The Korean War provided new challenges and opportunities for Army Aviation. Organic Army Aviation had acquired its first helicopters, thirteen Bell H-13 Sioux, in 1947, shortly before the U.S. Air Force became independent of the Army. In Korea, the Army employed the Cessna O-1 Bird Dog and other improved fixed wing planes, but also helicopters. The Army used its H-13s primarily for medical evacuation, command and control, and transport of lightweight and valuable cargo. Because of the rugged terrain of the Korean peninsula, the value of helicopters came to be recognized by all the services; the demand for both helicopters and trained aviators consistently exceeded the supply. In 1951 the Army began organizing five helicopter transport companies and training warrant officer pilots. There was, however, an ongoing rivalry between the Army and the Air Force concerning responsibility and resources for the aerial support of ground forces. Because of this rivalry, and also because of the shortage of helicopters, only two Army transport companies were supplied with Sikorsky H-19 Chickasaw helicopters in time to participate in the Korean War. Transport helicopters nevertheless proved themselves by moving cargo and personnel during the final months of the war and then by participating in prisoner exchanges and other functions after the cessation of hostilities. During the Korean War, the Department of Air Training at Post Field expanded, and in early 1953, it became the Army Aviation School. As a result of the expansion of both aviation and artillery training, Post Field became overcrowded, and the Army decided to move the Army Aviation School to a different post. When no satisfactory permanent Army post was found, a temporary post, Camp Rucker, Ala., was chosen.