IX Corps was a corps of the United States Army. For most of its operational history, IX Corps was headquartered in or around Japan and subordinate to US Army commands in the Far East. Created following World War I, the corps was not activated for use until just before World War II almost 20 years later. The corps spent most of World War II in charge of defenses on the West Coast of the United States, before moving to Hawaii and Leyte to plan and organize operations for US forces advancing across the Pacific. Following the end of the war, IX Corps participated in the occupation of mainland Japan.