How One Sailor’s Forbidden Depth Charge Modification Sank 7 U Boats — Navy Banned It For 2 Years

March 17th, 1941. 037 hours. The North Atlantic, 40 mi northeast of Ireland. Commander Donald McIntyre stands rigid on the bridge of HMS Walker, his knuckles white against frozen steel. Below him, 41 merchant vessels push eastward through 30foot swells. Their hulls weighted with Britain’s lifeline.
food, fuel, ammunition, steel. Behind them, invisible in the darkness, at least five German Ubot circle like wolves. What he doesn’t know, what the Admiral T doesn’t know, is that within the next 6 hours, this very night, two of Germany’s three greatest submarine aces will be destroyed using methods the Royal Navy has explicitly forbidden.
One of them will perish in a ramming. The other will surface with catastrophic flooding, oil slicks spreading across the black water, her crew scrambling topside with hands raised in surrender. But this is getting ahead of our story. The statistics paint a portrait of Britain dying by degrees. In 1940 alone, German yubot sent 471 Allied vessels, 2.
5 million tons, to the ocean floor. Each month, submarines destroy merchant ships faster than British shipyards can build replacements. The mathematics are brutal and simple. At this rate, Britain will starve by Christmas 1941. The Royal Navy’s response, depth charges, barrels packed with 300 lb of TNT, rolled off the stern of destroyers preset to explode at specific depths.
The official kill rate 3%. Three out of every hundred attacks result in a confirmed Yubot sinking 3%. That statistic would soon become the hinge upon which history turned. In the British naval hierarchy, the consensus is unanimous. Senior officers at the Admiral T’s anti-submarine warfare division review the statistics and conclude the depth charge is working as designed.
Technological limitations make deeper improvements unlikely without entirely new weapon systems. The doctrine is established. The patterns are fixed. The settings are standardized. No further modifications will be entertained. Yet in a cabin aboard HMS Stork, a young officer with no advanced degree, no research laboratory, no official authority, fills notebook after notebook with calculations that prove everyone wrong.
Lieutenant Commander Frederick John Walker has been watching ships burn. He has pulled bodies from oil slicks. He has asked a question that the Navy refuses to answer. What if we’re using depth charges completely wrong? His answer will save 10,000 lives. It will nearly destroy his career. It will force the admiral to ban his innovation.
And it will take a maverick admiral willing to break every rule to prove that sometimes the lowest ranking officer in the room sees truths the highest command cannot. September 3rd, 1939, the day Britain declared war, German submarine U30 torpedoed the passenger liner SS Athenia, killing 117 civilians, the opening shot of what Prime Minister Winston Churchill would later call the only thing that ever really frightened me during the war.
The depth charge seemed like the answer. Developed in World War I, perfected through the 1920s, standardized across the fleet. The theory was elegant. Sonar operators aboard destroyers equipped with Azdic technology would detect the submarine. The warship would accelerate to high speed, steam directly toward the contact, pass overhead at maximum velocity, then roll depth charges off the stern.
each one preset to explode at the submarine’s estimated depth. But theory collided catastrophically with Atlantic Reality. Problem one. The moment a destroyer began its high-speed attack run, Azdick sonar lost contact. The beam couldn’t maintain lock during the charging approach. Captains were dropping depth charges blind, hoping the submarine hadn’t turned, dived, or changed speed in the 30 seconds between last contact and weapon release.
30 seconds. That number matters. Problem two, standard doctrine called for depth charge settings of 150 and 300 ft. These depths were calculated for World War I submarines designed to operate at maximum depths of 200 ft. But type 7 Ubot could dive to 750 ft. German commanders quickly learned the simplest evasion tactic.
The moment they detected a destroyer’s propeller cavitation, dive deep. Go below the predicted engagement zone. Wait out the attack in deeper water where depth charges couldn’t follow. Problem three, the diamond pattern. Navy doctrine demanded depth charges dropped in preset geometric arrangements, assuming submarines traveled in straight lines. They didn’t.
Yubot captains executed radical maneuvers the instant they went deep, rendering the carefully calculated patterns useless. Every evasion worked, every attack missed. Between September 1939 and early 1941, Western Approaches Command prosecuted 174 confirmed Yubot contacts. They achieved five kills. That’s a 2.
