The 10th Mountain Division was first activated on July 15, 1943. It was one of the last U.S. divisions to enter combat, not starting to fight together as a unit until January 1945.

The development of a specialized unit began before the United States entered World War II. In 1940 the War Department began working with the American Alpine Club and the National Ski Patrol Committee of the National Ski Association to develop equipment and training for winter and mountain warfare. The 87th Mountain Infantry Regiment was activated at Fort Lewis, Washington on November 15, 1941, drawing its initial members from men already in the Army who had previous ski and mountaineering experience. Thereafter the National Ski Patrol recruited volunteers for the unit, under a contract with the War Department. In 1942 and 1943 additional regiments that became part of the division were activated. The 87th Regiment participated in the assault landing on Kiska, August 15–August 17, 1943. The attackers found the island completely deserted by the Japanese, but suffered some casualties from friendly fire and booby traps.

Soldiers from the division provide cover for an assault squad. The division was activated on July 15, 1943 at Camp Hale, Colorado as the 10th Light Division (Alpine). It was renamed the 10th Mountain Division on November 6, 1944.

The unit saw its first actual combat in Italy. Elements of the division began arriving in Italy in late December 1944, and after a brief training period entered combat, January 8, 1945, near Cutigliano and Orsigna. Preliminary defensive actions were followed on February 19, 1945, by a concerted attack on the Silla-Mount Belvedere sector, and the peak was cleared after several days of heavy fighting. In early March the division fought its way north of Canolle, taking several more peaks, and moving to within 15 miles of Bologna. Maintaining defensive positions for the next three weeks, the division jumped off again in April, captured Mongiorgio, April 20, and entered the Po Valley, seizing the strategic points Pradalbino and Bomporto. The 10th crossed the Po River on April 23, reaching Verona April 25, and ran into heavy opposition at Torbole and Nago. After an amphibious crossing of Lake Garda, it secured Gargnano and Porto di Tremosine, April 30, as German resistance in Italy ended. After the German surrender in Italy, May 2, 1945, the division went on security duty, receiving the surrender of various German units and screening the areas of occupation.

The division was deactivated on November 30, 1945. However, it was reactivated on July 1, 1948, after being redesignated as the 10th Infantry Division. Ten years later, on June 14, 1958, it was deactivated.

The 10th Mountain Division was reactivated in Feb 1985 and is currently the most deployed unit in the US Army.