GEOJE, SOUTH KOREA — The Republic of Korea Navy and the Defense Acquisition Program Administration (DAPA) launched the ROKS Seo Hui (SS-088) on November 3, 2026. The submarine is the second vessel of the 3,600-ton Jang Yeong-sil-class (KSS-III Batch-II) and was built at Hanwha Ocean’s Okpo Shipyard in Geoje.
The launch ceremony took place around five years after Hanwha Ocean signed the construction contract in 2021. National Assembly Speaker Cho Jeong-sik attended as the guest of honour, alongside approximately 200 government, military and defence industry officials.
Named after a Goryeo Dynasty diplomat, Seo Hui follows the lead submarine ROKS Jang Yeong-sil (SS-087), launched in October 2025. The Batch-II submarines introduce several upgrades over the earlier 3,000-ton Dosan Ahn Chang-ho-class (KSS-III Batch-I).
Larger Design and Improved Strike Capability
ROKS Seo Hui measures approximately 89.3 metres in length and displaces 3,600 tons on the surface, with submerged displacement reaching approximately 4,000 tons. Its larger hull provides additional space for weapons and equipment compared with the earlier Batch-I submarines.
A major upgrade is its vertical launch system (VLS), which has expanded from six to ten cells. The system supports submarine-launched ballistic missiles, providing greater capacity for long-range precision strikes.
The submarine also features upgraded combat management and sonar systems to improve target detection, information processing and engagement capabilities.
Lithium-Ion Batteries and Improved Stealth
The submarine combines a hybrid diesel-electric propulsion system, air-independent propulsion (AIP) and domestically developed lithium-ion batteries.
The lithium-ion batteries replace the lead-acid batteries used in earlier submarines. They are designed to support longer submerged operations and sustained high-speed underwater movement.
The design also includes noise and vibration reduction measures to improve stealth. Its upgraded sonar system supports underwater surveillance and target detection.
Increased Domestic Equipment Production
South Korea has localised 70 types of equipment for the Jang Yeong-sil-class Batch-II submarines. This includes 12 additional systems compared with the earlier Batch-I generation.
The increased domestic integration is intended to strengthen South Korea’s technological independence, simplify logistics support and improve the competitiveness of its submarines in the international defence market.
Delivery Planned for 2028
Following its launch, ROKS Seo Hui will undergo sea trials and systems testing before its planned delivery to the South Korean Navy in 2028.
After delivery, the submarine will complete its force integration process before entering operational service.
The Jang Yeong-sil-class programme is part of South Korea’s broader effort to expand its undersea warfare capabilities through the development and construction of submarines using domestic technology.
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