South Korea launches second KSS-III Batch-II submarine

Seo Hui , the second KSS-III Batch-II submarine, seen here during its launch ceremony at Hanwha Ocean's Okpo shipyard on 3 November 2026. (Republic Of Korea Navy)

South Korean shipbuilder Hanwha Ocean has launched the second KSS-III Batch-II submarine on order for the Republic of Korea Navy (RoKN).

The 3,600-tonne vessel has been named Seo Hui, and it took to the water on 3 November 2026 at Hanwha Ocean's Okpo Shipyard in Geoje, the RoKN said in a statement issued on the same day.

The keel for Seo Hui was laid down in July 2024.

Hanwha Ocean, then known as Daewoo Shipbuilding & Marine Engineering (DSME), secured a KRW985.7 billion (USD735 million) contract to build the boat in 2021, and steel for the vessel was cut in the same year.

It is part of a programme to build three KSS-III Batch-II submarines that are slightly larger than the earlier Batch-I boats that measure 83.5 m in length and displace 3,300 tonnes.

The Batch-II submarine has an overall length of 89 m.

Unlike the earlier vessels, the Batch-II submarines incorporate an air independent propulsion (AIP) system powered by hydrogen fuel cells, alongside domestically developed lithium-ion batteries.

This increases underwater submerged endurance and top-speed sprint duration over traditional lead-acid designs.

Another difference in the Batch-II design is the inclusion of 10 vertical launch tubes for submarine-launched ballistic missiles (SLBMs), an increase from the six tubes fitted on the Batch-I boats.

The new vessels are also equipped with improved combat management and sonar suites to better detect, track, and target multiple long-range threats simultaneously, said DAPA in a separate statement that was also issued on 3 November.