at Walker AFB, New Mexico, was the first dedicated air refueling unit in history. On 2 March 1949, the Lucky Lady II, a B-50A of the 43d Bombardment Wing, completed the first nonstop round-the-world flight, having covered in 94 hours and 1 minute (249.45 mph). Lucky Lady II was refueled four times in the air by KB-29 tankers of the 43d Air Refueling Squadron, which had made only one operational air refueling contact before the mission. For this outstanding flight, the Lucky Lady IIs crew received the Mackay Trophy, given annually by the National Aeronautic Association for the outstanding flight of the year, and the Air Age Trophy, an Air Force Association award, given each year in recognition of significant contributions to the public understanding of the air age. In 1953, the jet age came to Davis–Monthan when SAC units on the base converted to the new Boeing B-47 Stratojet. The 303d Bombardment Wing, Medium, was initially established on 27 August 1951, and activated at Davis–Monthan AFB on 4 September 1951. The wing operated B-29s until January 1952, when it was equipped with KB-29s. On 20 January 1953, the 303d transitioned to the Boeing B-47 Stratojet for its three bomb squadrons, while an additional air refueling squadron equipped with KC-97s was assigned to the wing between 18 February 1953, and 1 February 1956. A standard SAC Alert Area ramp was constructed in the southeast corner of the base adjacent to the runway and the 303d assumed nuclear alert responsibilities when final conversion and checkout in the B-47 was complete. In April 1953, the Air Defense Command's (ADC) 15th Fighter-Interceptor Squadron was activated with F-86A Sabres. A year later, the unit transitioned into F-86Ds followed by a transition to F-86Ls in the fall of 1957. In the spring of 1959 the unit received Northrop F-89J interceptors which it flew for only a year when it transitioned into McDonnell F-101Bs. On 24 December 1964, the 15th FIS was inactivated. In 1962, the Strategic Air Command's 390th Strategic Missile Wing (390 SMW) and its 18 Titan II ICBM sites around Tucson were activated. The 390 SMW was one of only three Titan II missile wings in SAC and represented the heaviest land-based missile and the largest single warhead ever fielded by U.S. strategic deterrent forces. In July 1963, the 4028th Strategic Reconnaissance Weather Wing, equipped with U-2 strategic reconnaissance aircraft, began flying global