Fred Hoyle An observer of the world and a ponderer on its problems ...

… After going through this process of responding to an air-raid siren several times, you wondered, as you crouched under your table, what the Germans thought they were doing. They had occupied a fair fraction of the time of their best aeronautical and engineering brains to design the bombers that were now throbbing overhead. A big manufacturing effort had then been made to produce them. They were piloted by the cream of German youth, some of whom would not return from the present mission. And to what end? To the deaths of an average of forty ordinary British civilians per day. It seemed an extraordinarily convoluted and expensive way of killing people.

Those who remain anxious to support the high-explosive myth might argue that the Allied raids of later years were much more cost-effective in killing ordinary people. But this would be yet another illusion. The 90,000 who are said to have lost their lives in the British attack on Hamburg did so, not because of high explosives, but because the city of Hamburg contained a lot of wood and other combustible materials. Hamburg and other German cities were chemically susceptible to destruction by fire. The bombers were, in effect, simply so many matches. Cities made of sand or concrete or mud would not have experienced disasters of such magnitude.

Pursuit of the high-explosive myth is the surest way for a nation to beggar itself. Excessive expenditures on the Navy early in the twentieth century set off the decline of Britain. More recently, the Soviet Union was brought to a similar pass. And even the United States, which has the world's strongest economy, has been placed under considerable strain, running itself seriously into debt in pursuit of the myth.

A naval bombardment is an order of magnitude more effective than bombardment by land-based artillery. In a comparison between Nelson and Napoleon, Nelson's cannon weighed ten times more than Napoleon's and were ten times more accurate. They could be moved by sea from place to place at ten times the speed and at one-tenth the cost. Yet, even at sea, high explosives are not entirely overwhelming. The sinking of Germany's powerful battleship Bismarck required immense and sustained gunfire from the King George V, the Rodney, and the Dorchester, even after the Bismarck had been disabled by a torpedo from a tiny swordfish plane from the Ark Royal. The contrast between the effectiveness of the torpedo and the relative inefficiency of traditional gunfire requires explanation.

Compared with the amount of energy released by a nuclear explosion, the amount released by detonating a quantity of a chemical explosive is very modest. It is about the same as that released in burning a lump of coal of similar size. The damage comes from the speed of the release, which causes a destructive pressure wave to spread out from the explosion point. In air, the strength of the blast falls off rapidly with distance from the explosion point, essentially as the square of the distance. It is this rapid falloff that explains why bombardment, to be effective in war, must be heavy enough for the explosion points of shells and bombs nearly to overlap each other. An explosion in water is different, however. In water, the blast wave falls off less rapidly, more as the distance than its square. Thus, explosions in water are a whole order of magnitude more damaging than explosions in air, which explains the efficiency of the torpedo that crippled the Bismarck, and it explains also the grim sense of danger everybody felt in response to the threat of the U-boats. Where U-boats were concerned, however, what was sauce for the goose was sauce for the gander. Just as torpedos from U-boats delivered their explosive energy into water, so did the depth charges with which the Allies hoped to destroy them. It is said that, of those Germans who were drafted into the U-boat service, only a quarter survived.

As I studied the Admiralty reports during my first weeks at Nutbourne, it was gradually borne in on me how extraordinarily fragile ships are and how vulnerable they are to underwater explosions. I could see that everything possible was being done already to protect ships against submarine attack, but could anything be done about attacks from the air? The Bismarck had not yet been sunk, but it was already apparent that torpedo attacks from the air could, on occasion, be even more serious than underwater attacks. This indeed was to become very apparent in the early spring of 1941, at the time of the Battle of Cape Matapan, when far too many British ships were sunk from the air in their efforts to assist army landings in Greece and Crete.

