Today marks 75 years since United States forces towed a captured German sub, U-505, into Bermuda waters under a cloak of secrecy.

The U-boat was brought into the Great Sound with 57 prisoners, as well as its Enigma code encryption machines and code books that allowed the Allies to crack German messages.

It was less than two weeks after troops had fought their way ashore at Normandy on D-Day, June 6, 1944, and the Allied invasion of Nazi-held Europe was raging. But two days before the biggest maritime invasion in history, the prize catch of U-505 had been forced to the surface under American fire 150 miles off the West African coast.

Its German crew had to abandon their stricken sub before it could be scuttled, delivering U-505 to the Allies with her precious cargo intact. The US Navy needed to hide their find, which they reported as sunk, and brought it to their Naval Operations Base in Southampton, at what is today Morgan’s Point.

Derek Waller, a retired air commodore with the Royal Air Force, has spent years writing about the U-boats that came into Allied hands.

“U-505 was not part of the ten that were allocated to each of the three main Allies: the USSR, the USA and the UK,” Mr Waller said. “It was captured, rather than surrendered.”

Absent from the list of prisoners brought on shore to Bermuda was Ewald Felix, 21, a junior crewman who Mr Waller’s research reveals had helped keep the damaged submarine afloat and thus aided the Allied side in its capture.

Felix was taken separately on board the USS Guadalcanal, while his fellow crewmen were told that he had died and been buried at sea.

Mr Waller writes that Felix was concealed from colleagues who “might well have punished him harshly for facilitating the capture”.

A German historical magazine, Kristall, claimed in 1956 that Felix had been killed in a prison camp by his fellow prisoners of war as punishment for being an informer. In fact, he had been spirited to a PoW camp in Norfolk, Virginia.

By 1956, Felix was living in Poland with his parents. He later moved to Germany, where he resided until his death in the 1990s. Mr Waller said that it was “imperative” that the capture be kept secret “lest the Germans would discover that fact and change their U-boat code books before June 6”.

“Thus, the US Navy decided to tow it to Bermuda and keep the whole event totally secret.”

The Americans held the rest of U-505’s crew under wraps in Bermuda for the six weeks.

The sub’s commanding officer, Lieutenant Harold Lange, who had been seriously wounded and lost a leg, was also separated: he stayed nine months on the island, while the rest of the crew were interned in Camp Ruston, Louisiana.

Their confinement broke the terms of the Geneva Convention of the treatment of prisoners of war, but the US Navy stuck to security as a pretext.

The Royal Gazette reported in 2014, for the 70th anniversary of U-505’s landing here, how Captain Lange befriended Kate Perinchief, a Bermudian woman who lived near the base, and exchanged letters with her after the war.

Another article from the Gazette, which never reached publication, was written at the time of the landing by Ford Baxter, a reporter tipped off by a lighthouse keeper about the incoming U-boat.

US authorities threatened him with arrest after receiving Mr Baxter’s query about the vessel.

With the intercession of Lord Burghley, the Governor, the story was quietly held.

Mr Waller said he had explored the history of U-boats, and U-505, as a hobby during his wife’s illness, and had contacted local historians such as Edward Harris and Andrew Bermingham as part of his research.

The full story of U-505 was published in the July 2018 in Volume 21 of The Bermuda Journal of Archaeology and Maritime History, maintained by the National Museum of Bermuda.