Winter War

The Soviet Union invaded Finland in November 1939 after Finland refused to cede territory near Leningrad. Small Finnish units on skis, armed with Suomi submachine guns and Mosin rifles, held the Mannerheim Line for months in deep snow and extreme cold and inflicted heavy losses on a much larger army.

Outcome: Moscow Peace Treaty, March 1940: Finland kept its independence but gave up about a tenth of its territory, including Karelia.