Why German U-Boat Captains Couldn’t Explain How British Aircraft Found Them In Total Darkness

May 15th, 1943, 0237 hours, the Bay of Biscay. A Type 7C U-boat is on the surface charging her batteries. The diesels are running hard. The watch on the bridge is four men in oilskins scanning the horizon by eye because the night is moonless and the sea is black. The first watch officer is a professional.

He has done this 200 times. He knows the procedure. The boat is 40 miles from the nearest reported convoy. The Metox receiver below his feet is silent. The aerial, the wooden cross they call the Biscay cross, is turning in the wind and hearing nothing. No British radar, no threat. The book says they are safe.

At 0239 hours, the engine note in the sky arrives a quarter second before the light. A 24-in searchlight mounted in the belly of a Wellington bomber opens directly above them at 1 mile. The light is, by the records of the Royal Air Force, 22 million candlepower. It turns the conning tower into a stage. The first watch officer has time for one order. He does not finish it.

Six Torpex depth charges straddle the casing. The pressure hull splits behind the engine room. The diesels are still running when the water reaches them. 47 men go down with the boat. The Metox receiver below their feet is still silent. Pause on that sentence. It is still silent. This is not a story about a searchlight.

This is not a story about a Wellington bomber. This is a story about a piece of copper the size of a paperback book machined 3 years earlier in a basement laboratory at the University of Birmingham that a German U-boat captain in May 1943 could not hear, could not detect, could not believe in, and could not survive. Part 1.

To understand what was happening to the U-boats in the spring of 1943, we need to understand what the U-boats believed. They did not believe they were blind. They believed the opposite. They believed they had the most advanced radar warning equipment in the world. The receiver was called the Metox. The full designation was Funkmessbeobachtungsgerät 1, type A 600A.

It was manufactured in occupied Paris by the firms Metox and Grandin. It entered service in August 1942. By the spring of 1943, every operational U-boat carried one. The Metox worked. That is the thing the story has to concede first. The Metox worked beautifully against the British radar of 1942. The British radar of 1942 was called ASV Mark II, air to surface vessel Mark II.

It transmitted on a wavelength of 1.5 m. The Metox was tuned to listen across roughly 1.3 to 2.6 m. When a British aircraft fitted with ASV Mark II swept its beam across a surfaced U-boat, the Metox heard the pulse from about 30 mi away. The bridge alarm rang. The captain ordered an emergency dive. The boat was beneath the surface long before the aircraft could see her.

This was the system. This was the doctrine. For 8 months it worked. In November 1942, the wolf packs sank 117 Allied merchant ships totaling 744,000 tons. In March 1943, in the first 20 days alone, they sank more than 500,000 tons. Stephen Roskill, the official historian of the Royal Navy, wrote that, in his words, “The Germans never came so near to disrupting communications between the New World and the Old as in the first 20 days of March 1943.

” Pause on that sentence. The official historian. The first 20 days of March. The man commanding the German submarine arm believed he was winning. His name was Karl Dönitz. He had 240 operational U-boats. He had 118 of them at sea. He had a son in the boats. He had the Atlantic by the throat. His scientist had a theory.

The theory was that British radar operated on long wavelengths because long wavelengths were the only wavelengths on which radar could operate at useful power. The director of the Telefunken radar laboratory, a physicist named Wilhelm Runge, had argued the case formally. “Centimeter waves,” he said, “would reflect specularly.

They would bounce off ships like light off a mirror. The return signal would be too weak, and no transmitter in the world,” he said, “could generate centimeter waves at high power. The physics did not allow it.” In November 1942, the German Air Ministry, on Runge’s advice, shut down its centimetric and decimetric radar research laboratories.

The decision was reaffirmed on January 15th, 1943. His assessment was not insane. It was based on available data. The problem was that it was 2 years and 7 months out of date. Part two. The piece of copper had been made on February 21st, 1940. The two men who made it were named John Randall and Harry Boot.

They worked at the University of Birmingham in the physics department, in the Poynting building. Their head of department was an Australian physicist named Mark Oliphant. Oliphant had been given an Admiralty contract to produce a transmitter capable of generating 1 kW of power at a wavelength of 10 cm. Oliphant had looked at the American klystron and judged it too weak.

He gave the problem to Randall and Boot, and went back to his own work. Randall and Boot were not famous. They were not professors. They were a lecturer and a research fellow. They had no production line. They had no theoretical breakthrough. They had a workshop, a hand drill, a block of solid copper, and an idea.

