The Secret History of British Radar

In the summer of 1940, Britain fought for its very survival in the skies over southern England. But the full story has never been told. Churchill's few had gained a huge tactical advantage from the work of a brilliant team of scientists. In just four frantic years, Robert Watson Watt led the team that designed and constructed Chain Home, the world's first radar defence system. There was no plan B. The entire defence of Britain was gambled on Watson Watt and his boffins. The Battle of Britain was in fact won some years before by a decision to build Chain Home and to develop the very effective communication system between it and fighting a man. That's something which one can't underestimate because the use of the information was so important. It's exceedingly unlikely that we would have won the Battle of Britain in 1940 without the ability to preserve our Hurricane and Spitfires and our pilots on the ground until a real attack was developing. Radar gave the Royal Air Force a crucial 20 minutes early warning. This enabled Fighter Command to scramble and direct its fighters to exactly where they needed to be. As the world's largest air force began its assault on Britain, Luftwaffe commander Herman Goering boasted he would seize control of British skies in a matter of days. Destroying the RAF was the prelude to Operation Sea Lion. The invasion of Britain. If air supremacy had passed to the Germans they would have attempted Sea Lion and had they done so it would probably have been successful. The RAF fought the Battle of Britain under the assumption that the Germans knew all the secrets of British radar. There could be no other reason behind the Zeppelin spy flight in those last weeks of peace. The conclusion we reached was that they had located all the stations and therefore the most probable thing would be an attack on them in the early stage of the war. So why had the Germans not destroyed British radar before the battle? The mystery of the Zeppelin spy mission was not solved until long after the war. When the guns finally fell silent in 1918, the world had been traumatized by the horrors of modern warfare. Further conflict in Europe seemed inconceivable. After the immediate end of the First World War there was a widespread feeling among the public that they didn't want any more war. That would be the end of war. And so defences were run down immediately. The RAF which had been created in 1918 became a fraction of itself. Partly because there was no sense that there was really any enemy up there who was now going to attack Great Britain. But things were about to change. The defeated Germany was soon ravaged by hyperinflation, unemployment and civil unrest. From this chaos a sinister new force emerged. Hitler's rise to power was born of the resentment of the harsh reparations imposed at the end of the First World War. He promised a new and stronger Germany. By the time Hitler came to power in 1933, they were close to the point where they could now begin to build once again a military air force. And a military air force with advanced technology. He made his sidekick Hermann Göring Minister for Air. Forbidden to rearm, the German aircraft industry had turned to civil aviation. This became part of Göring's plan to construct a secret air force. By the mid-1930s German aviation was leading the world. But these new high-speed airliners and mail planes were barely disguised bombers. This was something I think the British had always anticipated. But they soon became terrified that all the rumours coming back about aircraft that had been seen camouflaged about developments of secret air bases and so on, suggested to them that Germany was going to be the real threat. For centuries the sea had been Britain's natural defence. But a new and terrifying scenario now loomed. A new generation of German bombers could strike targets across the country before the RAF had time to intercept. Britain was no longer an island. It desperately needed an early warning system. During the First World War sound locators were a successful method of being able to track aircraft close into the British coast. And during the 1930s the British government decided to build even larger sound locators in the hope of detecting aircraft many miles away from the coast. If proven effective, these concrete sound locators could be developed into a national warning system. With the massive 200-foot sound mirror just completed, everything now depended on a crucial test. And there's a classic story of the air staff all assembled for a demonstration listening to the incoming bomber formation. It sounded very much as if one of the planes had a faulty engine. And all they saw was the local dairy farmer with his milk cart and his milk shards rattling together. And that was the state of our air defence in 1934. Amongst those who witnessed the fiasco was the head of air ministry research, Hugh Dowding. And one of his scientists, A.P. Rowe. Rowe realised that the day of the sound locator was over. He wrote to his boss and said that unless urgent action was taken, Britain would lose the next war. It had taken a milk float to rattle the government into action. The RAF had neither