Hamburger Hill (1987)

It's standard procedure in War movies to use the men's downtime between skirmishes to concentrate on characterisation, so that when conflict breaks out we can compare and contrast how the individuals perform under pressure. It's the same in Hamburger Hill, but there's something in the film that makes those scenes seem better than most of the others that I've seen. And the violence when war breaks out, sometimes sudden and unexpected, is bloody and brutal, showing the horror of war without reservation. (It was based on an actual event, the U.S. Army's 101st Airborne Division assault on 'Hill 937'.)
It got overshadowed by Oliver Stone's Platoon (1986), which was also set in Vietnam, but I'd pick Hill over Platoon any day of the week.

4 sacks of mud out of 5