Hanwha Ocean launched the Republic of Korea Navy’s first KSS-III Batch-II submarine, ROKS Jang Yeong-sil (SS-087), at Geoje shipyard on October 22, 2025.
On October 22, 2025, Hanwha Ocean held the launching ceremony for the South Korean Navy’s first KSS-III Batch-II submarine, ROKS Jang Yeong-sil (SS-087), at Geoje shipyard. The 3,600-ton vessel features new lithium-ion battery propulsion, ten vertical launch cells, and advanced sonar and combat management systems. The submarine will undergo testing and trials before commissioning in 2027 as part of South Korea’s ongoing KSS-III program.
The 3,600-ton diesel-electric submarine represents a significant structural and technological evolution from the preceding Dosan Ahn Changho-class of Batch-I submarines. The launch ceremony was conducted under the supervision of the Navy, with the vessel named after Jang Yeong-sil, a 15th-century Korean scientist. Compared to the earlier class, the new submarine features enhanced detection and strike capability, improved stealth performance, and upgraded combat and sonar systems. The vessel’s endurance has been strengthened through the installation of rhythmic lithium-ion cells, allowing extended underwater operations. After completion of electrification, systems testing, and sea trials, the Jang Yeong-sil is scheduled for commissioning by late 2027, joining the Navy as the first of three Batch-II submarines planned through 2031.
The KSS-III Batch-II program forms part of the broader Korean Attack Submarine (KSS) initiative, which includes 27 submarines across three phases: KSS-I (Jang Bogo-class), KSS-II (Son Won-il-class), and KSS-III (Dosan Ahn Changho and Jang Yeong-sil classes). The KSS-III series is the first to be completely designed and built in South Korea, establishing the country as the eighth nation capable of independently developing submarines of over 3,000 tons. Construction of the Batch-II began following a Defense Acquisition Program Administration contract with Daewoo Shipbuilding & Marine Engineering (now Hanwha Ocean) in 2019, with total program investment reaching approximately 3.41 trillion won. The second hull was laid down in July 2024, and a third will start construction in late 2024. Each submarine will be constructed at Hanwha Ocean’s Geoje facility and delivered sequentially in 2027, 2028, and 2031. Batch-II is expected to reach more than 80 percent domestic production of components, up from the 76 percent achieved in Batch-I.
The Jang Yeong-sil class has a length of 89.3 to 89.4 meters, a beam of 9.6 to 9.7 meters, and a displacement of 3,600 tons surfaced and 4,000 tons submerged. It employs diesel-electric propulsion with an air-independent propulsion (AIP) system integrating four 150 kW PH1 polymer electrolyte membrane fuel cells developed by Bumhan Industries. Samsung SDI lithium-ion batteries replace the previous lead-acid type, providing higher power density, faster recharging, longer cycle life, and improved safety. The submarine achieves 12 knots on the surface and 20 knots submerged, sustaining extended submerged operations for more than 20 days. Crew capacity remains at approximately 50 personnel. The hull structure is made of HY-100 high-tensile steel capable of withstanding deep-sea pressure, while advanced non-acoustic stealth measures, such as acoustic anechoic coatings, elastic mounts, and vibration damping, reduce radiated noise. Propeller modifications with shaped cap pins have been introduced to further minimize vibration and cavitation.
The submarine is fitted with ten Korean Vertical Launch System (K-VLS) cells, an increase from six on the Dosan Ahn Changho-class. These cells enable the deployment of the Hyunmoo 4-4 submarine-launched ballistic missile (SLBM) and the future Chonryong land-attack cruise missile. Forward armament includes six 533 mm torpedo tubes capable of launching LIG Nex1 Tiger Shark heavyweight torpedoes, UGM-84 Harpoon anti-ship missiles, and Haeseong-III land-attack cruise missiles. The submarine also accommodates naval mines and anti-submarine torpedoes. The weapons are integrated through Babcock International’s Weapons Handling and Launch System, which provides hydraulic water-ram launching for both torpedoes and missiles. The Batch-II’s new VLS structure allows for heavier payloads and larger missile compartments while preserving buoyancy control. With this configuration, South Korea continues to expand its conventional submarine fleet’s capacity for precision long-range strikes without employing nuclear propulsion.
The Jang Yeong-sil class incorporates multiple upgraded onboard systems to strengthen undersea detection, surveillance, and combat management. Its combat suite is based on Hanwha’s Naval Shield Integrated Combat Management System (ICMS), linked to an enhanced sonar array developed by LIG Nex1. The sonar network includes a flank-array sonar, a towed-array sonar, an intercept-passive sonar, a continuous-active sonar, and mine-avoidance sonar developed by Thales. Electronic warfare support is provided by Indra’s Pegaso radar electronic support measures (RESM). The periscope mast has been replaced by Safran’s Series 30 optronic surveillance system, which integrates optical and infrared sensors for target identification. ECA Group steering consoles and locally developed noise-analysis processors provide improved control, maneuverability, and situational awareness. These elements collectively advance underwater situational management, enabling improved detection range, reduced operator workload, and higher data fusion speed during submerged operations.
Programmatically, the Batch-II development followed a defined process of exploratory and system development phases. After a 705 billion won exploratory contract in 2016, Daewoo Shipbuilding & Marine Engineering began full-scale system development in 2019 with a follow-on contract worth 1.11 trillion won for the first hull. A second contract of 985.7 billion won was signed later that year for the second submarine, and Hanwha Ocean received a third contract valued at 1.1 trillion won in December 2023. Construction of the first Batch-II vessel began in August 2021, followed by the second in December 2021. The program also incorporates NATO-standard communication interfaces such as the prospective Link 22 data system and is preparing integration concepts for unmanned undersea vehicles to support combined manned-unmanned operations by 2030. Each submarine is expected to operate with a 20-year service life and a refit interval adjusted for lithium-ion system maintenance.
The Jang Yeong-sil-class succeeds the three Batch-I submarines, ROKS Dosan Ahn Chang-ho (SS-083), Ahn Mu (SS-085), and Shin Chae-ho (SS-086), which entered service between 2021 and 2024. Those vessels, measuring 83.5 meters in length and displacing 3,750 tons submerged, were equipped with six VLS cells, six torpedo tubes, and a hybrid diesel-electric and AIP system. They achieved up to 10,000 nautical miles of range and up to 20 days of submerged endurance. The Dosan Ahn Chang-ho successfully launched a Hyunmoo 4-4 SLBM in 2021, confirming the Republic of Korea as the eighth country capable of deploying a submarine-launched ballistic missile. Batch-I achieved 76 percent domestic production and introduced several indigenous technologies, including the Naval Shield CMS and Korean-made sonar arrays. The Jang Yeong-sil class extends these capabilities with larger missile capacity, new lithium-ion propulsion technology, and an upgraded acoustic management system.
The KSS-III program demonstrates South Korea’s consolidation of indigenous submarine design, manufacturing, and integration capabilities. Construction and integration are divided between Hanwha Ocean and HD Hyundai Heavy Industries, with contributions from national electronics, propulsion, and energy system manufacturers. The cost of each submarine, estimated at around $900 million, aligns with the previous generation’s procurement scale. As of late 2025, three Batch-I units are active, three Batch-II hulls are in construction, and three additional Batch-III units are projected for the early 2030s. With the introduction of the Jang Yeong-sil class, the Republic of Korea Navy aims to expand its submarine-based deterrent capacity, enhance anti-surface and anti-submarine warfare performance, and sustain continuous at-sea patrols through improved endurance and automation.
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