Finnish conscript Atte Ohman readied himself aboard a U.S. landing ship to storm a snow-swept Norwegian beach as part of a rapid response unit pushing out an invading enemy.

"There is a saying that 'if you want to keep the peace, you need to prepare for war'," the 19-year-old corporal said, clutching his automatic rifle. "That's what we're doing."

The simulated assault on NATO's frigid Arctic fringe was part of its sprawling, four-month Steadfast Defender exercise — the largest drills staged by the U.S.-led military alliance since the Cold War.