In 1918, at the end of World War I, the United States sent two intervention forces to Russia. The 339th Infantry and supporting units were sent to European Russia, the region surrounding the cities of Archangel (Arkhangel’sk) and Murmansk near the Arctic Circle, initially to protect supplies and help reopen the Eastern Front against Germany. The 27th and 31st Infantry were sent to the Vladivostok region of Siberia, to assist Czechoslovak military units trying to make their way out of Russia to the Western Front. These two forces became part of broader efforts by the Allies and others to oppose the Bolshevik revolutionaries who had taken power in Russia. Separated by thousands of miles, the two forces did not interact with each other.
The 31st and 339th Regiments have both taken the name Polar Bears, and both use the polar bear in their regimental crests, but it is the intervention in European Russia that has come to be nicknamed the "Polar Bear Expedition." The 339th Infantry and supporting units were made up mainly of draftees from Michigan and Wisconsin.