March 17, 1943 — The Moment German Intelligence Realized The Strategic Tide Had Turned | WWII

March 17th, 1943. 0900 hours. Deep beneath the streets of London, in a reinforced concrete bunker, the staff called Lenin’s tomb, Commander Roger Wyn stared at an enormous plotting table covered with colored pins. Each pin represented a German submarine. Each cluster of pins represented death stalking Allied shipping lanes.

For 9 days, the codereers at Bletchley Park had been completely blind. The naval Enigma Cipher had gone dark on March 10th, and now two convoys carrying nearly a million tons of vital supplies were sailing directly into the largest concentration of hubot the war had ever seen. In the freezing gray swells of the Mid-Atlantic, where the water temperature hovered just above freezing and survival time for a man in the ocean measured in minutes, over 40 German submarines were converging on convoys HX229 and SC122.

The merchant ships carried 170,000 tons of petroleum, 150,000 tons of frozen meat, 600,000 tons of ammunition, aircraft parts, tanks, locomotives, and military vehicles. Everything Britain needed to survive the coming year, everything the Allied invasion of Europe would require. And that morning, before the sun had fully risen over the convoys churning wake, the killing had already begun.

Within 24 hours, 14 ships would be torn apart by torpedoes. Within 72 hours, 22 merchant vessels would lie on the ocean floor 3 mi beneath the surface, taking more than 360 men with them into the permanent darkness of the abyss. German radio would proclaim it diga jalites of Schlaon, the greatest convoy battle of all time.

At the Admiral Ty in London, officials would reach a conclusion that chilled every man who read it. It appeared possible, they wrote, that convoy itself could no longer be regarded as an effective system of defense. Yet within 10 weeks of this catastrophe, Grand Admiral Carl Donuts would withdraw his submarines from the North Atlantic entirely.

In his war diary, he would write simply that Germany had lost the Battle of the Atlantic. This is the story of how the hunters became the hunted in the span of 70 days and how a 10-week arc from disaster to triumph changed the course of the Second World War. The Battle of the Atlantic was the longest continuous military campaign of World War II, stretching from September 3rd, 1939, when Britain declared war on Germany to May 8th, 1945 when Germany surrendered.

5 years, 8 months, and 5 days of unrelenting warfare beneath the waves. It was fought across an ocean covering 41 million square miles in conditions ranging from Arctic storms in the Denmark Strait to tropical heat in the Caribbean. Men died in freezing darkness and burning fuel oil. Ships sank in seconds or lingered for hours, their crews watching the sea rise around them.

Winston Churchill, who had led Britain through the darkest hours of the Blitz, who had faced down the threat of German invasion in 1940, and who would see the war through to final victory, later confessed in his memoirs that the only thing that ever really frightened him during the war was the Yubot peril.

Not the Luftwafis bombs raining on London, not RML’s tanks threatening Egypt and the Suez Canal, not even the fall of Singapore and the loss of the Far East. The Atlantic, he understood with perfect clarity, was the jugular vein of the Allied cause. Sever it, and the war was lost. Britain was an island nation, utterly dependent on the sea for survival.

This had been true for centuries, but by 1943, it had become a matter of life and death on an almost inconceivable scale. The nation imported nearly 70% of its food. All of its oil came from overseas, primarily from Venezuela, the Caribbean, and the United States. All of its rubber came from Malaya and the Dutch East Indies, now under Japanese occupation, or from synthetic plants in America.

Most of its raw materials for war production. The iron ore and boite and copper and manganese had to cross the ocean. Every bullet fired by a British soldier came from a factory supplied by imported materials. Every gallon of aviation fuel burned by an RAF Spitfire or Lancaster bomber originated in an American refinery and crossed the Atlantic in a tanker.

Every tank rolling off the assembly lines at Birmingham and Coventry required steel made with imported ore, rubber for its tracks, and fuel for its engine. The entire British war machine depended on a continuous flow of merchant ships crossing 3,000 mi of ocean through waters patrolled by enemy submarines. The mathematics were stark and unforgiving.

Britain required approximately 1 million tons of imports per week simply to survive and maintain its war effort. The nation’s pre-war merchant fleet had totaled approximately 21 million gross register tons. By March 1943, Yubot had already sunk over 13 million tons of Allied shipping. If ships stopped arriving, the nation would begin to starve within weeks.

Factories would fall silent. Aircraft would be grounded for lack of fuel. The war effort would collapse not through military defeat on some distant battlefield, but through slow, grinding strangulation. The German strategy was devastatingly simple in concept. Grand Admiral Carl Donitz, commander of the Yubot Arm and now commanderin-chief of the entire German Navy, had calculated that if his submarines could sink 700,000 tons of Allied shipping per month, Britain would be forced to surrender within a year. He called this

approach the tonnage war. Every ship destroyed, regardless of its cargo or destination, brought victory closer. Donuts did not need to win traditional naval battles with battleships and cruisers. He did not need to contest command of the sea in the classic sense. He simply needed to sink ships faster than the allies could build them.

