South Korea Launches Second KSS-III Submarine ROKS Seo Hui, Due for Delivery in 2028

South Korea launched the second Jang Bogo-III (KSS-III) Batch-II submarine, ROKS Seo Hui (SS-088), at Hanwha Ocean’s Geoje shipyard on November 3. The ceremony marked a further step in the country’s push to deepen indigenous submarine technology.

Seo Hui displaces roughly 3,600 tons and measures about 89 meters, placing it in a larger hull class than the 3,000-ton Batch-I boats. The submarine carries a domestically developed and safety-certified lithium battery system, which extends underwater endurance and the time the boat can sustain top speed.

An upgraded combat system and sonar suite allow detection and precise engagement of multiple targets at long range. Noise-reduction technology has been improved, and an auxiliary propulsion system preserves maneuverability if the main propulsion fails. A traditional periscope running through the hull also allows direct observation should electro-optical sensors go down.

Compared with the Batch-I boats, Seo Hui incorporates 12 additional domestic components, bringing the total count of indigenous equipment to 70. That increase reflects South Korea’s systematic push to reduce dependence on foreign suppliers across its submarine supply chain.

Construction began with a 2021 contract and steel-cutting ceremony. The keel-laying ceremony followed in 2024, and the program advanced another step with the November 3 launch. After sea trials, Seo Hui is scheduled for delivery to the Navy in 2028.

The lead boat of the Batch-II series, Jang Yeong-sil (SS-087), was launched in October 2025 and introduced a 10-cell vertical launch system, a major capability jump over Batch-I. With Seo Hui now in the water, the program’s second leg is in place, while Hanwha Ocean continues building the third and final Batch-II boat.

Lee Sang-woo, head of the Defense Acquisition Program Administration’s (DAPA) nuclear submarine program group, described Seo Hui as “a world-class diesel submarine.” Rear Admiral Lee Gu-seong, chief of planning and management staff at Navy headquarters, called the vessel “a state-of-the-art national strategic asset.”

According to officials, Seo Hui will play a key role in deterring maritime security threats around the Korean Peninsula and in maintaining a robust strategic response posture in a crisis. The rising share of domestic equipment is also expected to strengthen South Korea’s competitiveness in the submarine export market; Hanwha Ocean has already pitched KSS-III Batch-II derivatives to the Philippines and Saudi Arabia.

The vertical launch cell increase from six on Batch-I to ten on Batch-II shows the Navy gradually expanding the strategic-strike reach of its submarine fleet. Seo Hui and sister boat Jang Yeong-sil are being designed not just for reconnaissance and patrol but for long-range cruise-missile launch, pushing the conventional diesel-electric submarine category toward a hybrid capability profile.

The export dimension matters too. Hanwha Ocean has previously offered the KSS-III Batch-II derivative to Saudi Arabia at the World Defense Show and separately in talks with the Philippines. The domestic-content gains made visible with Seo Hui’s launch strengthen the technical credibility of those pitches and bolster Hanwha Ocean’s position in the mid-size submarine export market.

For Türkiye, the program offers a useful benchmark against its own Reis-class and MİLDEN submarine efforts. South Korea’s strategy of steadily raising localization and converting that know-how into exports runs parallel to paths Turkish shipbuilding programs are also pursuing, while Hanwha Ocean’s growing export visibility signals a heavier competitor in regional submarine tenders Türkiye also contests.

Sources

• Naval News, “South Korea Launches Second KSS-III Batch-II Submarine, ROKS Seo Hui”, November 3, 2026 (https://www.navalnews.com/naval-news/2026/11/south-korea-launches-second-kss-iii-batch-ii-submarine-roks-seo-hui/) — primary source for specifications, construction timeline and official statements.
• Asia Economy (Asiae), “Second 3,600-Ton Submarine Named ‘Seo Hee'”, July 2026 (https://view.asiae.co.kr/en/article/2026070309005523049) — verification of the naming process and program context.