A U.S. nuclear-powered submarine arrived at a key naval base in the southeastern city of Busan on Tuesday to replenish supplies and provide rest for crew members, Korea's Navy said. The USS Greeneville, a Los Angeles-class attack submarine, entered the naval base in Busan earlier in the day, the Navy said. "The Navy plans to boost exchanges and cooperation between the navies of Korea and the United States and strengthen our combined defense posture on the occasion of the USS Greeneville's entry," it said.