Doing some research I found out that my uncle was on a ship torpedoed by U96 the boat featured in the book and film.
The book/film is based on an actual cruise.
My uncle was an officer on the tanker Clea which broke down and wandered away from the convoy (HX106).
He was due to pick up his masters ticket on return to the UK.
I had always enjoyed (if that's the right word) the book and film but had not appreciated the relevance until doing the research.
None of my uncles siblings were aware of exactly how his ship was sunk, only that it had been torpedoed.
It's a fantastic film with a little bit extra now I know the story.