During World War II, the medal's award criteria varied widely depending on the theater of operations, the aircraft flown, and the missions accomplished. In Europe, the airspace was considered completely controlled by the enemy and heavy air defenses were encountered, so the criteria were altered from those of the original medal. Bomber, photographic reconnaissance, or observation crewmembers and air transport pilots received it for five sorties, fighter pilots received it for ten sorties, and individual pilots or air crewmen received one award per enemy aircraft shot down.