F-22 stealth fighter jets belonging to the US Air Force move to take off at a US air force base in Osan, south of Seoul April 3, 2013. The US 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. [Photo/Agencies]