for prompt and sustained offensive and defensive air operations. The Air Force shall be responsible for the preparation of the air forces necessary for the effective prosecution of war except as otherwise assigned and, in accordance with integrated joint mobilization plans, for the expansion of the peacetime components of the Air Force to meet the needs of war. Section 9062 of Title 10 US Code defines the purpose of the USAF as: to preserve the peace and security, and provide for the defense, of the United States, the Territories, Commonwealths, and possessions, and any areas occupied by the United States; to support national policy; to implement national objectives; to overcome any nations responsible for aggressive acts that imperil the peace and security of the United States. Core missions The five core missions of the Air Force have not changed dramatically since the Air Force became independent in 1947, but they have evolved and are now articulated as air superiority, global integrated ISR (intelligence, surveillance and reconnaissance), rapid global mobility, global strike, and command and control. The purpose of all of these core missions is to provide what the Air Force states as global vigilance, global reach, and global power. Air superiority Air superiority is "that degree of dominance in the air battle of one force over another which permits the conduct of operations by the former and its related land, sea, air, and special operations forces at a given time and place without prohibitive interference by the opposing force" (JP 1-02). Offensive Counter-Air (OCA) is defined as "offensive operations to destroy, disrupt, or neutralize enemy aircraft, missiles, launch platforms, and their supporting structures and systems both before and after launch, but as close to their source as possible" (JP 1-02). OCA is the preferred method of countering air and missile threats since it attempts to defeat the enemy closer to its source and typically enjoys the initiative. OCA comprises attack operations, sweep, escort, and suppression/destruction of enemy air defense. Defensive Counter-Air (DCA) is defined as "all the defensive measures designed to detect, identify, intercept, and destroy or negate enemy forces attempting to penetrate or attack through friendly airspace" (JP 1-02). In concert with OCA operations, a major goal of DCA operations is to provide an area from which forces can operate, secure from air and missile threats. The DCA mission comprises both active and passive defense measures. Active defense is