The XXI Bomber Command (XXI BC) was a unit of the Twentieth Air Force in the Mariana Islands for strategic bombing during World War II. The command was established at Smoky Hill AAF, Kansas on 1 March 1944. After a period of organization and its assigned groups receiving their B-29 Superfortress aircraft, the command transferred first to Peterson Field, Colorado, the deployed to the central Pacific, being headquartered at Harmon Field, Guam, in the Mariana Islands. Its assigned units engaged in very long range bombardment operations primarily against Japan until mid-July 1945.