Jang Yeongsil class submarine: South Koreas new sub

• The KSS-III Batch-II, officially designated as the Jang Yeongsil class.
• Weaponry has also seen a marked upgrade
• The project, initiated in 2016, is slated for completion in 2029, with a substantial financial commitment of KRW 3.41 trillion allocated to bolster South Korea's defence capabilities.

The KSS-III Batch-II, officially designated as the Jang Yeongsil class, marks a significant advancement in South Korea's submarine capabilities, specifically tailored for the Republic of Korea Navy (ROKN). Developed collaboratively by Hanwha Ocean, this ambitious initiative encompasses the construction of three formidable submarines. Each vessel is designed to measure eighty-nine meters (approximately 292 feet) in length and boasts a displacement of 3,600 tonnes. The project, initiated in 2016, is slated for completion in 2029, with a substantial financial commitment of KRW 3.41 trillion allocated to bolster South Korea's defence capabilities.

The origins of the KSS-III program trace back to a pivotal moment during the 16th Defence Acquisition Program Promotion Meeting in 2007, which highlighted the country's need for a robust submarine acquisition strategy. The Jang Yeongsil class is heralded as the first of the Batch-II series, succeeding the Dosan Ahn Changho class submarine and delivering notable enhancements in terms of technological sophistication and operational versatility. A standout feature of the Jang Yeongsil class is its larger vertical launch system, which has expanded from six to an impressive ten cells, specifically designed to accommodate advanced submarine-launched ballistic missiles (SLBMs) capable of striking distant land-based targets with precision.

The naming of the class honours Jang Yeongsil, a revered scholar and innovator from the 15th century who played a pivotal role in advancing science and technology during the Joseon Dynasty. His legacy is encapsulated in the submarine’s design, which symbolises the integration of innovative technology into the nation's defence infrastructure. The Jang Yeongsil class made its official debut on October 22, 2025, during a ceremonial launch at Hanwha Ocean's esteemed Geoje Shipyard, a significant milestone for the country's naval advancement.

From a design perspective, the Batch-II submarines exhibit increased overall dimensions in both length and width when compared to their predecessors. The Batch-I vessels had a length of 83.5 meters (273 feet eleven inches) and a displacement of 3,000 tonnes, while the Batch-II series has been enlarged to 89.4 meters (293 feet four inches) and a 3,600-tonne displacement. This augmentation not only allows for increased firepower but also facilitates advancements in engineering and operational efficiency.

A groundbreaking feature of the Jang Yeongsil class is its integration of lithium-ion battery technology, the first of its kind in the ROKN. This innovative power source is paired with an air-independent propulsion (AIP) system, significantly enhancing the submarine's submerged operational capabilities. Compared to traditional lead-acid batteries, lithium-ion systems offer superior energy density, reduced heat generation, and quicker recharge times, resulting in a more extended underwater operational time—providing the vessel the ability to sustain submerged missions for approximately three weeks. The submarine can undertake missions covering a range of 7,000 nautical miles, achieving submerged speeds of twenty knots (37 km/h), and operating at depths exceeding four hundred meters (1,300 feet).

Weaponry has also seen a marked upgrade, with an expanded vertical launch system accommodating a wider array of SLBMs, thereby strengthening the submarine's offensive capabilities. In terms of combat and sonar systems, the Jang Yeongsil class features innovative enhancements that vastly improve information processing, target detection, and engagement capabilities against both maritime and land-based threats. Dominating this upgrade is the implementation of a curved array sonar system, developed through domestic technological innovation, which provides threefold detection elements compared to conventional cylindrical array systems. This advancement enables the submarine to accurately track targets without the need for course adjustments, enhancing its stealth and operational efficiency. Additionally, measures such as anechoic coatings, dual-elastic mounts, and specialised fins on the propeller assembly work collectively to minimise noise, ensuring the Jang Yeongsil class remains undetected during critical missions.