frightened the enemy pilots and helped to prevent accurate bombing. People living on the outskirts of London will testify to the number of bombs which fell on the outskirts and even in the open country, which is the best and only proof that the enemy was often afraid to enter London.
Once a means had been devised to enable the guns to fire at unseen targets, intense efforts were made to improve the accuracy of fire. It seemed that the only way to do this would be to produce a new and better equipment that could itself measure an angle of elevation. In fact such an equipment had already been designed, and arrangements have been made for production. This equipment was to be known as GL Mk, II. But the GOC-in-C, AA Command, was not content to sit and wait for it to come out and do nothing to improve GL Mk. I. He approached another famous scientist and told him the problem. A few days later this scientist returned to HQ, AA Command. He reported that he had got a box of tricks which he could attach to the GL Mk. I to measure angle of elevation. The box of tricks was in his car, and he was rushed out to a gunsite and told to fit it on to a GL MK. I. This he did and it worked. Orders were immediately placed for one for every GL Mk. 1 in AA Command, and very soon they began to come out from the factory.
The first few were fitted at London gunsites and tests were made. It was found that the answers were different on nearly all sites – in other words the angle of elevation measured by the box of tricks (now called the E/F attachment) was not always accurate and the accuracy varied from site to site. This set all the scientists thinking furiously. First of all they thought that it was something to do with the soil on which the GL stations stood, as the reflection of the radio wave from the aircraft hits the ground before it is received at the GL. So a geologist was employed by AA Command to go round gunsites and examine the sub-soil.
Eventually it was discovered that the slope of the ground affected the results and the condition of ground also made a difference: the answer was not the same on a dry day as on a day when the ground was wet. Eventually someone hit on the brilliant idea of constructing a false reflecting surface around the GL. An experimental reflecting surface constructed of wire netting fixed on poles was set up at HQ AA Command, and a GL was tried out on it. It showed that the result was most satisfactory and that there were no differences due to damp and changes in the weather. It was found, however, that the “mat”, as it was called, had to be exactly level, that all joints in the wire had to be soldered and that complete electrical continuity had to be maintained over the whole surface. The size of the mat was the subject of some considerable argument, and of many scientific papers, and it was eventually found that the size varied with the wave length of the GL.
As a result of these investigations and experiment, the GOC-in-C, AA Command, ordered that a mat be constructed of 390 ft diameter around every GL. The next problem was to get the material and the labour to put them up. Practically the entire country’s stock of the required type of wire netting was used for these mats. The Sappers offered to help the Gunners to build them, and very soon at every site on which there was a GL one saw a shining octagonal wire netting mat with a catwalk leading to the GL at the centre.
All this time the Hun was battering away at London and other big cities of this country. All the time the AA gunners were firing the guns all night, operating instruments that gave a sort of answer but which were nothing like accurate enough to take on, really effectively, bombers which could not be seen from the ground. All the time they were working all day, building their sites and mats and cleaning their equipment and guns.
Nor were the scientists and the factories idle, although to the AA gunners it did sometimes seem as if the rate of production of GL Mk. II were very slow. By the end of 1940 only one or two GK Mk. II equipments had come to AA Command, and from November 1940 to the end of May 1941, only twenty in all were received. Although the new GL was a better job than the old GL, its range of pick-up of targets greater, and although it measured angle of elevation without having to have a “box of tricks” attached to it, and was a more robust equipment – its accuracy was not very much greater than the Mk. I. The scientists, however, were working hard on a Mk. III equipment which was to be in comparably better than the Mk. II. It was to work on a very much shorter wave-length, it would be vastly more accurate and would not suffer from a great many technical limitations inherent in the design of the Mks I and II. These technical limitations were a source of tremendous worry to the AA gunners, for although the GL Mks. I and II enabled the position of the target to be determined fairly accurately, the accuracy was not sufficient to enable the rate of change of these positions to be measured by the predictors with anything like sufficient accuracy.
