Geiger was a tough Marine Commander who fought in the Pacific. He first saw action in Guadalcanal in September 1942, but was recalled to the Marine Corps Headquarters to become Director of Aviation. In November 1943 he returned to active service and led the I Marine Amphibious Corps on Bougainville. Thereafter he commanded the redesignated III Marine Amphibious Corps and led the invasion of Guam in July and August 1944. Before the invasion Geiger warned his troops ‘it will be a tough and bitter fight against a wily, stubborn enemy who will doggedly defend Guam against this invasion.’ He also led the III Corps at Okinawa.