the men or aircraft to maintain a constant patrol over the entire eastern seaboard. German bombers could attack across the North Sea anywhere from the Orkneys down to the Isle of Wight, a vast area of 70,000 square miles. If an early warning system could be developed with a range of a hundred miles, then RAF fighters could remain on the ground until the enemy was detected. In 1935, the idea of a warning system that would cover 70,000 square miles was the most utter science fiction. In the cinemas, popular serials were full of fantastic and futuristic ideas. Evil empires, robots, poison gas and ray guns. Britain's defence establishment also got caught up in this science fiction fever. Rumours began to circulate that the Germans were developing a death ray. A high energy beam that would boil the blood of a pilot. This was taken seriously by Air Ministry and they offered a prize of an award of £1,000 for anyone who could kill a sheep at 200 yards. The death ray challenge found its way to the obscure radio research station near Slough. Its chief scientist was a lively Scot called Robert Watson Watt. Watson Watt was a marvellous little chap. He bubbled away the whole time talking. He could certainly charm a monkey out of a tree, certainly without the slightest effort. Watson Watt asked his able assistant Skip Wilkins to get to grips with the death ray conundrum. He soon found the energy required would be out of this world. But Watson Watt sensed an opportunity with the Air Ministry. Watson Watt was a marvellous salesman. He could sell refrigerators to Eskimos without the slightest effort. Watson Watt replied saying absolutely impossible but I believe I can use radio energy to detect an enemy bomber. But this extravagant claim was based on little more than a hunch. Watson Watt had been tracking thunderstorms by radio direction finding when he became puzzled by some mysterious reflections. Wilkins suggested they might be echoes from passing aircraft. So when the Air Ministry demanded he prove his claim, he turned again to his young assistant. Wilkins estimated how much radio energy could be reflected from an aircraft. The answer surprised everyone. It was very favourable. Air Marshal Dowding, the head of Air Ministry research and development, saw the calculations but said these scientific fellows can prove anything with figures. I want a demonstration. Within a few days, Wilkins devised a pioneering experiment. The mobile laboratory was an old ambulance packed with hastily improvised equipment. A Hayford bomber would fly a course between the BBC transmitter at Daventry and the van. Any radio reflections from the aircraft would disturb the display. A.P. Rowe from the Air Ministry joined them as they anxiously awaited the bomber. As the engine drone grew louder, the spot refused to move. The Hayford turned and made a second approach. Wilkins had made Britain's first radar contact and Watson Watt was quick to realise the significance. Well Skip, Mr Rowe, Britain is an island again. With deep irony, Wilkins' success came on the very same day that Hitler revealed the Luftwaffe to the world. It was the first exhibition of military might by the self-appointed Führer. In just two years, the Nazis had constructed the world's largest air force in total secrecy. Hitler's old henchman, Hermann Goering, was given supreme command. The threat to Britain was now all too clear. Following that first radar experiment, Air Marshal Dowding took decisive action. £10,000 of funding allowed Watson Watt to gather a small team of scientists at a remote aerodrome in Suffolk. The conditions in the actual laboratories where we worked on radar were completely primitive. They were just wooden huts. All our test gear had to come over on the boat. Everything came over on the boat and there simply wasn't much test gear anyhow. As the team explored the design of a national early warning system, some of the more fanciful ideas began to raise alarm. Watson Watt, in addition to being a good theoretical scientist, was also a practical champ. And he was not carried away by what they could eventually do as being the most wonderful thing. He would give people what was available at a time. He knew that the RF needed something quickly and he provided them with something. And if he gave them the third best, that was good enough. Watson Watt knew the frantic race to defend Britain could only be won by developing existing technology. But keeping it simple came with drawbacks. The problem was that to transmit enough radio power with existing technology required the aerials to be over 300 feet high. A national network would require dozens of these huge towers to be linked together to form a coastal chain. The echoes of any aircraft within that transmission area were picked up by a receiving system which could tell the direction from which the echo was coming. Watson Watt's third best system became known as Chain Home. Many still considered Watson Watt's ideas total fantasy. But he was gaining rapid progress. By July of 1935, Watson Watt and his team were successfully detecting aeroplanes out to 50, 60 miles. The radar team had cracked the basic mechanics of radar. It now had to evolve into an air defence