Donuts had spent the years between the wars perfecting wolfpack tactics known in German as rud tactic, specifically designed to overwhelm convoy escorts through coordinated mass attacks. The system worked like a deadly choreography rehearsed a thousand times. Ubot would spread out in long patrol lines stretching hundreds of miles across the projected routes of Allied convoys.

Each submarine in the line was positioned roughly 15 to 20 m from its neighbors. Close enough that a convoy could not slip through undetected, far enough apart to cover maximum motion. When one submarine spotted a convoy, it would not attack immediately. A single submarine attacking a defended convoy faced overwhelming odds.

Escorts would drive it down. depth charge it, force it to break off. Instead, the spotting boat would shadow the formation, maintaining contact from the edge of visibility, and transmit a contact report to Yubot headquarters in France. The message would include the convoys position, course, speed, and composition. At headquarters, Donits or his chief of operations, Admiral Ebahard got would plot the convoys position on a massive wall chart and calculate which hubot could reach it.

Every available submarine within range would receive orders to converge at maximum speed. The boats might take 12, 24, or even 48 hours to reach the convoy, running on the surface at their maximum speed of 17 to 18 knots, faster than most merchant ships and many escorts. The attack would come at night when the submarines could operate on the surface in near total invisibility.

The low silhouette of a surfaced Uboat, barely 8 ft of conning tower above the water line, was almost impossible to see against the black water. The submarines would penetrate between the escort ships into the columns of merchant men. They would fire their torpedoes from pointblank range, often less than a thousand yards, and slip away in the confusion.

By the time escorts could react, multiple ships might already be sinking, their crews dying, their cargos lost. By early 1943, Dennits commanded nearly 400 Yubot. This was more than triple his strength at the start of the war when he had possessed just 57 submarines and more than double the number he had considered the minimum necessary to defeat Britain.

German shipyards working around the clock despite Allied bombing raids were now producing roughly 20 new boats every month, a production rate that exceeded combat losses. On January 30th, 1943, Hitler promoted Dunits to Grand Admiral and Commanderin-Chief of the entire German Navy, replacing the cautious Eric Ryder, who had favored surface raiders over submarines.

Yet, Donitz retained personal control of Yubot operations. He was not merely an admiral now, but remained the Wolfpack commander, coordinating every major attack from his headquarters. The Allies possessed one weapon the Germans did not suspect. A weapon that could read the enemy’s most secret communications. At Bletchley Park, a Victorian estate 50 mi northwest of London, over 10,000 mathematicians, linguists, clerks, and technicians worked around the clock in wooden huts and brick buildings to crack the German Enigma cipher. The work was so secret

that most people in Britain had never heard of Bletchley Park and would not learn what happened there until decades after the war ended. The Enigma machine, which resembled a typewriter connected to a panel of lights, used a system of three or four rotors and a plugboard with 26 connections to encrypt messages.

Each keystroke sent an electrical current through the rotors, which scrambled the input according to their internal wiring. The rotors advanced with each keystroke, so the same letter pressed twice would produce two different encrypted outputs. With the rotors set at any of billions of possible positions, and the plugboard adding additional complexity, the number of possible settings exceeded 150 million million million.

The Germans believed the cipher was mathematically unbreakable. No human could test all the combinations. No mechanical device could process them fast enough to matter. They were wrong. The man who made the breakthrough possible was Alan Turing, a brilliant Cambridge mathematician who had published a groundbreaking paper on computable numbers in 1936.

Turing arrived at Bletchley Park on September 4th, 1939, the day after Britain declared war on Germany. He was 27 years old, awkward, eccentric, and possessed of one of the finest mathematical minds of the 20th century. Turing took on the challenge of naval enigma because, as he later explained with characteristic bluntness, no one else was doing anything about it, and he could have it to himself.

Turing designed the bomb, an electromechanical device standing 6 ft tall and weighing roughly a ton that could test thousands of possible Enigma key settings per hour. He developed banarismas, a statistical technique using sequential conditional probability that dramatically reduced the number of rotor settings that needed to be tested.

The method exploited subtle patterns in the way German operators chose their daily key settings, patterns that would have been invisible to anyone without Turing’s mathematical insight. The classified history of hut 8, the section responsible for naval enigma, later recorded that if anyone was indispensable to the entire effort, it was Turing.

But mathematics alone could not crack naval enigma. The breakthrough required physical capture of codebooks and machine components that would reveal the current settings. On May 9th, 1941, Sublutie Lieutenant David Balmer led a boarding party onto the sinking U110, which had been forced to the surface by depth charges from HMS Bulldog during an attack on convoy OB318 in the North Atlantic.

Balmy climbed down through the Conning tower hatch into the abandoned control room, expecting the submarine to sink at any moment or explode from scuttling charges. Working by flashlight in a compartment half flooded with seawater, he recovered an intact Enigma machine along with the crucial short signal code book and other documents.

