In 1971, political friction increased between the Army and the Air Force over the close air support (CAS) mission. The Air Force asserted that the Cheyenne would infringe on the Air Force's CAS mission in support of the Army, which had been mandated with the Key West Agreement of 1948. The Department of Defense (DOD) conducted a study which concluded that the Air Force's A-X program, the Navy's proposed Harrier, and the Cheyenne were significantly different and that they did not constitute a duplication of capabilities.