South Korea and the USA are scheduled to begin joint naval exercises today in the South China Sea and the Yellow Sea. To quote from a story in the BBC -
The latest drill, which will run until 9 September, "will focus on anti-submarine warfare tactics, including detecting and destroying North Korean submarines", an unidentified military official told South Korea's Yonhap news agency.
Meanwhile, the Chinese navy began its own series of live-fire "naval exercises" in the South China Sea on September 1st, exercises which official sources describe as -
"annual routine training, mainly involving the shooting of shipboard artillery"
In late August, China conducted a series of air exercises in the area, which were seen by many observers as a response to recent US interest in the region.
See also previous entries on the Spratly Islands dispute here and here