The material reached Bletchley within days and allowed the codereers to read the dolphin cipher used by Atlantic Ubot. For the rest of 1941 and into early 1942, the submarine tracking room in the Admiral Ty could read German communications, often within hours of transmission. They could route convoys around Wolfpack patrol lines.

Shipping losses dropped dramatically. But on February 1st, 1942, the Germans introduced a new four rotor enigma machine for their submarine fleet using a cipher code named Triton. Bletchley called it Shark. The fourth rotor, called Gamma or Beta, depending on its setting, increased the machine’s complexity by a factor of 26.

The bombs designed for three rotor enigma were suddenly inadequate. For over 10 months, from February to December 1942, Bletchley Park was completely blind to Yubot communications. During this terrible blackout, German submarine attacks surged catastrophically. Allied shipping losses reached over 700,000 tons in a single month, exceeding Donuts’s victory threshold.

The Wolfpacks operated with near impunity, intercepting convoy after convoy that Bletchley could no longer reroute. The crisis was existential. The breakthrough that restored Allied intelligence came through extraordinary courage and terrible sacrifice. On October 30th, 1942, the destroyer HMS Patard, commanded by Lieutenant Commander Mark Thornton, cornered U559 in the Eastern Mediterranean near Port Say after a 16-hour pursuit.

Thornton’s crew had subjected the submarine to repeated depth charge attacks throughout the day and night. Finally, at approximately 2200 hours, the damaged Yuboat was forced to the surface in the darkness. As the German crew abandoned their sinking vessel, three British sailors made a decision that would change the course of the war.

Lieutenant Anthony Fasum was 29 years old, the first officer of Patard, a career naval officer from Lantern near Jedbur in Scotland. He was described by his captain as the bravest officer he had ever met. Able Seaman Colin Graasier was 22 from the village of Tamworth in Staffordshire. a quiet young man who had joined the Navy at the outbreak of war.

Tommy Brown was the ship’s 16-year-old canteen assistant, technically too young for combat service, who had lied about his age to join. Without waiting for orders, Fon and Graier stripped off their clothes and dove into the dark water. They swam to the sinking yubot and climbed up onto its listing deck. Tommy Brown followed.

The three men climbed down through the conning tower hatch into the flooded control room. Working in near total darkness with water rising around them with the submarine settling deeper every minute, Facon and Graier located vital documents in the captain’s cabin and the radio room. They recovered the second edition of the short weather signal code book, which contained the cribs Bletchley needed to break into the daily cipher settings.

They recovered the short signal code book used for contact reports. They recovered other materials critical to understanding German submarine communications. Tommy Brown standing on the conning tower relayed the waterlogged papers to a motor launch that had come alongside. Then U559 suddenly plunged beneath the waves. There was no warning.

The submarine simply dropped out from under them. Fasen and Graasier went down with it. They drowned inside the submarine they had been stripping of its secrets. Their bodies never recovered. Both men received George Crosses, Britain’s highest civilian award for bravery. Tommy Brown received the George Medal. At 16, he was the youngest recipient of that decoration in World War II.

The material the three sailors recovered reached Bletchley Park on November 24th, 1942. The crypt analysts worked around the clock. By December 13th, just 19 days later, they cracked back into Shark. The four rotor enigma was broken. The renewed intelligence saved an estimated 500,000 to 750,000 tons of shipping in the first two months alone.

Convoys could once again be routed around Wolfpack patrol lines. Yubot would wait in their designated patrol areas while convoys passed safely miles to the north or south. But the reprieve was fragile. The Germans had achieved their own intelligence triumph, one the Allies would not fully understand until after the war ended.

The Bedinst Germany’s Naval Signals Intelligence Service had broken Allied naval cipher number three, the convoy rooting cipher used jointly by British, American, and Canadian navies to coordinate the movement of Atlantic convoys. The cipher had been in use since January 1942, and Bedinst crypt analysts had been reading it with increasing success.

From December 1942 through May 1943, BDInst was reading approximately 80% of intercepted messages in this cipher. Donuts’s son-in-law, Ga Hesler, later stated that they had reached a stage when it took only one or two days to decrypt British radio messages. On some occasions, only a few hours. This meant Donuts could read Allied convoy routing instructions and position his wolfpacks directly in their path.

While the Allies thought they were rooting convoys around Yubot concentrations, the Germans were reading those rooting orders and moving to intercept. It was a deadly intelligence stalemate that neither side fully recognized. The Allies believed they had the advantage through Ultra. The Germans believed they had the advantage through BD inst.

Both were partially right. Both were reading the others mail. Then disaster struck at Bletchley Park. On March 10th, 1943, the Germans changed their short weather report format. This was a routine procedural change, the kind of minor administrative adjustment militaries make constantly, but it had catastrophic consequences.

The stereotyped text of the old weather format had provided cribs, fragments of probable plain text that Bletchley used to test Enigma settings. Without cribs, the bombs could not work efficiently. The daily key could not be broken in time to be useful. For nine critical days from March 10th to March 19th, the submarine tracking room was effectively blind to Ubot positions.

