South Korea, one of the world's most advanced shipbuilding nations, doesn't yet operate a nuclear-powered submarine. That could be about to change.
At the 2025 APEC summit in Gyeongju, President Trump announced he had given South Korea permission to build a nuclear-powered attack submarine—a breakthrough that President Lee Jae Myung had sought throughout months of trade and security negotiations. The details are still being worked out.
What matters now is how Seoul and Washington go about turning words into warships. This is not just a Korean capability upgrade. In an era of intensifying undersea competition and growing demands on U.S. forces, this is a strategic opportunity for the alliance, as well as for security in the Indo-Pacific.
Nuclear Propulsion Is an Evolution, Not Revolution
South Korea already builds some of the world's most sophisticated vessels, from liquefied natural gas (LNG) carriers to advanced conventionally powered submarines. As a key U.S. ally committed to revitalizing American maritime power, its pursuit of a nuclear-powered submarine is a natural next step.
Korea is also well-positioned to succeed. Its shipyards lead the world in tonnage and technological sophistication, producing everything from LNG carriers to advanced warships—complex, safety-critical vessels built to exacting standards. The industrial base behind this work includes precision manufacturing, automation, rigorous quality control, and systems integration. These are exactly the capabilities nuclear submarine construction demands.
South Korea already designs, builds, and operates highly capable conventionally powered submarines. Its KSS-III program showcases expertise in advanced hull design, air-independent propulsion, quieting technologies, combat systems integration, and extended undersea operations. A nuclear-powered submarine would mark an evolution in endurance and power generation, not a conceptual leap from what Korea's navy already does well.
A nuclear-powered submarine would mark an evolution in endurance and power generation, not a conceptual leap from what Korea's navy already does well.
Nonproliferation Is Not an Obstacle
Concerns about nuclear proliferation are inevitable—but can be mitigated in this case. Nuclear-powered attack submarines can be designed and operated in full compliance with the Nuclear Non-Proliferation Treaty (NPT). One option is to use existing low-enriched uranium (LEU) naval reactor designs, which avoid weapons-grade material altogether. France already takes this approach with its nuclear submarine designs.
Another path could prove even more valuable. South Korea and the United States could jointly develop the infrastructure to produce high-assay low-enriched uranium (HALEU), which is central to advanced reactor concepts, including naval microreactors. Today, only China and Russia possess large-scale HALEU manufacturing capability. That is a strategic vulnerability. As U.S. interest in small modular reactors grows for both civilian and military use, America will need a secure domestic or allied HALEU supply chain.
A Korean nuclear submarine program could serve dual purposes: advancing Seoul's submarine ambitions while building a trusted allied ecosystem for next-generation nuclear fuel. With appropriate safeguards and transparency, this approach would not only comply with the nonproliferation regime, it would also reduce reliance on adversarial suppliers.
A Contested Undersea Domain
The geopolitical and military case for a Korean nuclear-powered submarine is also compelling. Alongside its nuclear program, North Korea continues to invest heavily in undersea warfare, including ballistic missile submarines, special operations insertion platforms, and increasingly sophisticated sensors. Countering these threats requires a persistent, survivable, and flexible undersea presence. That is precisely what nuclear-powered submarines provide.
From an alliance perspective, the United States stands to benefit substantially. A South Korean nuclear-powered submarine fleet would add a highly capable partner in a domain that is both resource-intensive and strategically critical. The logic mirrors Australia's decision to acquire nuclear-powered, conventionally armed submarines under AUKUS: The United States is stronger when its close allies shoulder more responsibility at the high end of military capability.
A Korean nuclear-powered submarine also aligns with the broader alliance goal of balanced burden-sharing. Seoul has shown its willingness to invest in advanced military capabilities that contribute to collective deterrence—and nuclear-powered submarines would be among the most consequential. While these vessels would remain sovereign assets of the Republic of Korea, operated under its national command authority, their presence would ease the strain on a U.S. submarine force already stretched thin by global commitments. In undersea warfare, more capable allied players complicate adversary planning and strengthen deterrence for all.
In undersea warfare, more capable allied players complicate adversary planning and strengthen deterrence for all.
