U.S. Secretary of Defense Chuck Hagel, joined by U.S.

U.S. Secretary of Defense Chuck Hagel, joined by U.S. President Barack Obama and Chairman of the Joint Chiefs of Staff U.S. Army Gen. Martin Dempsey, gives his remarks during the 9/11 commemoration ceremony at the National 9/11 Pentagon Memorial 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 Gregory L. Jones/Released)