system. It was not developed as a scientific device. It was developed as a war weapon for the use of fighter command. And the requirements of fighter command were of overriding priority. The expanding research team had outgrown the primitive huts at Orford Ness. Just down the coast, the imposing Bawdsey Manor became the perfect home for Watson Watt's new wave of recruits. The drive was on to collect the best brains from Britain's universities. The impact of Bawdsey Manor and all the equipment on me as a young man in my mid-twenties was colossal. As Bawdsey's scientific elite grew, they gained a name that would stick with them. The Boffins. We all felt the war was coming, but we only had a little time in which to be ready to defend this country. And that was the atmosphere. That year, things to come gave cinema audiences a terrifying spectre of modern war. One of the key features, really, I think, of British society in the 1930s was fear of bombing. They were told all the time, they were told by Stanley Baldwin, if I miss it, a bomb will always get through. That contributed to this strong apocalyptic fear that somehow the bomb represented the end of civilisation. A year later, that fear became real. The public saw the Germans in Spain and the bombing of Guernica, which became high profile. The weekly newsreels left the public recoiling in horror. Played a very important part in building a strong business idea of waging another war again. The Spanish Civil War proved the perfect testing ground for the destructive power of the Luftwaffe's men and machines. But it was not just in military aviation that Germany led the world. The Hindenburg was the latest of Count von Zeppelin's great airships. The 800-foot Leviathan was a potent propaganda tool, a symbol of a renewed Germany. That all changed on the evening of the 6th of May, 1937. The disaster at Lakehurst spelt the end of passenger-carrying airships. But still under construction was the LZ-130, the new Graf Zeppelin. Once complete, it languished in its hangar, an enormous white elephant. As the first of the giant 350-foot towers went up at Bordsee, Watson Watt's confidence grew. He summoned the top mandarins of Whitehall for a full-scale demonstration. Well, the great day dawned, and this great fleet of aircraft left the dock at Felixstown, and then they were going to make an attack on Bordsee. Watson Watt told them how marvelous radar was and what a great replacement it would be for sound location. And the time came, of course, for these aircraft to appear, and nothing much was seen by the three observers. I was one of the observers. It became increasingly embarrassing. And then, finally, Watson Watt gave up talking, because nothing was appearing on the tube at all, and of course he could see no explanation for that, nor could he think of any explanation for it. And in the quiet, after he stopped talking, we began to hear the distant hum of aircraft engines. And at the same time as we heard them, or possibly one second before, we saw some faint echoes on the cathode ray tubes. As a demonstration of the efficacy of radar, it was about as bad as you could possibly get. The top brass stormed back to London, convinced that Watson Watt was little more than a charlatan. Radar was all but finished. The disaster left only one senior figure still with confidence in the boffins. Air Marshal Hugh Dowding understood the huge technical challenges they faced. I'm quite sure Dowding could see no other solution to the effective defence of this country. Use of standing patrols and other means of detecting and directing fighter aircraft against incoming bomber streams was clearly well beyond the capability of the resources of the country. Radar had to be successful and Dowding kept on supporting it right up to the hill. Dowding was never afraid to push the boffins to their limits. And I recall a meeting at Fighter Command, which I was at, when he was having a great deal of trouble with the stability of the CH system. At this meeting, he was trumping the table, demanding why he couldn't have a stable system. And the senior scientist there, Harold Lander, said, well, sir, the scientists say it's not possible. And I remember beating the table and saying, if the scientists say it's not possible, get me another set of scientists. Dowding was an absolutely dedicated individual who drove forward the idea of making Radar the backbone of Britain's fighter defence. Radar gave Fighter Command a method of locating the attacking bomber. But that was only half the problem. The other half was to direct the fighter effectively to intercept. Dowding's new system would keep fighters on the ground until the enemy was detected by Radar. 