South Korea to Build Nuclear-Powered Submarines in Historic U.S. Deal

Seoul and Washington have reached a historic agreement allowing South Korea to build nuclear-powered submarines. As part of a wider trade and security deal, the U.S. has given its approval in principle, and both countries plan to collaborate on shipbuilding, nuclear energy, and expanded defense cooperation.

What was agreed

Under the new deal, South Korea gains U.S. consent to construct nuclear-powered submarines. At the same time, the agreement expands Seoul’s rights to handle uranium enrichment and spent nuclear fuel reprocessing within limits set by existing civil nuclear cooperation rules. The deal is part of a larger trade and investment package. South Korea is pledging large investments in U.S. industry, including shipbuilding, in return for lowered tariffs.

Speaking at a news conference with foreign media at Cheong Wa Dae last week, President Lee Jae Myung emphasized that South Korea’s acquisition of nuclear submarines and nuclear fuel reprocessing would not violate the Treaty on the Non-Proliferation of nuclear weapons.

Asked by ABC News whether he is aware of nuclear proliferation concerns in Washington, Lee said “nuclear nonproliferation is an international principle we must respect,” stressing that the treaty restricts the spread of nuclear weapons but not all nuclear technologies.

Why it matters

For decades, South Korea operated only diesel-electric submarines. These vessels must surface or snorkel periodically, limiting underwater endurance. Nuclear-powered submarines, by contrast, can stay submerged far longer, increasing stealth, range, and strategic flexibility.

Seoul regards this as a decades-long goal and a strategic asset for peace and stability on the Korean Peninsula. Analysts also suggest that stronger submarine capabilities could help deter threats from the north and strengthen South Korea’s maritime defense.

Significant challenges remain

Despite the approval, major technical, legal, and practical hurdles remain. The deal does not yet specify where the submarines will be built, whether in the U.S. or South Korea. The question of nuclear fuel supply and technology transfer is delicate.

To operate a nuclear submarine safely and legally, enriched uranium and reactor management technology are needed. This requires strict compliance with international nuclear safeguards agreements. Under a long-standing civil nuclear agreement between the two countries, South Korea is restricted in how it can use nuclear material. Expanding those rights to military-adjacent uses may require further negotiations and legal adjustments.

Because of these uncertainties, some experts argue the ambitious submarine program will be a long-term project rather than providing immediate capability.

Responding to former President Trump’s suggestion that South Korea’s nuclear-powered submarines should be built in U.S. shipyards, Lee said it would be far from realistic.

“We have no intention of deviating from the basic agreement between the two Koreas,” Lee said. He added that pursuing nuclear weapons at the cost of economic and international sanctions would be a foolish act.

Which countries already operate nuclear-powered submarines

A small group of nations currently possess nuclear-powered submarines: the United States, Russia, China, the United Kingdom, France, and India. Brazil is developing one but has not yet deployed it. South Korea’s entry into this group would significantly shift the naval balance in the Indo-Pacific, where advanced underwater capabilities are increasingly central to strategic competition.

Regional reaction and potential consequences

The agreement has attracted considerable attention across the region. Some neighbors and observers warn it could fuel an underwater arms race in East Asia, prompting other countries to reconsider their submarine or defense policies.

Proponents in Seoul, however, say that nuclear-powered submarines are not about aggression but about self-defense and deterrence, strengthening South Korea’s ability to protect its waters and respond to threats.

Deeper analysis: what this shift really means

South Korea’s push for nuclear-powered submarines marks a major change in regional security. It shows that middle powers in Asia are no longer content to rely solely on U.S. extended deterrence as strategic competition grows.

The move reflects concern over North Korea’s advancing nuclear and missile capabilities. It also fits a broader pattern of states preparing for a more contested maritime space shaped by China’s rapid naval expansion.

Nuclear submarines offer more than military endurance. They are a symbol of permanence, resolve, and technological maturity. Their introduction into North Asia’s complex security environment will increase strategic tension, especially for China, which may see South Korea’s entry into the nuclear-submarine group as another pressure point alongside AUKUS.

This development could accelerate a quiet arms modernization cycle, pushing Japan to rethink its own submarine plans and encouraging Southeast Asian states to consider how their sea lanes might be affected by more capable submarines.

For New Zealand, which maintains a nuclear-free stance and relies heavily on diplomatic stability for economic security, the deal is a reminder that the Indo-Pacific security order is moving toward harder power. Wellington will likely need to navigate a more nuclear-adjacent region while preserving its moral positioning, as the Pacific becomes increasingly involved in great-power competition beneath the waves.

What it means for New Zealand and the Asia-Pacific

For New Zealand, the deal signals a shift in regional maritime security. While New Zealand does not operate nuclear submarines, the move strengthens U.S.-aligned security networks in the Pacific and increases underwater capabilities in the region.

This may prompt New Zealand to monitor deployments, adjust maritime cooperation with allies, and continue advocating for non-proliferation. Across the wider Asia-Pacific, South Korea’s nuclear submarines could alter the naval balance, prompt Japan and Australia to reassess maritime strategies, serve as a deterrent against North Korea, create tensions with China, deepen industrial ties with the U.S., and reinforce the U.S.’s role as a security guarantor in East Asia.

What happens next

Both governments have agreed to form working-level groups on shipbuilding and nuclear cooperation to implement the agreement. Detailed negotiations will now begin on reactor fuel, construction sites, maintenance, and regulatory compliance.

Given the complexity, especially around nuclear fuel supply and international non-proliferation rules, it may take several years before a submarine is built and operational.

-Asia Media Centre