From left, President Barack Obama, Secretary of Defense Chuck Hagel and Chairman of the Joint Chiefs of Staff U.S. Army Gen. Martin Dempsey render honors during the playing of the national anthem as part of a ceremony at the Pentagon in Arlington, Va., Sept. 11, 2014, to mark the anniversary of 9/11. 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.