A U.S. Marine Corps crew chief from the 203rd Vertical Marine Attack Squadron in Cherry Point, N.C., marshals in an AV-8B Harrier II at the Kentucky Air National Guard Base in Louisville, Ky., April 20, 2012. A special segment of the six-hour Thunder Over Louisville air show on April 21 will highlight Marine Corps aircraft in recognition of the Corps' 100th year of flying operations. The United States Marine Corps began its aviation program May 22, 1912.