Commander Wyn fell back on intuition, traffic analysis, and what he called useful fictions, educated guesses about where the submarines might be. During those nine days, two convoys sailed into the largest ambush of the war. Convoy SC122 departed New York on March 5th, 1943. It was a slow convoy of 50 merchant ships making 7 to 8 knots, the maximum speed of its slowest vessels.

The ships carried cargos ranging from grain and lumber to fuel oil and military vehicles. The convoy was escorted by Commander Richard Bole’s B5 escort group aboard the destroyer HMS Havlock supported by four corvettes and two other escort vessels. It was standard escort strength for the time, but badly inadequate for what lay ahead.

Convoy HX229 departed 3 days later on March 8th. This was a faster convoy of 40 ships making 9 to 10 knots, including several tankers carrying aviation fuel desperately needed by the RAF and several cargo vessels loaded with disassembled aircraft, ammunition, and military vehicles destined for the buildup of American forces in Britain.

The convoy was escorted by the B4 escort group under Lieutenant Commander Gordon Luther in the destroyer HMS Volunteer. Luther was a competent officer, but he was on only his second Atlantic crossing. The regular group commander, Commander Edward Day, was unable to sail because his ship, HMS Highlander, was in dock for urgent repairs.

Luther found himself in command of an escort group he barely knew, protecting a convoy of nearly 100,000 tons of critical supplies, sailing into the deadliest waters in the world. The situation was even worse than it appeared. When HX229 reached its Mid-Atlantic escort rendevous point on March 14th, not a single warship was waiting.

A miscommunication, a scheduling error, the kind of administrative failure that plagues every military operation, had left the convoy completely undefended at the most dangerous point of its crossing. Commodore Maurice Mel, the senior merchant marine officer commanding the convoy, had no choice but to press forward into yubotinfested waters for nearly 24 hours until the B4 escort group finally caught up on the evening of March 14th.

Meanwhile, German intelligence was working with devastating efficiency. BDNS had intercepted and decoded the rooting orders for both convoys. Dunits knew exactly where they would be and when. Three wolfpacks were deployed to intercept them. Group Ralgraph, meaning robber baron, contained 13 submarines deployed in a patrol line across the expected track.

Group Sturma, meaning daredevil, had 19 submarines. Group Danganger, meaning Harrier, had 11 submarines. Over 40 Yubot formed a steel net across the mid-atlantic air gap. The 350 nautical mile stretch of ocean beyond the range of any land-based aircraft. German submariners called this area dust toadus lock the death hole because convoys caught there had no air protection whatsoever.

Aircraft could not reach them. They were utterly alone with the wolves. The greatest convoy battle of the war was triggered by pure accident. U653 commanded by Capitane Loit and Ghard Failure was not even supposed to be hunting. The submarine was heading home to France with serious mechanical problems.

Crewmen had been swept overboard during a storm. Fuel was running dangerously low. Only a single torpedo remained aboard, and testing had shown it was probably defective. On the morning of March 16th, Filer’s exhausted lookout cited HX229 heading east through the gray Atlantic swells. The convoy was a dark mass on the horizon, barely visible, recognized only by the telltale smoke rising from dozens of funnels.

Had the lookouts been less alert? Had they turned away a moment sooner, the convoy might have passed unnoticed. Failure immediately transmitted a contact report, broadcasting the convoys position, course, and speed. At Yubot headquarters, Donuts and Got plotted the coordinates on their wall chart and recognized the opportunity.

Here was a major convoy in the air gap with inadequate escorts. Orders went out by radio to every submarine in range. All of Rabgraph was directed to pursue at maximum speed. Sturmer and Dranganger were ordered to form a blocking line ahead of the convoy’s projected track. Within hours, over 40 submarines were converging from every direction.

The first night was devastating beyond anything the convoy escorts had experienced. Eight ships were torpedoed in just 8 hours between dusk on March 16th and dawn on March 17th. U603 commanded by Capitan Lloyd and Hans Yoim Bertlesman sank the Norwegian freighter LN K. U758 commanded by Capitan Loitant Helmouth Mansk sank the Dutch vessel Zanland.

U6000 commanded by Capitan Lloyitant Bernhard Zurlan sank the British tanker Southern Princess the largest ship in the convoy at over 12,000 gross register tons. When Southern Princess went down, she took with her thousands of tons of fuel oil desperately needed in Britain. The worst single blow came from U91 commanded by Capitan Lloydant Hines Walkering.

Shortly after midnight on March 17th in the darkest hours before dawn, Walker maneuvered his submarine between the escort screen and penetrated into the columns of merchant men. He selected the American freighter Harry Lukenbach, a Liberty ship carrying a mixed cargo that included ammunition.

