With one exception, these echelons are those that are or were above the wing level: air divisions (and equivalent, like aerospace divisions and missile divisions), numbered Air Forces, major commands (and equivalent, but only those classified as combatant commands), Headquarters, United States Air Force, and joint organizations (e.g., U.S. Space Command, U.S. Strategic Command). The aforementioned sole exception is host wings, for ICBM units only. During the early 1960s, most Atlas and Titan I squadrons were located at bases with flying wings, usually a bombardment wing, and the missile units were assigned to these.