“They Called It A Sinking U-Boat” — Until American Sailors Found Germany’s Secret Codes Inside

On June 4th, 1944, deep in the Atlantic Ocean at coordinates 21°30′ N, 19°20′ W, Task Group 22.3 was running a standard anti-submarine sweep. They were situated approximately 105 miles off the coast of Rodero in West Africa. The escort carrier USS Guadalcanal and five destroyer escorts had been hunting U-boats off the Cape Verde coast for nine grueling days.
At 11:09 that morning, the USS Chatelain registered a definitive sonar contact. What followed unfolded with terrifying speed, taking less than four minutes. Chatelain fired her Hedgehog mortars and rolled a barrage of depth charges into the churning sea. Above, two Grumman F4F Wildcats from the Guadalcanal dove low, strafing the water where the contact registered.
Below the surface, U-505, a Type IX submarine on her twelfth war patrol, was rapidly losing ballast control. Trapped and taking catastrophic damage, her crew opened the flooding valves as standard procedure dictated. The fundamental rule of the Kriegsmarine was absolute: you sink the boat before the enemy takes her.
Yet, the scuttling process failed to work as intended. U-505 breached the surface, forcing her panicked crew to abandon ship into the swelling Atlantic waves. She sat riding the swell, slowly taking on water and apparently dying.
Captain Daniel V. Gallery Jr. watched the scene unfold from the deck of the Guadalcanal. He had spent two long years preparing for this exact moment, leading his men through 17 rigorous rehearsals. The single question Gallery had never been able to answer remained: would the boat go down before they could get inside?
By June 1944, the Allies had been fighting U-boats across the globe for 57 grueling months. In all that time, only one enemy warship had been captured at sea by the United States Navy, and that had occurred way back in 1815 during the War of 1812.
That historic record was not incidental; it directly reflected the operational reality of submarine warfare. A U-boat crew’s standing orders were explicit and uncompromising: destroy all codes, flood the boat, and scuttle.
The critical window between a stricken submarine surfacing and its final descent into the abyss was measured in mere minutes, sometimes even seconds.
The broader intelligence picture made the stakes of this brief window agonizingly precise. Since February 1942, German U-boats had been using a complex four-rotor Enigma configuration code-named Shark by Allied cryptanalysts.
When that fourth rotor went active, Bletchley Park effectively went blind. In the ten terrifying months that followed, 635 Allied merchant ships were sunk in the Atlantic, representing 3.1 million gross tons of vital cargo lost.
The monthly loss rate reached a devastating peak in November 1942, with 119 ships sent to the ocean floor. Cryptanalysts at Bletchley’s Hut 8, led by Alan Turing, had made the harsh mathematical reality explicit in their March 1942 assessment.
A purely mathematical attack on the four-rotor Enigma was simply not feasible without captured keying material. This was not defeatism on their part; it was an accurate statement of theoretical mathematics.
Physical capture had produced monumental results before. On May 9th, 1941, HMS Bulldog boarded the stricken U-110, retrieving a working Enigma machine and current codebooks.
That extraordinary haul allowed three-rotor Dolphin traffic to be decrypted for months, though U-110 ultimately sank under tow before reaching port. However, the introduction of the fourth rotor made that earlier material completely insufficient against the revised Shark cipher.
The United States Navy’s own signals intelligence division, Op-20-G, had begun constructing its own four-rotor Bombe machines in late 1942. They worked in tight partnership with the National Cash Register Company of Dayton, Ohio.
By early 1944, 211 of these massive units were in production or fully operational. Yet, successful decryption still relied entirely on obtaining current keying material, physical rotors, short signal codebooks, and weather cipher tables to construct the cribs that made the processing useful.
In short, the Bombes were running at full capacity, but what they desperately needed was current material that only a physical capture could provide.
Daniel V. Gallery had been quietly obsessing over the idea of capturing a U-boat since 1942. Born in Chicago in 1901, he was the son of an Irish Catholic lawyer who actively encouraged his sons to debate and argue.
Gallery graduated from the Naval Academy in 1921, eventually flying combat missions over the Atlantic starting in 1941. By 1943, he was commanding Naval Air Station Londonderry in Northern Ireland.
