The first time the music starts, it’s chiefly a logistical surprise: Where are these soldiers hiding their instruments? And won’t this late-night outdoor concert betray their location to the enemy? The second time the music starts, our interest shifts to director Serge Bozon’s static camerawork: Might this be the least glamorous movie musical ever filmed?

Mr. Bozon’s trippy genre experiment, “La France,” which makes its debut Friday at Anthology Film Archives, is a rousing act of derring-do, an unlikely — and, in the hands of another director, perhaps even impossible — fusion of musical, star-crossed romance, and war film. The tale begins far from the front lines, with an unmistakably familiar scene involving a distraught wife. Camille (Sylvie Testud) is waiting desperately for a letter from her husband, who is off fighting for France during World War I. When it finally arrives, Camille is chastised by the man delivering it, a close friend, for seeming so melancholy. It’s a sign of weakness, he says. But his mockery is silenced when Camille reads the letter aloud: Her husband is alive, but he is never coming home.

For Camille, the words are marching orders, and she sets out to the front to track down her man, determined to discover why he has lost all hope. After being stopped by the police for the offense of being a woman, Camille cuts her hair, tapes down her breasts, and passes herself off as a teenage boy. Once in the forests, she locates what appears to be a company of troops heading to the front lines, and Camille forces herself upon them, becoming an observer of their drudgery. She’s also there in the evening, when the group sits around a campfire and strikes up a tune that is one part folk music and two parts bubblegum pop.

Of course, there have been plenty of quirky movie musicals to prepare us for this dark marriage of war and whimsy, but what makes “La France” resonate more deeply is the naturalistic tone that persists, even when music fills the air. In most musicals, the first strumming of a chord elicits a rousing burst of color — something akin to Lars von Trier’s “Dancer in the Dark,” in which a story of abject poverty gave way to rapturous dance sequences that amplified the distinction between real life and fantasy. But Mr. Bozon keeps the focus tight, the faces grim, and the camera still. Even as the story switches from a few depressed soldiers talking around a campfire to a group of giddy singing troubadours, the aesthetic remains eerily unchanged.

At first, the effect is almost comical. But then secrets are divulged, identities are altered, and motives are re-examined. It turns out Camille isn’t the only one projecting a false front, and as the plot thickens the music plays an increasingly complex role in the parsing out of wartime morals. Where most war films streamline their stories and present war as an intractably one-dimensional event — a hellish ordeal, a place for heroes, a time for common men to tap their inner philosophers — Mr. Bozon prefers, with each subsequent musical sequence, to accentuate how guns and uniforms tell only half the story, and to underscore the contradictions of men who would rather make art than war. He injects into this macabre setting a dose of magic, but then also tempers the accompanying giddiness with the grim faces of men at the brink who cannot forget where they are, even if they are singing about better days.

In the movie’s lengthiest monologue, Camille is taken aside by her fellow soldiers and told the story of one young private who went to war and lost his ability to dream. In almost any other war film, such an anecdote would seem woefully naïve, but in “La France,” the loss of one’s imagination is considered the worst possible casualty of war.

In the story on the screen, it is Camille, who is given life by a lifeless and drained Ms. Testud, who has lost her ability to dream. As her comrades endeavor to preserve their souls with song, Camille’s soul is rapidly slipping away. She has sacrificed her personality, appearance, and emotions to scour the fields of war for her other half. Mr. Bozon drives home his moral through the prism of this disconnect: Music, like human beings, is not suited to the realties of war. Yet in “La France,” as songs pop up in places where they surely do not belong, the melodies and harmonies only intensify our curiosity, opening our eyes to the soldiers’ desperation and our ears to what might just be the saddest music in the world.

ssnyder@nysun.com