His torpedo struck amid ships. The explosion was catastrophic. The ammunition cargo detonated in a blinding flash, visible for miles across the dark ocean. All 80 persons aboard died instantly. 54 merchant seaman of the American Merchant Marine and 26 sailors of the United States Naval Armed Guard were killed in a single moment.

Not a single body was ever recovered. Not a single piece of identifiable wreckage was ever found. The Harry lookbark simply ceased to exist, vaporized in a column of fire that rose hundreds of feet into the night sky. Also lost that first night were the British ships Corissero and Turcoili, the latter going down with 36 of her merchant seaman.

The American Liberty ship James Ogulthorp was torpedoed and sank with 44 of her crew. The American freighter William Eustace went down with most hands. Walker reported to headquarters that the convoys defenses were apparently weak. He was right. Two escort vessels had dropped out of the screen to rescue survivors from torpedoed ships, leaving gaps through which more hubot were penetrating.

March 17th, 1943 was the single darkest day of the entire Battle of the Atlantic. That morning, while the sun rose over HX229 and the surviving crew members counted their losses, the situation deteriorated further still. At approximately 0900 hours, U338 commanded by Capitan Litant Manfred Kinsel cited the slow convoy SC122 approximately 120 mi from the position of HX229.

Kinsel was an aggressive commander who had already sunk several ships in previous patrols. He attacked immediately with lethal speed and accuracy. In rapid succession, in the span of less than 3 hours, Kinsel torpedoed and sank four ships. The British freighter Kingsbury went down with her cargo of military supplies.

The Welsh ship King Gruff was torpedoed and sank with 22 of her crew. The British vessel Aldderamin was sent to the bottom. The Canadian ship Fort Cedar Lake, loaded with war materials bound for Britain, joined them on the ocean floor. It was one of the most effective single attacks by any submarine commander in the entire war.

Donuts realized that two convoys were within striking distance and made a fateful decision. He split his wolfpacks to attack both simultaneously. What followed was wholesale slaughter. Approximately 14 ships were sunk across both convoys on March 17th alone. It was the single worst day of merchant shipping losses in the entire war.

The carnage continued through March 18th. U221 commanded by Oopnet Hans Hartwig Troger found HX229 again at dawn and launched another deadly assault. He torpedoed and sank the American Liberty ship Walter Q. Gresham, killing 27 of her crew. Then he attacked the British refrigerator ship Canadian Star, which was carrying frozen meat for the British population.

She went down with 34 of her crew and passengers. Troger was awarded the Knights Cross of the Iron Cross by radio transmission during the battle itself. It was an almost unprecedented honor, a mark of how highly German naval command valued his achievement. He received the message on the surface between attacks, read it to his crew, and then dove to continue the assault.

6 months later, on September 27th, 1943, Troj and his entire crew of 50 men would be killed when U221 was sunk by a British Halifax bomber of coastal command south of Ireland. He never wore his Knights Cross ashore. Panic began spreading through the convoy. Merchant crews who had survived one or two torpedoings before found their nerve-wracking.

The American freighter Matthew Lukenbach, her crew terrified by the surrounding slaughter, broke convoy discipline and attempted to escape independently at her maximum speed. It was a fatal mistake. A ship alone was far more vulnerable than a ship in convoy. She sailed directly into the Wolfpack, attacking SC122 and was torpedoed first by U527 and then by U523.

She went down with heavy loss of life. The British steamer, Clarissa Radcliffe, had separated from SC122 during a storm on March 9th and had been sailing alone for 10 days, struggling to catch up with the convoy she had lost. On March 18th, she was spotted by U663. The submarine closed to attack range and fired a spread of torpedoes.

All 53 persons aboard perished. No distress signal was received. No survivors were ever found. The Clarissa Radcliffe simply vanished from the face of the ocean. Her final position never precisely determined. By March 19th, Allied reinforcements finally began arriving, and the balance shifted at last.

Very long range Liberator bombers from RAF Coastal Command, flying from bases in Iceland at the very limit of their range made some of the first effective patrols into the air gap. Their presence forced Yubot to dive and lose contact with the convoys. A submarine underwater could make only four or five knots compared to a convoys 7 or eight.

Once forced down, the Yubot fell behind and had to surface and race to catch up, exposing itself to air attack. The only German submarine lost in the entire battle was U384 commanded by Oloit and Hans Aim von Rosenberg Grushchinsky. The boat was caught on the surface by an RAF flying fortress and straddled by depth charges before it could dive deep enough to escape. All 49 crew members were killed.

It was poor comfort for the Allies who had lost 22 ships, but it marked the beginning of change. Donuts called off the assault. Both convoys limped into Liverpool on March 23rd. The final toll was catastrophic. 22 merchant ships sunk. Over 146,000 gross register tons lost. More than 360 merchant seaman and naval armed guard killed against a single yubot destroyed.