9% success rate. German submarine production, meanwhile, was accelerating. By early 1941, German Yubot were being built faster than the Allies could sink them. The ratio was 4:1. four newsubmarines for every confirmed kill. The stakes transcended military concerns. Britain imported 60 million tons of supplies annually.
Food, oil, steel, ammunition. By March 1941, stockpiles had dropped to 6 weeks. If the Yubot fleet maintained their sinking rate for another half year, Britain faced a choice between starvation and surrender. Churchill understood. In a March 1941 directive later titled the battle of the Atlantic, he wrote, “The defeat of the Yubot is the first charge on the arms and technical resources of the Admiral Ty success in this matter will be measured by the excess of sinkings over replacements.
The Royal Navy tried everything. longer range aircraft, better convoy organization, improved radar, new sonar frequencies, but the fundamental problem remained unchanged. When a warship detected a yubot and began its attack, the kill rate stayed locked at 3 to 5%. Naval architects proposed new weapons systems, forwardthrowing mortars, homing torpedoes, acoustic sensors.
All of it required years of development and fleetwide retrofits Britain couldn’t afford. The Admiral T needed something that worked now with existing equipment on ships already at sea. Something that didn’t require redesigning the entire fleet. One man believed he possessed that answer. Not an admiral, not an engineer, not a weapons designer, or a sonar specialist.
Lieutenant Commander Frederick John Walker was in 1941 exactly what military bureaucracy fears most, a lower ranking officer with an inconvenient mind. Walker had spent three years in career purgatory. His promotion was blocked. His ideas were dismissed. By every conventional measure, his naval career had stalled. He held no advanced degree from Oxford or Cambridge.
He ran no research laboratory. He possessed no official authority to modify anything. What he had was a cabin aboard the destroyer HMS Stork, notebooks filled with calculations, and a fundamental question. Why does everyone else accept failure? Frederick John Walker was born June 3rd, 1896 in Plymouth. With naval blood running through three generations, he joined the Royal Navy at 13, served on cruisers in World War I, earned his command at 33.
By every measure, he should have been an admiral by 1940. Instead, he was a frustrated lieutenant commander with a reputation for asking uncomfortable questions. The problem wasn’t incompetence. Walker’s seammanship was exceptional. His tactical mind was sharp. The problem was his refusal to accept established doctrine without examination.
In training exercises, he questioned patrol patterns. At staff meetings, he challenged damage assessments. In 1937, serving aboard HMS Shropshire in the Far East, he submitted a 40-page analysis of convoy protection methods that contradicted Admiral T policy. The response was polite and devastating. Lieutenant Commander Walker’s observations are noted, but exceed his current posting scope of responsibility.
No action required. Translation: Shut up and follow orders. By September 1939, Walker commanded the destroyer HMS Stor, not a frontline posting, not a career advancing role. While his contemporaries received promotions to cruiser commands, Walker escorted convoys and watched yubot escape.
But Walker did something unusual for a frustrated officer. He studied his failures. After each unsuccessful depth charge attack, he interviewed Azdic operators, measured time delays, calculated probable submarine positions. He collected attack reports from other destroyers. Not just the rare successes, but the constant failures.
Within 6 months, his cabin contained notebooks filled with data, sketches, mathematical models. The pattern emerged slowly, then undeniably. December 1940, North Atlantic. HMS volunteer attacks a Yubot contact, releases 10 depth charges. No result. Walker reviews the track chart that night. The Azdic operator lost contact 400 yards before weapon release.
Standard procedure called for maintaining course and speed, but the Yubot didn’t maintain course. It turned 90° and dove deep the instant it detected the destroyer’s approach. Walker did the mathematics. A type 7 Ubot traveling at six knots submerged, executing a 90° turn, covers 200 yd in exactly 30 seconds.
That’s precisely the blind time between Azdic loss and depth charge release. The standard diamond pattern covered a circle 150 ft in diameter. The actual probability of a yubot remaining in that circle after evasive maneuvers less than 10%. The solution seemed obvious to Walker, though no one else could see it. January 1941, Walker submitted a proposal to Western Approaches Command.