Our ships had been provided with early-warning radar-Type 79, it was called. A ship's captain could therefore know an air attack was coming and could greet incoming enemy planes with all the barrage his ship could throw up into the air. But, for the reason I have just given, such barrages were more impressive in appearance than in their results. Guided ship-to-air missiles were still decades away, although their possibilities were being contemplated even at that early date. The best defense against air attack was interception by planes launched from aircraft carriers, but aircraft carriers were large and ungainly in shape and were themselves seriously vulnerable to attack in the same way. In the autumn of 1940 the balance between the defensive capabilities of carriers and their exposure to attack lay in favor of the enemy-or so it seemed to me as I read the Admiralty reports during my first days at Nutbourne.

The reports made it clear that, if each of our intercepting planes could know the altitude of an attacker as well as its range, the balance of advantage might be changed. Knowing the altitude could make the difference between attackers being driven off and carriers being sunk. Unfortunately, altitude information had not been a requirement when Type 79 radar was designed, and the hardware could not be modified to provide it in a direct way. But could the information be provided indirectly? It was from a report on the aerial design of Type 79, written by Ross, that I got the idea that eventually solved this problem. ...

Cockley Moor,
Dockray,
Penrith,
Cumbria



Professor R. V. Jones. F.R.S.,
Department of Physics,
The University,
ABERDEEN.
3rd July 1978

Dear R.V,

I have just finished reading your book 'Most Secret War' with great interest and pleasure. The trouble (from your point of view) is that it has awakened a flood of memories, which I shall probably feel impelled to set down in what I expect may turn out to be a long letter.

In 1939 (although not now I think) I was quite a bit to the left of your own position. My father fought in the first world war, for three years in the trenches as a machine gunner. This made him caustic of government and of high-ranking service officers - a view which you almost arrive at in your post-1945 chapters. Not all my father's cynicism rubbed off onto me, however, but some of it did, especially after the Nazis were permitted to enter the Rhineland in 1936. These views stopped me from pressing myself into 'war work', as I think we used to call it, although if there had been anything effective in the offing, doubtless I would have been glad to do it. I remember a tea-break in the Cavendish just after the German occupation of Czechoslovakia, when Philip Dee remarked that the time had come for us to have a bit of a go ourselves. I remember agreeing with Dee quite strongly, but owing to somewhat odd circumstances I didn't happen to go with the Cavendish group to TRE in 1939.

To that point I had been a student of Rudolf Peierls, who had recently left Cambridge to take up a professorship at Birmingham. Partly because I preferred to continue in Cambridge, and partly because Cockroft, Dee and Bennett Lewis intervened rather vigorously in a priorities issue on my behalf, the connection with Peierls was broken. After a few months with Maurice Pryce, who then left for Liverpool, I ended up (remarkably enough) with Paul Dirac as research supervisor. This I think led to my being classified as a similar impractical type to Dirac himself (actually Dirac was very practical - he had been an engineer as an undergraduate). At all events, nobody was concerned to approach me concerning the war until mid-1940, when I had a letter from Brundrett at the Admiralty.

In the autumn of 1940 I therefore found myself in what later became Admiralty Signals Establishment.The change from Cambridge was a headlong descent into an intellectual pit, like the descent of Satan from Heaven. From the airy realms of quantum field theory, I found myself surrounded by electrical engineers who would tell me next to nothing of what they were doing (later I found this had been deliberate policy). Conscious, for the first time I think, of the appalling deficiencies in my knowledge of classical physics, I remember spending a week sitting in a hut on the south coast, about halfway between Portsmouth and Chichester, reading Abraham and Becker's Classical Theory of Electricity and Magnetism from cover to cover, thereby hoping to pick-up some faint clue as to what the chaps around me were doing.