The exchange rate of 22 to1 was devastating. Germany could sustain such losses indefinitely while the allies bled. German radio triumphantly proclaimed it droit Schluck Ala Zaiton the greatest convoy battle of all time. Newspapers in Berlin celebrated the victory. At the Admiral Ty in London, the mood was grim. The official assessment written by men who understood exactly what the numbers meant concluded that it appeared possible that convoy itself, the foundation of Allied maritime strategy since World War I, could no longer be

regarded as an effective system of defense. This was not bureaucratic pessimism. It was honest analysis. If convoys could not protect shipping, there was no alternative strategy. Britain would be strangled. The crisis triggered urgent action at the highest levels of Allied command. On March 18th, while the convoy battle was still raging in the Mid-Atlantic, President Franklin Roosevelt took an extraordinary step.

He made one of only two direct military orders he issued to his commanders during the entire war. Roosevelt ordered Admiral Ernest King, Commanderin-Chief of the United States Fleet, to transfer 60 Liberator bombers from the Pacific to the Atlantic immediately. The aircraft were to close the air gap that had allowed yubot to operate with impunity.

There would be no discussion, no delay, no bureaucratic review. The president had spoken. Admiral Sir Max Horton seized the moment to implement changes he had been demanding for months without success. Horton had taken command of Western Approaches, the Royal Navy Command responsible for protecting Atlantic convoys on November 17th, 1942.

He was perhaps the most qualified officer in any navy to hold such a position. Horton was a legendary World War I submarine ace who understood yubot vulnerabilities because he had once been a submarine commander himself as a young lieutenant in September 1914 just weeks after the war began.

Horton had taken his submarine E9 into the German defended anchorage at Keel and torpedoed the cruiser Hela. It was one of the first submarine victories in naval history. He spent the rest of the war prowling the Baltic, sinking German ships, and developing the tactics that would later make submarines such devastating weapons.

Now, 30 years later, Horton was fighting against submarines rather than commanding them. On his first day in command of Western approaches, he had written that the urgent need for support groups to reinforce convoy escorts was critical. Unless a reasonable number of long endurance destroyers and long-range aircraft came shortly, a very serious situation would develop on the Atlantic lifeline.

His warning had been prophetic. The serious situation had arrived. Horton’s decisive innovation was the support group. These were formations of experienced warships not permanently assigned to any particular convoy. Instead, they could be dispatched wherever needed and held in reserve until crisis struck.

Critically, they were free to hunt submarines to destruction for hours or even days. Regular convoy escorts faced an impossible tactical dilemma. When they detected a submarine, they could attack with depth charges. But then they had to return to their convoy. The merchantmen could not be left undefended while escorts chased a contact.

A skilled yubot commander understood this perfectly. He could simply go deep, rig for silent running, and wait for the escort to leave. Then he would surface and resume the pursuit. Support groups changed this equation entirely. They had no convoy to protect. They could persist on a contact relentlessly, attacking again and again for 2 or 3 days, if necessary, until the submarine was destroyed or forced to the surface by exhausted batteries and suffocating crew.

Horton’s staff ran a war game based on the HX229 disaster, adding hypothetical support groups to the scenario and replaying the battle. The results were striking. The simulation predicted that eight of the 21 ships lost would have survived with support group assistance. Horton presented the findings to the Admiral T. They could no longer refuse.

Five support groups were approved in April 1943, just in time for what the Germans would come to call Black May. The operational embodiment of the new aggressive doctrine was Captain Frederick Walker, known as Johnny to his men and to every officer in the Royal Navy who followed anti-ubmarine warfare. Walker became the most successful anti-ubmarine commander of the entire war.

Ultimately credited with sinking or assisting in the destruction of approximately 20 German submarines. No other officer in any navy came close to his record. Walker had proven his methods with convoy HG76 in December 1941 when his 36th escort group fought a running battle with a wolfpack for 5 days. His ships sank four Ubot in that single engagement.

During one attack, Walker Depth charged U574 and then deliberately rammed the submarine with his own ship HMS Stalk, crushing its pressure hull with his reinforced bow. In February 1943, Walker took command of the second support group aboard the sloop HMS Starling with sister ships Wild Goose, Ren, Woodpecker, Signit, and Kite.

His standing orders to his captains were revolutionary in their simplicity and their aggression. The object of the second support group is to destroy Yubot. This was a fundamental departure from existing doctrine, which focused on safe and timely arrival of the convoy. Walker did not want merely to protect ships.

He wanted to hunt and kill submarines. He invented what became known as the creeping attack. One ship would maintain sonar contact with a submerged yubot from a flanking position, tracking the targets course and speed. Meanwhile, a second vessel would creep up silently from behind at slow speed, its own sonar secured to avoid alerting the submarine with active pings.

The directing ship would calculate the geometry and signal when the attacker was positioned directly over the target. Depth charges would release before the yubot had any warning. The first indication the German crew would have was the thunder of explosions above them. Walker also developed the barrage attack in which three or more ships in line would release overlapping patterns of depth charges simultaneously.

