# Hanwha Ocean Launches 3,600-Ton Submarine Seo Hui in Geoje *The second KSS-III Batch-II boat integrates lithium-ion batteries and 10 vertical launch tubes, expanding South Korea's naval reach and its defense export bid.* **Published:** November 4, 2026 **By:** Hyun-jung Lee **Section:** Shipbuilding & Defense — South Korea **Format:** Breaking **Confidence:** medium **Source:** https://eastasiabrief.com/shipbuilding/hanwha-ocean-launches-3-600-ton-submarine-seo-hui-1105 **Publisher:** East Asia Brief (https://eastasiabrief.com/) --- ## What to know - Hanwha Ocean launched 3,600-ton submarine Seo Hui on Nov. 3 under a 3.41 trillion won program - Indigenous lithium-ion battery system triples underwater maximum-speed cruising duration - Shipyard will conduct sea trials before official delivery to the navy in 2028 ![Shipyard workers look on as the submarine Seo Hui slides into the water at Hanwha Ocean's Okpo shipyard in South Korea. (AI-generated image)](https://eastasiabrief.com/media/2026-11-03-2b9d9788b8c6.webp) *Shipyard workers look on as the submarine Seo Hui slides into the water at Hanwha Ocean's Okpo shipyard in South Korea. (AI-generated image)* South Korea's Defense Acquisition Program Administration and the Republic of Korea Navy launched the 3,600-ton submarine Seo Hui at Hanwha Ocean's Okpo yard on Nov. 3, 2026. The vessel is the second hull in a three-boat program capitalized at 3.41 trillion won ($2.5 billion), representing the final domestic procurement tier of the country's conventional submarine fleet. The submarine measures approximately 89 meters in length with a surfaced displacement of 3,600 metric tons, expanding displacement by 600 tons over Batch-I boats. Submerged displacement reaches roughly 4,000 tons, providing internal volume for heavier strike systems and upgraded acoustic suites. The navy named the vessel after Seo Hui, a diplomat of the Goryeo dynasty who secured border territories in 993 without military losses. National Assembly Speaker Cho Jung-sik and Vice Defense Minister Lee Doo-hee attended the ceremony alongside 200 naval and defense officials. Hanwha Ocean signed the construction contract with the procurement agency in 2021 and completed the keel-laying step in 2024. The shipbuilder launched the lead vessel of the class, ROKS Jang Yeong-sil, in October 2025 at the same Geoje facility. The launch marks the operational deployment of indigenous lithium-ion battery banks developed jointly by Samsung SDI and Hanwha Aerospace. The lithium-ion battery modules replace traditional lead-acid cells, allowing the boat to maintain maximum cruising speed for three times as long, the agency said. High energy density enables silent underwater cruising for up to three weeks when paired with hydrogen fuel-cell air-independent propulsion. Bumhan Industries supplies the four air-independent propulsion fuel-cell modules, which generate electricity underwater using stored liquid oxygen and hydrogen fuel. The auxiliary propulsion system provides emergency steerage and reserve power in the event of primary engine failure, the navy said. Engineers integrated a penetrating periscope system alongside optronic masts, retaining an optical viewing pathway if sensor cables experience battle damage. The hull incorporates an expanded 10-cell vertical launch system, compared to six cells installed on the earlier Dosan Ahn Chang-ho class. The vertical tubes can fire Hyunmoo-IV-4 submarine-launched ballistic missiles as well as long-range land-attack cruise missiles. LIG Nex1 provides the ship's wire-guided Tiger Shark heavyweight torpedoes, which deploy from six forward 533-millimeter launch tubes. The agency confirmed that 70 separate equipment categories aboard the vessel are domestically produced, adding 12 localized items not present on Batch-I hulls. Localization covers the integrated combat management system and the bow-mounted cylindrical sonar array designed to detect quiet diesel targets at long range. The naval program represents a critical revenue pillar for Hanwha Ocean, whose special ship division holds over 5 trillion won in domestic military backlogs. The shipyard expanded its automated submarine module assembly shops in Geoje to prepare for larger export hulls in the 4,000-ton class. South Korea is pitching the KSS-III Batch-II design to Canada for its 12-boat Canadian Patrol Submarine Project to replace Victoria-class submarines. The shipbuilder is competing against Germany's ThyssenKrupp Marine Systems, emphasizing the Arctic range and early delivery timelines of the South Korean hull. Hanwha Ocean has also submitted submarine procurement bids based on the KSS-III platform to Poland and Greece, targeting European fleet renewal budgets. Hanwha Ocean has not published a standalone corporate filing detailing unit construction margins or profit contributions for the vessel, leaving official financial terms tied to state program releases. Hanwha Ocean will conduct dockside integration tests and builder sea trials before delivering Seo Hui to the navy in 2028. ## Impact map | Event | Korea | China | Japan | Global impact | | --- | --- | --- | --- | --- | | KSS-III Batch-II launch | Hanwha Ocean advances 3.41 trillion won sub program with 70 localized systems | PLAN monitors longer-endurance conventional strike platform in Yellow Sea | JMSDF faces regional peer with comparable lithium-ion submarine technology | Hanwha Ocean leverages proven hull in Canada 12-boat patrol submarine tender | ## In this story - **Companies:** Hanwha Ocean, Samsung SDI, Hanwha Aerospace, LIG Nex1 - **Tickers:** 042660.KS, 006400.KS, 012450.KS, 079550.KS - **Exposed:** ThyssenKrupp - **Policy:** Procurement Rules - **Impact:** Order Book, Supply Chain, Capex ## Primary sources 1. thelec.net 2. koreaissuejournal.co.kr 3. koreaherald.com 4. seawaves.com 5. navalnews.com --- Cite as: East Asia Brief, "Hanwha Ocean Launches 3,600-Ton Submarine Seo Hui in Geoje," November 4, 2026. https://eastasiabrief.com/shipbuilding/hanwha-ocean-launches-3-600-ton-submarine-seo-hui-1105