In this Friday, Feb. 1, 2013, photo, the USS San Francisco, a U.S. nuclear-powered submarine, is docked before South Korea and U.S. joint military exercises, at Jinhae naval base, South Korea. South Korean and U.S. troops began naval drills Monday, Feb. 4, 2013, in a show of force partly directed at North Korea amid signs that Pyongyang will soon carry out a threat to conduct its third atomic test. (AP Photo/Yonhap)
In this Friday, Feb. 1, 2013, photo, the USS San Francisco, a U.S. nuclear-powered submarine, is docked before South Korea and U.S. joint military exercises, at Jinhae naval base, South Korea. South Korean and U.S. troops began naval drills Monday, Feb. 4, 2013, in a show of force partly directed at North Korea amid signs that Pyongyang will soon carry out a threat to conduct its third atomic test. (AP Photo/Yonhap)
