Just as the Germans were ill-prepared for "General Winter" in their 1940 invasion of the Soviet Union, the Soviets were surprised by the Finnish Winter of 1939-40. For example, Soviet vehicles were winterized for temperatures down to -20F, which was normally adequate for that region. But that Winter, temperatures dropped down to -40, and thousands of Soviets froze to death along with their vehicles.

Finnish rifleman, Winter War

This is a photo of Simo Häyhä, a Finn also known as "The White Death" - and is widely known and accepted as the World's Greatest Sniper. The photo was taken during the Winter War (1939-40) with Russia. He has over 500 confirmed kills, and died only recently. He didn't use a scoped rifle - he prefered shooting over open sites. You can read about him in many places, but here's one for starters: http://mosinnagant.net/finland/simohayha.asp

The World's Greatest Sniper

A Finnish-made  81mm Tampenella short-barreled mortar.