The five-day exercise involves some 4,500 personnel and all four branches of the military, according to South Korea’s Yonhap news agency.
Seoul, which oversaw an international investigation into the March sinking of the Cheonan, claims a North Korean submarine sank the corvette and is demanding an apology. A multinational investigation also found North Korea responsible. Pyongyang has vehemently denied the accusation.
Prior to the Cheonan’s sinking, the South Korean navy had largely discounted the threat of submarines in the Yellow Sea, due to the shallow waters in the area.
North Korea said via state media that it would undertake “strong physical retaliation” and warned fishermen to stay clear of the Northern Limit Line, the disputed maritime border between the Koreas.
The drills amount to an “undisguised military intrusion,” Pyongyang has said.