Why German Defenders Couldn't Explain How British Bombers Mapped Cities At Night

[00:00:00]February 1943.

[00:00:02]A cold room in Berlin. On a workbench under hard electric lights sits a wrecked machine that should not exist.

[00:00:09]It has been carried across occupied Europe in pieces. Pulled from the belly of a British bomber that came down in a Dutch field. Its glass smashed, its wiring scorched, its metal skin torn by the crash, and by the fire the crew set before they died or were taken. Around the bench stand some of the finest radio engineers in Germany. Men from Telephunan, the great electrical firm.

[00:00:32]Men who have spent their careers building the radar sets that guard the night skies over the Reich. They are looking at a small block of copper. It is drilled with a ring of round holes machined with a precision that is almost beautiful and they cannot explain it.

[00:00:48]They cannot explain it because a few weeks earlier in the middle of January, an order had gone out through the German research establishment. an instruction to stop at once all work on radar that used centimeter wavelengths. The men in that room had been told in effect that this whole field was a dead end, that nothing useful could be built there, that the short waves were a waste of scarce men and scarce money. Some of them had argued for that decision. Some of them had signed off on it. And now on the bench in front of them is proof that the enemy had gone down exactly the road they had just closed. That the British had built a working machine out of the physics the German high command had just declared worthless. One of them will hold that copper block up to the light.

[00:01:29]He will turn it over in his hands. He wants to know how it works. He wants to know what it is for. And when the answer comes, when they finally rebuild the set and switch it on and watch a glowing picture form on its screen, a picture of the ground below, a picture of a German city drawn in light. The men in that room will feel something close to fear because they will understand what it means. The British bombers coming over in the dark had not been guessing. They had been looking down at a map of the target, a map the British were drawing for themselves at night through cloud from four miles up. Pause on that for a moment because this is not a story about a broken radar set on a workbench. This is a story about how a nation decides what is possible and what is not and who gets to decide it. This is a story about the difference between a country that trusts its odd balls and a country that does not. This is the story of how Britain learned to see in the dark. To understand why a German engineer could not explain the machine on the bench, you first have to understand how badly the British had been failing only 18 months before.

[00:02:34]Because the truth in the first years of the war was that RAF bomber command could not hit what it aimed at. It could barely find what it aimed at. For a long time, nobody in authority admitted this.

[00:02:46]The crews flew out over the North Sea in the dark. They pressed on through flack and fighters and weather, and they came home and reported that they had bombed the target. The maps in the operations rooms filled up with confident marks.

[00:02:58]And because the aircraft carried no reliable way of proving where their bombs had actually fallen, the reports were believed. It was a comfortable arrangement. It was also, it turned out, almost entirely false. The man who broke it open was not a pilot or a commander.

[00:03:12]He was a civil servant. His name was David Beneserson But, and he worked in the secretariat of the war cabinet, a quiet economist with a sharp eye for numbers.

[00:03:23]In the summer of 1941, he was asked on the authority of Winston Churchill's chief scientific adviser to do something nobody had done before, to take the night photographs that the bombers were now bringing back. The pictures snapped automatically when the bombs dropped and simply count, to match the photographs against the targets and work out coldly how many crews had actually put their bombs anywhere near the aiming point. He examined more than 600 photographs from raids flown in June and July of that year. And on the 18th of August 1941, he delivered a report that landed like a cold bucket of water on the whole Enterprise. Of the crews recorded as having attacked their target, but found only about one in three had dropped their bombs within 5 mi of it. Over the industrial haze and heavy defenses of the ruer, the most important target region of all, it was worse. There it was only about 1 in 10. Read that number again. 1 in 10. And that was only counting the aircraft that were recorded as having attacked at all. It left out the ones that turned back, the ones that got lost, the ones that never found the target and jettisoned their load into the dark. Count those, and the picture was bleaker still. A 5m circle is not a pinpoint. It covers more than 70 square miles of countryside. For most German towns, that meant a bomber could be inside but's generous circle and still be dropping its bombs on empty fields, on farms, on forest, on nothing at all.

[00:04:49]This was the frame that had failed. The whole idea of night bombing, as it stood in 1941, rested on an assumption that quietly turned out to be false. The assumption that a trained crew, given a target and a map and a compass and the stars, could find a city in the dark and hit it. They could not, not reliably, not through cloud, not against a blacked out landscape where the rivers and the coastlines that navigators relied on vanished into a uniform gray. The men were brave and they were skilled and they were doing their best. The task itself was simply beyond the tools they had been given. And here is the important thing. The problem was not a lack of courage and it was not a lack of effort. It was a problem of knowledge.

[00:05:31]The bombers did not know where they were. That was the wall. and no amount of heroism was going to fly a Lancaster through it. What was needed was not braver men. What was needed was a new way of seeing. The question was where that new way of seeing would come from.

