South Korea Fast-Tracks New Nuclear Submarine Project to Hunt North Korean Ballistic Missile Subs.

South Korea has approved the launch of its Jang Bogo N program to develop a new generation of nuclear-powered attack submarines capable of conducting extended surveillance and strike missions. The future vessels, which could displace more than 8,000 tons, are intended to improve the Republic of Korea Navy's ability to track North Korean submarines and respond to ballistic missile threats. However, the project remains dependent on negotiations with the United States over the supply of nuclear fuel.

Hanwha Ocean's Jangbogo III Batch-II conventional submarine underway. The South Korean Navy plans to develop the nuclear-powered Jang Bogo N as the next generation of its submarine fleet. (Picture source: Hanwha Ocean)

 Key Tactical Insights:

• Extended underwater surveillance: Nuclear propulsion would allow the Republic of Korea Navy to maintain a sustained presence near North Korean naval bases without the battery-recharging constraints faced by conventionally powered submarines.
  
  
• Evolution of strike capabilities: The KSS-III Batch-II submarines already feature ten vertical launch cells. The Jang Bogo N could provide greater endurance for strike missions, although its final weapons configuration remains classified.
  
  
• Dependence on Washington: The program envisages using low-enriched uranium, but U.S. restrictions on transferring nuclear materials for military purposes could affect its schedule.

The Jang Bogo N program, also designated KSS-III Batch-III, represents a change in South Korea's naval capabilities. Until now, Seoul has developed conventionally powered submarines capable of conducting intelligence gathering, anti-submarine warfare, and land-attack missions. The transition to nuclear propulsion is intended to substantially extend their underwater endurance while providing the navy with greater freedom of movement in the waters surrounding the Korean Peninsula and across the wider region.

The schedule calls for a South Korean shipbuilder to be selected through a competitive bidding process in 2027, followed by a contract award before the end of that year. Hanwha Ocean and HD Hyundai Heavy Industries are expected to be the main contenders, as both companies have experience building submarines for the Republic of Korea Navy. Hanwha Ocean recently launched the Seo Hui, the second KSS-III Batch-II submarine, on November 3, 2026, at its Okpo shipyard on Geoje Island. No shipbuilder has yet been officially selected for the Jang Bogo N program.

On November 6, 2026, South Korea's Defense Acquisition Program Administration (DAPA) approved the program's basic acquisition strategy during the 179th meeting of the Defense Project Promotion Committee. According to information published on November 7 by the South Korean newspaper Chosun Ilbo, the decision clears the way for design work to begin in 2027, with an initial budget of 96.6 billion won. The project could involve three submarines displacing more than 8,000 tons, with an estimated total cost of 28.9 trillion won, although these figures have not been officially confirmed. The design phase is expected to take three to four years, followed by more than five years of construction. The first submarine could be launched around 2035, with entry into service expected in the late 2030s or later.

Related News: South Korea officially unveils Jangbogo-N Project to launch first nuclear submarine by 2030s

Nuclear Propulsion Marks a Major Change From Existing KSS-III Submarines

The Jang Bogo N would represent a technological departure from previous generations of South Korean submarines. The KSS-III Batch-I vessels, displacing approximately 3,300 tons and measuring 83.5 meters in length, are equipped with six vertical launch cells for ballistic missiles. The Batch-II submarines displace approximately 3,600 tons and measure 89 meters, with ten vertical launch cells. They also incorporate lithium-ion batteries, an air-independent propulsion system using fuel cells, and improved detection and combat systems.

These features already allow the Batch-II submarines to conduct longer submerged operations while improving their detection and strike capabilities. However, their diesel-electric propulsion systems remain subject to limitations associated with energy generation and storage. Nuclear propulsion would enable the Jang Bogo N to maintain sustained speeds underwater and conduct extended patrols without periodically relying on an air-dependent battery-recharging system. This would be particularly useful for tracking hostile submarines over long distances or maintaining surveillance in sensitive maritime areas.

