第21爆撃集団
XXI Bomber Command arrived on Saipan on October 12, 1944, and from the start Hansell was beset by a host of serious command problems, the worst of which were continued teething problems with the B-29, tardy delivery of aircraft, aircrews untrained in high altitude formation flying, primitive airfield conditions, lack of an air service command for logistical support, no repair depots, a total absence of target intelligence, stubborn internal resistance to daylight operations by his sole combat wing, subordinates in the XXI Bomber Command who lobbied for his removal, and Hansell's inferiority in rank in dealing with other AAF commanders in the theater. Furthermore, Hansell was soon prohibited from flying combat missions with his command, possibly because of limited knowledge of the atomic bomb or the perception that he knew the existence of Ultra.