A-10 jets belonging to the U.S. Air Force move to take off at a U.S. air force base in Osan, south of Seoul April 3, 2013. The U.S. has positioned a warship off the Korean coast as a shield against ballistic missile attack, and also deployed radar-evading F-22 Raptors on Sunday to take part in the annual joint military drills it carries out with South Korea. REUTERS/Lee Jae-Won (SOUTH KOREA - Tags: MILITARY POLITICS TRANSPORT)