A crew member aboard the Nimitz-class USS George Washington works in the Combat Defense Center during joint military exercises between the U.S. and South Korea in South Korea's East Sea on Monday, July 26, 2010. U.S. and South Korean warships and helicopters practiced anti-submarine maneuvers off the Korean Peninsula Monday that officers said they hope would serve as a warning to Pyongyang that aggression in the region would not be tolerated. (AP Photo/ Lee Jin-man, Pool)

Photo by: Lee Jin-man

A crew member aboard the Nimitz-class USS George Washington works in the Combat Defense Center during joint military exercises between the U.S. and South Korea in South Korea's East Sea on Monday, July 26, 2010. U.S. and South Korean warships and helicopters practiced anti-submarine maneuvers off the Korean Peninsula Monday that officers said they hope would serve as a warning to Pyongyang that aggression in the region would not be tolerated. (AP Photo/ Lee Jin-man, Pool)