Two U.S. Air Force F-22 Raptors arrive at the Kentucky Air National Guard Base in Louisville, Ky., on April 14, 2011, in preparation for the Thunder Over Louisville air show. The Raptors will be one of show?s marquee events when Thunder takes place over the Ohio River on April 16. The annual event has become one of the nation?s largest air shows, with nearly 60 aircraft slated to perform this year for a crowd that?s expected to top 750,000. (U.S. Air Force photo by Maj. Dale Greer)