At the beginning of this chapter we saw how an error in speed of under 2 per cent would cause the bursst to be some distance from the target. Errors of 20 and even 30 per cent could be incurred owing to the technical limitations of the GL Mks. I and II. It must be remembered that the predictors were designed to work with almost perfect data provided by following an aircraft visually through telescopes: in such cases the errors in bearing and angle of elevation are only very slight – almost imperceptible. But with the GL the error could be quite large and it fluctuated from one side to the other. The predictor, therefore, faithfully followed these fluctuations and could not do otherwise than assume that the target was flying in a most peculiar manner. Thus it would predict in all sorts of unexpected directions.
These difficulties were examined by the scientists early in 1941. A special section of scientists was formed to work with AA Command in an attempt to solve these difficulties which at first looked insoluble. After an enormous amount of research work a brilliant modification to one type of predictor used on gunsites was thought of, which completely altered the method by which it got the answer. This modification was eventually carried out on all predictors of this type, although it was a slow and laborious job producing and fitting the new parts.
During the period under review, however, these modifications to the predictor had not arrived, and GL sets themselves were few and far between, so resort had to be made to a far less accurate method of fire – putting up concentrations of shells from as many guns as possible in the path of the approaching aircraft. The sky is a large place, and an aircraft very small, and it is not surprising that this method had very little lethal effect on the enemy, though it undoubtedly played its part in deterring and preventing accurate or aimed bombing. The relief with which the advent of the more accurate fire control was later welcomed can be well imagined.
By the end of May 1941, the AA gunners had completed nine months of continuous battling against the night bomber. They had been firing almost every night, and all night from sunset to sunrise. During the day few enemy aircraft were seen, but the AA gunners had no time for sleep, for the ordinary duties of the soldier had to be attended to. Guns had to be cleaned, ammunition replenished, sites looked after, huts and emplacements built, mats built and maintained; training had to be carried out and new drills to meet the new conditions had to be learnt and practiced. All the pre-war conceptions of AA gunnery had gone. The slow targets, flying at 180 m.p.h., and about 10,000 ft, that could be seen and followed visually, was something that now just did not occur. The target that had to be taken on was one at 18,000 ft height, flying at 250 to 300 m.p.h. one that could not be seen at all by the human eye. This meant a new technique – a new kind of eye – new instruments, new guns that propelled the shell with greater speed, new fuses that functioned with greater accuracy. Only when they became available was AA gunnery able to keep up with the developments in aircraft and in night bombing technique.
As for the skill and rapidity with which the AA gunners had been able to put into effect the new techniques, let the results tell the story.
At the end of 1940 it required an average of 9,000 shells to destroy one “unseen” German bomber; by the spring of 1941 it required only 4,000. Moreover, this much more accurate shooting was achieved in spite of the much more violent evasive action which the German pilots learned to take.
From September to November 1940, the guns shot down 87% of all German aircraft destroyed over Britain at night. This percentage gradually decreased, of course, as fighter successes improved. From December 1940 to February 1941 it was 80%. With the great up-surge of fighter successes in March, April and May, the guns shot down over 30% of the night raiders destroyed over this country. In addition to these confirmed figures of destruction of aircraft, there were also the unknown advantages of severe damage to the aircraft and crews who managed to stagger back to their bases – it was estimated that, for every raider destroyed, some 40 were more or less severely damaged.
In spite of the seemingly impossible problem which the gunners had been presented, they had solved it. Of the several reasons which led the German High Command to cease large-scale air operations against Britain in June 1941, not the least was that of the A.A. guns.
There is one statistic which emphasises the true greatness of the achievement. The number of night sorties by German aircraft over this country, almost all “unseen”, from September 1939 to May 1940 is almost exactly the same as the number of R.A.F. bombers sent over Germany during daylight from July to October 1944. Yet although the R.A.F. bombers flew in daylight, and the German A.A. gunners had four years of experience and development behind them, the number of German raiders shot down by A.A. guns alone during the former period was greater than the total number of R.A.F. bombers lost during the latter to all the German defences, including their fighters.
