Filmed on the set of Hogan's Heroes (1965). The series had already been cancelled, and, on learning that the movie had the camp being burned down at the end, the set was given over to save the cost of demolition.
When one of the prisoners uses the machine gun at the end of the movie you hear the shots but as the bandoleer is not moving (meaning that no ammunition is loaded into the gun) it is not firing at all.