This brings me to the first point I want to make about your book, the problem you had with 'experts' about radio diffraction around the Earth. Within a few weeks I fastened at last onto a worthwhile problem. Already operating in the Navy there was an early-warning radar set operating between 7 and 8m (RDF 79 if my memory is right). It had no ostensible means for determining the height of incoming enemy aircraft, however, and this was felt to be an increasing handicap. So I looked into the question of whether there was any simple way of distilling the required information from the existing equipment. It was soon obvious that, if a set were reasonably tuned, the maximum range of detection of a plane gave a tolerable indication of its height, assuming the height was not too small. I mention this to show that range was a matter much in my mind. We were indeed detecting German aircraft, say at 15000 feet, from a distance of 50 miles or more. If this were so for 2-way radar transmission, it would immediately have been clear to people concerned with RDF 79 that the Germans could surely use a single-way beam at frequencies between 30 MHz and 50 MHz from distances of 200 miles or more.

Here I am assuming that the incoming German bombers would fly at about 25,000 feet. What I can't understand about the claims of the 'experts' is why it wasn't understood that diffraction effects could be adequately reduced by the planes simply flying high enough. For ranges up to 200 to 300 miles there would be no technical problems in achieving the necessary height. And why did the 'experts' not do the experiment of putting a transmitter in one of our own aircraft and simply measuring the received signal strength at ground level as the aircraft flew out to 200 miles? Perhaps they claimed to have done this test, but hadn't done it properly.

It is true that diffraction problems were something of a black art at that time. Everybody as I recall was given to using an expansion due to van de Pol, an expansion that was woefully slow in its convergence. A year or so later we became entirely exasperated with this situation. Maurice Pryce, who had also landed himself in ASE, gave a magnificent rediscussion of the general problem, which led to a much more rapidly convergent series. Cyril Domb, who was working for me by then, did extensive calculations using the Pryce expansion, from which we constructed an easily read set of about a dozen graphs, using which one could solve any radio diffraction problem from 10m down to 10cm in a few minutes. I imagine this work, which was of course sent to the Admiralty Scientific Directorate in London, was not passed any further.

Although I ended in 1945 only one step from the top of ASE, I never at any time saw anything further of the Admiralty Scientific Directorate - anything after my one meeting with Brundrett. I remember being frequently irritated and puzzled by the nature of the connections of ASE with the Admiralty. Again as I recall, we derived our entire authority (e.g. for placing orders with manufacturers) through Naval Officers, first in Portsmouth and later in Haselmere. The head of ASE when I joined was C.E. Horton, who I think deserves much of the credit for pushing through the RDF 79. The RDF 79 remained in service to the end of the war. No ship would consent to have it removed, and if by any chance it was U/S for a while, everybody on board became jumpy. In retrospect, and particularly after reading your book, I suspect it must have been Horton who saw that the only way to get anything done was to short-circuit his superiors in London, and this he managed to do by routing authority through officers active in the Navy. I now realise that ASD gunned for Horton perpetually. Indeed Brundrett warned me against him at our one meeting. Horton survived because he was supported by the Navy. All our connections were thus horizontal, with daily contact directly to the Navy, and none at all so far as I could see with Whitehall. Still again and in retrospect, I wish I had done more to get to know Horton personally. After the war, although he must then have been fifty, he left a comfortable pensioned job, to become managing director of a small electronics company in the Ipswich area. For many years I used to get letters from him deploring what you call "The Year of Madness" and its consequences.

After an organisational shake-up in 1941, I found myself the head of a small investigative group. We were never more than six, we were about as apparently untidy as you imply your group was, and we got through a great deal of work. After the war, four of the group eventually became Fellows of the Royal Society - Bondi, Gold, Domb, as well as myself. I believe everything you say on the effectiveness of the small group. The trouble with it of course is that in proportion to its success it attracts enemies, and being small it rarely has the political strength to survive. The war ended soon enough to prevent my group from being splintered, but it would not have survived for another year. Otto Böhm was never a member of my group but I worked very closely with him for more than a year. I don't know if the name means anything to you, but in case it doesn't I will explain that Böhm had been managing director of the Telefunken Company. Although Jewish, he had rather surprisingly been left unmolested in his position until very late, for the reason that as well as being an experienced businessman he was also a splendid scientist. Although in his sixties, he took up the fine detail of technical work again, to the point where every aerial put out by ASE after 1942 was of Böhm's design. Unlike the older established scientists from universities, whom we came to think of as a joke (I can confirm that I never saw any one of them do much that was significant), all we young people had an overwhelming respect for Böhm.