Meanwhile, on the Searchlight side of AA Command the same problems were being faced. True, the problem is not quite so complex. Whereas a shell takes time to climb and there is inevitably a short pause between one shell and the next, a search light beam is continuous.
Those who have seen the remarkably good contemporary work of searchlights in finding and holding enemy aircraft, in spite of most violent evasive action by the pilots, must wonder why better results could not have been achieved in the winter of 1940/41. The answer lies once again in the difficulties of using sound as a means of locating the aircraft.
At the time the battle opened searchlight sites were arranged so that they formed a cordon round the most vulnerable part of Britain. They were, for the most part, about 3 to 4 miles apart and so arranged that no gaps were left. In many of the more important centres they were much more densely packed. Trials held in 1936 showed that this closer spacing would have been better everywhere but that the extra number of men required would have been enormous.
As it was, nearly all the searchlight units in the country at the out-break of war were Territorials. Some were the original Searchlight Regiments of the Royal Engineers; some were converted Infantry Regiments; a few were newly formed in 1938. By Autumn 1940 all were Royal Artillery and a great many new Regiments had been formed by using a selected body of trained and seasoned men from the older Regiments to start new ones: so gradually bring in more and more untrained men as they were called up.
Like the rest of the British Army, they all suffered the tedium of inaction. Lack of an enemy to fight and new living conditions producing a feeling of frustration. A large proportion of them were townsmen who found, like evacuees, that country life can be trying in long doses until one gets used to it. A searchlight site usually consisted of about ten men, a searchlight, a sound locator and a lorry in a field. The men were lucky if they had a hut; if not they had a tent.
Both the men and their equipment, at the time the Blitz started, were capable of dealing with the sort of aircraft that had been provided for their training in peace time – the Airspeed Oxford and the earlier Blenheims. But neither could cope with the newer types whether Hurricane or Messerschmitt, nor with the constantly changing enemy tactics. In the early days of the battle quite a lot of the enemy aircraft were successfully held in concentrations of searchlights; the enemy answered that by flying higher and faster and by manoeuvring more violently. That the pilot hated being held by searchlights is clear – our own pilots feel the same way about the German searchlights. It is like being in a dark room with a torch shining on you, knowing that somewhere in the darkness is a man with a gun. Your greatest desire is to get out of the light.
The night fighter also has his problems; he must be quicker than the enemy: he must be in the right place at the right time. In 1940 most of the fighters were designed for day work, most of the pilots trained in day flying; it took time for men to learn by bitter experience and patient triumph the very difficult technique of night interception. In those days pilots took off and patrolled a line, waiting to see a cone of searchlights, so often to see instead what they called “a forest of waving beams”.
The reason for this was of course that any sound locator, however elaborate, could only tell the man on the ground where the target WAS when it made the sound. While the sound is travelling slowly down, the aircraft is flying quickly on. Nor is it bound to keep the same height, course or speed.
In order to solve this problem, A.A. Command improved their sound locators; they made bigger and better trumpets to collect the sound; they put the trumpets further apart to make them more accurate; they fitted a most ingenious device which automatically told the operator when the course of the target changed; they fitted an even more ingenious system of electric listening which gave greater accuracy and relieved the listener of some of the enormous strain of concentrating for minutes at a time on the sound of one aircraft – a strain difficult to imagine to those who have never used a sound locator. But nothing the wit of men – even of scientists – could devise could really cope with the changes of speed and height and course.
In his early encounters with searchlights the enemy had learned that it paid him to keep clear of them. Enemy pilots took to flying higher for that reason, and of course to make it more difficult for guns, whether on the ground or in the air, to reach them. This meant that on the average night in this country it was very difficult to see the aircraft even when it was in the beams. When searchlight beams look particularly brilliant it is because they are wasting their brilliance on moisture and dirt in the atmosphere. It is essential that light should reach the aircraft and to be reflected back. Accordingly, this winter, searchlights of more powerful beam were installed: the less powerful 90 cm projectors being slowly replaced by 150 cm projectors of more than twice the candle power – actually 510 million candlepower.
