The X-1's high sink rate and the problems of keeping the plane in sight amid Florida's frequent clouds also added two more votes in favor of the Army Air Force's decision to go to Muroc. This aircraft, later flown by then-Captain (Brigadier General, USAF, Retired) Chuck Yeager, would be the first aircraft in history to successfully exceed the speed of sound in level flight. With the X-1 project transferred, Pinecastle AAF was closed and the entire site was transferred to the City of Orlando in 1947 with a reversal clause for future military use if deemed to be necessary for national defense purposes. Cold War Air Training Command As a result of the outbreak of the Korean War, the United States Air Force's Air Training Command (ATC) reacquired and reactivated the facility, renaming it Pinecastle Air Force Base on 1 September 1951. ATC immediately began a $100 million military construction (MILCON) program at the World War II facility, to include lengthening the existing north–south runway and constructing a parallel north–south runway, both over 12,000 feet in length. Actual flight training operations, however, did not begin until early 1952. The 3540th Flying Training Wing (later redesignated the 4240th Flying Training Wing) was activated at the base for the purpose of training personnel in Strategic Air Command's (SAC) new Boeing B-47 Stratojet medium jet bomber. Eighty-four B-47s were allocated for the training, and SAC transferred thirty experienced aircraft commanders to Pinecastle to serve as instructors. According to the basic plan, ATC would train forty-nine crews by the end of 1952. But from the beginning, mechanical problems with the B-47 and a lack of equipment prevented training. In addition, the base was inadequate at the time with regards to training facilities. The first B-47 class arrived at the base on 6 November 1952 and the first B-47 crew training program started a few weeks later when Class 53-6A entered combat crew training on 22 December 1952. The first trained B-47 crews graduated from training during the first half of 1953. On 1 January 1954, Air Training Command transferred both the B-47 crew training mission at Pinecastle AFB and jurisdiction of the base to the Strategic Air Command. 321st Bombardment Wing and 19th Bombardment Wing On 15 December 1953, the 321st Bombardment Wing (Medium) was activated at Pinecastle AFB, absorbing all B-47 bombers and KC-97 tankers at the base. The B-47 combat crew training