War on film can come in many shapes and sizes. From Saving Private Ryan’s beaches of Normandy to Black Hawk Down’s Mogadishu to the CIA black sites of Zero Dark Thirty to a bug-covered planet on the other side of the galaxy in Starship Troopers, war runs the gamut from the very personal to the thoroughly detached. The warfare at the heart of ‘71, the new film from director Yann Demange working with a screenplay from Gregory Burke, is as personal as it gets, a pitched battle on the streets of Belfast in the middle of its most bloody riots between Protestant and Catholic sects of the city. When the battlefield is a city’s streets and the niceties and expectations of warfare are stripped away, the simplicity of friend or foe becomes shrouded. With no way to determine who to trust, no one can be trusted.

Such is the lot in life of Private Gary Hook (Jack O’Connell) of the British army, a fresh enlistee from Derbyshire whose first mission brings him to Belfast in a vain attempt to keep the peace between the Protestants and the Catholics. On his first street mission, his unit, led by Lt. Armitage (Sam Reid, looking a bit like a Michael Fassbender in training), is ambushed by an increasingly agitated mob who seem to show no fear when confronted with armed uniformed officers. When a very young boy steals one of the men’s rifles, Hook chases him into the crowd alongside another soldier, only to have the rest of his battalion forced to retreat from the scene, leaving them behind. When his fellow soldier is shot to death, Hook is left completely on his own, chased through streets and back alleys, disoriented and in pain, with no one to trust and no way out.

The first act of ‘71, covering approximately thirty minutes of running time, is perhaps among the best urban warfare films have to offer. Demange and Burke smartly dispense with much of the buildup, giving a minor backstory to Hook and reducing the standard basic training sequences into a breezy montage. In what feels like no time at all, his unit descends upon the streets of Belfast, only to discover that all of their careful planning is for naught due to an utter lack of street signs. As the soldiers move from door to door searching houses for weapons, the locals ominously and menacingly clatter trash can lids on the sidewalk, an unholy din that cannot possibly end well for the interlopers. Suddenly a riot erupts and the scene morphs into unadulterated chaos, a crash of faces, screaming and spitting and fearlessly throwing anything they can get their hands on at their much more heavily armed invaders. The pace of these moments is impossibly quick; just as things seem to have started, Hook is lying next to his fallen comrade, surrounded by that crash of faces, only able to escape due to the kindness of a stranger in the crowd. This kindness awards him little more than a thrilling chase sequence through unknown roads and back alleys, gunshots peppering the walls just above his head.

It is a thrilling sequence of sequences, one that does more to establish ‘71’s central themes of alienation and chaotic confusion more than any monologue ever could. It employs arguably too often used shaky cam (we can thank the first Hunger Games for discovering the true horrors of its overuse) to great effect, with a driving editing cadence and a pulse pounding score from David Holmes. That thirty minutes, from the opening credits to the moment Hook finds some modicum of safety huddling in an outhouse, is more than worth the price of admission on its own, but the film is not particularly interested in letting up its tension, even as it transitions from outright war into a quieter, more paranoid thriller for its remaining 70 minutes. The plot ramps up at this point, focusing in on Hook’s attempts to find sanctuary via the help of strangers, even as he cannot be sure who, if anyone, he can count as a friend.

He is being chased by a group of rebels who seek to finish him off before the full wrath of the British army comes down on their city, including a young man named Sean (Barry Keoghan) who seems to be thoroughly in over his head. He is being tracked by undercover agents allied with the Brits who may or may not have his best interest in mind, and is taken in by a doctor (Richard Dormer) and his daughter (Charlie Murphy), but even they might not be what they seem. The ensemble is roundly excellent, even if their thoroughly localized accents can be at times incomprehensible to the untrained American ear (this is a film that could be benefitted a tad by subtitles on a home release). O’Connell continues to build on his star-making performance from Starred Up (and his more high profile but less beguiling work in Unbroken), acclimating himself well to the vulnerability of the role. The bravado of his character in Starred Up is replaced by mute traumatization; much of his work is silent, relying on the fear in his eyes and tremble in his lips as he must constantly reassess the threats around him. It is unfortunate that O’Connell’s first brush with the mainstream was a dud, but as long as he continues to cultivate performances like this, he’ll be just fine.

There are times, however, where the screenplay’s eyes are a tad too big for its stomach. The second act is dominated by political infighting and espionage, a series of backroom meetings and double-crosses between the Brits, the Catholics and the Protestants. There are times, perhaps due to the language barrier, perhaps due to a couple of the actors having similar appearances. This causes the proceedings to drag when the story pulls away from Hook, and while it never stops being interesting, the momentum is upset slightly until O’Connell returns to the screen. Luckily, its final confrontation is more akin to its first thirty minutes than its second, and it leaves the audience wanting more. At its best, ‘71 is absorbing, gripping drama, a powder keg at the brink of explosion seemingly at any time. Its weak moments are few and far between, and its star continues to prove he is a force with which to be reckoned. It is a tense, powerful piece of work not to be missed.