5. sergeant york was my first war movie, thus it left a deep impression. was a boy and had nightmares of trench warfare.

4. paths of glory, where french officers in ww1 court-martialed their own soldiers for losing a skirmish. kirk douglas was superb. so were the accounts of 3 french soldiers undergoing court martial.
3. apocalypse now, iconic movie of the vietnam war. unforgettable.
2. full metal jacket, another vietnam war movie. r. lee ermey as the drill instructor in boot camp was unparalleled. 25 years later, the history channel still has him as the drill instructor host in many episodes about army weapon systems.
1. they were expendable, starring john wayne. it has to be a ww2 movie with john wayne in it, although richard widmark in marine movies would be ok too.