The idea was to take the existing magnetron, which was an old device, and to drill six cylindrical holes in a ring around its cathode. Each hole would be a resonant cavity. Electrons crossing the gap between cathode and anode, twisted by a magnetic field, would excite the cavities into oscillation at a frequency determined by their dimensions.

The vacuum would be inside the copper block itself. The heat would dissipate into the copper. There would be no glass envelope to fail. They machined the anode. They sealed the cathode ports with two halfpennies and a smear of wax. They evacuated the chamber. They turned on the power. On the bench, the neon indicator lamps in the laboratory began to glow.

The wavelength was 9.8 cm. The power was 400 W. 9.8 cm. Read that number again. The Germans had decided that cm radar was impossible. Two men in a basement in Birmingham with a hand drill and a block of copper had it working on a Wednesday morning in February 1940. By June, the GEC works at Wembley had built a sealed production version.

By September, it was producing 100 kW. By the following May, it was producing 1 MW. It was, by the most conservative comparison, 1,000 times more powerful than the American klystron of the same year. 1,000 times. That is the money number. 1,000 times. Hold it in your mind for the rest of this story because every U-boat that died in May 1943 died because of a factor of 1,000.

In August 1940, with the Battle of Britain at its height, Winston Churchill agreed to send the device to the United States. The mission was led by Sir Henry Tizard. The magnetron, serial number 12 from the GEC works, was carried across the Atlantic by an Australian physicist named Edward Bowen, who slept with the locked metal deed box at his feet for the entire voyage.

On September 12th, 1940, he opened it in Washington. The American official historian, James Finney Baxter III, later wrote that those who brought it to America had carried, in his exact words, the most valuable cargo ever brought to our shores. Pause on that sentence. The most valuable cargo ever brought to our shores.

Men like Randall and Boot who built it, men like Bowen who carried it, men like the Coastal Command crews who would soon fly it over the Bay of Biscay, they deserve to be remembered. Every like on this video keeps the story of that copper block in the deed box visible for a few more people. It does not cost anything.

It matters more than it should. Part three, the instrument the Coastal Command crews flew was called ASV Mark III. The development was led at the Telecommunications Research Establishment at Malvern by Bernard Lovell, who later built the radio telescope at Jodrell Bank, and by Robert Hanbury Brown. It was, at its heart, the bomber radar called H2S adapted for the anti-submarine role.

It operated at 10 cm. It could see a surfaced U-boat at 9 to 12 nautical miles in any weather, in total darkness. It was carried by the Vickers Wellington Mark XII, by the Consolidated Liberator, and by the Short Sunderland. It was first carried into action on the evening of March 1, 1943.

Two Wellington Mark XIIs of 172 Squadron took off from RAF Chivenor in Devon and flew west into the Bay of Biscay. The first kill credited to the new set was on March 20, 1943, when Wellington G George of 172 Squadron, captained by Flying Officer Stansbridge, sank U-665. The U-boats heard nothing. They heard nothing because the Metox receiver, tuned to 1.

5 m, could not hear 10 cm. It was deaf. From the night of March 1st, every surfaced U-boat in the Bay of Biscay was deaf. They did not know they were deaf. The set was on. The aerial was turning. The reading was zero. The reading was zero because the receiver could not hear, not because the sky was empty. You need to imagine the cumulative effect of this.

A man on a bridge in oilskins, in a moonless sea, who’s been told by the most senior officers in his service that he is protected, who looks at the gauge, who sees zero, who believes the gauge. Now, place the searchlight above him. The searchlight was called the Leigh Light. It was the invention of a Royal Air Force officer named Humphrey de Verd Leigh.

It was a 24-in carbon arc lamp, retractable, mounted in the belly of a Wellington. The radar found the U-boat at 9 mi. The pilot closed at 145 knots. At 1 mi, the light came on. At 300 yd, the depth charges left the rack. The combination was first used in earnest in the summer of 1942. By the spring of 1943, with the new 10 cm set replacing the old meter set, it became something for which the German navy had no answer.

The allies called the months that followed by their proper name. They called them black May. Part four. 41 U-boats died in May 1943. The figure is the count of Karl Dönitz himself in his post-war memoir. It is the count of the official British historian. One U-boat every 18 hours. There were three convoy battles inside that month, and the names of those battles are the spine of the story.

