U.S. Sailors stand in ranks during a 9/11 memorial ceremony Sept. 11, 2014, at Naval Support Activity Naples, Italy. It was the 13th anniversary of the 9/11 terrorist attacks. 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.