I first saw David Niven in "Death on the Nile", a 1978 film in which he played alongside Peter Ustinov as Hercule Poirot. I later learned that Ustinov was Niven's batman during WWII.
I think I read this anecdote about David Niven some time ago. Still it never fails to fill me up with enormous respect for the man every time I read it:-
After Great Britain declared war in 1939, he was one of the first actors to go back and join the army. Although Niven had a reputation for telling good old stories over and over again, he was totally silent about his war experience. He said once: "I will, however, tell you just one thing about the war, my first story and my last. I was asked by some American friends to search out the grave of their son near Bastogne. I found it where they told me I would, but it was among 27,000 others, and I told myself that here, Niven, were 27,000 reasons why you should keep your mouth shut after the war."