The program is expected to incorporate a compact nuclear reactor, although its technical specifications remain classified. DAPA plans for the government to supply the selected shipbuilder directly with certain strategic components, including the nuclear propulsion system and major weapons systems. The proposed fuel would be low-enriched uranium, with an enrichment level below 20%. The reactor's power output, maximum submarine speed, operating depth, and exact endurance have not been disclosed.

Future Weapons Could Extend South Korea's Underwater Strike Capabilities

The Jang Bogo N's armament remains one of the program's main unknowns. DAPA plans to provide certain major missile systems directly through the government but has not disclosed their types or quantities. Earlier KSS-III submarines nevertheless provide an indication of the capabilities the Republic of Korea Navy may seek to retain or develop.

The Batch-II submarines feature ten vertical launch cells, compared with six on the Batch-I, along with eight 533 mm torpedo tubes. These vessels can employ South Korean heavyweight torpedoes and feature a vertical launch architecture associated with the Hyunmoo-4-4 submarine-launched ballistic missile.

The future submarine's principal military advantage would be its ability to sustain underwater operations for longer periods. North Korea continues to develop submarine-launched ballistic missiles, particularly through its Pukguksong programs, and has presented submarine projects intended to expand its naval strategic capabilities. Nuclear-powered South Korean submarines could monitor approaches to North Korean naval bases for longer periods, track hostile submarine movements, and help detect preparations for potential missile launches.

The program is also intended to support South Korea's Kill Chain concept, which focuses on detecting and potentially neutralizing imminent threats before they can be employed. The future submarines could contribute to this architecture through intelligence collection, target tracking, and strike capabilities, depending on their eventual weapons configuration. Their effectiveness in this role will also depend on the sonar systems, communications equipment, and combat management systems selected for integration, none of which have yet been publicly detailed.

U.S. Nuclear Fuel Restrictions Could Delay South Korea's Submarine Fleet

Securing nuclear fuel remains the main external obstacle to the program's schedule. Following a bilateral summit in October 2025, U.S. President Donald Trump gave political approval for South Korea to pursue nuclear-powered submarines. However, this endorsement does not automatically authorize the transfer of nuclear materials intended for military propulsion.

U.S. legislation strictly regulates exports of nuclear materials and technologies. A separate agreement between Washington and Seoul would be required to enable the supply of U.S. nuclear fuel for the future submarines' reactors. An initial round of bilateral discussions took place in June 2026, but no second meeting had been scheduled when the program's launch was announced.

The political situation in Washington could further complicate negotiations. According to Chosun Ilbo, the Democratic Party's victory in the November 3, 2026, U.S. midterm elections could increase congressional obstacles to transferring nuclear fuel. The new congressional majorities will not take office until January 2027. Several Democratic lawmakers have already raised concerns about the implications of such transfers for the international nuclear non-proliferation framework. Four senators sent a letter to Donald Trump in January requesting clarification of the risks associated with this cooperation.

The issue arises as the United States continues its cooperation with Australia and the United Kingdom under AUKUS, which includes plans for Canberra to acquire nuclear-powered attack submarines. However, the legal and strategic framework established for AUKUS does not automatically apply to South Korea, whose program requires separate negotiations with Washington.

The Jang Bogo N program now depends on two parallel processes: South Korea's industrial ability to design and build a nuclear-powered submarine and the conclusion of an agreement ensuring access to nuclear fuel. Without a solution to the second issue, Seoul could advance the construction of its future vessels without securing the materials required to operate them, potentially delaying the introduction of South Korea's nuclear-powered submarine capability beyond the currently anticipated timeline.

Written By Erwan Halna du Fretay - Defense Analyst, Army Recognition Group
Erwan Halna du Fretay holds a Master’s degree in International Relations and has experience studying conflicts and global arms transfers. His research interests lie in Security and strategic studies, particularly the dynamics of the defense industry, the evolution of military technologies, and the strategic transformation of armed forces.

Explore More Defense News

• Land Defense News
• Naval Defense News
• Defense Aerospace News