[00:05:46]There is a piece of this story that has to be told before we step into the laboratories. Because it explains why the British believed when so much evidence said otherwise that radio could beat the dark. They believed it because they had already seen it done to them against them. In the autumn of 1940, during the worst of the German bombing of British cities, a young scientific intelligence officer named Reginald Victor Jones, known to almost everyone as RV Jones, became convinced of something his superiors found nearly impossible to credit. He believed the German bombers finding their way to English targets in the dark were being guided by invisible radio beams laid across the sky from transmitters in occupied Europe. A bomber would fly along one beam toward its target and the crew would listen for the moment a second beam crossed the first and there they would drop their load. The German system was called nicer bean, a word that means crooked leg. Jones argued that Britain had to find these beams and then bend them. It sounds like something out of a boy's adventure story and the men at the top were slow to believe it, but Jones was right. The beams were real. Special aircraft went up and hunted for them and found them. And then British engineers did something quietly audacious. They did not simply jam the beams into silence. They interfered with them so cunningly that a German crew could believe it was still flying straight down the center of its beam while it was in fact being eased gently off course, coaxed into scattering its bombs across open fields.

[00:07:16]The British came to call this hidden struggle the battle of the beams, and Churchill later called it the Wizard War. When the Germans brought in a more precise beam system laid by a specialist pathfinding unit of their own, the British studied that too and learned to bend that too. The heavy ray that gutted the city of Coventry in November of 1940 was flown down one such beam. It is a reminder that this new science was never a British monopoly. It was a weapon both sides reached for in the dark. But here is the lesson the British drew, and it is the hinge of everything that follows.

[00:07:49]Radio navigation worked. A beam could carry a bomber to a city at night, and a beam could be beaten, jammed, bent, deceived. The British had proven both halves of that truth in the skies over their own burning cities. So when the butt report landed and told them their own bombers were lost in the German dark, they did not conclude that the dark could not be beaten. They concluded that they had been fighting it with the wrong tools. They had watched radio do this very job already. Now they had to build a version the enemy could not so easily turn back against them. And the men who had fought the battle of the beams knew exactly where such things were made. It was a scattering of requisitioned buildings on the south coast of England and the strange informal faintly ramshackle culture that grew up inside them. The place was called the telecommunications research establishment. Everyone who worked there simply called it TR. It had started life before the war as a small radar station on the suffuk coast then moved as the bombing threat grew first to Scotland and then to a cluster of huts and houses at Worth Matravers near Swanage in Dorset perched on the cliffs above the channel. Later in the spring of 1942 the laboratory had to move for its own safety and the reason is a small story worth telling on its own. In late February of that year, British airborne troops carried out a daring raid on the French coast at a place called Brunal. A company of paratroopers under a young major named John Frost dropped in the dark fought their way to a German radar station perched on the cliffs and held it long enough for a radar mechanic they had brought with them. A Royal Air Force flight sergeant named Charles Cox to strip the key parts out of a German set called Vertsburg while under fire before the whole party was taken off the beach by the Navy. It was a brilliant piece of scientific burglary, and it taught the British a great deal about how German radar worked, but it also raised an uncomfortable thought. If the British could raid a coast and steal an enemy's radar, the Germans could do the same.

[00:09:48]And there sat TR stuffed with the nation's most precious secrets in a cluster of huts on an exposed cliff, a short boat ride from occupied France.

[00:09:57]The fear of a German raid was enough. So TR packed up and moved well inland to the buildings of Malvin College in Worershare where it stayed for the rest of the war. What mattered about TR was not where it sat. It was how it thought.

[00:10:12]The man in charge was a scientist named Albert Persal Row, known to everyone as Jimmy Row, and he ran the place on a principle that would have horrified a German research director. He held open meetings. He called them, half joking, the Sunday Soviets. On a Sunday in a plain room, you might find an air marshal and a junior physicist and a squadron leader fresh from operations and a professor of electronics all in the same conversation, all allowed to speak, all allowed to disagree. A 25-year-old with a good idea could say so to a man three ranks and 30 years is senior. And if the idea was good, it could be taken up on the spot because everyone who could say yes was already in the room. The men who worked in places like this had a nickname. They were called boffins. It was RAF slang, affectionate and slightly mocking at once for the civilian scientist attached to the war effort, the clever eccentric working at the seam between pure research and the hard practical needs of the men who flew and fought. The word seems to have been born among the radar researchers themselves, and the Boffin was not an accident. He was the product of something deep in British life. A long peculiar tolerance for the gifted amateur. The country parson who classified Beatles in his spare time.

[00:11:26]The retired officer who bred prize orchids. The self-taught engineer who tinkered in a shed and changed the world. Consider the company these men kept. Frank Whittle was a serving RAF officer who worked out the principle of the jet engine and patented it in 1930 and who spent years being plightly ignored by official before his engine finally lifted a small experimental aircraft off a runway in May of 1941.