The first was ONS 5. 42 slow westbound merchantmen in ballast, escorted by Commander Peter Gretton in HMS Duncan with escort group B7. They were attacked by more than 40 U-boats from the wolf pack Star Spect and Fink. A force 10 gale reduced the convoy to under three knots for three days. On May 3, with 4% of his fuel remaining, Gretton was forced to turn for St.

John’s, and command passed to Lieutenant Commander Robert Sherwood in HMS Tay. On May 5, the weather changed. The wind dropped. A thick fog rolled in. The fog blinded the German lookouts on the bridges of the U-boats. It did not blind the British. The British escorts had a centimetric ship-borne radar called type 271. It was made of the same physics as the magnetron.

In one night, six U-boats were sunk. U531, U638, U125, U192, U438, U630. Six commanders, six crews. None of them saw the escort that killed them because the escort was in the fog. Roskill wrote of that engagement that in his exact words this seven-day battle fought against 30 U-boats is marked only by latitude and longitude and has no name by which it will be remembered.

But it was in its own way as decisive as Quiberon Bay or the Nile. The second battle was HX237 eastbound. Three U-boats sunk, no main convoy ships lost. Among the dead was Kapitänleutnant Max-Martin Teichert in U-456, a holder of the Knight’s Cross, the man who had crippled HMS Edinburgh in 1942. He was killed on May 12 by a new American weapon called the Mark 24 mine, which was not a mine at all.

It was an acoustic homing torpedo dropped from the air that listened for the sound of his propellers and ran him down. It was the first operational kill of that weapon in the history of war. It was dropped by a Liberator of 86 Squadron flying out of RAF Aldergrove in County Antrim. The third battle was SC130 eastbound, 11 to 25 May.

Escort Group B7 again, Gretton again, reinforced by the first support group with the River Class frigate HMS Jed and the Banff Class sloop HMS Sennan. On May 19, southeast of Cape Farewell at 54° 54′ N 34° 19′ W, Jed and Sennan fired their Hedgehog mortars at a contact below the surface. The bombs burst on the casing of U-954.

U-954 was on her first war patrol. She was commanded by Kapitänleutnant Otto Loewe. His father had been an Imperial Navy airship commander killed in the North Sea in 1916. Loewe’s second watch officer was a 21-year-old Leutnant zur See named Peter Dönitz. Two days later in Berlin, the commander-in-chief of the U-boat arm was told that his son’s boat had failed to report. 47 men, all hands, no survivors.

You need to know something about Karl Dönitz on the day he received that signal. He was not a fool, he was not a coward, he was a serious professional officer who 3 years earlier had nearly broken the British Empire by his own clear strategic insight. His son was dead. His boats were dying every 18 hours.

He had 240 submarines, the most he had ever had, the most Germany would ever have, and they were no longer winning. In his war diary entry of May 24, 1943, he wrote that in the formal language of the document, the enemy’s radar makes battle in the previously favorable concentration areas no longer possible. He wrote that the losses were too high.

He withdrew the wolf packs from the North Atlantic and redirected them south of the Azores. In his post-war memoir, with 20 years to think about it, he wrote a shorter sentence. He wrote, in his exact words, “In May 1943, we lost 41 U-boats. We had lost the Battle of the Atlantic.” Pause on that sentence. The man who started the U-boat war, the man who designed the wolf pack tactic, “We had lost the Battle of the Atlantic.

” If your father or your grandfather or your great uncle served in the Royal Navy in the Atlantic convoys or in Coastal Command or in the Merchant Navy, I would be grateful to hear their name and ship or squadron in the comments. These stories are how the memory survives. Part five. The German Navy did not understand what was killing them.

That is the part of the story that is hardest to hold in the mind because hindsight makes the cause seem obvious. From inside the U-boat in May 1943, it was not obvious. The Metox was on. The aerial was turning. The reading was zero. The German naval staff convinced themselves of an explanation. The explanation was that the Metox itself was betraying them.

They came to believe that the local oscillator inside the Metox receiver radiated a small signal of its own and that the British aircraft were homing on that signal. On July 31, 1943, Dönitz signaled the fleet to stop using the Metox. In mid-August, he ordered the equipment removed from the boats and locked away.

They were right that the Metox was useless. They were wrong about why. The MeTox was useless because it could not hear 10 cm. The signal it was leaking was a fiction. The British aircraft were not homing on MeTox emissions. They were not homing on anything emitted by the U-boat. They were sweeping the ocean with the copper block from Birmingham and reading reflections in the dark at 9 mi.