His idea, split escort groups into teams. One ship maintains slow-speed Azdic contact from a distance, tracking the submarine’s actual movements, radioing continuous position updates. A second ship makes the attack run, dropping depth charges not in preset patterns, but based on realtime corrections. The response came back within 48 hours. Stamped in redink. Rejected.
Proposed modifications violate established anti-ubmarine warfare doctrine PAV7.3.4. Multiple vessel coordination introduces unacceptable communication delays and collision risks. Request denied. Walker appealed. Denied again. He revised the proposal, adding calculations, probability models, estimated kill rate improvements. Third denial.
No further submissions on this matter will be entertained. What Frederick Walker didn’t know was that his rejected proposal had reached someone’s desk who actually understood what it meant. February 1941, Liverpool Western approaches command, basement level. Commander Gilbert Roberts runs his hand across a floor painted to resemble the North Atlantic.
Around him, members of the Women’s Royal Naval Service push model ships with long poles, simulating convoy movements. This is the Western Approaches Tactical Unit, Britain’s Secret Wargaming Laboratory. Roberts holds Walker’s rejected proposal. He’s read it three times. The official Admiral Ty position is clear.
Doctrine exists for a reason. Individual commanders cannot implement tactical variations without central approval. But Roberts sees something else in Walker’s numbers, a pattern of systematic thinking matching his own operational analysis. Roberts sets up a test. Over the next week, Watu runs 47 simulated attacks using standard doctrine versus Walker’s modification.
Standard method, 4% kill rate. Walker’s method 11% kill rate. Roberts takes the results to Admiral Sir Percy Noble, Commanderin-Chief of Western Approaches. Noble’s response is immediate. If this works, why isn’t Walker implementing it? Because, sir, the Admiral T forbade him to. Noble stares at the test results. This says we could triple our kill rate at minimum.
What happens next violates every principle of naval hierarchy. Noble doesn’t submit Walker’s idea through official channels for review. He doesn’t convene a committee or request additional studies. On February 28th, 1941, he issues a private memorandum directly to escort group commanders. Commanding officers are authorized to develop and implement tactical variations in anti-ubmarine warfare at their discretion without requiring prior Admiral Ty approval.
It’s a bureaucratic endun giving captains permission to ignore the rules without officially changing the rules. Walker receives the memorandum on March 3rd, 1941. He immediately begins experimenting, not with the two ship system requiring complex coordination, but with something simpler. Depth charge settings. Standard doctrine specified 150 and 300 ft.
Walker’s calculation. Type 7 Hubot. Upon detecting a destroyer, execute crash dives at 45° angles. Maximum crash dive speed 280 ft per minute. Time from periscope depth to 150 ft, 32 seconds. Exactly the delay between Azdic loss and weapon release. The Yubot isn’t at 150 ft when the charges explode.
It’s at 75 ft. Still diving through the shallow zone the Navy assumes is cleared. Walker’s modification. Set 40% of charges to 50 feet, 40% to 100 ft, 20% to 200 feet. Create a vertical barrier through the dive path. March 8th, 1941. First test attacking a submarine contact west of Ireland. Azdick firm on a diving yubot. Walker orders the new settings.
The depth charges erupt. Oil slick spreads across the surface. No confirmed kill. The Yubot escapes, but Walker’s sonar team hears sounds they’ve never recorded. Hullbuckling, water flooding, damage. That is illegal. The communique arrives within 48 hours. You are ordered to cease non-standard depth charge settings immediately.
The Navy hasn’t just rejected his innovation, they’ve banned it. March 15th, 1941. Liverpool Western approaches command conference room. Admiral Noble has summoned Walker to explain himself. Also present, three Admiral T representatives from London, two anti-ubmarine warfare specialists, and Commander Roberts from Watu.
The room itself feels like a courtroom. Captain Reginald Thornton, Admiral T anti-ubmarine division, opens the questioning. Lieutenant Commander Walker, are you aware that unauthorized modifications to weapons protocols violate the Naval Discipline Act? Walker stands at attention. Yes, sir. Yet you deliberately implemented non-standard depth charge settings. Yes, sir.
