Its toughest soldiers - the Jaeger Corps, Frogmen, and the legendary Sirius Dog Sled Patrol - are sharpening their skills for any scenario, from counter-terrorism to extreme weather warfare.

Sirius is the world's only military dogsled patrol. The job—low pay, no holidays—entails journeying with a partner and a dog team for 26 months and more than 5,000 miles. Injuries are ...