sentences:  It was replaced by the SAC 4310th Air Division which absorbed the mission and personnel of the 5th AD.The 5th Air Division (5th AD) originated on 19 October 1940 at McChord Field, Washington.Its initial mission was air defense of the northwest United States with three bombardment groups (12th, 17th and 39th) flying early B-17 Flying Fortresses (B-17C/D), as well as the B-18 Bolo and its B-23 Dragon variant.