3-1-1, Wing Commander speaking. Take off at once and patrol your area. Now, report by radio as soon as you're on patrol. That's all. Good luck. Once in the air, a constant stream of instructions by two-way radio would guide them to intercept. Orbit, Angel 15, and transmit for 6, over. OK, listening up. Scramble, Bandits and Angels became the new language of Fighter Command. Vector 350, over. Vector 350. Hello, Hazel 22. How is answering? Damn good show. As the development of Radar progressed, Watson-Watt knew that his first priority was the defence of London. London was less than 90 minutes flying time from major Luftwaffe bomber bases. At the start of 1938, five Radar stations began construction around the Thames estuary. The new Radar network was going to need hundreds of trained personnel. Foreseeing a lack of manpower in wartime, the RAF began to recruit women operators. Nobody could be told what they were doing. It was absolutely Britain's top secret. We marched up and down. We saluted people. And so it went on for two weeks. And then we were all called into a hut and told where we were going to be sent. And I was told I was going to be a clerk special duty. And everybody wanted to know what it was. I couldn't tell them. I had no idea. And we had our first lecture when they told us the secret of Radar. When you were operating on the set, you had what was called a trace, which is a line of light across the screen, full of little things wiggling up and down like that. And these were either noise interference or the real thing, what you were looking for, the echoes coming off aircraft. By spring of 1938, the five Thames radar stations gave London a 20-minute warning. But air exercises were revealing a daunting problem. 20 minutes was proving too little time for the RAF's biplanes to climb to height. The air defence of London would require a new generation of high-speed monoplane interceptors. But the complex Spitfire airframe was proving difficult to put into mass production. And the Hawker factory could not yet give full priority to the construction of the Hurricane. By March 1938, just 16 had reached the front line. A few weeks later, the Reichstag rose to the news that Austria was to unite with Germany. The new Graf Zeppelin made a triumphant flight over Vienna. It was no longer a white elephant, but a potent symbol of Nazi power. The flight was cover for a top-secret spy mission. The Graf headed east to shadow the Czechoslovakian border. On board, a team of military and wireless experts gathered intelligence on the Sudetenland. It was Hitler's latest territorial claim, and it brought Europe to the brink of war. As the Czech crisis deepened, Prime Minister Neville Chamberlain flew to Munich to confront Hitler head-on. The problem for Chamberlain when he arrives in Munich was that they were close to declaring war in defence of the Czechs. But he knew perfectly well that Riyadh was still in an immature state. It had been going on now for three or four years in Britain, but the plan was really to have it completed by 1939-40, the very earliest. Chamberlain had just been briefed on Britain's readiness for war. I don't know how strong Chamberlain's poker face actually was, but at the time of Munich, Britain's air defences can best be described as dire. Munich became a deadly game of bluff. Chamberlain was aware that we had just 406 fighter aircraft. Of those, only 70 were Hurricanes, and just 14 were Spitfires, not even operational. All the rest were obsolete biplanes. Air raids on London, Chamberlain had been told, would result in hundreds of thousands dead. Provoking Hitler risked creating that enormous catastrophe. And as Chamberlain flew back from Munich, his plane was plotted. By the five coastal CH stations, passed to the filter room, and passed up to operations group, the fighter command. Mollifying Hitler had brought a fragile peace. But Chamberlain's peace for our time hit a secret race to complete Britain's defences. A new Hawker factory was now producing Hurricanes in significant numbers. And the problems that had dogged the mass production of the Spitfire were finally solved. By the summer of 1939, five frontline squadrons had the RAF's fastest fighter. With the frantic construction of 14 new stations, radar coverage was extended from Newcastle to the Isle of Wight. The year after Munich was critical. During that year, the chain home system came into full operation. It had taken just four years from that first experiment, to put chain home at the cornerstone of Britain's defence. This led us to ask ourselves the question, the Germans must know what we're doing. We're building these stations with all this activity going on, 360 foot steel towers, 240 foot receiving towers. They can't have missed it. One German had been watching the towers. General Wolfgang Martini was the head of German radar. The latest reconnaissance alarmed him. Could the mysterious towers be British radar? Martini knew that war was only weeks away. He desperately needed to know more about the towers. And on the 3rd of August 1939, the radar station just north of the Thames at Canuden spotted an echo moving in towards the Thames estuary. A massive echo, bigger than anything one had ever seen before, moving at some 60, 70 knots. Fighter command went into high alert. Could it be an invasion fleet or a huge formation of circling bombers? It turned out to be the German airship LZ-130, the Graf Zeppelin. And over some hours, they plotted the movement of the echo from somewhere off the coast of Essex up to the north of Scotland. On board were the Luftwaffe's top wireless team, just returned from a spy mission on the Polish border. Martini's experts spent the next 24 hours combing the