In the late autumn of 1939, shortly after Second World War had commenced, the Soviet Union invaded Finland. This act of military aggression, henceforth known to history as the Winter War, was ostensibly carried out to secure a buffer state and better protect major urban areas such as St. Petersburg (then known as Leningrad). The Red Army's attack through the forests of northern Finland was a poorly calculated operation-in the little more than 3 months that the conflict lasted, the Soviets suffered extensive losses. The hit-and-run tactics of the small, winter-savvy Finnish Army resulted in a not significant number of Red Army casualties. But from the Soviet perspective, the Finnish soldiers were merely an annoyance compared with the real enemy--the environment. Cold injury reached epidemic proportions in the Red Army during this short conflict, apparently caused in large part by ignorance of environmental realities by the Soviet high command. Paradoxically, the Soviets arguably possessed the most extensive and sophisticated body of knowledge about cold injury prevention and treatment on earth by the late 1930s. There were significant lessons learned by the Soviets during the Winter War, however. When Germany invaded the Soviet Union in 1941, the Red Army very successfully applied these lessons during 4 years of vicious winter battles on the Eastern Front.