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.