All Quiet on the Western Front - Possibly THE anti-war movie, which has obviously withstood the test of time.
Twelve O'Clock High - A personal favorite about a CO turning around a hard luck unit. Oscar for best supporting actor.
The Best Years of Our Lives - Although about life after the war, in my opinion one of the ten best movies ever made. Several Oscars including best picture and supporting actor, who actually lost both hands in a training accident during the war.
Zulu - I think it was Micheal Caines first film. Great story and superb action about a true battle in the Zulu war.
The Wind and the Lion - Another personal favorite about a true story involving a women and her two kids, Barbary pirates, Marines, Germans, etc.; look closely as the detail is superb.
Das Boot - An uncle was on a 'pig boat' in the 1950's and he said that it was the only realistic submarine movie that he ever saw.
The Bridge Over the River Kwai - In my opinion one of the ten best movies ever made, with one of the best knife scenes in a movie; while holding a knife in the air Holden is yelling "KILL HIM" to the young commando facing Alec Guiness.
Saving Private Ryan - Possibly one of the best war movies I've seen, but I'll have to see how it ages over the years. Very moving, but it could be that I'm just turning into a wimp as lately I find that such things bother me more than they use to. Also on my ten best list.
Full Metal Jacket - A personal favorite. The best rendition of boot camp that I've seen.
The World at War - a made for TV documentary that is superb, the best that I've seen. I managed to record all 24 or so one hour episodes. The Unknown War is also very good.
Dr. Strangelove - One of my favorites and a much needed break from the cold war.