U.S. Navy chief petty officers and chief petty officer selectees stretch after a 9/11 memorial workout in the hangar bay of the aircraft carrier USS Nimitz (CVN 68) in the Pacific Ocean Sept. 11, 2014. 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.