A gameplay element included in Ace Combat 5: The Unsung War, the Kill Bar is, as its name states, a bar that increases as enemy forces are defeated with a certain aircraft. As enemy targets are destroyed, the bar fills. When it's full, the next aircraft in the family will be unlocked. For example, filling the KB of the F/A-22A Raptor unlocks the F/B-22 Concept. As airborne targets are usually worth more points than ground targets, the mission "Blind Spot" can be exploited in this manner. Kill Bars are stored within saved games, so once the campaign has been beaten and saved going back and replaying missions with certain aircraft will allow the player to quickly fill Kill Bars and unlock additional planes for the actual campaign.
In Ace Combat:Assault Horizon Legacy, the kill bar is now the kill rate gauge, but serves the same purpose.