Pentagon employees applaud as Chairman of the Joint Chiefs of Staff U.S. Army Gen. Martin E. Dempsey, not pictured, addresses the audience during the Pentagon Community 9/11 observance at the center courtyard of the Pentagon in Washington, D.C., Sept. 11, 2013. Terrorists hijacked four passenger aircraft Sept. 11, 2001. Two of the aircraft were deliberately crashed into the World Trade Center in New York; one was crashed into the Pentagon; the fourth crashed near Shanksville, Pa. Nearly 3,000 people died in the attacks. (U.S. Army photo by Eboni Everson-Myart/Released)