A Second World War US Navy officer who held one of the most closely guarded secrets of the conflict has died at the age of 100.

Jim Humphreys was one of the few people who knew a German U-boat captain was being held in Bermuda to hide that his submarine and top-secret Enigma code machine had been captured.

His daughter, Paget Humphreys-Jackman, said her father was a kind, funny and devoted man.

She added: “He always wanted to help other people. He loved Bermuda and always felt it was his home, even though he only arrived here as a young naval officer.”

Mr Humphreys served at Morgan’s Point Naval Base in Southampton from 1945 to 1946 as a supply and security officer.

He met his Bermudian wife, Shirley, who at the time worked as a volunteer nurse’s aide while stationed at the base. The couple married in 1945.

It was as a result of this relationship that Mr Humphreys discovered the Allies’ secret, as his future wife was tasked with caring for the U-boat’s commander, Captain Harald Lange, for nine months while he was held in Bermuda.

She was given strict instructions not to reveal the capture of Captain Lange, but she confided in Mr Humphreys, who kept their secret for decades.

Mr Humphreys said in 2014: “At that time we were not married and Shirley had been told that she could not tell anyone because the Germans did not know the submarine had been captured and did not realise the Allies knew their code.

“She told me what was going on and gave me clear instructions that I could not repeat it to anybody.”

Mr Humphreys and his wife later moved to the United States, but the couple returned to the island in 1980 when they retired.

Mrs Humphreys-Jackman said her father was a deeply devoted husband who always supported his wife.

She said: “When my mother had breast cancer, she was very disappointed to find the island didn’t have a support group.

“She helped to start Just Between Us, and every time that they met, he would be there to set the chairs up under her directions.”

Mrs Humphreys-Jackman said her father also helped raise funds for organisations such as St Paul’s Church in Paget.

She said Mr Humphreys loved the island, and enjoyed hosting his eight grandchildren and 13 great-grandchildren in Bermuda.

She added: “He would have them down here, get them up first thing in the morning and take them out to the golf course or a museum.”

Andrew Bermingham, an island historian, said: “Mr Humphreys was a standard-bearer for the US Navy and was always very proud of his work.”

Mr Bermingham said the capture of the U-boat, and the secrecy surrounding it, played a crucial role in the war effort as it allowed Allied forces to know the rendezvous points of all German U-boats operating in the Atlantic.

He said: “Even today, Harald Lange was never officially in Bermuda. There is no record of him ever being here.”

He added that Mr Humphreys was crucial in revealing the untold story of the captured U-boat after he and his wife kept the secret for more than 50 years.

Mr Bermingham said: “It really is thanks to him that this story was told, and it is now still being told as even more information is being unravelled. The story has become folklore and the best-kept secret of the Second World War.”