Don Siegel's Hell Is for Heroes (1962) is the bleakest, starkest war movie I've ever experienced, with an ending that leaves you as sick and empty as you should feel after watching a film about possibly the greatest humanitarian calamity of our age, if not all our shared history. Steve McQueen is one of a handful of American soldiers who stumble across an entire platoon of Nazis. The only reason the Americans aren't wiped out instantly is because the Nazis think they're facing a force of equal size. What follows is a hushed cat-and-mouse game as the Americans use a number of clever tricks to fool the Nazis into thinking that assumption is correct.
It goes about as well as it can, which is to say that one by one the Americans die badly. One man has his hands blown off by a land mine; another has his intestines torn out and lives long enough to scream "My guts! My guts!" for a few minutes before dying in the midst of his comrades, who are completely unable to save him.
In the closing minutes, McQueen's character makes a last-ditch attempt to save the day by throwing satchel charge into a pillbox. He manages it, but is shot in the back as he retreats, and the Nazis toss the satchel back out of the firing slit. Knowing he's going to die anyway, McQueen uses his dying breath to grab the satchel charge, cradling it like a baby, and roll into the pillbox, killing himself and the Nazis within.
In the meantime, a platoon of American troops has finally arrived, and the film ends with the battle still raging. Every main cast member is gone; only the anonymous masses are left, fighting over some worthless hills. It's as disturbing an image as I've seen in film, and an instructive one.