Despite this improvement in the equipment and the enormous efforts being made by officers and men to produce the answer by training and still more training, the results were disappointing: so disappointing in fact that the night fighters lost faith in them and planned new methods of “unseen shooting” using radar. The men on the searchlight sites in some cases were not allowed to put their beams up at all for some weeks: in their disappointment those men saw the future as literally black.
Meanwhile, quick and very active steps had to be taken to find at any rate a temporary solution. Pilots grumbled about the forest of beams. The supply of the improved sound locators was inadequate. The number of large projectors was limited. So, to deal with all these difficulties at once, it was decided in November 1942 to “cluster” – that is, to use only one out of every three sites but to put all three searchlights on that site. This produced a carpet of cluster sites about 6 miles apart, with one large and two small projectors on each site. The large one was directed by the latest type of sound locator fitted with course-finder and electric listening; the two small ones followed the “master”. So the fighter pilot saw what appeared to be fewer, but much brighter and better directed beans. These sites could also be giving better supervision. Their communications were better. Control was simpler. But although some improvement was obvious it was clear that sound-location remained the searchlight’s greatest problem.
It was the scientist who finally solved the problem. By applying radio-location to the searchlights, so that operators no longer relied on sound for their information, the effective power of the light was enormously increased. Unfortunately these improvements did not come until the bitterest part of the night battle was over.
If the problem of shooting down an aircraft by gun-fire at night can be compared with shooting with a rifle at a bee in a dark room, then the problem of finding an aircraft in the night sky, without radio means, is rather like trying to catch a small moth in a forty acre field.
The sky is an enormous place. During the height of the Battle of Britain, when it might sometimes have seemed that the sky was full of planes, the density of aircraft over the battle area was 1 in 700 cubic miles. The Germans at this time were sometimes sending over to England as many as 800 aircraft in a day, mostly in the concentrated area of south-east England. As we have seen from the late 1940 night raids on Coventry, Birmingham, Bristol and other industrial cities, the average number of German night raiders was, on the larger raids, about 300. But it was often less, and the area of attack was much wider than in the day raids. If we put the number of raiders at 200 and multiply the area of attack only by four we shall get some slight idea of the enormous cubic space of night sky in which a pilot might have to search for a single plane.
Now there are two very different conditions under which night-fighting can take place. The first is on dark nights, when there is no moon at all; and the second when the moon is up, that is from the first quarter, through full moon, to the last quarter. When a pilot takes off on a really dark night he will see practically nothing outside his cockpit until he has climbed to a considerable height and he will then see, if the atmosphere is clear, an horizon. In these circumstances most of his flying must be done by instruments, which entails a great deal of concentration. But on a moonlight night the problem is much simpler. The pilot is then able to see things on the ground before he takes off and once he becomes airborne he will be able to see the ground fairly clearly. The problem is in fact much like that experienced in the black-out. One can see hundreds of yards, and may even read a newspaper, in full moonlight. In the darkness one can see for hundreds of inches.
In exactly the same way there arises the question of how far a pilot can see out of his cockpit at night. It has been found that when there is no moon he will be able to see objects within a range of up to about 1,000 feet; whereas on a moonlight night he should see objects that are about 3,000 feet away. These distances are approximate, and may vary, but they bring out the point which is the essence of the whole night fighting problem. This is the absolute necessity of bringing the fighter close enough to the enemy to enable the pilot to see it, engage it and ultimately to shoot it down.
All this had been realised before the war began. It was realised too that to send pilots roaring about the night sky searching for enemy aircraft in hundreds of cubic miles of space would be worse than futile. Some means had to be devised by which a pilot could be controlled and directed to the known course of an enemy raider. The solution to all of this was radiolocation.
