When Gilbert Lamb found four castaways off St David’s in 1942, he had to help.

The Canadian merchant marines were emaciated after rowing their lifeboat 400 miles; their schooner Helen Forsey sank after a German U-boat attack.

After Mr Lamb guided the men to shore, they gifted him their lifeboat.

The rescue is one of the stories in U-boats off Bermuda, the second book by Eric Wiberg, a frequent visitor to the island.

“There were over 70 ships sunk off Bermuda during the Second World War, but often they just get a line in the history books,” the American author said.

“It’s the survivor stories that interest me.”

He’s sailed to the island 31 times but only started writing in 2009, after he lost his job with a shipping company.

“I used to sail boats for other people,” he said. “I first came to Bermuda in 1989 on a boat called Tempo owned by the Brown family, the same Browns who started Brown University. I was amazed there was such a beautiful place like Bermuda, such a short distance from New England.”

The former executive recruiter became a manual labourer after the US economy crashed. In his lunch breaks he’d Google U-boat sinkings around the Bahamas, where he was raised.

“I realised there were no books on the topic so I started putting together one of my own,” he said. “It took four years.”

He returned to Bermuda to research his second book. People here, including relatives of the late Mr Lamb, were happy to help.

They revealed that he’d kept the lifeboat for years and called it Ralph, after Helen Forsey captain John Ralph, one of the men rescued.

“They give you the research; they don’t bill you,” joked Mr Wiberg about his experience. “There was Deborah Hollis at the Bermuda Archives who was extremely helpful.

“Dr Edward Harris from the Bermuda National Museum wrote the forward of the book.”

Mr Wiberg got interested in U-boats because he’d heard rumours that Swedes in the Bahamas helped the Nazis during the Second World War.

“Because my family had Swedish heritage it felt like they were accusing someone in my family,” he said.

Much of the suspicion swirled around Swedish entrepreneur Axel Wenner-Gren who was said to have built a canal in the Bahamas to help the Germans invade.

“But the canal wasn’t very deep and he only built it as a public works project,” said Mr Wiberg. “He was trying to help people.” The author has no plans for book signings in Bermuda as of yet, as his finances are tight.

“I hope both Bermudians and tourists read it,” he said.

Buy the book on Amazon.com. Read about the author on ericwiberg.com.