We are awash in war films, and why is it that nonfiction films such as Dirty Wars or Iraq in Fragments increasingly resort to the dramatizing techniques of narrative film, while fiction films strain toward procedure, as if to avoid the sticky business of interpretation altogether?

For the better part of its first hour, Lone Survivor — a fact-based procedural about four Navy SEALS dispatched to document the activities of a high-ranking Taliban operative in Afghanistan — rehearses preparation in obsessive detail. Sure, there are the familiar faces you'd expect from a men-at-war action picture: Mark Wahlberg, Ben Foster, Taylor Kitsch, Eric Bana, as well as one (Emile Hirsch) you might not. A back story is sketched in here and there to heighten the pathos of what follows. No spoilers necessary; the grisly outcome, if not the finale, is all in the movie's title and its opening sequence.

But mostly it's ripped male muscle being put through its excruciating paces by yelling drill sergeants, meticulous planning at Bagram Air Base, the loading of high-tech gear, the whir of choppers — all the busy stuff of a brutally efficient Peter Berg movie.

Until, that is, everything goes quiet, the four are on their own, and the Watershed Moment arrives. On a steep mountainside, the SEALS are confronted with a family of shepherds, one of whom — a handsome boy — stares at the Americans with hatred in his eyes. The inscrutable patriarch carries a walkie-talkie. Are they for or against the Taliban? Do the rules of engagement apply or the rules of survival?

The panicked debate that follows about whether to kill the shepherds or let them go is an unnerving stew of ethics, protocol and naked calculation. But what's great is that no Ethical Angel appears, nor any correct answer. There's only someone who's willing to break the stalemate and make a choice.

Whatever the SEALS do will have fateful consequences, and from here on the outcomes are all in the meticulous detail. In the contrast between the lightning speed with which the Afghan boy leaps down the craggy mountain like one of his goats and the Americans' slow, huffing ascent as they try to call the whole thing off and discover that a communications glitch has cut them off from HQ, we see the debacle to come.

When you don't know the terrain and you don't know who's for or against you, heroics are either beside the point or they extend only as far as survival and solidarity. In this regard, Berg is relentlessly unsparing — in Lone Survivor, we discover what it is like to topple downhill from rock to rock, and what it is like to reach for your gun and find that your hand is missing — but never Tarantino-sadistic.

There's courage aplenty in Lone Survivor — the day when grunts were made to stand in for American imperialism is long gone and rightly so.

But the movie is resolutely anti-heroic until the very end, when triumphalism creeps in, bringing a tattered happy ending belied by photos of the real-life casualties. Even then the lone survivor, confronted with possible rescue and a little boy with huge dark eyes, screams his intention to blow his saviors away. Is that his training or has he been pushed to a place where the rules of engagement no longer apply?

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