Originally formed at Fort William McKinley in the Philippine Islands on 13 August 1916 using troops from several existing regiments—the 8th, 13th, 15th, and 27th—the 31st Infantry Regiment’s first assignment was as part of American Expeditionary Force Siberia. Deployed to Vladivostok in August 1918 with a variety of mission objectives, the Soldiers of the 31st and 27th Infantry Regiments spent as much time and effort fighting the elements as it did trying to rescue a force called the Czechoslovak Legion and safeguard American military supplies. In addition to earning credit for two campaigns (Siberia 1918 and 1919), the Regiment also acquired a nickname, “Polar Bears,” that served as inspiration for the design of its Distinctive Unit Insignia.
After spending several months in China in 1932 guarding the International Settlement from Japanese invaders (earning the Yangtze Service Medal in the process), the Regiment returned to Manila and was there when the Japanese invaded on 8 December 1941. The Regiment helped cover American and Philippine forces as they retreated to the Bataan Peninsula, but in the end all American forces surrendered and would endure hellish captivity until the island was liberated in 1945.
The Regiment would go on to take part in ten Korean War Campaigns, a dozen campaigns in the Vietnam War, and a yet-to-be-determined number of campaigns in the War on Terrorism. A review of the astonishing number of decorations the unit has been awarded over the years gives you a good idea of how seriously the Regiment takes its motto of PRO PATRIA (“For Country”): Seven Presidential Unit Citations (from both Army and Navy), four Valorous Unit Awards, three Meritorious Unit Commendations, three Republic of Korea Presidential Unit Citations, and a Philippine Presidential Unit Citation—and this does not include unit decorations designated for individual companies.
As of Summer 2023, the 4th Battalion, 31st Infantry Regiment is the only remaining active unit representing the "Polar Bears." It is assigned to the 2nd Brigade Combat Team, 10th Mountain Division.