Saipan had been occupied by the Japanese since World War I, and by mid-1944, the Americans had advanced inside the Japanese ring of defense in the Pacific Theater. By establishing air bases in the Mariana Islands, the United States Army Air Forces could establish bases to conduct long-range strategic offensive air operations over the Japanese Home Islands with the new B-29 Superfortress, which, during early 1944, was operating ineffectively from bases in China. Bringing the superfortresses into the Central Pacific and stationing them in the Marianas would bring Japan within the range of the B-29, as well as provide the Twentieth Air Force with reliable means of support from the western ports of the United States.