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South Korea’s Nuclear-Powered Submarines: A New Strategic Option and Policy Under Challenge |
| November 17, 2025 |
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Peter WardResearch Fellow, Sejong Institute | pward89@sejong.org
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The Trump administration’s approval of South Korea’s construction of nuclear-powered submarines was the most significant development to emerge from the APEC summit in Gyeongju. Given the steadily intensifying threat posed by North Korea, South Korea has ample justification for pursuing such capabilities.
In January 2021, at the Eighth Party Congress, Kim Jong Un unveiled a plan to build a nuclear-powered submarine as part of the Five-Year Defense Development Plan. Subsequently, in March of this year, North Korea released photographs showing Kim inspecting the hull of a nuclear-powered submarine under construction. The potential incorporation of a weapon with speed, stealth, and sustained operational capability into North Korea’s nuclear forces raises serious concerns.
The ROK–U.S. summit between President Lee Jae Myung and President Donald Trump attracted particular attention following the South Korean government’s prior indication that revisions to the so-called 123 Agreement, which restricts uranium enrichment and reprocessing capabilities between the two countries, could be considered.
However, the outcome of the summit took a different direction. This reflected a long-standing objective that successive South Korean governments have consistently pursued since the 1990s, namely, securing nuclear propulsion technology for submarines, obtaining construction approval from the United States government, and ultimately receiving authorization for the supply of nuclear fuel for propulsion purposes.
This Sejong Focus examines the issue of nuclear-powered submarines. It reviews the strategic rationale underlying nuclear-powered submarines and assesses the measures currently under consideration by the governments of South Korea and the United States. It also discusses potential options for minimizing the time and costs required for construction. -
Nuclear-powered submarines constitute the apex predators of the maritime domain. Operating at significantly higher speeds than diesel-powered submarines, they represent a far more formidable military asset. They can engage not only maritime targets, including surface vessels and other undersea platforms, but also, depending on their armament, strike land-based targets through ballistic or cruise missiles.
In addition, depending on the level of enrichment of the nuclear fuel employed, whether low-enriched or highly enriched, nuclear-powered submarines may require refueling only once every ten to twenty years, or potentially not at all over their operational lifespan. By contrast, diesel-powered submarines must replenish fuel at nearby bases every few months and face inherent limitations in sustaining submerged operations beyond several weeks. These constraints stem from the need to surface periodically in order to operate diesel engines and recharge batteries used for underwater propulsion.
This suggests that, if North Korea were to acquire such capabilities through Russian technical assistance or comparable support, it could gain a substantial advantage in the maritime domain. Compared to its aging Romeo-class submarines with comparatively poor acoustic stealth, as well as the recently unveiled Hero Kim Kun Ok submarine, reportedly capable of carrying tactical nuclear weapons, North Korea would be able to operate in the waters surrounding the Korean Peninsula with markedly greater speed, stealth, and persistence.
In addition, North Korea could seek to establish a continuous-at-sea deterrent posture, similar to those maintained by the United States, the United Kingdom, and France. Such a development would make North Korea’s nuclear forces significantly more difficult to detect, enhance their survivability, and increase their usability in a first-strike context. Ultimately, this would strengthen the credibility of direct nuclear coercion against South Korea.
Furthermore, nuclear-powered submarines could enhance the credibility of North Korea’s threat to strike civilian targets on the U.S. homeland from closer forward maritime areas. Should North Korea deploy nuclear-powered ballistic missile submarines (SSBNs) in the Western Pacific, it would become virtually impossible for the United States to completely neutralize the threat of a North Korean nuclear strike.
Under such circumstances, South Korea would need to acquire capabilities to counter this evolving threat. Nuclear-powered submarines would enable South Korea to project power into North Korean waters within a short time frame and provide a credible second-strike capability, even in scenarios where North Korea attempts to neutralize South Korea’s conventional ground forces through nuclear means. Even if South Korean nuclear-powered submarines were equipped solely with conventional weapons, their high degree of stealth and precision-strike capability would substantially reinforce the effectiveness of decapitation operations targeting North Korea’s command leadership.
Nuclear-powered submarines could also be deployed to support anti-submarine warfare (ASW) operations not only in waters adjacent to the Korean Peninsula but across the Western Pacific, the areas surrounding the Japanese archipelago, and the broader East Asian maritime domain. Such deployments would support the modernization of the ROK–U.S. alliance, reinforce the credibility of the United States security commitment to South Korea, and strengthen effective deterrence against North Korea. In addition, these capabilities could exert a positive stabilizing effect on South Korea’s security relationships with neighboring countries, including Japan. -
The APEC summit in Gyeongju marked a major development in South Korea’s security posture, as it opened a pathway for the country to acquire capabilities essential for its national defense. However, differences in perspective between South Korea and the United States were evident.