At the end of 1940 the problem has not been solved, and the country was in a desperate situation. Winter had just begun. The snows of a bitter January piled up on icy ruins in practically every large city in the country. It was felt everywhere that if the fire-blitz of December 29 could be repeated for a week there would be no knowing the consequences. In the months of October, November and December 14,715 civilians had been killed. Yet for the last six months of the year a monthly average of only 20 night-raiders – mostly by A.A. fire – had been destroyed. But what the living had lost in property, work, homes, faith, heart and tears was something that no statistician has ever computed. It was these things that made up the life of the nation and it was these things, if the night bombers were not defeated soon, that would come crashing down as the pillars of the temple had come crashing down about the blinded Samson. After months of such beating it was reasonable to assume that no nation could hold up.
It is not too much to say, therefore, that the year 1941 opened as a race against disaster. Perhaps it could be truer to call it a prolonged series of disasters – fire after fire, blitz after blitz – which might finally reach such an intensity of chaos and destruction that the remedy we found against it would, however effective, prove too late. We not only needed a remedy therefore; we needed it very quickly. We needed it desperately.
Having summarised the problem like this, with the enemy already very far ahead in the race, let us look at what the scientists, the Air Force experts and the Government were doing. As the blitz increased in intensity they too had increased the pressure of their efforts to defeat it. They were working night and day.
Before the war it had been realised that the geographical position of England in relation to the continent made it extremely vulnerable to attack. Our position was dangerously simple, and was roughly this: if a hostile aircraft approached the north-east coast of Kent, for example, and its position as it crossed the coast was immediately communicated to the headquarters of Fighter Command, its speed would be such that it could complete its mission to London, bomb the city and be flying homeward over the coast before Fighter Command could dispose its defending aircraft. Such a position could have meant that Fighter Command would have had to keep, all about the coast of Britain, constant standing patrols of fighters on the watch for approach raiders. Such a form of defence would have been, of course, enormously expensive and in practice impossible.
It was therefore imperative to have a system of warning that would detect the approach of an aircraft at least 35 miles before it reached our coast. This warning would give Fighter Command time to dispose its defending fighter squadrons, and it was this warning, given by means of radiolocation, that had enabled the Battle of Britain not only to be won but in fact to be fought by us at all.
The information given by this system was accurate enough to enable a fighter aircraft to be put within approximately 5 miles of an approaching aircraft. This accuracy was quite sufficient for daylight interception. But it was clearly quite inadequate for night interception where an accuracy of feet and not miles was essential. Under the system used for the control of fighter aircraft by day it does not necessary to get R.D.F. (radar) information on the fighter itself, because its position could be fixed by ordinary wireless methods. It was also impossible to get a greater accuracy than ± 5 miles under such a system, since both the R.D.F. and wireless fixing systems had their own peculiar inaccuracies which bore no relation to each other. But it was seen that if the fighter could be controlled by the R.D.F. station that was also “seeing” the bomber – i.e. if both enemy and defender could be controlled from one point on the ground – then the system had the greatest possibilities for night work. A fighter could then be told where he was in the darkness, and could be guided onto the very tail of the enemy. He would no longer be groping about like a man trying to catch a moth in a dark field.
It was towards the perfection of this idea that scientists and others had been working literally night and day since 1939. And as the result of the long and often arduous experiments they had had some success. They had already produced a new kind of radio station, as distinct from a purely detecting station, known as G.C.I, – Ground Control Interception. This proved an immediate success and enabled a ground controller to place a fighter aircraft within approximately one mile of the aircraft being intercepted.
But one mile, as we have seen, is more than five times the distance a pilot can see on the darkest night, and it is the limit of his vision at full moon. It was this gap that had to be bridged, and the solution of the problem seemed to be in providing the pilot himself with some instrument by which he could bring himself to within visual range of his target after Ground Control had got him as near as possible. This instrument too was produced and when war began it was already being used, experimentally, in Blenheim aircraft.
In January 1941, therefore, experiments had been going on for two years; a method of control from the ground had been evolved; and the necessary apparatus had been provided for the aircraft. Yet in practice there were few results. The Intelligence Officer of a night-flying squadron could only hold up his hands in despairing farewell to the year 1940, and in January of the New Year, though the blitz continued intensely, only four night raiders were to be shot down over Britain, and these in fact by day fighters operating at night. The scientists had provided the things demand by theory, and yet in practice we faced failure. Why?
