For a Danish Leopard 2A7 tank crew, more used to the warm interiors of a high-end battle tank, jumping into an ice-cold lake is ever so slightly beyond their normal training routine.

"It is a little outside their comfort zone," says Captain Vesti, the Deputy Commander of the 2nd tank squadron of the Jutland Dragoon Regiment. "But everybody understands that it is part of being an army soldier and needs to be trained as well."

Cold weather training of a NATO force doesn't just consist of jumping into a lake. The soldiers – also tankers – have to build a certain skill set in order to be able to operate out in the open in adverse weather conditions. It encompasses i.e., bivouacking, handling their weapons in the cold and knowing when and how to light a fire from whatever is available in the natural environment. 

The Danish service members jump fully clothed into the lake one by one. They find that the first few seconds aren't so bad, when body's numb sensory systems try to figure out how to respond to the shock of extreme cold. 

It is the half-minute or so, when the soldiers wait for permission to get out that really tests their resistance to extreme cold. 

"What's 13 plus 13?", asks an instructor, looking intently at an immersed soldier. Only once he gets a correct reply, which he gets every time, can the soldier climb up onto the ice. He or she then walks back slowly up to a clearing and begins the process of drying up and changing clothes. The heat from a wood-burning open fire helps. 

All around, the comrades – completing their own drying process – congratulate the latest cold weather training graduate in between telling jokes and laughing congenially with each other.

This kind of training builds morale,

says Captain Vesti. "That's one of the objectives. Lighting a bonfire is part of the training but it also a way to have a good time together."