I came into the office one day to find him in tears. By way of explanation he showed me an an Army report. Two months earlier, the Army had asked us to design a big 10cm aerial to cope with sneak bombing raids on the south coast. We were asked because we had just beaten TRE to the production of the first operational 10cm radar. (We beat TRE largely because we had a superb co-ordinator. His name was Langdale. In peacetime he was managing director of Younger's Brewery.) As a big rush-job Böhm had designed the aerial in a week-end. According to the intelligence report, a bomber had come in low and its stick of bombs had fallen directly on a school with several hundred pupils. But in the 4 minutes, between the first warning from Böhm's aerial and the dropping of the bombs, the pupils had all been shepherded out of the classrooms into the school shelters, and everyone was safe. I still remember how, without being able to speak, Böhm thrust the intelligence report into my hand.

I assume from your chapters on German radar that you never talked to Böhm. If you had, I think he could have told you a lot of the things you wanted to know. He himself while at Telefunken played a considerable role in the design of the Würzburgs. Of this he spoke often, but he knew much else besides, because (as he told me) the Germans had tended to freeze their designs rather early, at least until the later stages of the war. I believe Böhm arrived in England as late as 1938 (although it might have been in the latter part of 1937). He was immediately given a handsome retainer by the Marconi Company, but this was not done, as he soon discovered, because Marconi wanted his services, but because the retainer prevented hIm going to any of Marconi's rivals. Probably the Marconi directors thought that their service contracts might be adversely affected if it was seen that a German was working for them, and as Böhm began to insist that he be given something useful to do the directors eventually had the idea of sending him to the Admiralty itself. At all events, Böhm used to complain to me that he had tried repeatedly to pass on what he knew of German radar, and yet so far as he could determine nobody was interested (except me).

If it is really the case that you were never informed about Böhm, then the behaviour of the Admiralty Scientific Directorate was highly reprehensible.

Your passages about the lack of precise performance figures rings an enormous bell in my head. One of the jobs of my section was to interpret service requirements in terms of electronic hardware. The Navy would give us their requirements and we would next calculate what size of aerial, what power of transmitter etc., would be sufficient to meet the requirements. We could not afford to be overgenerous in our estimates, because the size of its aerials could have a significant effect on a ship's top weight (or at least the ship designers were always telling us so). The game therefore was to pare things to reasonable practical limits. After being bitten once or twice (i.e. after a couple of boobs) I found that all our electronics people were making errors of 1 to 2 db. The aerials were 1 to 2 db worse than I was told, so was the feeder system, and the transmitter, and the receiver ... There was nothing for it, since nobody else would do the job, but to set up our own attempt at precision measurements. Tommy Gold took over this aspect of the work, opening up an attic at King Edward's School, Witley for that purpose (by then ASE was occupying the buildings of this school). I mention this small development in detail for as an outcome of it we were I think the first group to obtain a solution to the Window problem.

I was delighted to understand after more than thirty years the ins-and-outs of the Window story. I still remember my profound amazement when I first read a short one or two page report on Window, amazed at the Most Secret marking of the report, and amazed when Horton told me that it not only said Most Secret but I must really treat it as Most Secret. So far as aircraft were concerned our thoughts had always been of defence, but I felt certain that if the problem had been turned round for us, to confusing instead of assisting the defence, we would surely have come up with the Window idea. Hence my astonishment at why it should be so very secret, literally to a point where Naval officers spoke in whispers almost when they mentioned it.

We had thought of the Doppler shift in connection with observing aircraft through ground clutter, but had regretfully concluded that we couldn't control frequencies, especially of the local oscillator, accurately enough. One of our receiver chaps wanted to have a go at the problem but the rest of us were pessimistic at that time. The first solution came otherwise.