They had been told the answer. They had been handed the answer. On the night of February 2, 1943, a short Stirling of 7 Squadron Royal Air Force, on only the second operational H2S raid in history, had been shot down near Rotterdam by a German night fighter. In the wreckage was the cavity magnetron. The Germans recovered it.

They named it the Rotterdam Gerät, the Rotterdam apparatus. The committee that examined it met for the first time at Telefunken in Berlin on February 22nd, 1943. 3 weeks. The Germans had 3 weeks between holding the answer in their hands and the first Coastal Command patrol that would use it to kill them. They could not move fast enough.

The German countermeasure, receiver called Naxos that could hear 10 cm, did not reach the U-boats until October 1943. By then, the boats were already losing the Atlantic and the Allies were already moving to a new wavelength of 3 cm that Naxos could not hear either. The Germans were not stupid. They were locked inside an assumption.

The assumption had been signed off by their most senior radar scientist in November 1942. The assumption was that no one could build a centimetric transmitter at useful power. They had told themselves it was impossible. Two men in a basement in Birmingham with a hand drill and a block of copper had made it work in 1940.

At Nuremberg in May 1946, Karl Dönitz testified to the tribunal. He said, in his exact words, “The airplane, the surprise by airplane, and the equipment of the planes with radar, which in my opinion is, next to the atomic bomb, the decisive war-winning invention of the Anglo-Americans, brought about the collapse of U-boat warfare, the decisive war-winning invention. Read that line again.

The man who commanded the U-boats, the man who tried to break Britain said it at Nuremberg under oath. The verdict. Why couldn’t German U-boat captains explain how British aircraft found them in total darkness? Because they had been told by their own scientists that the instrument that was finding them could not exist.

They had been told it by professionals. They had been told it on the basis of physics that was correct as far as it went, but 2 years out of date. And by the time the wreckage of the Stirling at Rotterdam disprove the doctrine, it was 3 weeks too late and 41 boats too late and one son too late.

The Germans had a theory of physics. The British had a hand drill and a block of copper. The Germans had a receiver tuned to the wavelength they expected. The British had a transmitter on the wavelength the Germans believed impossible. The Germans had a doctrine signed off in committee. The British had two men in a basement who did not know they had won the war.

This is the British amateur tradition at its most lethal. Not a great industrial program, not a heroic individual genius. Two physicists who were not famous given a problem by a head of department who had something else to do working with a piece of metal and a hand drill in February 1940.

The Royal Air Force Coastal Command lost 5,863 air crew in the Second World War. They are buried across the Atlantic seaboard from Iceland to Cornwall to Northern Ireland. They are not as famous as Fighter Command. They are not as famous as Bomber Command. Their war was, in Winston Churchill’s words, not the form of flaring battles and glittering achievements.

It was, in his words, statistics, diagrams, and curves unknown to the nation. They flew at night, in weather, over water, alone, for 10-hour patrols for a chance at one contact against an enemy who could dive. They were the men who carried the copper block to its work. Squadron Leader Terence Bullock of Lisbon, two Distinguished Service Orders, two Distinguished Flying Crosses, the most successful anti-submarine pilot of the war.

Squadron Leader Peter Cundy, DSO and bar. Flight Lieutenant Wright of 86 Squadron, the first man to kill a U-boat with an acoustic homing torpedo. Flying Officer Stenbridge of 172 Squadron, the first man to kill a U-boat with centimetric radar. Flying Officer Proctor of 120 Squadron, who killed U-258 at SC130. These are the names that should not be allowed to disappear.

And on the other side, Kapitänleutnant Otto Loewe of U-954, son of an airship commander, killed by the same physics that had killed his father. Kapitänleutnant Max Martin Teichert of U-456, who had crippled HMS Edinburgh. Kapitänleutnant Wilhelm von Messenhausen of U-258, born in Sydney to a German consular family. Worthy men, professional men, killed in the dark by something they did not know was there. Karl Dönitz survived the war.

He outlived his sons. Peter died in U-954 in May 1943. Klaus died in a torpedo boat in the channel in May 1944 on his 24th birthday. Dönitz wrote in his memoir, in his exact words, “We had lost the Battle of the Atlantic.” He never explained how it had happened. He never could. The answer was 400 watts of microwaves generated by a block of copper sealed with two halfpennies and a smear of wax on a bench in a basement at the University of Birmingham on a Wednesday morning in February 1940. That is the answer. That

is the whole of the answer. Subscribe if you want the next chapter because there are more of these, more instruments, more inventors, more men who flew at night over the Atlantic.