[00:11:51]Regginald Mitchell designed the Supermarine Spitfire, one of the most beautiful and deadly aircraft ever built. While he was dying of cancer, Alan Turing, a shy and unworldly mathematician, sat in a hut at Bletchley Park and helped break the German enigma cipher by imagining a machine that could think faster than any man. None of these people fitted neatly into a hierarchy.

[00:12:14]All of them were, in their way, boffins, and Britain, for all its class snobbery and its bureaucratic caution, kept finding room for them. Kept, in the end, letting them into the room. Now hold that thought against how Germany did its science. German research in the war was superb and it was hierarchical. It ran through great corporations and state institutes through telefun and seammens and the research arms of the armed forces through committees and specifications and chains of command that ran upward to men like Herman Guring. It produced astonishing things.

[00:12:48]Rockets that reached the edge of space, jet fighters, submarines of remarkable design. But it produced them in a particular way, from the top down, by decision. And a system that works from the top down has a weakness that a system built from the bottom up does not. When the men at the top decide that something is impossible, the whole structure below them stops looking.

[00:13:09]There is no back garden. There is no Sunday Soviet. There is no junior man permitted to stand up and say with respect that the men at the top are wrong. This is the deeper machinery of the whole story. Not that German engineers were worse. They were not. It is that the British system had accidentally left a door open and the German system had bricked one up. And through that open British door in the middle of the war walked three ideas that would let a bomber see a city in the dark. The first was the simplest, and it came first. It was a way of telling a navigator where he was. Its name was G and it was largely the work of a TR engineer named Robert Dippy who had first sketched the idea before the war as a way of guiding aircraft home to land. G did not drop bombs and it did not take pictures. What it did was answer quickly and coldly the one question the crews over Germany could never answer for themselves. Where am I right now? To within a mile or two. The way it worked was elegant. Back in England, a group of radio stations sent out precisely timed pulses. One station was the master. The others spaced out across the country were the slaves, and they fired their own pulses in exact step with the master. High above Germany, a receiver in the bomber, a small unit the crews called the Gbox listened for those pulses and measured the tiny differences in the instant each one arrived. Because radio waves travel at a known and constant speed, each of those time differences drew an invisible curved line across the map, a line along which the aircraft had to be sitting.

[00:14:43]Measure two such differences from two pairs of stations, and where the two curves crossed there was the aircraft.

[00:14:49]The navigator read the differences off his set, laid them against a special chart printed with a web of these curves, and in 3 or 4 minutes he had a fix, a real position, not a guess.

[00:15:01]G reached a little over 300 m from the English coast, far enough to cover the ruer and much of western Germany. Though its accuracy softened the further out you went, it was never a blind bombing device. Early hopes that it could put bombs on a target through cloud came to nothing. What it did instead was quietly transform the whole business of the bomber offensive. It kept the crews together in a loose stream instead of scattered across the sky. It got them to the right patch of Germany. And just as precious to the young men flying, it got them home. Took away the terror of coming back over England, low on fuel and lost in merc, hunting for a flare path that might be anywhere. It went into large-scale use in March of 1942 over Essen and then over Cologne, and the difference was immediate and obvious. There was a deeper gift hidden inside G, and it is worth understanding because it changed the shape of the whole offensive. Because G let every navigator know where he was and hold a common track at a common time, the bombers no longer had to straggle across Germany as lone aircraft strung out over hours of darkness. They could be gathered into a single dense river of aircraft, all following the same route, all crossing the target inside a few minutes of one another. The British called this the bomber stream, and it was as much a weapon as any bomb in the bay. To see why, look again at the enemy. The great German defensive belt worked by carving the sky into a chain of boxes. And each box at any one moment could really only handle a single night fighter chasing a single bomber under the eye of its ground controller. That was efficient enough against a thin trickle of aircraft wandering through over many hours. It was hopeless against a concentrated stream. If 400 bombers poured through one box in 20 minutes, the lone fighter waiting there could be steered onto only one or two of them, and the rest swept past untouched into the dark. The stream did not defeat the German boxes by destroying them. It drowned them. It gave each box more targets in a few minutes than it could ever hope to engage. The most dramatic proof came early at the very end of May in 1942 when the commander of bomber command scraped together every aircraft he could beg, borrow or pull from his training schools more than a thousand bombers in one force and flung them in a single stream against Cologne. The operation was called Millennium and it was held together in large part by G keeping that vast crowd of aircraft on track and on time. It was meant to prove a point to the British government and to the enemy at once that the bomber force could be concentrated into a hammer and swung. It proved it and the principle it proved concentration in time and in space would run straight through everything the pathfinders later did over the burning cities. The Germans of course did not sit still. Radio can be jammed and a signal beamed from England into Germany as a signal the Germans can hear and drown out. By August of 1942, about 5 months after G began, German jamming had made it unreliable deep over the Reich. That was not a failure. That was the nature of the game. G remained a fine tool for navigation over Britain and the sea for the rest of the war. But over the target itself, something better was needed. Something the enemy could not so easily shout down.

