1917

War has always provided a rich but bloody vein of material for Hollywood, but while other conflicts, like Vietnam and the Second World War, have been depicted on screen countless times, the First World War is relatively underserved.

One reason is that the senseless slaughter of millions for a cause whose value people still dispute is less fertile ground for storytelling than heroically seeing off evil Nazis or the morality tale of America's great misadventure. However, Sam Mendes' 1917 may just be the film to do it justice.

Mendes' movie, which was inspired by the experiences of his grandfather Alfred, is an audacious undertaking. Like Alejandro González Iñárritu's Birdman, it gives the impression of being shot in one take - starting out behind the lines with two young Lance Corporals Blake (Dean-Charles Chapman) and Schofield (George MacKay), who are chosen for an unspecified mission.

After winding their way through communication trenches, they are given their orders by the stoic General Erinmore (Colin Firth), who reveals that aerial reconnaissance photographs show that a German retreat is, in fact, a trap - and that another company, including Blake's brother, are being drawn into a trap that will result in their slaughter when they advance. With their communication lines having been cut by the Germans, the only way to warn those in peril is for Blake and Schofield to cross No Man's Land and seemingly abandoned German trenches to deliver a message by hand.

The first thing that strikes you about 1917 is its bright colour palette - although there's plenty of mud, Mendes eschews the dirty browns and greys that are usually associated with films trying to get across the message that war is hell. It sits well with a movie that, as well as capturing the claustrophobia of the trenches and dugouts, is also at pains to show you the wide-open spaces Blake and Schofield must traverse to reach their goal. It's a directorial decision that adds a strange sense of reality - and one that makes the intrusion of a rotting corpse, trudging through a quagmire or a crawl through a booby-trapped dugout more shocking.

The true star of the film is the camera. Mendes has drawn on his theatre background to use his set like a stage - choreographing his two lead actors' march across the lines, to give a sense of constant movement that accurately reflects their disorientation. This is just when they are walking - as there are also spectacular sequences, like when a German airman crash-lands almost at the feet of Blake and Schofield - an astonishing feat of filmmaking that is complemented by an understated approach to the film's most fateful moment.

It's easy to see 1917 as just a technical triumph - but credit must also go to its two leads, whose performances, though not traditionally showy ones that are likely to grab awards attention, are perfectly pitched. In addition to having to keep up with Mendes' dizzying direction and hit marks in shots lasting up to nine minutes, MacKay and Chapman play Schofield and Blake as ordinary young men who wouldn't seem out of place in a modern soap opera. Ordinarily, that might not be a compliment, but it's perfect in a movie about how ordinary young men were pushed to become heroes.

If there's one criticism of 1917, it's that after more than an hour of painstaking world-building that makes you feel like you are alongside the soldiers in a real, three-dimensional landscape, the final act does feel slightly rushed and contrived. However, it's a flaw that's largely rectified in a heart-wrenching emotional finale.

Ultimately, 1917 brings a tear to the eye not because it is a dazzling feat of filmmaking, which it is, but because it brings you close to the heartbreaking real stories of a war in which the heroes were not necessarily Hollywood-friendly men of action, but ordinary boys fighting for their survival.