wavelengths for any evidence of British radar. Fighter command was in complete shock. The appearance of the Zeppelin could only mean one thing. The conclusion we reached was that they had not only located all the stations, they would have measured their frequency and other important characteristics. And therefore, the most probable thing would be an attack on them in the early stage of the war. And indeed, we thought that Bordsee would be the prime target. As the German war machine rolled into Poland on the 1st of September 1939, Watson Watt decided the risk of attack was too great. Bordsee must be evacuated. A.P. Rowe was now the superintendent of radar research. He ordered the entire Bordsee scientific team to the safety of Scotland by any means possible. Rowe not only feared air attack on the radar stations, but the electronic jamming of the entire chain home system. On September the 2nd, Rowe summoned me and told me, everybody will be going to Dundee, but not you. You will stay and modify the whole chain. Jimmy Atkinson had developed a new type of display tube that filtered out enemy jamming. Every radar station in the country would need urgent modification. I said, well, what about transport? And Rowe said, well, just do the best you can, use your initiative. Jimmy's ancient Austin became the latest secret weapon in the defense of the realm. He recruited his wife Mona to help with the driving. Now, I was paid subsistence, but of course, she didn't exist, even though she had to do most of the driving. And I slept during the day, ready to work at the next station at night. Each station was taken off the air while Jimmy fitted the top secret device. In September, we covered a total of 2,648 miles. The adventure was only complete when the intrepid couple had toured all 18 radar stations. In Dundee, the Boffins found a home in the austere teacher training college. The magic of Boardsy Manor had gone forever. Attention, everybody. We've just been announced by the prime minister. We are at war with Germany. From now on, anything may happen. As war was declared, fighter command braced itself for a German onslaught on the radar chain. But it didn't happen. And we couldn't understand why. The nation dug in and prepared for the worst. But the feared air raids on British cities never came. In April 1940, the phony war came to a dramatic end. The German blitzkrieg rampaged through Holland and Belgium. A large British expeditionary force was supporting the defense of France. But the fast-moving panzers encircled and trapped them on the beaches of Dunkirk. Over 300,000 troops were snatched to safety by the Royal Navy and a flotilla of small boats. It was a miraculous escape. Amongst the vast amounts of materiel abandoned in the maelstrom was some secret radar equipment. The British radar sets which had been captured were very crude mobile models. And the Germans concluded that whatever British radar was, it certainly wasn't up to much. The Boffins had little idea of the German intelligence picture of British radar. But with the Zeppelin mission and the capture of the equipment at Dunkirk, they feared the worst. The fall of France had taken just six weeks. Hitler now turned to Operation Sea Lion, the invasion of Britain. One of the factors that played a role in persuading Hitler, Operation Sea Lion, was a possibility. It was that Hermann Göring really wanted to prove that his force could do it, that his force could win air supremacy over Britain. And I think people say that Göring was a fantasist. He's a boaster. But actually, if it annihilated the Polish Air Force in a matter of days, they defeated all the aircraft thrown at them in the Battle of France with relative ease. The idea that you couldn't use the same tactics and destroy the RAF in four days, Göring thought, is not as implausible as it now looks. With the towers of Dover radar station clearly visible across the channel, the Luftwaffe began an attack on British ports and shipping. At first, the Kanalkampf seemed to go the Germans' way. Then the RAF began to appear. Dowding carefully positioned his fighters for the best advantage. The Germans began to think to themselves, well, why are we always beating them? We don't think it's very big, and yet here they always are. It began to ring rather quiet alarm bells in the German Air Force about whether the British actually had got some kind of system to detect incoming aircraft. Martini took his fears directly to Luftwaffe high command. But Göring was an old-school thinker. Hermann Göring was a successful First World War fighter pilot. For him, the offensive spirit of the Luftwaffe would be the deciding factor. Nothing at all to do with gadgetry. If Göring could draw the RAF into a decisive battle with his Messerschmitt aces, then the Spitfire and Hurricane could be wiped from the sky. But the events of the 11th of August were to shatter this confidence. The Luftwaffe mounted three widely separated raids across southern England. But Dowding had seen the build-up, and had swarms of RAF fighters ready to intercept. In just a few hours, the Luftwaffe lost over 45 aircraft, damaged or destroyed. But Martini had been monitoring RAF radio communications. His suspicions were beginning to grow. From intercepts, they were able to identify that fighters were being directed by radio towards the German bombers. Therefore, radar must be the basis of the British air defence system. Martini was also puzzled by the powerful signals they could detect from the towers. They were crude, but somehow they must play a part in guiding British fighters. Göring finally conceded. The towers must be destroyed. Early on the 12th of August, a crack ground attack squadron crossed the Channel. The frontline radar stations of Dover, Rye, Pevensey and Dunkirk came under direct attack. At Ventnor, on the Isle of Wight, a direct hit caused major damage. In the following days, Stukas joined the onslaught. 