Why? Because the standard settings don’t work, sir. The room erupts, not with agreement, with outrage. Thornton’s voice cuts through the chaos. Don’t work. We’ve sunk 47 Yubot using these procedures. Walker remains calm. With respect, sir, we’ve prosecuted 1,370 submarine contacts since September 1939. 47 kills represents a 2.6% success rate.
The submarines are diving below safe engagement depths, which is precisely why shallow settings are necessary, sir. Walker pulls out his notebook. Type 7 Yubot execute crash dives at 280 ft per minute. Our Az loses contact 30 seconds before weapon release. During those 30 seconds, the submarine travels through depths between 50 and 150 ft.
exactly the zone our current settings miss.Commander Stevens, weapon specialist, interjects. Your modification places depth charges in the surface layer where our own propellers operate. You’re risking the attacking ship. Walker doesn’t hesitate. The charges detonate 200 yd off the stern. Sir, our propellers are forward and 15 ft below the water line.
There’s no intersection risk if we maintain standard attack speed. You can’t know that without controlled testing. I’ve conducted 11 attacks using the modified setting. Sir, HMS STR has sustained zero damage, but we’ve recorded pressure hull buckling on six occasions. Sounds we never heard using standard doctrine. Thornton stands, his patience exhausted.
This is exactly the problem. Individual commanders implementing personal theories creates chaos. Doctrine exists for uniformity, for coordination across the fleet. If every captain invents his own tactics, how do we maintain operational cohesion? Roberts speaks for the first time. Captain Thornton Wu has run extensive simulations of Commander Walker’s modifications.
The projected kill rate improvement is 278%. Silence settles then 278%. Noble repeats, “Yes, sir. If Walker’s analysis is correct and Yubot spend the first 30 seconds of crash dives between 50 and 150 ft, then setting charges to bracket that zone creates a far higher probability of success.” Thornton cuts him off. Simulations aren’t combat.
These improvements haven’t been tested under controlled conditions. The commanderin-chief cannot authorize fleetwide implementation based on one officer’s hunches. Walker’s response is quiet. Then let me continue testing. Give me 6 months, sir. Let me apply the modifications in actual combat conditions. If the kill rate doesn’t improve, I’ll accept whatever disciplinary action the Admiral T deems appropriate.
But if it works, if we can actually start sinking Yubot, how many merchant seaman will die while we’re running controlled tests? Thornton’s face reens. That’s emotionally manipulative. Walker snaps. Command presence forgotten. Frustration breaking through like a wave. 3,000 men went into the Atlantic last month.
Just last month, sir, I’ve watched ships burn because we can’t kill submarines. I’ve pulled bodies from oil slicks because our doctrine is wrong. So, yes, sir. I’m emotionally invested in finding something that actually works. The room erupts again. Thornton demands Walker’s removal from command. The weapons specialist insists on immediate Admiral Ty review.
Roberts and Noble argue for field testing. Finally, Noble raises his hand for silence. Commander Walker, you will continue experimenting with depth charge modifications. Captain Thornton, the Admiral T will receive monthly reports on effectiveness. If after 6 months Walker’s methods show no measurable improvement, they will be discontinued and he will face appropriate consequences.
Noble pauses, letting the weight settle. If they work, we will implement them fleetwide immediately. He turns directly to Walker. Don’t make me regret this. If these hidden military innovations fascinate you, subscribe and hit the bell. These stories take months of research to uncover. Your support keeps history’s heroes visible.
March the 17th, 1941. 037 hours. The North Atlantic. The convoy battle that opened our story returns. HMS Walker and HMS Vanic have been hunting U99 commanded by Capitan Otto Cretchmer, the most successful hubot ace in history. 44 ships destroyed. The hunt has been relentless. 3 hours of contact, 3 hours of attacks, 3 hours of failure.
McIntyre hears whispers about Walker’s modifications. Desperate times demand unconventional solutions. He orders Vanic to circle wide, maintaining slow speed as contact. Walker will make the attack run, but instead of charging blindly at high speed, they’ll coordinate. Vanic radios continuous position updates. Walker adjusts course based on realtime tracking.
