U.S. Marines, Sailors and coalition partners with Regional Command Southwest salute as a U.S. flag stands at half-mast during a 9/11 memorial ceremony Sept. 11, 2014, at Camp Leatherneck, Afghanistan. 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.