The ocean would be saturated with explosions across hundreds of yards. A submarine could not evade in any direction, and he perfected the hold down, a tactic of patient attrition in which escorts would patrol continuously over a submerged submarine for 2 or 3 days. They would not attack constantly, only often enough to keep the submarine down.

Eventually, with batteries exhausted and air growing foul, the yubot would be forced to surface. The waiting escorts would be ready. The reversal from the catastrophe of March to the triumph of May did not result from any single innovation. It came from a sudden convergence of multiple technologies reaching operational maturity simultaneously.

Each exploited a different German vulnerability. Together they proved devastating. Highfrequency direction finding universally called Huffduff exploited the fundamental flaw of Wolfpack tactics. Ubot had to communicate by radio to coordinate their attacks. The contact report, the position update, the attack orders from headquarters, all required radio transmissions.

British engineers developed shipborne receivers that could instantaneously determine the bearing of a radio transmission using an oscilloscope display. When a yubot transmitted, two or more equipped escort ships could triangulate its position within minutes. The standard response was to run down the bearing at high speed.

Often the escort would catch the submarine on the surface, still transmitting, and attack with guns and depth charges before the boat could dive. Even if the submarine escaped, it had been driven underwater and forced off the convoy’s track. Huffduff contributed to approximately 24% of all Ubot losses during the war. Sentimentric radar was the technology the Germans never anticipated.

The cavity magnetron invented by John Randall and Harry Boot on February 21st, 1940 at Birmingham University enabled 10 cm wavelength radar. The resulting ASV Mark III system could detect a surfaced submarine at ranges of 10 to 16 km. The critical advantage was that Germany’s MOX radar warning receiver operated only in the 1.5 m wavelength band.

It could not detect the new centimetric emissions at all. Hubot equipped with met believed they were safe from radar detection when no warning sounded. They were wrong. The first indication they had of an attacking aircraft was the explosion of depth charges alongside. The first operational patrol with ASV Mark III flew on March 1st, 1943, just 2 weeks before the convoy disaster.

Within weeks, coastal command aircraft were attacking yubot almost daily in the Bay of Bisque and across the Atlantic. The Germans were baffled. They suspected everything except the truth. They investigated whether the British had detection gear that homeed on metox emissions. They investigated whether the British had infrared sensors that could detect warm submarine exhausts.

They did not discover the existence of centimetric radar until September 1943 when they examined wreckage from a crashed bomber that still contained the magnetron. Their countermeasure, a receiver called Knakos, arrived too late and proved unreliable. The Lee Light, a powerful 22 million candela carbon arc search light mounted under patrol aircraft, solved the problem of the final approach at night.

Radar could detect a surfaced submarine, but lost contact at about 1 kilometer due to surface clutter. The final attack run had to be made blind. The Lee light changed this. The search light was switched on only in the final seconds of approach, blinding the yubot lookouts and illuminating the target for attack. The submarine had no time to dive.

After introduction of the Lee light in combination with centimetric radar, German submarines were forced to charge their batteries during daylight hours. dramatically increasing their vulnerability. Escort carriers finally brought continuous air power to the mid- ocean gap where land-based aircraft could not reach.

USS Bogue, commissioned on September 26th, 1942, began her first operational Atlantic voyage on March 5th, 1943. Built on a merchant ship hull, she could operate 18 to 24 aircraft, including Grumman Wildcat fighters and TBF Avenger torpedo bombers. Escort carriers provided constant air cover anywhere in the Atlantic.

On May 22nd, 1943, an Avenger from Bogue sank U569 after a directionfinding contact led the carrier group to the submarine. No convoy escorted by Bogue ever lost a ship to submarine attack. American escort carrier task groups would ultimately sink 53 Ubot between May 1943 and the end of the war. Very longrange B-24 Liberators finally closed the air gap that had allowed Ubot to operate unmolested.

These modified aircraft sacrificed armor, removed gun turrets, and carried extra fuel tanks to extend their range to approximately 2300 m, enough to cover the Mid-Atlantic from bases in Iceland and Northern Ireland. But allocation had been scandalously slow. In February 1943, only 18 very long range aircraft operated over the entire North Atlantic.

The United States Army air forces had resisted transferring bombers from strategic bombing campaigns against Germany. The March crisis and Roosevelt’s direct order broke the bureaucratic log jam. The hedgehog forwardthrowing mortar solved a critical problem with conventional depth charges. Standard depth charges were rolled or thrown from the stern of an escort ship after the vessel had passed over its target.

This required breaking sonar contact during the final approach, giving the submarine a crucial window to evade. The hedgehog changed the geometry entirely. Hedgehog fired 24 contactfused projectiles 250 yards ahead of the attacking ship while the target remained within sonar range. Each 29 kg projectile carried 16 kg of torpex, an explosive 50% more powerful than TNT underwater.

The weapon only detonated on contact with a submarine hull, so a miss produced no explosion and did not disrupt the sonar picture. The statistics were stark. Hedgehog attacks achieved one kill for every 5.7 attempts. Conventional depth charge attacks achieved one kill for every 60 attempts. The new weapon was more than 10 times as effective.

