Apologies if this film has been featured on this board before!
It's one of my absolute favourites with a really good cast (John Mills, Michael Redgrave, Basil Rathbone, Rosamund Johns, Douglass Montgomery etc. There's a very young Richard Attenborough in a small part)
I always sob my heart out at the parts where 1) Michael Redgrave's character gets shot down and John Mills reads a poem he has written and 2) where the American airman (Douglass Montgomery) crashes his aeroplane with the bomb on board to save the whole village from being destroyed. His friend then goes to the children's party to which he was going to be the star turn and tells them "he just couldn't make it."

I've watched and enjoyed it many times and it never fails to choke me up!