19-year-old Avis Parsons was on duty at Poling, near Chichester. And as a Stuka dies, it screams the most hideous noise. It's very, very frightening. And then the bombs began to fall. I kept going as long as I could, and suddenly my line went dead. And the building next to where I was, was just a heap of rubble. The attacks on Chain Home had been feared since the Zeppelin spy mission. But after three days, they mysteriously stopped. This remained a very great puzzle, because we knew the extent of the damage they'd done, and we knew what they had to do to finish it. They didn't. The returning airmen reported extensive damage to the towers. But when Martini's experts checked their frequencies, they were astonished by what they found. The radar signals were still there, a little fainter, or on different wavelengths. Unknown to the Germans, the source of the signals were mobile radar vehicles that had been brought into operation when the main radar stations had been knocked out by the bombing raids. Despite the extensive destruction, the mobile stations had kept the radar chain on the air. The damage to the towers was rapidly repaired. We had all those four stations back in operation by midnight that night, plotting to find a command. Quite unintentionally, the mobile reserve had been a perfect deception. With the radar stations appearing undamaged, Martini's ideas were sidelined. Beppo Schmidt, the head of Luftwaffe intelligence, also had a strong view on the British radio towers. Major Beppo Schmidt was a long-standing Nazi party member and a drinking buddy of Hermann Göring. He has never been accused of being an intellectual genius. And he considered that the tall radio masts were nothing other than radio direction finding, as used in the First World War. Göring called a conference on the 15th of August and instructed his Luftwaffe commanders to waste no more time on these radio installations, get on and fight the war. Göring's frustrations were growing. He now had a plan that would call on every man and aircraft on the Western Front. The chain home stations began to track the gathering formations, extending from 5,000 to 20,000 feet. And it was then that we began to get the very large numbers of aircraft. Because 100-plus had never been seen on a radar screen before. Adlertag, or Eagle Day, was Göring's plan for a decisive hammer blow. The target soon became clear. Will you warn your controller that this looks like yet another attack on airfields? The thing was to assault the RAF, its airfields, its bases, depots, and aircraft production in southern England. Once you've degraded the RAF, you then moved on to attacking communications and administrative centres, and then the invasion would take place. The RAF airfields were taking a pounding. Squadrons were broken up, and fighters became scattered across southern England. There were points in late August and early September 1940, where the system was almost on the point of collapse. With Dowding's ability to deploy his fighters fast disappearing, the Battle of Britain was on the brink. Then came a timely twist of fate. On the night of 24th August, the Luftwaffe attacked an oil refinery in the Thames estuary. But the raid went badly wrong. Crews got lost, and some jettisoned their payloads. For the first time, bombs fell on central London. Hitler had forbidden any attack on the capital, fearing a reprisal. He was right. Within 24 hours, Bomber Command was over Berlin. The token raid did little damage, but Hitler was outraged. Goering changed his tactics again. Leopold Schmidt, the head of German air intelligence, had been telling Goering over and over again that the RAF was finished, basically. There's a couple of hundred planes left. We've achieved air supremacies. And so it was possible to make this switch to the bombing of London without much danger. Late in the afternoon of the 7th of September, the chain stations plotted large formations grouping over France. Soon, Hermann Goering had assembled the largest air armada the world had ever seen. 370 bombers headed directly to their target, London. Goering's daily bombardment continued for weeks. But shifting his attention away from the airfields proved to be a huge tactical error. Had the Germans sustained their attacks on the sector airfields and the sector controls in particular, it would have been impossible for Fighter Command to continue the defence of Britain. With the heat off the airfields, the RAF quickly returned to strength. As Goering