Soldiers from some of NATO's warmer climates have been learning how to operate in freezing conditions as part of Exercise Trident Juncture in Norway.
Personnel from 31 nations are taking part in activities designed to help them acclimatise to sub-zero temperatures.
After getting used to driving large vehicles in slippery conditions, personnel have been tackling a test involving being up to their shoulders in near-freezing water in just their underwear.
Danish Army Survival Training Instructor, Sergeant First Class Jan Agger says the normal response is to get out, but the soldiers must learn to overcome that instinct:
"To calm themselves and get control of their breath. They can actually be out there for a long time."
He added it could be up to 15 minutes before the effects on the body become dangerous.
The soldiers spend around three minutes in the cold water to learn how their bodies cope then they return to the shore where a pre-made fire warms them up before embarking on a run to reinvigorate their muscles.
Private Dean Briggs of Royal Logistic Corps, 6 Regiment, was among the troops needing help to get dressed after emerging from the water. He said the effect was "a dead, tingling sensation":
"It's not that bad when you're in there, then it gets worse and worse."
Trident Juncture 2018 is NATO’s largest exercise in over a decade and involves 150 aircraft, 10,000 vehicles and 40,000 personnel.
It is designed test the ability of alliance to deal with a large scale attack.