[00:18:11]The second idea was by any measure the most accurate bombing system of the entire war. Its name was Obo. The mind behind it belonged to a TR engineer named Alec Reeves. A brilliant and slightly otherworldly man who in peace time had invented a way of turning sound into precise digital pulses. Work that lies at the root of nearly all modern telephones. He developed Obo with a colleague named Frank Jones and the concept was so clever that it is worth taking slowly.

[00:18:40]Obo used two radio stations in England.

[00:18:42]Engineers being engineers gave them animal names. One was the cat, one was the mouse was each station sent a pulse to a small transponder in the aircraft which bounced it straight back. And by timing that round trip, each station knew to a remarkable degree of precision exactly how far away the aircraft was.

[00:19:02]Now, here is the trick. The CAT station used its distance measurement to hold the aircraft on the edge of a vast invisible circle. A circle drawn so that its curved edge passed directly over the target. If the aircraft drifted inside the circle, the pilot heard a stream of Morse dots in his headphones. If he drifted outside it, he heard dashes.

[00:19:22]Only when he was exactly on the line did the dots and dashes merge into one steady, continuous note. So the pilot did not navigate. He listened. He flew the note. He held that pure tone in his ears and let it curve him through the darkness along the edge of a circle he could not see. The system was so sensitive that a wander of only about 17 yd to either side was enough to break the tone into dots or dashes. Meanwhile, the second station, the mouse, tracked the aircraft's progress along that curve, and a small computing device worked out the precise instant to release. At the release point, the crew heard a last signal, five dots and a dash, and let the bombs go. The whole thing was accurate to a few hundred y from more than 250 mi away, an almost unbelievable figure for the time. It was so accurate that British surveyors had to go back and check that their maps of the European coast were correctly lined up with the mapping on the far side of the channel because the system was now more precise than the maps it depended on. Obo had one great limitation and it came from the curve of the Earth itself.

[00:20:26]Radio at these wavelengths travels in straight lines. So the higher the aircraft flew, the further over the horizon the ground stations could reach it. To get the range to cover the ruer, the obo aircraft had to fly very high indeed. The answer was the dehavlin mosquito, the astonishing wooden aircraft that flew faster and higher than almost anything the Germans could send up and which could ride its obo arc at a height where fighters struggled to follow. The Germans could see the strange curving flight paths on their own radar, and they gave the system a nickname of their own. They called it the boomerang. What they could not do was work out how the boomerang knew exactly where to turn. The first obo raid went out just before Christmas of 1942 against a power station in the occupied Netherlands. It was rough, plagued with equipment faults, but it showed the promise. The real arrival came in March of 1943 when obo mosquitoes flew ahead of the main force and laid their markers with pinpoint accuracy on the great corrupt armament's works at Essen. The very target that Butt's report had shown the bombers hitting only one time in 10. This time the markers fell almost exactly on the aiming point, and the bombers behind them bombed the markers, and the heart of German heavy industry took a blow it had not taken in 3 years of trying.

[00:21:42]For the commander of bomber command, this was the night the real offensive began. But Obo, for all its genius, could only reach as far as those ground stations in England could see. It could serve the ruer, sitting just across the water. It could not follow the bombers to Hamburg, to Berlin, to the deep cities of the east. For that, the crews needed to carry their eyes with them.

[00:22:02]They needed a machine in the aircraft itself that could look down through the cloud in the dark and draw a picture of the ground. And that brings us to the machine that ended up on the workbench in Berlin. Its name was H2S.

[00:22:14]And to understand it, you have to go back to a single component, a small block of copper machined in a laboratory in the English Midlands. At the University of Birmingham in February of 1940, two young physicists named John Randall and Harry Boot switched on a device they had built almost by hand. It was called a cavity magnetron, and it was quietly one of the most important inventions of the 20th century.

[00:22:40]The problem with radar in those days was wavelength. Existing radar used long waves which needed enormous aerials and gave blurry coarse results. Everyone knew that if you could push radar down to very short waves a few centime long, you could build small aerials and get sharp detailed pictures. But nobody had a way of generating enough power at those tiny wavelengths to be useful.