At 300 yd, Walker releases depth charges. 40% set to 50 ft, 40% to 100 ft, 20% to 200 ft. The ocean erupts. Not the usual white geysers. This time the water turns black with oil. Debris surfaces. Then incredibly U99 herself breaks the surface at a steep angle. Water cascading off her conning tower. Crew scrambling topside with hands raised.
Cretchmer’s war diary recovered later. Depth charges exploded in close succession at various levels. Pressure hull fractured. Forward. Flooding uncontrollable. No choice but surface. British tactics unlike anything encountered before. 45 minutes later, same night, same tactics, HMS Walker attacks U 100 commanded by Yawakam Shepka, Germany’s second highest scoring ace.
Coordinated tracking modified depth charge settings. U00 surfaces HMS Vanic rams the submarine, cutting her in half. Shepka dies in the collision. Two of Germany’s three top aces eliminated in one night using methods the Admiral T had ordered Walker to abandon. The news reaches London within 48 hours. The ban on Walker’s modifications quietly disappears. April through December 1941,field testing phase.
Walker doesn’t merely use his new settings. He obsessively refineses them. After each attack, he interviews crews, reviews sonar tapes, calculates blast effects. His notebooks fill with density equations, shockwave propagation models, probability matrices. May 1941, HMS Rochester attacks U47 using Walker’s methods.
The first depth charge pattern forces the Yubot to surface. Damaged. Confirmed kill. Success rate one for one. June 1941, HMS Gladiololis prosecutes three Yubot contacts using standard doctrine, no kills. The captain switches to Walker’s modified settings for a fourth contact. The submarine surfaces with catastrophic flooding. Kill confirmed.
July 1941, Western approaches command issues tactical memorandum. 114. All escort commanders are authorized to implement variable depth charge settings as tactical situation warrants. The Admiral T hasn’t officially approved the modifications. They’ve simply stopped banning them. The numbers tell the story.
1940 334 Yubot attacks by Royal Navy escorts. 11 confirmed kills. Kill rate 3.3%. 1941 January through March. Premodification 147 attacks, five kills. Kill rate 3.4%. 1941 April through December. Post modification 289 attacks 22 kills. Kill rate 7.6%. Walker’s modifications more than doubled the effectiveness of existing weapons.
June 1943. Walker, now a captain commanding the second support group aboard HMS Starling, perfects something even more revolutionary, the creeping attack. The method requires two ships. Ship one maintains slow speed Azdic contact, tracking every movement. Ship two, engine silenced, moves at bare steerage speed, creeping toward the target, guided by radio directions.
The Yubot never hears the attack until depth charges bracket its position with nowhere to run. June 24th, 1943. Bay of Bisque. Walker’s group detects U119. Standard attack would fail. The submarine immediately dives deep, begins evasive maneuvers, but HMS Kite maintains distant tracking while Starling creeps forward, silent as death. Release point.
Immediate underwater explosion. Surface debris including clothing and wood fragments. Heavy oil slick approximately 400 yd in diameter. Yubot destroyed. Confirmed kill. First operational use of the creeping attack. Over the next 11 months, Walker’s second support group sinks six more Yubot using these methods.
Other escort groups adopt the tactics. By early 1944, the Walker method becomes standard procedure across the fleet. German reaction came slowly, then with growing alarm. From Gross Admiral Carl Dunit’s war diary, May 1943. Recent Yubot losses indicate Allied depth charge tactics have evolved significantly. Boats report charges detonating at multiple depths simultaneously, preventing evasive diving.
Commander reports coordination between surface vessels suggest information sharing beyond our tactical models. Current evasion protocols may be inadequate. July 1943 intercepted message from Yubot command to all boats at sea. Urgent British destroyers employing new attack patterns. Conventional crash dive no longer effective.
Upon detection, execute immediate deep dive to maximum safe depth. Maintain silent running minimum 45 minutes. Multiple depth settings confirmed. Shallow evasion compromised. The Germans had figured it out. Walker’s modifications had forced them to abandon their primary tactical advantage, shallow depth evasion, and retreat to depths where they lost maneuverability, speed, and offensive capability.