It was a frontline airbase where the grim wreckage statistics and survival rates of the North Atlantic crossed his desk every single week. He was not primarily a theoretical strategist; he was a pragmatic man who read operational patterns the way an attorney reads legal precedent.
What he noticed was a consistent pattern: damaged U-boats were surfacing, their crews abandoning ship in panic with hatches left wide open. The window was remarkably short, but it unmistakably existed.
Scuttling charges were not always successfully set by the fleeing sailors. Flooding valves were not always opened correctly in the chaos of battle.
The crews were abandoning ship in the desperate seconds between the decision to surface and the iron discipline required to destroy everything of military value. Gallery began drafting formal capture procedures while still stationed at Londonderry.
He submitted a formal proposal to the Commander in Chief of the US Atlantic Fleet, Admiral Jonas Ingram. He requested explicit permission to train specialized boarding parties and equip a hunter-killer task group specifically for this capture mission.
The ambitious request was met with deep skepticism, but it was ultimately approved. He relentlessly drilled his crews on 17 simulated boardings long before Task Group 22.3 ever departed Norfolk.
His instinct was not mystical or reckless; it was purely managerial. He had simply observed the operational gap between when a U-boat surfaced and when it sank, deciding that someone ought to be ready to cross it.
The institutional resistance to Gallery’s plan was far from irrational. Admiral Ernest J. King, Commander-in-Chief of the US Fleet, had built the 10th Fleet precisely to destroy U-boats, not to preserve them.
The entire logistics chain of hunter-killer task groups was designed around killing submarines as rapidly as possible to defend crucial Allied convoys.
Adding a capture mission to an anti-submarine warfare escort group introduced dangerous variables: slowing ships down, exposing boarding parties to enemy fire, and creating a massive intelligence liability.
If the Germans ever realized a boat was captured, they would instantly know their codes were compromised. That concern was by no means hypothetical.
After the British capture of U-110 in May 1941, the Royal Navy maintained such fanatical secrecy around the Enigma haul that Prime Minister Winston Churchill personally forbade telling President Roosevelt for nearly a year.
The intelligence community’s overarching fear was specific and terrifying: if the Germans ever suspected their primary cipher was broken, they would immediately alter it.
If that happened, every piece of intelligence gained over years of blood and sweat would be lost overnight. Gallery’s counterargument to the leadership was strictly operational.
He argued that a captured U-boat, if properly concealed from view, would never reveal itself as having been taken. The submarine could be repainted, assigned a cover designation, and towed quietly to a remote port.
The captured codebooks, rotors, and cipher documents could then be transferred to Bletchley and Op-20-G under total, highest-level classification.
The Germans would be informed through normal channels, and would fully believe, that their boat had been sunk with all hands lost in deep water.
This cover strategy was not theoretical; it had been successfully used once before. The capture of U-110 had been kept completely secret for the entire duration of the war.
Gallery’s concept underwent an informal practical test in April 1944. Task Group 22.3 conducted a timed boarding drill using a decommissioned vessel in Norfolk Harbor.
Eight men equipped with full damage control gear executed the assault under strict timing constraints. The result was impressive: the team successfully reached all simulated key compartments in under four minutes.
Gallery submitted the successful drill report, and the official mission was formally authorized. Yet, the moment it nearly died came not from military opposition, but from raw timing.
In May 1944, Task Group 22.3 was abruptly reassigned to routine convoy escort duty in preparation for Operation Overlord. Gallery lobbied fiercely to have his group return to offensive hunter-killer patrols before the June sailing window closed.
The reassignment decision was reversed with a mere nine days to spare. On June 4th, 1944, at precisely 11:09 a.m., the USS Chatelain established its historical contact.
She fired immediately, and depth charges erupted violently on both sides of the sonar return. Above the chaos, two Wildcats from Guadalcanal spotted the dark shadow of U-505 at periscope depth and began strafing the surface.
Below, the submarine was rapidly taking on water. Her commander, Oberleutnant zur See Harald Lange, was hit by strafing gunfire and briefly lost consciousness on the bridge.
Upon reviving, he ordered his men to abandon ship immediately. The crew opened the ballast tanks to flood the vessel, but the comprehensive scuttling routine was never completed.
At 11:22, U-505 burst through the surface. Her terrified crew spilled over the sides into the ocean.
The USS Jenks maneuvered into position to pick up the surviving German sailors. Gallery saw his moment and gave the long-awaited order.