[00:23:05]Randall and Boots magnetron did exactly that. That little ring of copper cavities, when energized, poured out an unheard of blast of power at a wavelength of around 10 cm. It was a leap of hundfold. It made everything that followed possible. 10 cm. Hold on to that number because it is the number that matters in this story. 10 cm was the wavelength the British had learned to master. 10 cm was the wavelength German science in the middle of January 1943 officially gave up on. Everything turns on those 10 cm. The men at TR soon noticed something intriguing. When they pointed one of these new shortwave radars at the landscape, the picture that came back was not uniform. Water gave one kind of echo, weak and dark.

[00:23:53]Open countryside gave another. And towns and cities, all that stone and brick and steel, threw back a strong, bright, unmistakable echo of their own. A city seen by sentimentric radar glowed. And if a city glowed on a radar screen, then an aircraft carrying such a radar looking straight down could in principle draw a rough map of the ground beneath it. A map that did not care about cloud or darkness or the enemy's blackout because radar makes its own light. At the start of 1942, a team at TR under a young astronomer named Bernard Levelvel set out to build exactly this. Levelvel would go on after the war to become one of the great figures of British science, the founder of the Judrell Bank Observatory, the builder of a radio telescope so large it could listen to the far side of the galaxy. But in 1942, he was building something smaller and far more urgent, a downward-looking radar that spun a beam beneath the aircraft and painted what it saw onto a round screen, a cathode ray tube called a plan position indicator. On that screen, as the aircraft flew, a glowing map would slowly draw itself. The bright sprawl of a city, the dark ribbon of a river, the blank dark of open land. A picture of the target made of radio waves carried in the belly of the bomber. Progress on H2S was fast, and it was paid for in blood before it ever reached the enemy. On the 7th of June 1942, a Halifax bomber took off to demonstrate the new radar to a group of engineers from the EMI Company, who were helping to turn the laboratory device into something that could be built in quantity. Over the Welsh borders, one of the aircraft's engines caught fire. The wing burned through and the bomber fell out of the sky. Everyone aboard was killed, 11 men. Among the dead was Alan Blumline, an engineer of almost frightening brilliance, the man who had invented stereo sound and helped create British television and who had been leading EMI's work on the radar. His death and the deaths of the men beside him was a wound the project felt for the rest of the war. It remains the worst accident in the history of British flight testing. Lovevel went to the wreck and recovered the precious magnetron from the ashes and for a moment feared the whole effort had died in that Welsh field. It had not.

[00:26:11]Churchill himself insisted the work go on at the highest priority.

[00:26:15]There was a fierce argument about H2S and it was an argument about that same block of copper. To fly the Magnetron over Germany was to risk it falling into German hands. The copper was nearly indestructible. A crashed bomber might hand the enemy the very secret that made the whole thing work. Some argued for a safer, weaker device that would keep the secret even if lost. But the safer device was far less powerful, able to see a town at 10 mi where the magnetron could see it at 35. In the end, the decision was made to take the risk on the reasoning that even if the Germans captured a magnetron, it would take them a long time, perhaps 2 years, to build radar of their own around it, and that there was no sense assuming the enemy was not already trying. That gamble and that 2-year estimate would turn out to be almost exactly right. H2S first went to war on the night of the 30th of January, 1943.

[00:27:08]A small number of aircraft carrying the new radar flew ahead of the main force to Hamburg, looked down through the dark at the glowing shape of the city on the elbow and marked it for the bombers behind them.

[00:27:20]For the first time, a British aircraft over Germany had found its target not by dead reckoning, not by the stars, not by a lucky gap in the cloud, but by looking at a map it was drawing for itself as it flew. Reading that glowing screen was a skill in its own right, and it did not come easily. The picture was no photograph. It was a crude flickering greenish thing, a smear of light and shadow that a tired man had to interpret in seconds while the aircraft shuddered around him and the flack climbed up toward the belly of the bomber.

[00:27:54]What the best operators learned to do was hunt for the shapes that could not lie. A coastline where the bright echo of land met the dark silence of the sea, the black thread of a wide river winding through the glow of a builtup area. the particular way an estie opened out or two rivers met or a lake lay dark against a bright shore. Hamburg sitting on its broad river with the sea not far beyond was a gift to an H2S operator.

[00:28:22]Its shape on the screen was unmistakable.

[00:28:25]That is part of why Hamburg was chosen for the radar's first outing and part of why the later attacks on it were so accurate and so terrible.

[00:28:33]Other cities were far harder to read.

[00:28:36]And the hardest of all was Berlin.

[00:28:38]Berlin was a problem precisely because it was so vast. On the screen, a truly enormous city did not appear as a tidy shape with clear edges. It spread and spread until it filled the display, one great shapeless blaze of light with no single feature the eye could seize on.

