Relentless and surreal, “1917” tries to capture the chaos of being at war.

The Golden Globe winner’s story is quite simple: Two boyish Brits, Schofield (George MacKay) and Blake (Dean-Charles Chapman), are ordered to leave their World War I trench, run through enemy territory and deliver a message to another battalion that is about to launch an offensive against the Germans, who appear to have retreated.

The message? The retreat was a trap and, if the battalion does attack, all 1,600 soldiers, including Blake’s older brother, will walk into a massacre.

In execution, “1917” is anything but simple. The action of the two-hour movie spreads out over about eight hours but “1917” has been assembled to look as if it’s a single, uninterrupted take (along the lines of Alfred Hitchcock’s “Rope”). The technique makes sense for a movie that, like “Rope” or “Birdman,” takes place in real time, but it’s a little off-putting in one that does not, like “1917.”

Still, it contributes to an atmosphere that I kept thinking of as unreal reality. Minute by minute, “1917” pulls us into the actual details of battle — the split-second decisions the young men make, the dozens of ways they get blindsided — and the continuous take creates an overwhelming surreal quality, which conveys that, when a battle is raging, it’s like you’re in another world.

Director/co-writer Sam Mendes has structured the movie as a series of what might be called mini-adventures if they weren’t so deadly. And many of these adventures have an unearthly quality, as if to underscore how completely unprepared for this mission Schofield and Blake are: the soldiers stumbling upon a battalion of men, sitting entirely still and listening to an eerily pretty ballad, or finding shocking signs of life in the midst of fields of death. (I don’t want to spoil the many surprises of “1917,” so I’m being a little cagey here.)

Besides Mendes, the other key contributor to “1917” is our greatest living cinematographer, Roger Deakins. He finally won an Oscar two years ago for “Blade Runner 2049” after losing 13 of them and he may win again for the astonishing technical achievement of “1917.” A few wonky special effects aside (don’t look too closely during a jump into a river), “1917” is a major visual achievement. And an aural one. Speaking of folks overdue for Oscars, 14-time loser Thomas Newman contributes a subtle but rousing musical score.

The way the movie is assembled undeniably acquaints us with the mayhem of war but it also pushes us away from the story. I admire the technique but I also think it draws attention to itself and prevents us from engaging with the characters as fully as we’d like to.

And, while you’re being distanced from the movie, it also may occur to you that, in order to make “1917” as action-packed as any 007 movie, Mendes has thrown in big-star cameos (Colin Firth, Benedict Cumberbatch, “Fleabag’s” Hot Priest Andrew Scott) and enough incidents to fill out an entire 12-episode series of a TV season. That’s why, I think, the movie feels overstuffed, like there’s no room to breathe.

It is worth seeing, though. On a technical level, if not always an emotional one, “1917” is like nothing you’ve ever seen.