Immediate Next Steps
A Regulatory and Industrial Foundation
The most crucial early step is establishing a dedicated nuclear regulatory framework for South Korea's nuclear-powered submarine program. Effective regulation of naval nuclear propulsion is essential to maintaining the public trust required to operate these vessels over the long term.
Maritime nuclear regulation differs fundamentally from civilian power regulation. It must create necessary friction between the regulatory authority and a warship's operational command—ensuring that nuclear-powered vessels are continuously certified for safe military operations without undue influence from the navy. Developing and approving this framework should be a top priority.
Naval nuclear propulsion must also account for the unique safety demands of a mobile, submerged platform—conditions that differ substantially from static, land-based power plants. Because sailors live, eat, and work in close proximity to the reactor for extended periods, the safety requirements are fundamentally different from those of civilian plants, which are located far from population centers and designed with physical separation between reactor systems and operators.
South Korea will also need a quality-assurance and safety program analogous to the U.S. Navy's SUBSAFE, which ensures submarines can recover from flooding and prevent catastrophic failures. Such a program would guarantee that these vessels can operate safely under all conditions of depth, pressure, and combat stress.
None of this is unprecedented or unmanageable. South Korea already has a strong foundation in nuclear governance through its civilian Nuclear Safety and Security Commission (NSSC), which was modeled on the U.S. Nuclear Regulatory Commission. Australia's ongoing effort to establish a military nuclear regulatory framework for its forthcoming submarine fleet offers a relevant case study. Given its civilian nuclear sector, institutional capacity, and alliance support, South Korea is well-positioned.
Plan for Technology Sharing
Early planning for technology sharing as part of a Korean nuclear-powered submarine effort would create substantial opportunities for bilateral technology collaboration and further development of the maritime industrial bases between the United States and South Korea. Collaborative work on reactor safety, propulsion integration, combat systems, and maintenance infrastructure would deepen industrial ties and strengthen both countries' defense sectors. Natural attention will be drawn to the nuclear power plant, but depending on the reactor design ultimately chosen, opportunities may or may not exist for significant collaboration on the submarine's engineering plant—the aft or “back” of the vessel. However, in all cases, there would be ample scope for cooperation on the “forward” half.
Seoul and Washington should establish a framework for technology cooperation—either at the treaty level, as with AUKUS, or through department-level initiatives involving the Department of War, Department of Energy, and Department of Transportation. As the submarine development advances, opportunities will multiply for collaboration on propulsion, combat systems, maintenance infrastructure, and supply chains.
The two navies will want to ensure that combat systems, acoustic suites, and information architectures are built around compatible data formats and interfaces. This would enable more effective post-mission analysis, intelligence sharing, and operational learning across the alliance. Harmonizing standards for submarine safety, certification, maintenance, and lifecycle support would also expand trusted supply chains for both navies. Such cooperation would be another benefit of the Korean submarine effort at a moment when industrial resilience is increasingly recognized as critical to military power.
Optimizing the Industrial Arrangement
Finally, decisions about where to build Korean nuclear-powered submarines should weigh strategic, political, and industrial considerations alongside physical construction factors. Korean shipyards are fully capable of designing and building these submarines in-house. But distributing portions of the work to U.S. shipyards could yield political and alliance benefits.
The Hanwha Philly Shipyard, for instance, could serve as a symbol of Korean industrial expertise integrated with American labor and facilities. It could also be a model of distributed or modular shipbuilding, an approach similar to what the U.S. Navy is proposing for new ship classes. This could produce mutual benefits: a broader and more resilient industrial base, reduced supply-chain risk, healthy competition among firms, and structured collaboration on best practices and technology. To be sure there are complicated strategic, political, and industrial interests at stake, so Seoul and Washington should begin hammering out the optimal industrial arrangement now.
The hardest political step has already been taken. The two governments have agreed in principle. And there is a clear sequence of early priorities ahead: establishing a dedicated regulatory framework, enabling technology sharing, and determining the industrial layout of where these submarines will be built.
South Korea has the shipbuilding expertise, nuclear governance experience, and alliance support to make this work. If Seoul and Washington move deliberately and collaboratively, a Korean nuclear submarine program can deliver benefits far beyond a single fleet. It can deepen allied interoperability, expand trusted industrial supply chains, and reinforce deterrence across the Indo-Pacific.
