 The Chaparral/Vulcan combination was always intended to be a stop-gap solution while a more powerful system evolved.However, in the 1970s the threat was perceived to change from tactical aircraft to missile-firing helicopters that would "pop-up" from behind cover.This suggested the use of a fast-acting gun system, albeit one with much longer range than the Vulcan's 1,200 m. Out of these studies came the "Division Air Defense" concept that was eventually filled by the M247 Sergeant York.