English: Design of the AH-56 "Cheyenne" began during the Vietnam War to replace the AH-1 Cobra, which was vulnerable to light antiaircraft fire and lacked agility. Because of cost overruns, delays, and changing Army requirements, the AH-56 never went into production. The AH-64 "Apache" eventually was chosen to fill the role for which the "Cheyenne" was developed. This is one of the ten prototypes built after Lockheed won the design for the Army's Advance Aerial Fire Support System (AAFSS)