In the eerie blue light of an Arctic sunrise, 20 US Marines are preparing for a war on the ice. Clad in white snow camouflage and cross-country skis, they careen awkwardly between positions on the Bl?tindan mountainside in the far north of Norway, surveilling a simulated enemy on the snow-laden peak. The second force reconnaissance company — an elite team that travels ahead of other forces, sending intelligence back to command and control — is expert in operating stealthily. But in this terrain they appear exposed, unwieldy. Heavy backpacks skew their balance, adding dangerous momentum to downhill stretches and unwelcome weight on the upward hike.

Nils, their Norwegian trainer, has spent a decade in the army, and now leads his own long-range reconnaissance patrol. He looks on from a concrete command post as one Marine topples sideways by a distant ridge, then another. The fallen men are smudges on the monochrome landscape, prone and indistinct against black pines and white snow. Nils watches them struggle to their feet. “The most important thing for them to experience,” he says, “is how difficult this is.”

In the depths of the cold war, US soldiers were a familiar sight in Norwegian garrison towns north of the Arctic Circle, but, in the decades after the break-up of the Soviet Union, they retreated. As hostilities with Russia have grown, they are back once again to learn how to fight in this inhospitable terrain. This spring, the Norwegian armed forces are training nearly 8,000 Nato troops in the art of cold-weather warfare.