Twelve O'Clock High. It blows any other movie on this thread away. It's used to teach leadership at the military academies, for Chrissake. If you haven't seen it, you don't have enough data to compile an accurate list.
The rest of the list, in no particular order
Bridge On The River Kwai
Best Years Of Our Lives
Paths of Glory
For the most part, these films were written, directed, and often acted by men who had experienced war firsthand. That's the difference between them and most of the other movies in this thread.
ETA: Add Mr Roberts to my list.
This post was edited on 1/23 at 12:30 am