On 31 March 1946, the following additional installation was also assigned to SAC: Kirtland Field, New Mexico (later Kirtland Air Force Base) Under the first SAC Commander in Chief, General George C. Kenney, initial units reporting to the Strategic Air Command headquarters on 21 March 1946 included the Second Air Force, the IX Troop Carrier Command and the 73d Air Division. Fifteenth Air Force was assigned to SAC on 31 March (15th AF's 263rd Army Air Force Base Unit—with SAC's radar detachments—transferred the same date directly under HQ SAC ), while the IX Troop Carrier Command was inactivated the same date and its assets redistributed within SAC. With postwar demobilization still underway, eight of the ten assigned bomb groups were inactivated before the Eighth Air Force was assigned to SAC on 7 June 1946 Despite the pressures of demobilization, SAC continued the training and evaluation of bomber crews and units still on active duty in the postwar Army Air Forces. Radar Bomb Scoring became the preferred method of evaluating bomber crews, with the last of 888 simulated bomb runs scored against a bombing site near San Diego, California during 1946, subsequently increasing to 2,449 bomb runs by 1947. In the wake of the successful employment of air-dropped nuclear weapons against Hiroshima and Nagasaki to effectively end World War II, SAC became the focus of the nation's nuclear strike capability, to the extent that Joint Chiefs of Staff (JCS) Publication 1259/27 on 12 December 1946 identified that, "...the 'air atomic' strategic air force should only come under the orders of the JCS." In addition to the strategic bombing mission, SAC also devoted significant resources to aerial reconnaissance. In 1946, SAC's reconnaissance aircraft inventory consisted of F-2 photo variants of the C-45 Expeditor support aircraft, but by 1947 SAC had acquired an F-9C squadron consisting of twelve photo-reconnaissance variants of the B-17G Flying Fortress. An F-13 squadron, the F-13 later re-designated as the RB-29 Superfortress, was also established. SAC conducted routine aerial reconnaissance missions near the Soviet borders or near the 12-mile international waters limit, although some missions actually penetrated into Soviet airspace. The flight profiles of these missions—above 30,000 feet and in excess of 300 knots—made interception by Soviet air forces difficult until the Soviet's 1948 introduction of the MiG-15 jet fighter. Project Nanook, the Cold War's first Top Secret reconnaissance effort, used the first RB-29 missions for mapping and visual