One of the first causes of failure, or at least delayed success, was undoubtedly the Blenheim itself. There were several other causes, and we shall see in a moment how they retarded the progress of things. But the truth with the Blenheim was that it was once again like the parable of putting new wine into old bottles. The difficulties are best illustrated by two combat reports of a night-fighting squadron. They are taken from the beginning of the blitz in 1941.
(1) “At about 22.20 I was patrolling at 5,000 feet. I was ordered by control to climb to 15,000 feet and investigate any searchlight activity. I was flying west at the time and was informed that one bandit was crossing my path from the North.
I then saw searchlights under the clouds which were at 8,000 feet approximately, and up to 1,000 feet thick, and went to them in a Northerly direction. I found nothing. Just after tuning, my operator reported bandit dead ahead about four miles. I was already going at full boost, and perceived the E/A for 10-15 minutes at full speed, out to sea. I was unable to gain and could see nothing ahead although the moon shone brightly. I then noticed my port engine was badly overheating and was obliged to give up the chase.”
(2) “I was flying on night patrol line at 11,000 feet in Blenheim. I was ordered to investigate a concentration of searchlights south-west of Ringwood. I flew into searchlight but was unable to see an E/A illuminated. I then made a right hand turn and flew into the concentration from the North. My operator then reported an aircraft on same course at approximately same height about three-quarter miles distant dead ahead. I opened up and gave chase. After about five minutes the operator then reported that although we were still on the tail of the enemy he was flying faster than we could. Therefore I abandoned the chase.”
The two stories have the same point. In the second the pilot goes on to say that none of his interception apparatus gave the slightest trouble. Both pilots were able to pick up, as scientific theory said they could, an enemy aircraft; and the ground control was correct in its information. Yet the enemy on both occasions escaped through superior speed.
It was clear that the best interception in the world would not, at this moment, have helped us. It was exactly as if the most expensive radio equipment had been fitted to a police patrol car with the top speed of 40 m.p.h. The bandit could be found, pursued and even seen, but there was not the slightest chance of his being caught.
We have already seen how, at the end of 1940, we had only 10 specialist night-fighter squadrons; and how two of these were equipped with unsatisfactory aircraft, and two with Blenheims. We see that the Blenheims were opposed to aircraft too fast for them; and we see why, also, mere quantity in aircraft is not in itself a guarantee of successful defence. A hundred squadrons of Blenheims, each fitted with interception apparatus, could not have improved our desperate situation.
You may ask why the new apparatus was fitted to Blenheims, already obsolescent, and not for example to Hurricanes, which had so magnificently helped to win the day battle, and which were more than 100 miles an hour faster. The answer is that the interception apparatus needed at that time an aircraft carrying a crew of more than one. Its lay-out and working was such that the pilot, concentrating on his flying, could not do all the work on it himself. He needed an observer, through whom all information from ground control was diffused. Through the observer the pilot would get the final and refined directions that enabled him to kill. We shall see, presently, how this necessity was in itself another cause of difficulty and failure.
There were in fact difficulties everywhere. Fighter Command had been forced to use Blenheims in the early part of the war because the only other aircraft of requisite night-fighting qualities, the Beaufighter was not then ready. There was in fact nothing wrong with the Blenheim simply as a night-flying aircraft. Its limitations as a night-fighter were lack of speed and fire-power.
Finally the Beaufighter arrived. It brought its own problems, and instantly created others. Its teething troubles were considerable. Its serviceability was low. It had all the promise of the excellent aircraft it has now become and yet it remained, for some time, so unsatisfactory that it was even called by one expert “a thoroughly bad aircraft”. Also it was a large aeroplane, weighing about ten tons, and consequently could not be flown very slowly when coming into land. This meant that when a Beaufighter pilot had to circle an aerodrome his circuit was some miles in radius. Unless some very special form of lighting was provided he could soon, therefore, lose sight of his landing ground.
