epa06365968 A South Korean F-15K fighter jet takes off from an air base in Gwangju, South Korea, 04 December 2017, as South Korea and the United States begin a five-day joint air force drill. The annual Vigilant Ace this year is the largest-ever combined air force exercise between the allies, with the US sending six F-22 Raptor stealth jets following North Korea's 29 November launch of what appears to be its most powerful intercontinental ballistic missile. EPA/YONHAP SOUTH KOREA OUT