To Be of Not to Be (1942)

This film is set in Poland during the Nazi occupation.  The depiction of the enemy in WWII while the war was going on by Ernst Lubitsch, a German Jew who had been in the United States almost 20 years by the time the Nazis started to spread out across Europe, is part Casablanca and part Hogan's Heroes, and very good indeed.

The setting is Warsaw, and while there are a fair number of bombed buildings, the movie is generous in it's depiction of Warsaw because the city put up a strenuous resistance and as a result, 85% of the city was reduced to rubble.  Joe and Maria Trura (Jack Benny and Carole Lombard) are Polish actors who become part of the Polish underground resistance.  Maria catches the eye of a young Polish airman (Robert Stack) who is falsely convinced that she will leave her husband for him. So there is the romantic triangle that Lubitsch so loved interwoven into the plot, but there is also the need to stop  a spy from giving all the information that he gathered about the Polish resistance to the Nazi's.  That part of the plot is handled as more of a dark comedy, and very deftly done.  Even with the hindsight of 70 years this film holds up well on many levels, and it is no wonder that Mel Brooks elected to remake it in 1983.