A lot of great cinema is made by happy accidents: certain intangible chemistries and tricks of timing that can’t be calculated even by the most exacting auteur. In the considerably rarer case of “ Real ,” the whole film is an accident, and one more vital than happy. Shot inadvertently while director Oleh Sentsov — not working as a filmmaker, but as a lieutenant in the Ukrainian Defense Forces — was holed up with his unit during a perilous battle in the early days of the war against Russia, the film captures the horror and claustrophobia of trench warfare with an immediacy that no big-budget fictional combat movie could hope to match, all courtesy of a GoPro camera on Sentsov’s helmet that he accidentally turned on while checking his equipment.

The result is both simple and hard to classify: In his director’s statement for “Real,” Sentsov rules out the terms “film” and “documentary,” though its cinematic pull and power are plain to see. Any cynical notions that the filming may not have been as unintentional as stated are thwarted by the relative lack of incident in the footage, which covers no particular crux point in the men’s plight as they anxiously await evacuation, and ends only when the camera battery runs out. Which isn’t to say “Real” wants for tension or urgent human drama: Premiering at the Karlovy Vary Film Festival in wholly unedited form, Sentsov’s film may not have the narrative breadth or shaping of recent Oscar winner “20 D.