This in itself created a fresh and enormous problem. Each difficulty indeed continually created another larger than itself. The interception apparatus created the need for a special aircraft’ the aircraft for a special aerodrome; the aerodrome for a whole extensive building plan for a chain of such aerodromes, specially illuminated and controlled, across the country. This in turn created the need for trained controllers, their staff and their equipment. These too were useless without trained pilots and observers and efficient maintenance staffs. And in the dark days of January 1941 perhaps not one civilian, looking up into the night sky and wondering where the night-fighters were, ever thought of all these things.
Meanwhile, as these difficulties grew out of each other, the inner difficulties also increased. One of the greatest of these was the old one that theory and practice, especially in war, are not quite the same thing. What happened, again and again, was that equipment which was very satisfactorily on the laboratory bench immediately gave very serious trouble in the air. This is quite understandable. Scientists are not normally engineers. The lash-up equipment produced by them, theoretically excellent, works well under cover, in warm dry conditions. The fact that it had to be hastily installed in aircraft parked in the open air of an English winter, subject to damp, changing temperatures, great vibration and all the hazards of flying, caused it to develop altogether unexpected tendencies.
One of these unexpected tendencies, unforeseen by the scientists, was for the air interception apparatus sometimes to catch fire. This fact retarded enthusiasm for any other virtues it may have possessed, and the early interception sets were in fact described as heart-breaking. That did not necessarily mean that they were bad. They were, of course, hurriedly produced or required to give a great deal of information. Much of it was the result of a complicated system which, to the people of an earlier age, would have been very like magic. But this information, though given on the laboratory bench, was often lacking, or was entirely inaccurate, in the air. For a time indeed the gap between theory and practice seemed an insoluble thing. In a moment we shall see how it was overcome.
Meanwhile there was a related problem which rose entirely from the extreme desperation of the moment. The situation all through the autumn of 1940 had been, and still was at the beginning of 1941, much the same as that of a group of men standing on a disintegrating precipice. Between them and the safety of the other side lay a bottomless pit. The only means of escape was to invent some means of conveyance for themselves to the other side of the abyss. Since the precipice was slipping from under their feet it was natural that their efforts should be a little desperate. The desire to put into practice the first remotely possible theory was very strong. The desperate moment called for the desperate remedy.
This was something of the position in early 1941. The Luftwaffe had been raiding us for many months now by night, inflicting immense damage and distress. It was very small comfort to the British people to learn, as an aeronautical journal remarked, “so ends a year with night-bombing on both sides, and neither side has any efficient defence against it.” Nor was it of any greater comfort to Fighter Command. It was quite natural in fact that they should have shown a very urgent desire to get the interception apparatus installed and working and to show some results.
All this, instead of speeding up the work, simply retarded it. Night after night pilots were flying and searching for bombers without results. The information given by the interception apparatus was often, as one of them has said, “hopelessly inaccurate”. The most extraordinary theories were propounded to explain these operational failures, but the real reason was really a very simple one. And it was only discovered after the whole theory and apparatus of air interception had been almost condemned, even in the highest quarters, as a complete failure. What was really the matter was not that the theory was wrong, or the apparatus wrong, or even that the aircraft was wrong. It was simply that too little allowance had been allowed for training. It was only after the Air Staff and the research scientists had grasped this fact and had insisted on properly conducted day trials that the defects of the interception equipment could be found and demonstrated. As soon as this could be done the gap between theory and practice began to be closed.
So by the beginning of 1941 there was a slight hope of better things. Training was being intensified’ apparatus was being nursed out of its teething troubles’ the Beaufighter was improving’ more aerodromes were coming into use’ more ground staff being trained. And the scientists, profiting by deficiencies revealed in practice, were working harder than ever, on clearer lines.
But before we look at the results of all this co-ordination let us go back and look at the blitz over Britain. Its power was still largely unchecked and the situation caused by it as desperate as ever.
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