As with the ground forces, the most veteran units of the Air Service were selected to form the new Air Service. A pursuit unit, the 94th "Hat in the Ring" Aero Squadron; a day bombardment squadron, the 166th; and four observation squadrons (1st, 12th, 88th, and 9th Night) were initially assigned. The demobilization of the AEF accelerated in December and January, and all but two of these squadrons returned to the United States. Mitchell was replaced in January as commander of the Third Army Air Service by Col. Harold Fowler, a combat veteran of the Royal Flying Corps and former commander of the American 17th Pursuit Squadron.