★★★½ out of four stars

Rating: R. 

Theater: Lagoon, Southdale.

This winter Jack O’Connell made his starring debut as a soldier put brutally to the test in “Unbroken.” He gave a striking performance in a genre-bending film that went much deeper than a drumbeating military adventure.

In “ ’71” he does it again, in a “war is hell” movie that won’t give up. For a second time, O’Connell creates a viscerally honest film experience that speaks more through action and emotion than words. Clearly we are watching the beginning of a big-name career.

This time the setting is Northern Ireland, at the height of its sectarian Troubles. We enter through a dark screen, hearing what could be any kind of tight battle. Instants later we enter director Yann Demange’s remarkable first shot of a barracks boxing ring echoing with the wham-wham rhythm of boxers’ gloves beating adversaries. O’Connell’s teenage Pvt. Gary Hook and his new platoon are being toughened up for duty in increasingly violent Belfast. It’s a painful start for a working-class boy with integrity whose biggest draw is visiting his younger brother at the children’s home that probably raised them both.

From the start, this is a man-against-man drama that punches holes through male archetypes. “This is the front lines, boys,” says an officer, explaining Belfast’s tribal geography. “Catholics and Protestants living side by side, at each other’s throats.” The ongoing attacks by each side speak volumes about their vision of a higher power.

The squad’s idealistic Lt. Armitage (sharply played in a “Cheerio, chaps” accent by Sam Reid) is himself a new boy here. He insists that the men go out in berets, not riot gear. “We need to go out there and reassure people,” he says. “We’re here to protect them. We need to look them in the eye and tell them that.”

In reality the hawks far outnumber the doves. When the recruits hit the roadway between Unionist and Republican centers, a mob attack erupts, an IRA bullet kills Gary’s partner, and he’s running alone and weaponless from armed pursuers. Demange, in handheld documentary style, makes a hellish maze of forbidding streets where marking signs were thrown out long ago.

Throughout the night, frightened Gary is hunted by soldiers, various locals and plainclothes intelligence officers, all with morally complex strategic and ethical choices to make. Demange makes thrilling tension out of whether the indigenous people Gary encounters see him as a hostage, a bargaining chip or a dead poster child promoting their cause.

Even the kids who appear in this tense urban crime story are troubling. Gary is a rookie compared with the preteen punk played with hilarious hot-as-mustard bravado by Corey McKinley. But it’s O’Connell’s film almost entirely. He turns a lost, largely silent everyman into the soul and center of the narrative. Every moment he experiences feels true. Almost every fatality we see has an emotional consequence.

Scripted by Scottish playwright Gregory Burke, whose deeply researched Iraq war play “Black Watch” won international acclaim, this film presents a war that viewers will feel they have experienced, not just witnessed. “ ’71” makes indifference to that sort of brutal conflict impossible, however briefly.