Geiger led this corps into action for the fourth time as part of the Tenth Army in the invasion and capture of Okinawa. On June 18, 1945, Geiger assumed command of the Tenth Army following the death in combat of Lt. General Simon Bolivar Buckner Jr for the final five days of the battle. He was relieved by General Joseph Stilwell. To this day, Geiger remains the only Marine Corps officer to ever hold command of a field army. Geiger was appointed commanding general of the Fleet Marine Force, Pacific in July 1945 and was promoted to lieutenant general. Geiger was the only Marine Corps representative at the surrender of Japan aboard the on September 2, 1945.