The exchange rate that had so favored Germany in March collapsed within weeks. In April, Allied shipping losses dropped by half while Yubot losses increased. 39 ships totaling 235,000 tons were sunk. 15 Ubot were destroyed. Then came May 1943. Despite deploying 240 operational boats with 118 at sea, representing peak operational strength, Allied losses plummeted while German losses exploded.

From May 10th to May 24th, 10 convoys crossed the North Atlantic. Only six of 370 ships were lost and three of those were stragglers sailing alone. 13 Ubot were destroyed defending against those 10 convoys. The exchange rate had reversed catastrophically. The critical turning point was the battle for convoy OS5 in late April and early May.

43 merchantmen faced attack by over 40 Yubot across a week of violent storms. 13 merchant ships were lost, but six yubot were sunk and seven more seriously damaged, so badly that they had to return to base for months of repairs. It was an exchange rate donuts could not sustain. Two weeks later, convoy SC130 passed through the same waters.

Five Ubot were destroyed. Not a single Allied merchant ship was lost. Among the German dead in May was the crew of U954. The submarine carried a special passenger, 21-year-old Peter Donuts, the son of the Grand Admiral himself. He was killed on May 19th, 1943 when the boat was sunk by a liberator of coastal command.

Donuts received the news at his headquarters. By month’s end, 41 Ubot had been destroyed. This represented 25% of operational strength lost in a single month, nearly three times the previous worst monthly loss. More boats were destroyed in May 1943 than Germany had lost in all of 1941 combined. On May 24th, 1943, Donitz made the decision he had never expected to make.

He ordered suspension of North Atlantic convoy operations. In his memoirs, he wrote that Wolfpack operations against convoys in the North Atlantic were no longer possible. He had withdrawn the boats. Germany had lost the Battle of the Atlantic. The human cost of this 5-year struggle was staggering beyond imagination.

Of approximately 40,000 men who served in German Hubot during the war, around 30,000 perished. a casualty rate of 75%, the highest of any military branch in any nation in World War II. Young men who volunteered for the submarine service knowing it was dangerous, discovered it was suicidal. On the Allied side, over 30,000 merchant seaman died in the Battle of the Atlantic.

More than 2600 merchant ships totaling over 13 million gross register tons were sent to the bottom. 175 Allied warships, including destroyers, frigots, corvettes, and sloops, were lost to submarine attack. The men of the merchant marine wore no uniform, and received little official recognition.

Their pay was stopped the moment their torpedoed ship sank. A sailor who survived a sinking, pulled from the freezing water after hours in a lifeboat, found himself unemployed before he had even dried off. Yet, as Churchill acknowledged, they were quite as certainly frontline warriors as the Guardsmen and fighter pilots. Tommy Brown, the 16-year-old who helped recover the code books from U559, survived the war.

He died in February 1945 in a house fire that also killed his younger sister, Moren. He was 18 years old. Captain Johnny Walker played a hunting we will go over his ship’s loudspeakers when returning to port after a confirmed kill. He drove himself without mercy, spending weeks at sea in the worst weather the North Atlantic could produce.

He died on July 9th, 1944, aged 48, from cerebral thrombosis attributed to exhaustion. The Navy said he had worn himself out in the service. Admiral Horton eulogized him by saying that in the days when the waters had welln overwhelmed them, their brother had set himself to conquer the malice of the enemy. In June 1943, 850 merchant ships arrived safely in North Atlantic convoys without losing a single vessel to Yubot attack.

The siege was broken. Britain would not starve. The war would continue. The battle of the Atlantic was decided not by any single technology or any individual act of heroism, but by the simultaneous convergence of centimetric radar, direction finding, escort carriers, very long range aircraft, support groups, improved weapons, operational research, and overwhelming industrial production.

Each innovation exploited a different German vulnerability. Together, they proved unstoppable. Without this victory at sea, there could have been no buildup of American forces in Britain, no accumulation of supplies for the liberation of Europe, no D-Day, the food that kept Britain fed, the fuel that kept the RAF flying, the ammunition and tanks and aircraft that would land on the beaches of Normandy in June 1944.

All of it had to cross 3,000 mi of ocean protected by the escorts and aircraft that won the Battle of the Atlantic. March 17th, 1943 was the day the convoy system nearly collapsed. It was the day German submarines came closest to severing the lifeline between the new world and the old. Within 10 weeks, the hunters became the hunted.

Within 14 months, Allied forces landed on the beaches of Normandy, supplied across an ocean that was finally secure. The merchant seaman who sailed those convoys faced yubot with nothing but thin steel hulls between themselves and the freezing Atlantic. When torpedoed, they took to lifeboats in waters so cold that an unprotected man could survive only minutes.

Many were torpedoed twice, even three times, and still volunteered for another voyage because the ships had to sail and someone had to sail them. Churchill called them the fourth service. They were the foundation upon which Allied victory was built.