SHANKSVILLE, PA - SEPTEMBER 11: Members of the Marine Wing Support Squadron 471bow their heads during the ceremony marking the 10th anniversary of the crash of United Flight 93 at the Flight 93 National Memorial on September 11, 2011 in Shanksville, Pennsylvania. An estimated crowd of 5,000 watched as the memorial wall was unveiled with the names of the 40 passengers who died when the plane crashed during the terrorist attacks on September 11, 2001.