"Tuesday, September 11, 2001, dawned cool and clear, with sunny skies all along the eastern seaboard. For Air Force aviators like Lt. Col. Timothy 'Duff' Duffy of the 102d Fighter Wing at Otis Air National Guard Base, Massachusetts, the day held the promise of perfect flying weather, at a time when the U.S. civil aviation system was enjoying a period of relative peace, despite concerns about a growing terrorist threat. More than ten years had passed since the last hijacking or bombing of a U.S. air carrier. That morning, however, the country came under a shocking, coordinated aerial assault by nineteen al Qaeda hijackers at the direction of the network's leader and cofounder, Islamist extremist Osama bin Laden (1957/1958--2011). The attack plan carried out by the suicide operatives had been years in the making. It was intended to cause mass, indiscriminate casualties and to destroy or damage the nation's financial, military, and political centers, four high-value U.S. targets selected by bin Laden, independent operator Khalid Sheikh Mohammed, and al Qaeda operations chief Mohammed Atef. Analysts in the United States immediately recognized the historic nature of the strikes, launched without warning against targets in New York City and Washington, D.C., and compared them to another deadly surprise aerial attack against the United States almost sixty years earlier. The December 7, 1941, assault by Japanese forces on the U.S. naval base at Pearl Harbor had been the most devastating attack against U.S. territory by a foreign adversary until the morning of September 11, 2001."
United States Air Force History Support Office: http://www.afhso.af.mil/