Ever since All Quiet on the Western Front, the least we’ve come to expect from a war-is-hell actioner is grungy realism. Yet in Sam Mendes’s 1917, the trenches are dry, wide and handsomely constructed. Uniforms look fresh out of Brooks Brothers. Even the rats seem pet-shop friendly. The flatlands of Flanders improbably furnish rapids and a plunging cataract, while corpse-strewn, shell-ravaged battlefields quickly give way to flower-strewn meadows. The incineration of a town becomes an alluring firework display.

This unconvincing backdrop foregrounds cardboard cutout protagonists devoid of backstory or interiority. Minor roles are cliched caricatures, peppered with pointlessly distracting star cameos. Wooden dialogue limits the scope for acting prowess. A bald, subplot-less storyline embraces both sentimentality and implausibility, as our hero-in-a-hurry takes time out to succour an abandoned baby with milk he happens to have picked up on the way, and skips across no man’s land miraculously immune to shot and shell.

In an exceptional year featuring masterworks from Tarantino and Scorsese, and the brilliance of Parasite and Marriage Story, who would imagine that a standard man-with-a-mission war film like this might snag that best picture Oscar? Well, the bookies certainly do, placing 1917 way in front of the competition. The film has already picked up best drama at the Golden Globes; since 2000, seven winners of that prize have gone on to take the Oscar. Even more auspiciously, it’s made best picture at the PGA awards, the most reliable predictors of Academy gold, with 13 of their post-millennium alumni copping the big one.

How come? 1917 owes everything to what unkind folks might call a gimmick. But this isn’t an awkward contrivance like the digital de-aging in The Irishman – a fancy bolt-on that sort of works and sort of doesn’t. Mendes has bet the farm on an all-encompassing technical feat that’s so successful it singlehandedly makes his film an unmatchable cinematic achievement. Famously, 1917 is shot with the camera following the hero, George MacKay’s Lance Corporal Will Schofield; we see the world as he sees it, for almost all of a relentless Ghent-to-Aix odyssey, in what gives the appearance of a single take.

A wooden war film with distracting star cameos or a piece of cinematic history? ... Benedict Cumberbatch in 1917. Photograph: François Duhamel/Universal Studios

This isn’t an original idea. Only five years ago, Alejandro González Iñárritu’s Birdman won best picture by telling the story of an action hero’s attempt at a Broadway comeback in what appeared to be real time. Back in 1948, Hitchcock hid the cuts in Rope by panning past clothing or furniture. Max Ophüls and Vincente Minnelli tried similar tricks. Godard’s Weekend featured a real-time, seven-minute traffic jam, while protracted opening takes adorn both Altman’s The Player and Cuarón’s Gravity. Yet 1917 is different.

Hitchcock needed to paper over his edits because 35mm film magazines had to be changed every 10 minutes. Digital cinematography knows no such limits. Thus, Alexander Sokurov was able to shoot his Russian Ark in 2002 in an uninterrupted, 96-minute wander through the Hermitage museum. Obviously, that degree of continuity would have been unattainable in the fast-changing location of complex-action war film, but developments in post-production now enable film-makers to stitch together long takes into an apparently seamless whole.

In 1917, these technical opportunities are exploited as never before. Schofield’s assignment is simply to deliver a message calling off an attack that is going to be ambushed. Yet as we accompany him, dodging bullets and wading through corpses, sharing experiences including the bizarre fate of his fellow messenger, feeling his terror, exhilaration and despair, we gain a more intense appreciation of the horror of war than anything cinema has previously managed. The film’s various eccentricities and deficiencies pale into insignificance as its singular modus operandi grips you by the throat.

Schofield has been compared to a computer-game avatar. There’s something in that, but this is an avatar made of flesh and blood, who feels and breathes. Once you’ve seen this film, you won’t forget it. You can’t necessarily say that of Once Upon a Time in Hollywood, which seems to be 1917’s main competitor for the top slot. Gorgeous and satisfying though Tarantino’s film is, it doesn’t quite make cinema history. 1917 does. And that’s why it deserves the statuette.