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Several American sailors climbed aboard the German submarine U-505, focused on saving it from sinking into the depths of the Atlantic Ocean. They did not know if the Nazi submariners who dove overboard had set scuttling charges beforehand, but the risk was worth it: the wealth of intelligence on board could help them shorten the time needed to crack messages from the elusive Enigma machine

It takes a heroic amount of intestinal fortitude to board a sinking ship rigged with 14 demolition charges for the express purpose of preventing the U-boat from being captured. But on June 4, 1944, the U.S. Navy successfully captured U-505, a German Type IX-C submarine. 

The concept of capturing a German submarine was hatched after a Navy hunter-killer team named the Guadalcanal Task Group had successfully destroyed a Nazi U-boat in 1943. After hammering U-515 with depth charges from both Naval destroyers and aircraft, it was damaged beyond saving. The Nazi commander ordered the submarine to the surface, where the U.S. Navy hammered it again, causing it to catch fire, explode, and sink. 

Daniel V. Gallery​​, the former commander of the USS Guadalcanal Task Group, recalled how they planned the capture of U-505 during an interview recorded on May 26, 1945, and archived by the Naval History and Heritage Command. 

“In analyzing this attack afterward, it occurred to us that if we had anticipated what was going to happen and had been ready for it with organized boarding parties, we might possibly have gotten aboard the U-515 in time to save her,” Gallery said during the interview. “So we determined that on the next cruise, we would anticipate such an event and be ready for it.”

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Each ship trained boarding parties with the plan to quickly board a submarine, disable scuttling charges, and pump out all the seawater from the damaged or intentionally opened valves. They had orders to remove as much classified material and intelligence as possible, knowing a damaged U-boat could be torn apart by explosives or sink at any minute.

Working on some of the latest intelligence on submarine locations, the task group searched for U-boats along Africa’s western coastline. They hunted a U-boat for several days, having disappearing sonar contacts and various other detection devices intermittently triggered by a U-boat presence. 

But one Sunday morning, at about 11:10, 150 miles west of Cape Blanco, the U.S.S. Chatelain reported that she had a contact on the submarine they’d been hunting. The Chatelain launched their first attack on the Nazi submarine with hedgehogs, which were v-shaped mortars that launch multiple depth charges in a pattern. The U-505’s commander, Capt. Harald Lange, ordered two torpedoes fired at the hunter-killer group. 

Two General Motors FM-2 “Wildcat” fighter planes from the escort carrier Guadalcanal spotted U-505, marked it with gunfire, and the Chatelain hit the area with the hedgehogs again. This time, oil started bubbling up, and the U-505 surfaced seconds later. 

The Nazi sailors tried manning their deck guns, but gunfire from the task group killed one of the Nazi sailors and forced everyone else overboard, including the submarine commander. U-505 had sustained major damage and its rudder was jammed, lights and electrical machinery out, and rapidly taking on water. 

An eight-man boarding team from the U.S.S. Pillsbury quickly caught up to the runaway U-boat and boarded while other teams were sent out to pluck the Nazi sailors from the water. Because the Germans evacuated so quickly, one of the diesel engines was left on, and the submarine started circling toward the task group. 

“They didn’t know what was down below,” Gallery said. “They had every reason to believe, from the way the sub was still running, that there were still Nazis left below engaged in scuttling, setting booby traps, or perhaps getting rid of confidential gear.” 

The boarding party didn’t find anyone in the submarine, but the ever-looming threat of the sinking ship was heavy on their minds as they hurried to collect intelligence and prevent any more seawater from entering.

While the boarding party worked, the Pillsbury tried to pull alongside the submarine twice, and the submarine’s bow pierced the destroyer each time, forcing the destroyer to maneuver away to address their flooding compartments.   

The boarding party plugged leaks and sealed the open valves letting water in. They attached tow lines and the Guadalcanal towed the U-boat at high speed, turning the electric motors over, and recharging the boat’s batteries. The American sailors aboard then used the U-boat’s pumps and air compressors to pump out the rest of the water, bringing the submarine back to the surface.

By the time the task group’s ships reached their destination in Casablanca, they were about to run out of fuel. The intelligence gathered from U-505 was invaluable, and included 900 pounds of codebooks and documents and two Enigma machines with the latest “Shark” coding. 58 Nazi sailors were captured and the U.S. and her allies had to keep the captured U-boat a secret. Hiding a 700-ton submarine proved to be a challenge almost as difficult as the capture itself. 

The U-505 was the largest intelligence victory during the WWII battle for control of the Atlantic Ocean. The seized documents and codebooks allowed U.S. Navy code-breaking teams to cut at least 13,000 computer hours, a major help for their decoding work for the rest of the war.

The U-505 was one of six U-boats captured during WWII, and every submarine captured provided valuable intelligence for locating and destroying the rest of the Nazi’s naval fleet. 

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