One of the big unknowns in assessing radar ranges against aircraft was of course the reflectivity of the aircraft itself. In the early days we dealt with this problem by calibrating equipment against a trial aircraft. But then there was trouble with different aircraft, and additionally we were always being given dark stories by radar officers, about aircraft that hadn't behaved as we said they should in our manuals. For a while we put these stories down to improper maintenance of equipment, especially as they always seemed to involve cases where aircraft had somehow slipped through the radar net. Eventually I became fed-up with the nagging uncertainty of the situation, and decided to lay the ghost at last to rest. Together with Tommy Gold, an experiment was designed in which a receiver with fast time discrimination (for those days) would display return pulses individually on a cathode-ray tube. Then Gold fixed up a device that drew film quickly past the tube and managed to photograph the pulses individually. (Actually Tommy's device was a commercial product from which he removed as many useless components as possible.) Getting aircraft trials laid on was always an appalling business. The pilots hated it, and either the plane didn't turn up where it was supposed to do, or the equipment didn't work, or more probably both. So I had the idea of taking our receiver and camera in a horse-box down to north Cornwall, to a strip of cliff-top between the Coastal Command Aerodrome at St. Eval and the sea. This gave us a plethora of aircraft, but it made the St. Merryn Naval Station furious, since they had to provide us with a guard. We obtained many, many hundreds of feet of film, arguing that we had better do a thorough job while we had the chance. It was a pleasant two or three weeks for Gold, and it gave me two or three days myself in Cornwall. The results astonished us. The reflected signal voltage from an aircraft could change by a factor 10 from our pulse to the next, and it often did so. In retrospect this result does not seem particularly strange, but it was I think quite new at the time. I recall that both radar groups at Malvern were equally surprised when we gave them the analysis of our results.

But to come back to Window. If we could remember a radar scan from one pulse to the next, the solution was now clear. Subtraction of one scan from the next would reveal aircraft, even through the thickest Window. There was no possibility of remembering a radar scan electronically at that time of course (i.e. for 2 milliseconds in our case). But we realised that we could convert a scan to supersonics and then hold the sound in a liquid. The liquid would need to be heavy (which meant mercury), but we told the Navy that only absolutely pure alcohol looked promising. Like the good fellows they were, the officers from Navy Supply delivered huge jars of alcohol to our lab.

The idea succeeded, but not soon enough to see the war. If we had worked with the intensity of 1940-42 I think we could have made it, but the spreading malaise which you discuss so interestingly in your last chapters was affecting us too. We were not conscious of its origin, although I think in retrospect it is clear that once it was seen that the war would be 'won', many people started to think mainly of themselves, and it was this spreading selfishness which brought the trouble. In a sense we were becoming selfish too, not in jostling for political power, but in beginning to think about research problems again. At all events the idea worked, as Gold showed when EDSAC 1 was built at Cambridge. Memory storage was achieved there by mercury delay-lines. The idea went no further because within a year or two IBM had a better system.

The chapter which took me right out of the wartime years was your 'Year of Madness', and the part played in it by Blackett. Your description of Blackett's character - the aristocrat laying down how things should be done - agrees very closely with my own opinions, modified a little in later years. I think now that Blackett was rather overawed by his own reputation, and that he was worried by how he should give an adequate account of himself. I came to realise that he was actually rather shy, and I think his imperious manner was a form of defence. But I would agree, a costly form of defence, to others. Although Blackett never did anything to impede me personally, and although possibly he may have spoken on my behalf on some occasions, candour compels me to say that I rarely heard him express an opinion that I thought to be correct. Underlying the apparent rationality was an insecure foundation of untested value-judgments.

If you have survived thus far, perhaps I can raise a final point? In your chapter on the Oslo Report you whetted my appetite for the later denouement. Did I miss it? Or are you still holding a card up your sleeve? On the facts as you reveal them, I found myself guessing a high-ranking German.

Once again with congratulations on your book, and
With best wishes,

Fred Hoyle

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