It’s easy to forget as you’re watching Christopher Nolan’s Dunkirk, that the film is in full color. The palette is so restricted—muted blue sky and white clouds; the beige of the French beach and the murky gray of the English Channel; the drab brown uniforms and green helmets over the pale-faced soldiers with their somehow perfect haircuts—that it seems parts of the spectrum have been blocked out. Flashes of brighter colors—a Union Jack, a red cross, purple smears of jelly on toast, or the yellow wings of a German fighter plane—break the spell, but not always to the best effect. Occasional bursts of flames, imperiling many of the effectively nameless characters, come as a relief from the chromatic tedium.

Dunkirk pairs its visual monotony with jumbled chronology. Nolan has been a specialist in scrambled timelines since his breakout 2000 feature Memento, which moved backward and forward to capture its protagonist’s anteretrograde amnesia. Then there was the fractured dreamtime of 2010’s Inception and the space-travel distortions of Interstellar, both movies that resolve into heartwarming family reunions. Nolan knows how to cap a couple of hours of thoroughgoing grimness with a dollop of schmaltzy redemption. At the end of his Dark Knight Trilogy, even Christian Bale’s frowning Bruce Wayne ends up on a Mediterranean vacation with Anne Hathaway’s Catwoman.

Dunkirk tells the story of the spring 1940 evacuation of the British army from the Continent. Allied troops were cornered on the northwest French coast, near the border with Belgium, and retreated in a hasty operation that required the Royal Navy to requisition small, private British boats and resulted in massive casualties. Yet anything less would have left Britain far more vulnerable to a German invasion. The film is split into three parts: “The Mole,” one week at the breakwater where ships docked to pick up men ushered out by Navy Commander Bolton (Kenneth Branagh); “The Sea,” a day on a small boat captained by Mr. Dawson (Mark Rylance) answering the government’s call for civilian vessels, the so-called Little Ships, to ferry soldiers across the Channel; and “The Air,” an hour with a few Royal Air Force Spitfire pilots led by Farrier (Tom Hardy), whose plane either has a busted fuel gauge or a leaky tank. It’s not much of a spoiler to say that the timelines will merge at the film’s end, the evacuation will be a success, and a substantial body count will pile up along the way. Four fleeing Brits are picked off by unseen Germans in the first scene alone, all the better to lend dramatic weight to the survival of their one lucky comrade Tommy (Fionn Whitehead) through his week of dodging bombs and keeping his head above water.

In America we’re used to encomia to the Greatest Generation and the veterans of the Second World War—though they’re diminishing, now nonagenarians wheeled out to give the crowd a wave on special occasions. After decades of this, we can now accept ironic reimaginings of the war, like Quentin Tarantino’s Inglorious Basterds, without worry that the memory of the Holocaust will be stained by a gory tongue-in-cheek revenge fantasy. But in Britain the pious death cult around the World Wars remains a feature of daily life, memorialized on each anniversary of a heroic slaughter. Since 2014, BBC Radio 4 has been airing The Home Front, a 12-minute daily serial tracing the First World War’s progress and the pursuit of normality in Britain across the full four years of the conflict’s centenary. For Nolan, born in London in 1970 to an American mother and a British father, Dunkirk is akin to checking a patriotic box and securing a pass to its permanent pageant of nostalgia and weepy self-congratulation.

The Dunkirk episode was trotted out by the Leave campaign in the runup to last year’s EU referendum, and it’s easy to mistake Dunkirk for a piece of pro-Brexit propaganda. Plucky nationalist myths and box office populism have a way of aligning, and Nolan has a track record of flirting with reactionary politics. See the NSA-style surveillance capabilities Batman develops in The Dark Night that just might be necessary to stop Heath Ledger’s Joker (a villain so much more charismatic than his adversary it was hard not to root for him), or the way Hardy’s demagogic Bane in The Dark Knight Rises coopts a streetside uprising that bore a suspicious resemblance to the Occupy movement. The memory of the Second World War is fodder for both sides in the Brexit debate: Remain to prevent that sort of thing from ever happening again; Leave to get out from under the thumb of the historic German foe and assert the spirit of the Sceptred Isle that long ago won the day against barbarism.

The Germans in Dunkirk are a faceless menace, and the desperate young British soldiers can be hard to differentiate, as Nolan eschews character study for a portrait of collective desperation. When Dunkirk does stray into character-based drama things can get treacly. When Mr. Dawson, sailing with a crew of two boys, picks up a shivering soldier (Cillian Murphy, credited as “Shivering Soldier”) hunched on a floating wreck, the soldier balks at going back to the beach he just escaped, and knocks one of the boys below deck. The fall will turn out to be fatal, but the blinded boy hangs on long enough to deliver a few lines about how he was never good at school and joined the amateur mission across the Channel in the hopes of doing something that might finally get his picture in the paper and make his father proud. Better for the dialogue to be sparse when it’s otherwise this platitudinous.

Aside from some gorgeous shots of planes in flight, most of Dunkirk consists of spectacles of survival, and they pile up in dreary repetition. There are three emergency landings, two on sea and one on land. There are three instances of rising waters in close quarters, two on boats and one in a plane’s cockpit. We get used to seeing members of the minimally delineated ensemble pull through. Hans Zimmer’s score is a manipulative set of variations on crescendos that never crest, mimicking sirens, heartbeats, and ticking clocks—until it breaks into a bright burst of strings when the Little Ships appear on the horizon, and Branagh’s commander is asked, “What’s that?” Tears in eyes, he replies, “It’s home.”

Despite their often incoherent action sequences, gimmicky time muddles, and turgid humorlessness, Nolan’s previous pictures usually remain watchable because of the presence of a well-deployed star: Ledger and Hathaway in the Batman films; Ellen Page in Inception; Al Pacino and Robin Williams in Insomnia. No one sparkles in Dunkirk, and as if to highlight the cast’s general listlessness, the voice of Michael Caine—elsewhere in Nolan’s universe usually reduced to the status of a butler—comes on the radio like a taunt. Harry Styles has a nice turn as a surly bloke ready to throw a French interloper overboard from a sinking ship—shades of Brexit indeed, though cooler heads prevail and the Frenchman is spared. Rylance’s Mr. Dawson is a cardboard version of stiff-upper-lip resilience. Like Dunkirk itself, his performance falls short of even clichéd Britishness. The film ends with a gutless recitation of Churchill’s “fight on the beaches” speech. Nolan has confused his native island with the anhedonia in his head.