I've seen this film a few times, but then my dad is the cameraman on it. He was injured whilst the film was made and was totally upset when he later found out that some of the guys he was with were killed, injured or "missing in action".
It follows the real life duties of a platoon of marines in Vietnam in 1966, if memory serves. There are all kinds of action, including those of the ambush variety, mines going off and young soldiers crying for their mothers due to the pain and shock of being injured.
This film works especially well because it IS REAL. Don't expect any swaggering heroes or special effects; they are completely unnecessary. I cannot stress enough, what you see is what actually happened all those years ago.
There's one bit where a sniper fires at the platoon. My dad says this was particularly scary as he'd just done the clapper board thing, setting the scene, when the rounds started pinging around in his direction. The camera was left running on its own whilst everyone dived for cover. The clapper board he was holding ended up with 5-6 rounds in it.