The Lee Jae Myung administration requested that the United States supply the fuel to be used for nuclear-powered submarines to be constructed in the future. This is because fuel supply constitutes the only critical element that South Korea cannot independently develop or produce domestically due to the constraints imposed by the ROK–U.S. Nuclear Cooperation Agreement. With the exception of this aspect, however, South Korea has made clear its intention to pursue independent development. This reflects a national commitment to sovereign defense capability, as well as the strength of South Korea’s world-class shipbuilding industry, particularly its advanced submarine construction capacity.
President Donald Trump expressed his support for South Korea’s acquisition of nuclear-powered submarines as part of a broader alliance expansion agenda framed under the slogan “Making American Shipbuilding Great Again (MASGA).” At the same time, he suggested that South Korea’s nuclear-powered submarines should be constructed at the Philly Shipyard, which is currently owned by the Hanwha Group, with Hanwha Systems holding a 60 percent stake and Hanwha Ocean holding the remaining 40 percent. This proposal was justified on the grounds that it would contribute to job creation, promote reindustrialization within the United States, and support the revitalization of the U.S. maritime and shipbuilding industry, which has largely deteriorated.
However, Hanwha Group and a number of other experts have pointed out that the Philadelphia Shipyard lacks not only the facilities required to construct submarines, but also the capability to handle nuclear materials. The shipyard’s current business plans are primarily centered on commercial and civilian vessels, and establishing the infrastructure and cultivating the specialized workforce necessary for submarine construction would require a substantial investment of time and resources.
Owing to these constraints, constructing nuclear-powered submarines at the Philadelphia Shipyard would likely result in substantially greater delays than building them in South Korea. By contrast, the Okpo shipyard in Geoje already possesses a well-established technological foundation for submarine construction, and the costs required for facility upgrades are expected to be considerably lower. Moreover, retraining an existing pool of skilled personnel would be far more efficient than developing a new workforce in the United States that lacks prior experience in submarine construction.
An examination of the current state of U.S. submarine construction further underscores the necessity of actively utilizing production facilities and skilled personnel in South Korea. Although the United States possesses world-leading submarine propulsion technologies and maintains a large submarine fleet, its shipbuilding industry has increasingly lost the capacity to sustain these assets on a continuous basis. The number of submarines awaiting maintenance has continued to grow, while the pace of new construction has failed to keep up with the procurement requirements of the U.S. Department of Defense.
Taking these structural constraints into account, it is unrealistic to expect South Korea to establish, within a short period of time, an entirely new infrastructure and workforce for the construction of nuclear-powered submarines in the United States. Even firms within the U.S. defense industrial base, despite operating on a domestic foundation and benefiting from the world’s largest military procurement system, face persistent challenges in maintaining stable supply chains. Under such conditions, it would be even more difficult for the Hanwha Group to build an equivalent production system in the United States. -
President Lee Jae Myung’s decision to raise China when requesting U.S. approval for the construction of nuclear-powered attack submarines (SSNs) from President Trump appears to have been intended to appeal to Washington’s core security priority of countering China. This move is also assessed to reflect South Korea’s serious concern that China’s installation of structures in the West Sea could encroach upon South Korean territorial waters. While South Korea’s pursuit of nuclear-powered submarines may become a source of friction in future ROK–China relations, it is therefore essential for South Korea, in its diplomacy toward China, to emphasize clearly that the SSN program is aimed at deterring North Korea and defending South Korea’s sovereign maritime domain, rather than targeting China.
In a recent briefing to the National Assembly, Chief of Naval Operations Admiral Kang Dong-gil stated that it would take more than ten years for South Korea to complete the development of a nuclear-powered submarine. Other industry sources, by contrast, indicate that the basic design phase is scheduled to be completed next year, a milestone that typically accounts for approximately 30 to 40 percent of the overall development process. On this basis, it is possible that a submarine capable of operational deployment could be fielded within a five- to seven-year timeframe. Even so, it remains uncertain whether the United States would be willing to provide nuclear fuel without seeking additional political or economic considerations in return.
What, then, could such quid pro quo take in practice? Some have suggested a modular production approach. Under this approach, certain components of the submarine, such as the hull and electronic systems, would be produced at shipyards and manufacturing facilities in South Korea, while the nuclear propulsion reactor would be manufactured in the United States. This would require parallel investment in facilities located in the United States, a model similar to that adopted by Australia under the AUKUS framework, where Australia invested in U.S. facilities to expand production capacity. Such an approach could help alleviate bottlenecks in the U.S. submarine supply chain, while at the same time contributing to an acceleration of South Korea’s nuclear-powered submarine construction timeline.