[00:28:54]And the deeper into that glare the aircraft flew, the less the operator could tell where in the spraw he actually sat. The very size that made Berlin the greatest prize of all made it through the early radar maddeningly hard to map with any precision. The answer, when it came later in 1943, was to drive the radar down to an even shorter wavelength, around 3 cm, which drew a sharper and finer picture. But that keener eye arrived too late to help the crews who flew against Berlin in the bitter heart of the offensive. Men who could see the capital shining on the screen in front of them and still not quite read it. But a clever machine is not the same thing as a way of winning a war. A radar in one aircraft only matters if the whole force can be made to use it. And that required not an invention but an organization. It required the pathfinders. By the middle of 1942, it was clear to some senior officers that the ordinary way of bombing, every crew finding its own way and aiming for itself simply spread the effort too thin. What was needed, they argued, was an elite, a specialist force of the very best crews flying ahead of everyone else, whose only job was to find the target and mark it so vividly that the hundreds of aircraft behind them could not miss.

[00:30:08]The idea met resistance at the very top of bomber command. Its commander disliked the notion of skimming off the best men into a core of favorites, fearing it would drain the spirit from every ordinary squadron. But the pressure from above was too strong. And in August of 1942, the Pathfinder Force was born. The man chosen to lead it was an Australian named Donald Bennett. And he was, by common consent, one of the most gifted airmen of the entire war. He was a superb pilot, a navigator of near genius, and enough of an engineer to understand every system his crews carried. He had been shot down attacking a German battleship in a Norwegian fjord earlier that year, and had walked out through the snow to neutral Sweden and made his way home. He was not yet 33 when he was promoted to lead the Pathfinders, the youngest man ever to hold his rank in the RAF. He was cold, exacting, tea total, and had no patience whatever for fools. He was not much loved. He was deeply respected, which in that trade mattered more. What Bennett's Pathfinders did was turn the new science into a method, a repeatable, teachable method for marking a city in the dark.

[00:31:14]They flew ahead in their mosquitoes and their heavy bombers, using obo and H2S and G to find the aiming point. And then they marked it, not with bombs, but with fire. They dropped target indicators, great cascading pyrochnic flares that burned in vivid colors and could be seen for miles laid down on the target so the main force had something unmistakable to aim at. It was a hard and lonely job to be first. The marker crews arrived over the target ahead of everyone. When the defenses were fully awake and there was as yet no stream of other bombers around them to divide the enemy's attention, they could not simply drop and turn for home either. Often they had to stay, orbiting the target in the flack and the search lights, watching their markers burn down and dropping fresh ones to keep the aiming point lit for the hundreds of crews still inbound.

[00:32:02]to fly straight and level over a defended German city on purpose again and again so that other men could see where to aim took a particular and unshowy kind of nerve. The whole method rested on it and they built a whole vocabulary for how to do it, naming the methods with a kind of homesick affection after the hometowns of the men who devised them. When the sky was clear enough to see the ground, they used a method they called paramatter after a town in Australia. Dropping the colored markers blind onto the aiming point by radar. When it was clearer still, they used New Haven after the English port where flares lit the ground and marker crews aimed the target indicators by eye. And when the target was buried under thick cloud so that nothing on the ground could be seen at all, they used the most difficult method of the three called Wanganui after a town in New Zealand, releasing colored flares to hang in the cloud itself, so that the main force bombed the glowing markers floating in the sky above the hidden city. When Obo fixed the release point, they added the word musical to the name.

[00:33:07]And over the target, a senior pilot, the master bomber, would circle in the fire and the flack and direct the whole attack by radio, calling the following crews onto the best markers, waving them off the ones that had fallen wide. It was, when it worked, an extraordinary piece of organized human machinery. The invention had become a system now crossed to the other side to the men in the dark who had to work out what was being done to them and could not. The German night defenses were formidable and they were built by clever methodical men. Along the coast of occupied Europe from Denmark down through the low countries and into France ran a great belt of interlocking defensive zones that the British came to call the Camhuba line after the general who built it. It was a marvel of organization.

[00:33:54]Longrange Freya radars watched far out to sea and gave the first warning. Then, as the bombers came on, pairs of precise Vertzburg radars took over, one locking onto a single bomber, the other guiding a single night fighter, while a controller on the ground watched their two blips converge on a plotting table and talked his fighter onto the kill. It was patient, systematic, and deadly, and it cost bomber command dearly. But look closely at what that system was and what it was not. It was a machine for finding and killing bombers that were already overhead. It told the Germans that the aircraft were coming and roughly where they were. It told them nothing at all about how those aircraft were navigating. Nothing about how they were finding a specific city on a specific night through unbroken cloud and marking its center so precisely that the bombs came down on the factories and not on the fields. The German defenders could watch the bombers arrive. They could not understand how the bombers knew where they were going. And the reason they could not understand it lay in a decision their own side had made. For years, influential voices in German radar research had insisted that the very short cime waves were not worth pursuing, that the future lay in the longer wavelengths where their existing sets already worked so well. A senior figure at Telephunan argued the short waves were impractical. The argument grew heated and it grew personal and in the middle of January 1943, it ended in an order. All work on centimetric radar was to stop at once. Think about the timing of that. Read it again slowly. In the middle of January, German research officially abandoned the 10 cm world. On the 30th of January, British bombers used a 10-cm radar to map Hamburg. The two events are separated by about 2 weeks. One side had just locked a door.

