The training is held in memory of three incidents near the western Northern Limit Line, the de-facto sea border between the two Koreas.

They are North Korea's torpedo attack on the corvette Cheonan in March 2010 which killed its 46 sailors, the North's artillery attack on the South's Yeonpyeong Island in 2010 which left two soldiers and two civilians dead and a naval skirmish called the 2nd Battle of Yeonpyeong in 2002 which killed six sailors.

The Navy held a West Sea Defense Day ceremony later in the day as part of the Navy's week to stress the importance of national security.

"We never forget the spirit of sacrifice of 55 comrades who lost their lives to defend the West Sea. We stand ready to retaliate North Korea's provocation," Rear Adm. Kim Myung-soo said in a statement.

"If North Korea provokes again, we will harshly revenge based on preparations so far. The area of an attack will be their grave." (Yonhap)