Nevertheless, a modular production framework or an arrangement under which portions of the submarines are constructed in the United States would require extensive negotiations and considerable time. As demonstrated by the AUKUS case, United States domestic regulations, particularly the International Traffic in Arms Regulations (ITAR), constitute a major factor delaying technology transfer and the supply of critical components. Accordingly, the process of concretizing a bilateral technology cooperation model between South Korea and the United States is unlikely to be realized in the short term.
Hanwha Ocean had previously come close to securing an indirect opportunity to participate in the U.S. Navy’s Virginia-class SSN program through its attempt to acquire the Australian shipbuilder Austal. Had the acquisition been completed, Hanwha Ocean would have obtained control over Austal USA, which produces components for Virginia-class nuclear powered submarines. The transaction, however, was blocked by the Australian government on national security grounds. Even so, this case may be interpreted as a precedent that illustrates the potential for future cooperation between South Korea’s nuclear powered submarine development efforts and U.S. submarine programs.
South Korean submarine component manufacturers and shipbuilding firms could explore options to expand construction capacity within the United States through joint ventures or co-production arrangements with prime contractors involved in the U.S. Navy’s Virginia-class program, such as General Dynamics Electric Boat. Such cooperation could help alleviate bottlenecks in the U.S. nuclear powered submarine program, while at the same time enabling South Korea, through prior agreements with the United States, to secure access to selected components and equipment for its own submarine program.
In addition, the Virginia-class program is also noteworthy for its supply chain security challenges. It is known to exhibit a high level of dependence on critical minerals, and this dependence has created vulnerabilities and instability within the supply chain. Cooperation between South Korea and the United States in this area could contribute both to strengthening the U.S. Navy’s stable shipbuilding capacity and to facilitating the transfer of nuclear propulsion technologies (in a manner similar to the AUKUS model).
South Korea possesses a range of assets that neither the United Kingdom nor Australia can readily provide. These include world-class shipbuilding and maintenance infrastructure, advanced electronics and components manufacturing capabilities, and highly developed metal casting and forging capacities. This industrial base and technical expertise could play a critical role in advancing the U.S. Navy’s plan to build and sustain a “355-ship fleet.”
Accordingly, a long-term strategy is required that leverages the respective strengths of South Korea and the United States in a complementary manner while enhancing the naval force structure and shipbuilding capacity of both countries. To this end, the establishment of a “ROK–U.S. Submarine Construction Committee” should be considered, with participation from officials of both countries’ defense ministries, the U.S. Department of Defense and the Republic of Korea Ministry of National Defense, as well as representatives from the defense industrial sector. Since a nuclear-powered submarine program can proceed only if complex policy, legal, technical, and nuclear regulatory issues are addressed, including nonproliferation obligations, nuclear legislation, and congressional approval, the involvement of the U.S. Department of Energy and the U.S. Congress constitutes a critical component of this process. In particular, encouraging congressional engagement will be essential for resolving challenges related to arms export controls such as the International Traffic in Arms Regulations (ITAR).
This committee would be tasked with easing shipbuilding bottlenecks through investment, joint production, and the formulation of supply chain plans, while also contributing to bringing forward the timeline for South Korea’s acquisition of nuclear-powered submarine capabilities. In addition, it would need to identify potential legal and regulatory issues in advance and take steps to address them accordingly.
Where feasible, the participation of Japan could also be considered. Japan possesses world-class shipbuilding and submarine construction capabilities, and interest in acquiring nuclear-powered submarines has been steadily increasing. If the three countries were to cooperate, procurement costs could be reduced while interoperability among systems could be enhanced, thereby maximizing the effectiveness of future combined maritime operations. To this end, the establishment of a trilateral ROK–U.S.–Japan consortium could be proposed to systematically manage supply chain investment and joint production.
While AUKUS will remain a separate framework, the United Kingdom and Australia likewise face structural limitations in their industrial bases and possess relatively weak maritime shipping and shipbuilding sectors. In this respect, broader cooperation with South Korea, and potentially Japan, would be mutually beneficial. Accordingly, South Korea can underscore the potential for complementary cooperation with AUKUS member states while highlighting the advantages of building an expanded multilateral network for shipbuilding and defense industrial collaboration.
| Why Does South Korea Need Nuclear-Powered Submarines?
| Current Plans and Their Limitations
| Policy Recommendations: Alternatives and Directions
※ The contents published on 'Sejong Focus' are personal opinions of the author and do not represent the official views of Sejong Institue