[00:35:43]The other had just walked through it, and neither side yet knew what the other had done. The German blindness did not last long, and it was ended by pure chance in the way such things so often are. On the night of the 2nd of February, 1943, only the second time H2S had gone out to war. One of the aircraft carrying it was shot down near Rotterdam. The crew could not destroy the set completely. German recovery teams reached the wreck, sifted the burned and broken pieces, and found among them the machinered copper block, the beating heart of a sentiment radar.

[00:36:16]the very thing their own science had just declared could not usefully be built. The find went straight up the chain to the head of Luftvafer signals who grasped its importance at once and ordered a crash program to understand it. The pieces were taken to Telephunen in Berlin and a special study group was set up to rebuild the machine and learn its secrets. They named the captured device the Rotterdam apparatus after the place it had fallen and the group took its name from the machine.

[00:36:45]When the German engineers examined the magnetron, they found it was better than anything they had. When they pieced the set back together, it is said that they set it up on one of the great concrete flack towers in Berlin, switched it on, and watched a glowing image of the city form on the screen. The capital of the Reich, drawn in radio exactly as a British bomber crew would see it in the seconds before they released. There is a grim comedy in what happened next. A second H2S set fell into German hands within weeks. Recovered from a bomber lost on a raid that in one of the war's crueler ironies is said to have damaged the very telephon offices where the first set was being studied and destroyed it. If that account is right, the Germans lost their first captured machine to a British raid guided in part by the same technology and had to begin again on the second. But now they knew.

[00:37:38]Now the mystery on the workbench had an answer. The British had built a machine to see cities in the dark, and it worked, and it was in the night sky over Germany every time the siren sounded.

[00:37:49]The reaction at the summit of the German command was, by one account that has come down to us, close to despair. The Reich's Marshall told that the enemy had a working centimetric radar when his own experts had sworn it was impossible is reported by the historian Alfred Price to have said that he had expected the British and the Americans to be advanced, but that he had never dreamed they would get so far ahead and that he had hoped, even if Germany was behind, at least to be in the same race.

[00:38:17]Those are not words a proud man says easily. They are the words of someone who has just discovered that the door he ordered bricked up had an enemy standing on the other side of it all along. And then came the final turn of the screw.

[00:38:30]The part of the story that is darkest and cleverest at once. Having captured the British radar, German engineers realized they did not necessarily need to build their own version to profit from it. Every H2S set every time it was switched on was shouting into the night on a wavelength the Germans could now recognize. So they built a receiver called Knax that did not map anything at all. It simply listened for the telltale emission of a British ground mapping radar and pointed toward it. They fitted it to their night fighters. And so the very machine that let the bombers see the city in the dark became a beacon that guided the fighters to the bombers.

[00:39:06]The eye that let Britain see had become a lamp that drew the moths. For a time this caused near panic among the British until careful study showed the losses were not in fact rising because of it and the campaign went on. But the lesson stands there is no perfect weapon. Every advantage in war cast a shadow and the cleverer the advantage the darker the shadow it throws. So we come to the reckoning, the honest accounting of what all this cleverness bought and what it cost. The question we began with was why German defenders could not explain how British bombers map cities at night. And now the answer can be stated plainly and it is not a story of German stupidity.

[00:39:45]The Germans had superb radar. The British had a strange laboratory on a cliff where an air marshal would listen to a junior physicist. The Germans had a research establishment that ran by decision from the top. The British had one that ran by argument from the bottom. The Germans had a system disciplined enough to declare the centimeter waves a dead end and make the decision stick all the way down. The British had a system disorderly enough that nobody could ever quite make such a decision stick. And so somebody in some hut kept working on the 10 cm problem anyway. The Germans built a magnificent wall to catch the bombers. The British built a pair of eyes to guide them. And the eyes came from a culture that trusted its eccentrics. And the wall came from a culture that did not need to. This is not a claim that one people was cleverer than another. It is not a moral judgment, and it is certainly not a racial one. It is an observation about how two different kinds of systems succeed and fail. A system that runs from the top is fast and disciplined and terrifyingly effective, right up until the moment the men at the top are wrong, at which point the whole thing marches confidently in the wrong direction, and nobody's allowed to say so. A system that runs from the bottom is slow and quarrelome and wasteful, and it lets a hundred bad ideas run loose for every good one. But every so often it lets the good one through when a tidier system would have crushed it. Britain, in this one narrow field, in this one stretch of the war, was lucky in exactly that way.

