Green Berets under the direction of U.S. Northern Command in Colorado Springs braved frigid Alaskan weather this month as part of a training exercise to prepare troops for arctic battles.

The Arctic Edge exercise involved 1,500 troops and was an early test of the command’s new special operations component, which oversees elite forces assigned to the command’s mission of protecting North America from attack.

The command said exercises included “conducting long-range movements in severe weather conditions over treacherous terrain with limited visibility that is challenging for even the most experienced operator.”

The Defense Department has been wary of battle in the extreme north in recent years as Russia has ramped up its Arctic efforts. But combat in Alaska involved more than human enemies, the command said.

“The teams have endured through subzero temperatures and near white-out conditions since the first team deployed March 7,” Northern Command said.

While the command disclosed the exercise, it took the unusual step of withholding the names of soldiers involved. In recent weeks, the Pentagon has pushed for increased secrecy amid a heightened focus on rivals in Russia and China.

The exercise tested Northern Command’s ability to defend mountainous terrain from would-be invaders.

“During the evolution, one advanced operating base team and two operational detachment-alpha teams, which consist of both mobility and mountain trained personnel, were deployed to Alaska’s Utqiagvik and Anaktuvuk Pass,” the command said.

The teams also pounded their way through long marches and also honed their ability to deploy by helicopter.

“The teams also utilized new communication systems to enhance their capabilities in a cold-weather environment,” the command said.

Already loaded with oil and mineral riches, the icy region around the North Pole has only become more contested as melting ice has opened sea lanes across the top of the globe.

That has brought more access to the arctic regions and increasing fears that they could become a battleground in a future war.

Colorado troops, whose names were not released, said war in the Arctic would be challenging.

“It’s cold in Colorado, but we don’t deal with the temperatures that they deal with up here,” one said on Northern Command’s website. “So the ability to come up here and train in Alaska is phenomenal.”