U.S. Air Force Airman First Class, Lee Simpson from Sportanburg, S.C., mans a machine gun atop a humvee, with South Korean soldiers during a joint military drill between South Korea and the United States near the Osan U.S. Air Base in Pyeongtaek, south of Seoul, South Korea, Thursday, March 14, 2013. (AP Photo/Lee Jin-man)

Photo by: Lee Jin-man

U.S. Air Force Airman First Class, Lee Simpson from Sportanburg, S.C., mans a machine gun atop a humvee, with South Korean soldiers during a joint military drill between South Korea and the United States near the Osan U.S. Air Base in Pyeongtaek, south of Seoul, South Korea, Thursday, March 14, 2013. (AP Photo/Lee Jin-man)