continued to pound London, Dowding used his radar advantage to the full. There is a major raid developing to the southeast. He chose to intercept every raid with small numbers of fighters rather than risk all in a pitched battle. This constant harassment left German intelligence only guessing at the strength of the RAF. They were told that Fighter Command was more or less finished. Every time they flew out, there were more of them. As bomber losses soared, Goering ordered his fighters to fly in close escort. But they lost their advantage of height and London was at the limit of their range. The Luftwaffe was forced to seek the cover of darkness. The daylight bombing raids were a disaster. Loss rates that the German Air Force simply couldn't support. And, of course, air supremacy had not been won. So Zealand was abandoned. The Battle of Britain had been won. But the mystery of the Zeppelin spy mission was still unresolved. Why had the Germans not destroyed British radar before the battle? The answer only came years later, after a chance encounter. It was only after the war, 1950, I, at the Farnborough Air Show, met General Martini, who was the Chief Civilian Officer of the Luftwaffe. And I said to General Martini, why didn't you destroy the radar system when the war broke out? He said, you didn't have a radar system when the war broke out. I said, well, how did we track the Royal Zeppelin? Should you track the Royal Zeppelin? Yes, I described precisely. He said, I don't believe it. I said, you have to, we did. The astonishing truth dawned. The Zeppelin spies had failed to identify British radar. The Luftwaffe's top wireless experts would have had no trouble finding the powerful chain home signals. But what they found baffled them. They expected to hear high pitch noises and musical tones that you would get from an oboe in the middle range of the piano. The latest German radar equipment could transmit pulses between 500 and 1,000 times a second. Nothing like the crude signals they were now receiving. Listening to CH, all you'd hear would be a dull sort of ticking, tick, tick, tick, something I didn't recognize at all. German and British radars were of completely different designs. German radar generated its own pulses. British radar, by contrast, sampled the pulses of the National Grid. The Boffins had not just used the power cycle of the National Grid as a simple economy. It was an ingenious way of synchronizing the entire system. All the CH stations all up the coast were locked together on the repetition rates. They all produced 25 pulses per second and they were all locked back to the mains frequency of 50 cycles per second so they were all transmitted in unison. To achieve a 100 mile detection range, Watson Watt had used the most powerful transmitters then available. Each station produced more than 600,000 watts and because they all derived their pulses from the National Grid, the entire chain acted as one enormous and hugely powerful transmitter. So as the airship flew up the coast, it picked up the same radiation all the way up, tick, tick, tick, tick, tick, ticking, without change. This huge wall of radio power was creating further confusion. They had very sensitive receivers in the main beam of the CH stations and they would have overloaded the receivers and broken through into other wave bands. So no matter how they tuned their receivers, they would have had this curious ticking all the way. As the LZ-130 approached Scotland, the Zeppelin spies still struggled for an explanation. The signals appeared to have no direction, just a general widespread ticking. With British radar still blaring from their headphones, they decided the ticking could only have one source, the National Grid. They were completely foxed by the fact that the repetition rate of the CH stations, 25 pulses per second, was quite unlike anything which they had used on their own radars, which the Germans mistakenly took to be arcing and sparking from the British electrical distribution system. The Zeppelin spies had made the greatest intelligence blunder of the war. The Royal Zeppelin returned and the head of the mission reported that there was no sign of any radar transmissions. Watson-Watt's basic, almost primitive system had spoofed the finest technical minds in the Luftwaffe. Ironically, if Watson-Watt had gone for anything more sophisticated than third best, the Germans would have been onto it immediately. Watson-Watt's great wisdom had been to keep chain homes simple. He knew there could be no delays in Britain's frantic race for radar. It was only just ready in time as it was. The Luftwaffe had botched the perfect opportunity to unravel all of the secrets of chain home a year before the Battle of Britain. The failure of the Zeppelin spy mission was a fundamental disaster for the Germans. They did not realise the effectiveness of British radar, nor the substantial size of the organisation behind it on which the whole of British air defence hinged. I believe the failure of the Zeppelin mission and the failure of Martini to persuade Goering that the stations had to be destroyed effectively cost Goering the Battle of Britain and that saved this country from a German invasion.