"Remember the warship Cheonan!"

Under the simple but desperate slogan, the South Korean Navy has significantly bolstered its underwater capabilities and combat readiness since North Korea's deadly sinking of the corvette five years ago.

On March 26, 2010, the 1,200-ton warship sank while on a training mission in the Yellow Sea, killing 46 out of the 104 sailors on board. A South Korean-led international investigation concluded that a North Korean submarine torpedoed the ship, though Pyongyang has denied responsibility.

"As we've experienced the enemy's attack, our focus has been on how to boost anti-submarine capabilities," said Cmrd. Choi Won-il, who led the ship at the time of the tragedy, stressing his and his colleagues' firm resolution to repel provocations by the North "at any cost."

According to Navy headquarters, the military has equipped its newest Type-214, 1,800-ton submarines and destroyers with Haesung, an anti-ship cruise missile which can fly some 1,000 kilometers.

Last month, the Navy also inaugurated a submarine command in the southern port city of Jinhae, becoming the world's sixth country to have such an entity. The command has taken full charge of submarine-related activities ranging from operations, education and training to maintenance and logistical support.

It now operates 13 submarines -- nine 1,200-ton submarines and four 1,800-ton subs, with the Navy to add five more 1,800-ton submarines by 2019 and to deploy nine 3,000-ton submarines capable of launching ballistic missiles starting in 2020.

In a move to beef up coastal defense capabilities, the Navy has been replacing 1,500-ton frigates and 1,000-ton patrol ships with 2,300-ton next-generation frigates which have a state-of-the-art sonar system and torpedo acoustic countermeasure equipment so they can avoid another torpedo attack.

"After a four-year project, the military completed building a three-dimensional geographic information analysis system for effective operations," a Navy officer said. "We've also bolstered coastal artillery forces in the Yellow Sea."

North Korea, however, has further heightened tensions by making good on threats of provocations and continuing its military build-up near the Northern Limit Line, the de facto inter-Korean sea border.

In October last year, South and North Korean patrol boats briefly exchanged fire after a North Korean naval vessel violated the NLL.

Declaring 2015 the year of completing unification, the bellicose regime has carried out maritime exercises in the Yellow and East Seas under the scenarios of striking a U.S. aircraft carrier and attacking South Korea's Spike missiles bases on the border islands, according to the Navy.

Pyongyang is also known to have been developing a submarine-launched ballistic missile in a move to boost its underwater missile strike capabilities after launching a new 2,500-ton submarine last year.

"North Korea has significantly boosted its ability to launch surprise infiltration by, for example, building small submarines for littoral operations," an officer of the Joint Chiefs of Staff said.

"Though it is believed to have superiority in the sheer number of submarines, we are confident in our capabilities to counter their attacks. Enemies will be sure to be buried exactly where they launch the provocations," he added.

The North has some 70 vessels, including about 20 1,800-ton Romeo-class submarines.

Later on Thursday, a memorial ceremony will be held at the national cemetery in Daejeon, 164 kilometers south of Seoul, to be attended by bereaved families, surviving crew members, senior government officials and military officers. Of the 58 rescued sailors, 32 are still in service. (Yonhap)