Years ago I saw a small bit of a movie that looked interesting, but business called me away from the TV. Set in a prison camp in England, German U Boot sailors almost in mutiny against camp guards. Something about some German's about to be hanged for some offense (murder?), Germans threatening to execute British POW's in retribution, I *think* Robert Shaw playing the charismatic German commander of the POW's, I recall a scene in the mess hall with German U Boot sailors pounding the tables singing some song or other, the British guard being called out with bayonets fixed. Anyone have the title? I seem to recall the claim it was based on a real incident.