On 1 February 1946, Kirtland was transferred to the Fourth Air Force for use as a flight test center. Kirtland Field was returning to B-29 Superfortress activity as the flight-testing headquarters for the 58th Bombardment Wing, which had been stationed at Roswell Army Airfield, New Mexico under the Fourth Air Force. This B-29 unit would assist the Z Division at Sandia Base with flight-testing new atomic weapons designs. The 428th AAF Base Unit (Flight Test) was activated as a unit of the 58th Bombardment Wing and the host of Kirtland Field on 1 February 1946. At that time, there were fewer than 300 officers and enlisted men at the field. Because there were so few personnel on hand, morale was low and workloads were strenuous for the installation throughout the early Cold War period.