In 1916, as a captain, Geiger became the fifth Marine Corps aviator. Following U.S. entry in World War I, as a major he commanded Bomber Squadron A of the 1st Marine Aviation Force in France. After the war, Geiger's career centered on Marine aviation and advanced schooling. He served with Marine air units, and from 1931 to 1935 he headed Marine Corps aviation, playing a major role in its development. Geiger won promotion to colonel in 1935. He graduated from the U.S. Army Command and General Staff School (1925), the Army War College (1929), and the Naval War College (1941). Promoted to brigadier general in 1941, Geiger took command of the 1st Marine Aircraft Wing, Fleet Marine Force that September.
From September 1942, Geiger led the 1st Marine Aircraft Wing at Henderson Field on Guadalcanal. He returned to the United States in May 1943 to direct Marine Corps aviation. Promoted to major general, in November 1943 he assumed command of the I Marine Amphibious Corps on Bougainville in the Solomon Islands, which he led—following its redesignation as III Amphibious Corps—in fighting on Guam, Peleliu, and Okinawa. Following the death of Lieutenant General Simon Bolivar Buckner in the struggle for Okinawa, Geiger briefly (18–23 June) commanded the Tenth Army on Okinawa, the first Marine officer to command a numbered field army. Promoted to lieutenant general in June 1945, the next month Geiger became commanding general of the Fleet Marine Force in the Pacific. He returned to Headquarters Marine Corps in November 1946 and died on 23 January 1947 at Bethesda, Maryland. By act of Congress in July 1947, Geiger received posthumous promotion to full general.
Brandon H. Turner
Henderson, R. P. "Roy S. Geiger, The First Air-Ground General," Marine Corps Gazette, 79, no. 4 (April 1995): 78–80.; Hough, Frank O., Verle Ludwig, et al. History of U.S. Marine Corps Operations in World War II. 5 vols. Nashville, TN: Battery Press, 1993.; Willock, Roger. Unaccustomed to Fear: A Biography of the Late General R. S. Geiger. Quantico, VA: Marine Corps Association, 1983.