The sound of gunfire echoed around the Norwegian fjords as a row of Swedish and Finnish soldiers, positioned prone behind banks of snow, trained rifles and missile launchers on nearby hills ready for an enemy attack.

The drill, in March, was the first time forces from Finland and Sweden have formed a combined brigade in a scheduled NATO exercise in Arctic Norway known as Cold Response. Neither country is a member of the NATO alliance. The exercise was long planned, but Russia's invasion of Ukraine on Feb. 24 added intensity to the war game.

"We would be rather naive not to recognize that there is a threat," said Swedish Maj. Stefan Nordstrom. "The security situation in the whole of Europe has changed and we have to accept that, and we have to adapt."