An eight-man boarding party from the USS Pillsbury, led by 24-year-old Lieutenant Albert David, launched rapidly in a motor whaleboat.
They crossed the open water in three tense minutes, scrambling over the U-boat’s conning tower. Inside, water was rising steadily through the unclosed flooding valves.
One German crewman remained aboard, already dead from strafing wounds sustained on the deck. The main hatch leading down into the control room was sitting wide open.
Lieutenant David descended directly into the dark, flooding hull. The team moved swiftly through the darkness, locating and desperately closing the critical flooding valves.
They gathered up key codebooks, active Enigma machine rotor settings, and current short signal weather cipher tables from the navigation and radio compartments.
They carried the priceless trove up through the conning tower to the waiting boat. The entire boarding, recovery, and initial damage control process had taken just 11 minutes.
Lieutenant David was later awarded the Medal of Honor for his incredible bravery. Pillsbury initially attempted to take the submarine under tow, but the heavy towline snapped.
Guadalcanal then closed in and managed to attach her own heavy towline directly to the captured U-boat. Three days later, the deep-sea fleet tug USS Abnaki arrived to assume the long tow.
The nearest Allied-controlled port was in French Morocco, but Gallery knew German intelligence assets operated openly in the region.
Instead of risk exposure, U-505 was towed an astounding 1,900 nautical miles across the ocean to Bermuda. Upon arrival, she was quickly repainted and secretly redesignated as the USS Nemo.
Her 58 surviving crew members were quietly shipped to Camp Ruston, Louisiana, a secure prisoner of war facility. They were held in a completely segregated compound, strictly denied any contact with the International Red Cross.
Their survival was kept officially unacknowledged by the United States government. The supreme secrecy held perfectly.
The Kriegsmarine officially recorded U-505 as lost with all hands in the deep Atlantic. The precious codebooks and Enigma materials reached Op-20-G and Bletchley Park within 72 hours.
Naval analysts later assessed that this single haul extended usable Shark decrypt coverage through the end of 1944.
It directly informed Allied convoy routing and U-boat interception operations across the entire central Atlantic.
Between May and August of 1943, Allied forces had already sunk 106 U-boats, which was 21 more than in all of 1942 combined.
The June 1944 capture extended and deepened that critical strategic advantage. It happened precisely when Admiral Karl Dönitz was desperately attempting to rebuild operational strength in the South and Central Atlantic.
The human cost on the other side was remarkably light for such an operation: out of U-505’s crew of 59, only one man died during the battle.
The remaining 58 spent the remainder of the war in Louisiana, entirely unaware that their homeland believed them to be dead.
Daniel V. Gallery was promoted to Rear Admiral for his extraordinary initiative and leadership. He later wrote a detailed memoir about the capture of U-505, which was published in 1956.
After the war, he actively lobbied against the Navy’s plan to use the historic U-505 as a target vessel for weapons testing.
He contacted his brother, a Catholic priest in Chicago, who in turn reached out to Lennox Lohr, the president of the Museum of Science and Industry.
Lohr enthusiastically accepted the proposition to save the submarine. In 1954, the United States government officially donated U-505 to the Chicago museum.
Dedicated Chicago residents raised $250,000 to cover the immense costs of her transport and permanent installation.
In 1989, U-505 was formally designated a National Historic Landmark in recognition of her unique role in naval history.
In 2004, she was moved into a massive, climate-controlled permanent underground gallery to preserve her for future generations.
She remains there to this day, an enduring artifact of the Battle of the Atlantic.
The vital intelligence materials recovered from her—the Enigma machine, rotor settings, and short signal codebooks—remained heavily classified for decades after the war ended.
Here is the profound fact that completely reframes the entire operation. Following the war, the Kriegsmarine conducted an exhaustive analysis to determine why U-boat losses had spiked so catastrophically in 1943 and 1944.
Their final official conclusion attributed the devastating losses entirely to advanced Allied radar technology and vastly increased aerial coverage.
They never once suspected that their central cipher system had been systematically broken. They never suspected that U-505 had been captured intact by American forces.
Grand Admiral Karl Dönitz went to his grave in 1980 still firmly believing that Enigma had never been compromised by the Allies.
He was utterly wrong, and he died never finding out the truth.