 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 that concluded that the Air Force 's A @-@ X program , the Marine Corps ' Harrier , and the Cheyenne were significantly different that they did not constitute a duplication of capabilities . On 22 October 1971 , the Senate Armed Services subcommittee on Tactical Air Power conducted hearings to evaluate the CAS mission and the pending programs . The most damaging testimony for the Army 's program came from the commander of the Air Force 's Tactical Air Command , General William W. Momyer , who cited helicopter casualty statistics of Operation Lam Son 719 . 
