South Korea launches second KSS-III Batch-II submarine Seo Hui

The Republic of Korea Navy and the Defense Acquisition Program Administration (DAPA) announced the launch of the Seo Hui (SS-088), the second diesel-electric submarine of the KSS-III Batch-II project. The ceremony took place on November 3, 2026, at the Hanwha Ocean shipbuilder in Okpo, Geoje City.

Vessel Specifications and Upgrades

The Seo Hui is approximately 89 metres in length with a displacement of approximately 3,600 tonnes. This displacement is 600 tonnes greater than the previous Batch-I series, which measured approximately 3,300 tonnes and 83.5 metres in length.

According to Hanwha Ocean, the revised design offers "longer submerged endurance, longer operation at maximum speed and reduced noise compared with Batch I."

Key technical features of the Batch-II series include:

• Armament: The submarine features an expanded vertical launch system with 10 vertical launch tubes designed for ballistic and cruise missiles, an increase from the six tubes found on Batch-I boats.
• Propulsion: The vessel utilizes a diesel-electric propulsion system with an air-independent propulsion (AIP) unit powered by hydrogen fuel cells, alongside domestically developed lithium-ion batteries.
• Survivability: The submarine is equipped with an auxiliary propulsion system to allow for maneuvering if the main system fails, and a conventional optical periscope to provide direct observation if electro-optical sensors fail.
• Sensors: Upgrades include a passive sonar with a conformal array and larger-aperture flank sonar arrays.

Domestic Content and Program Context

A total of 70 types of South Korean equipment have been installed on the submarine. This represents 12 more types of equipment than were installed on the first-series KSS-III submarines. DAPA officials stated that increasing the share of domestically produced components is expected to "simplify future maintenance and strengthen the competitiveness of South Korean submarines on the international market."

The KSS-III is an indigenous submarine development program intended to engage surface and underwater targets and carry out missile strikes. The first submarine in this program, the Dosan Ahn Chang-ho (SS-083), was commissioned into the South Korean Navy in August 2021.

Production and Delivery Schedule

The Seo Hui is the second of three planned KSS-III Batch-II submarines. The lead vessel of this batch, the Jang Yeong-sil (SS-087), was launched in October 2025 and is due for delivery by the end of 2027. The third and final Batch-II submarine is scheduled for completion around 2029 and delivery in 2031.

Construction of the Seo Hui began following a contract signed in 2021, with steel cutting occurring in 2021 and the keel being laid in 2024. Following the completion of sea trials, the Seo Hui is planned to be handed over to the Republic of Korea Navy in 2028.

Why it matters

The Batch-II program represents a significant step in South Korea's military shipbuilding industry development. By increasing the number of vertical launch systems and utilizing domestic lithium-ion batteries and AIP systems, the program aims to expand the Republic of Korea Navy's surveillance, reconnaissance, and patrol capabilities.

---

Sources

• militarnyi.com: South Korea Launches Second KSS-III Batch-II Submarine
• janes.com: South Korea launches second KSS-III Batch-II submarine
• navaltoday.com: ROK Navy launches second Batch-II KSS-III submarine - Naval Today
• zona-militar.com: South Korea's Navy launches its second KSS-III Batch-II submarine, with a displacement of 3,600 tons
• defence-industry.eu: Hanwha Ocean launches South Korea’s second KSS-III Batch-II submarine with expanded armament
• bairdmaritime.com: South Korea’s fifth KSS-III submarine floated out

This article was drafted with AI assistance and checked against the sources above. Company claims are reported as claims. Cover image is AI-generated.