The South Korean navy has begun to remake itself from a coastal patrol force intended to foil North Korea into a blue water fleet able to project power onto the high seas, which has implications rippling out from Seoul to Singapore.

In late May, the navy launched its first Aegis destroyer, a high-tech ship designed to fight other ships, chase submarines and defend against aerial attacks. Two more Aegis destroyers are to be added over the next five years, at a total cost of $3.4 billion, with possibly three more to come. (Aegis is an integrated missile-guidance system.)

Beyond that are plans for nine smaller destroyers, the same number of frigates, 32 corvettes, and more than 100 other patrol ships, minesweepers and logistic vessels to be built over the next 15 years. Two large amphibious ships, and maybe a third, will each carry a battalion of 750 marines and 15 helicopters. Added to that will be 23 landing craft.

For missions under the sea, the Koreans plan to acquire 36 diesel-electric submarines. The navy also plans to obtain eight to 16 P3C anti-submarine aircraft and nearly 60 helicopters.

And for good measure, a new base is on the drawing board for Cheju island at the southern tip of the peninsula, to give the new fleet access to the East China Sea and the Pacific Ocean.

The reasons for the buildup of the Republic of Korea Navy, its proper name, are many. At the launch of the new destroyer on May 31, President Roh Moo-hyun suggested that national pride was a priority for a Korea that he hopes will be reunified one day soon.

"South and North Korea will not keep picking quarrels with each other forever," the president said. Looking to a reunified Korea, he said, "We have to equip the nation with the capability to defend itself. The Aegis destroyer we are dedicating today could be the best symbol of that capability."

Roh returned to a theme that has marked his presidency for four years, which is to have South Korea rely less on the U.S. for security. "We have to build up an adequate ability in all areas that constitute war power," he said, "so that we will be able to defend ourselves without fail."

The name of the new ship, King Sejong the Great, is emblematic. Ruling from 1418 to 1450, King Sejong is best known for having fostered a simplified form of writing that enabled all Koreans to read and write. But he also sent Korean forces to fight Chinese in Manchuria and Japanese pirates.

Today, South Koreans are divided between those who would retain the alliance with the U.S. forged in the Korean War of 1950-53 and those who seek independence or a tilt toward China. Many naval officers, having operated with the U.S. Navy for years, favor a continued alliance. "The Korean navy," said an admiral, "should build a force that can support the ROK-U.S. alliance."

Those officers, however, appear to harbor the same antipathy toward Japan as most of their compatriots and suggest that their new fleet may one day confront Japan, which ruled Korea with an iron hand from 1910 to '45. At the very least, they see Japan as a rival whose fleet they aim to match.

American officials, who consider the U.S. alliance with Japan vital to U.S. security posture in Asia, privately lament the Korean attitude toward Japan. Some have urged the Koreans to put the past behind them and to dismiss what one called "the myth that Japan is going back to the militarism of the 1930s."

American officials suggested the U.S. would applaud the South Korean navy's plan, provided the Koreans continued to operate with the U.S. Navy and resolved their differences with Japan.

Senior Korean naval officers said that an essential reason for enlarging their fleet was to protect their sea lines of communication, what sailors call SLOCs. As it has expanded over the past three decades, the Korean economy has come to depend heavily on imports and exports.

That trade is seaborne because South Korea is cut off from mainland Asia by the demilitarized zone that splits the peninsula. Korea imports, for instance, 78 percent of its petroleum from the Middle East, and the SLOC through the Malacca Strait and the South China Sea in Southeast Asia is vulnerable to pirates and terrorists.

"There is no doubt," concluded a naval officer, "that the ROK's future prosperity depends on the use of the sea. Building a naval force to defend this maritime domain is becoming a key issue in the ROK's future national security strategy."

Richard Halloran is a Honolulu-based journalist and former New York Times correspondent in Asia. His column appears weekly in Sunday's Focus section.