[00:41:13]It was lucky in the shape of its disorder, and the price of it must be named because it was paid in full, and it was paid on both sides. It was paid by the air crew of bomber command and their bill was staggering. Of the roughly 125,000 men who flew with the command through the war, more than 55,000 were killed. That is not a casualty rate. That is a death rate of very nearly half. Not wounded, killed.

[00:41:37]These were volunteers, almost every one of them, and the average age at which they died was around 23. On the worst single night, a raid on Nuremberg at the end of March 1944, 95 bombers failed to return out of just under 800 sent, and more than 500 young men died in a single darkness. The machines that let them see the target did not make them safe.

[00:41:59]Nothing made them safe. They flew out into the longest odds of any branch of the British War, night after night, and half of them did not grow old, and the price was paid far more heavily still by the people beneath the bombs. The clearest and most terrible demonstration of everything these systems could do came at Hamburg in the last week of July 1943 in a series of raids. The British code named after the book of Genesis after the destruction of the cities of the plane, aided by good weather by H2S mapping the city on the Elby, by the Pathfinders marking it with cold precision, and by a new device that blinded the German radar with clouds of metal foil, the bombing achieved a concentration never seen before. On one dry, hot night, the fires the bombs lit did something the planners had not fully imagined and could not fully control.

[00:42:46]They joined together into a single firestorm, a tornado of flame that sucked in air at hurricane speed that reached temperatures that melted glass and asphalt that consumed whole districts and the people sheltering in their cellars beneath them. The exact number of the dead will never be known.

[00:43:01]It is most often given as around 37,000 people in a single week. Most of them civilians, many of them women and children who died not of fire, but of the poisoned air the fire pulled from their own cellars. This part of the story is not a triumph, and it should not be told as one. The morality of the bombing of cities is a vast and painful argument, and it is not the argument of this account. But the cost is part of the truth, and to leave it out would be a lie of a mission. The genius in the huts at Malvin, the courage of the boys in the bombers, the whole brilliant apparatus of seeing in the dark was built to do this, and it did it. Both things are true at once. The cleverness was real, and the suffering was real, and an honest telling holds them both in the same hand. Let me be careful and honest about the telling itself, too, because you deserve that. The scene this account opened with, the German engineers gathered around the wrecked radar on the workbench in Berlin, is drawn from the real events of that reconstruction, but it is a reconstruction, assembled from several accounts of how the captured set was studied. The recovery near Rotterdam was real. The study group at Telephun was real. The astonishment was real, and it is recorded. But no single transcript survives of one man holding the magnetron to the light. And so that opening moment stands in for the documented shock of many men across many days. The words attributed to the German commander come to us through a historian's account rather than from a recording made in the room. And they given here as that, as reported speech, not as a certain quotation. Everything else, the dates, the machines, the men, the numbers, is set down as the record has it. And where the record is uncertain, as with the dead of Hamburg, it has been said to be uncertain. What can be set down without any doubt at all is the names, and a few of them deserve to be spoken. David Benes and But the quiet civil servant whose honest counting forced a whole air force to face how badly it was failing. Robert Dippy, who gave the navigators a way to know where they were. Alec Reeves, who taught a bomber to fly a note through the darkness and who died with almost no public recognition for it. Bernard Lvel who built the eyes that saw the cities and who lived on to build a far greater eye that looked instead at the stars.

[00:45:19]Alan Blumlin and the 10 men who died with him over the Welsh hills before the machine they were perfecting ever reached the enemy. Donald Bennett, the hard, brilliant Australian who turned all that invention into a method that worked. And behind them the anonymous crowd of the huts, the buffins with their odd habits and their open Sunday arguments. the men a tidier country might never have let into the room. The machine on the workbench in Berlin was eventually understood. The Germans learned how it worked and built their receivers to hunt it and even began far too late to make centimetric radar of their own, roughly 2 years behind, exactly as the British had predicted on the day they decided to take the risk.

[00:46:01]But understanding how the eye worked was not the same as taking it away. To the end of the war, British bombers carried their own light with them into the dark and looked down and saw the cities laid out beneath them in glowing radio fire.

[00:46:14]The Germans on the ground never did solve the deeper puzzle, the one that was never really about copper and wavelengths at all. They never solved the question of why it had been the enemy and not themselves who had walked through that open door. The answer was not in the machine. The answer was in the two different countries that stood behind it. If you found something here worth keeping, the best thing you can do is say a name in the comments. If your father or your grandfather flew with bomber command or worked the radar sets or stood in one of those cold laboratories on the coast, tell us who he was and where he served. These men are slipping now past the edge of living memory, and a name spoken is a small light held up against that dark.

[00:46:55]Their story was that a country at war found its oddballs in time and listened to them and learned to see. It is worth remembering how close it came and what it cost and how strange and human the whole thing was from beginning to