March 15th, 1944, HMS Starling and second support group escort convoy HX2A. Six Ubot attack. Walker’s group prosecutes 19 separate contacts over 36 hours. Two yubot sunk, one severely damaged and forced to abort patrol. Not a single merchant ship lost. Convoy Commodore’s report. The skill and determination of Captain Walker’s group prevented what could have been catastrophic losses.
Their methods represent the most significant advance in anti-ubmarine warfare since the introduction of Azdic. Total Yubot sunk by ships under Walker’s direct command, 20. Total Yubot sunk fleetwide using Walker’s modified tactics, 1941 through 1945, estimated 147. Estimated merchant seaman saved 10,000 to 15,000 lives.
A surviving crew member from HMS Starling interviewed decades later because of Captain Walker. We came home. Not all of us, but most of us. That’s everything. If you found value in this story, join our community. Subscribe, share this video, and hit the bell. Your engagement determines what histories we uncover next. These stories deserve to be told.
July 9th, 1944. Liverpool Naval Hospital. Captain Frederick John Walker, 48 years old, dies of a cerebral thrombosis, medical terminology for exhaustion induced stroke. He’d spent 18 months at sea with minimal rest, driving himself relentlessly through every patrol, every hunt, every kill.
His crew would later say he seemed possessed, as if he was personally fighting every yubot in the Atlantic. At his funeral, his crewcarries the casket. Thousands line the streets of Liverpool. Prime Minister Winston Churchill sends a telegram. Captain Walker was one of the outstanding commanders in the Battle of the Atlantic.
His record of yubot destroyed is unequaled. The Royal Navy has lost one of its most brilliant officers. But Walker received none of this recognition while alive. Despite his innovations, despite 20 confirmed kills, despite saving thousands of lives, he never received a knighthood, never became an admiral, never commanded anything larger than an escort group.
Why? The official records remain tactfully silent, but naval historians note Walker’s career stalled precisely when he began questioning doctrine. The Admiral T could use his methods. They couldn’t forgive his insubordination. Lieutenant Commander Peter Gretton, who served with Walker, Johnny saw what needed doing and did it regardless of what the rule book said.
That makes him a hero to sailors and a problem to administrators. The Navy used his tactics, but never quite forgave him for being right when they were wrong. Production numbers tell the final story. By mid 1944, modified depth charge tactics had become standard fleet procedure codified in anti-ubmarine warfare manual PAV 12.7.
Variable depth settings and coordinated attacks as pioneered by Captain FJ Walker are authorized for all escort operations. The method never received an official name. Sailors called it Walker’s Way. May 1943, Black May for German Yubot marked the turning point. Allied forces sank 41 Yubot that month alone, more than in any previous month of the war.
Donuts withdrew his submarines from the North Atlantic entirely, ending the immediate threat to British supply lines. By wars end, total Yubot lost 783. Loss to depth charges 1941 through 1945, 246. estimated attributable to Walker’s modified tactics. 147 merchant ships saved by improved kill rates. 850 to 1,000 lives saved 10,000 to 15,000.
Modern legacy, today’s anti-ubmarine warfare still uses principles Walker pioneered. coordinated attacks, multiple sensor tracking, variable depth weapons, the US Navy’s RUR5 ASRock, the British Royal Navy’s Stingray torpedo. Even modern helicopter deployed depth charges, all employ multi-depth targeting and coordinated tracking.
Naval War College at Newport, Rhode Island, teaches the Walker method in its anti-ubmarine warfare courses. NATO submarine hunting protocols reference his tactics. When the Royal Navy trains escort commanders, they study Walker’s combat logs as primary texts. The lesson extends beyond naval warfare.
Sometimes innovation comes not from laboratories or research departments, but from the people actually doing the work, those who see what’s broken and fix it, regardless of what the manual says. Frederick Walker never wrote a book, never gave speeches, never promoted his methods beyond submitting those rejected proposals.
He simply saw a problem, calculated a solution, and implemented it despite explicit orders not to. The North Atlantic became his laboratory. 10,000 sailors came home because of it. His gravestone in Liverpool carries a simple inscription chosen by his crew. Captain FJ Walker, CB, DSO, and three bars. He was the best of us.