The United States Air Force (USAF) is the largest and most technically powerful air force in the world. It is an important part of the U.S. military force. It was officially established on September 18, 1947 to "protect the United States and its interests through force in the air and space" 。 USAF is composed of the Secretariat of the U.S. air force, the air force staff office and combat units, of which the highest administrative leadership organization is the air force department and the highest military command organization is the air force staff office. In February 2014, the US Air Force announced that it would replace BlackBerry devices with iPhones and iPads.
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