South Korea Should Lean into Nuclear-Powered Submarines

The art of the deal is back, and so is the price tag on alliances. In this context, South Korea’s ambitions to develop nuclear-powered submarines could become a critical factor in shaping its alliance with the United States. While the program is primarily aimed at countering North Korea’s advancing submarine-launched ballistic missile capabilities, it also carries broader strategic implications.

Despite concerns about the shifting priorities of South Korea’s political leadership — where transitions between conservative and progressive administrations often lead to shifts in diplomatic priorities and strategies — its nuclear-powered submarine program represents a tangible commitment to strengthening the country’s defense posture and assuming a greater share of regional security responsibilities. Even if enthusiasm within the Trump administration may be tempered by a focus on reducing U.S. military presence on the peninsula, South Korea’s investment in advanced capabilities like nuclear-powered submarines aligns with Washington’s long-standing demand for allies to contribute more to their own security.

What You Need to Know About South Korean Nuclear Submarines

South Korea has explored nuclear-powered submarines since the early 2000s, primarily to counter North Korea’s growing submarine and missile threats. In 2003, the secret “362 Project” aimed at developing a nuclear-powered submarine was canceled due to U.S. pressure and political concerns. Interest revived in the late 2010s, with President Moon Jae-in expressing support for an indigenous nuclear submarine program in response to North Korea’s advancing missile capabilities. However, South Korea lacks domestic nuclear propulsion technology but has sought alternatives, including potential collaboration with the United States or France. 

Despite these efforts, progress remains limited due to technological, diplomatic, and nonproliferation challenges, particularly regarding fuel enrichment and international agreements. While South Korea continues to seek solutions, significant obstacles must be overcome before a nuclear-powered submarine becomes a reality. 

Nuclear-Powered Submarines as a Tool for Burden-Sharing and Alliance Strengthening

South Korea’s nuclear submarine program is not merely about acquiring a new military capability, it is a strategic move to reinforce deterrence against North Korea while demonstrating a commitment to shouldering a greater share of regional security. Nuclear-powered submarines, with their superior endurance, stealth, and operational range, would enable Seoul to enhance its maritime deterrence without requiring direct U.S. military reinforcement.

From a U.S. perspective, this aligns with the Trump administration’s previous demands that allies invest more in their own defense rather than relying on American forces. Trump has historically emphasized reducing U.S. military commitments overseas —  South Korea’s nuclear-powered submarine program provides an opportunity to achieve this objective. By investing in a high-end military capability that reduces dependency on U.S. naval assets, South Korea is directly responding to Trump’s calls for burden-sharing.

While critics argue that South Korea’s shifting political landscape introduces unpredictability in its defense policies, the nuclear-powered submarine program is a long-term investment that transcends short-term political fluctuations. Regardless of the administration in power, acquiring nuclear-powered submarines would mark a fundamental shift in South Korea’s military posture — one that strengthens the alliance by reinforcing deterrence and reducing Seoul’s reliance on direct U.S. intervention in the event of a conflict.

The 123 Agreement Challenge: A Test for U.S. Commitment

One of the biggest hurdles for South Korea’s nuclear-powered submarine ambitions is the U.S.-Republic of Korea Agreement for Peaceful Nuclear Cooperation, commonly known as the “123 Agreement,” which prohibits South Korea from enriching uranium or reprocessing spent nuclear fuel. . Since nuclear-powered submarines require highly enriched uranium, moving forward with the program would require U.S. cooperation, either through exemptions or alternative arrangements.

For Washington, this presents a critical decision: whether to support a key ally’s security ambitions or prioritize strict adherence to nonproliferation norms. The Trump administration, which has historically taken a more flexible and transactional approach to alliances, could view the nuclear-powered submarine program as an opportunity to modernize the U.S.-South Korean partnership while reducing America’s direct military commitments in the region.

Instead of viewing South Korea’s ambitions to develop nuclear-powered submarines as a challenge, the United States could utilize these efforts to enhance a broader alliance strategy. Facilitating access to nuclear propulsion technology — whether through a controlled framework similar to AUKUS or alternative agreements — would reinforce South Korea’s role as a capable security partner. This would also provide tangible evidence of U.S. support for South Korea’s defense modernization, countering the perception that Trump’s transactional approach undermines alliance credibility.

Beyond North Korea: Aligning with U.S. Indo-Pacific Strategy

While the primary justification for South Korea’s nuclear-powered submarine program is deterrence against North Korea, the broader strategic implications cannot be ignored. China’s expanding naval power and assertive maneuvers in the South China Sea and Taiwan Strait pose long-term challenges to regional stability.

A key shortcoming in America’s ability to deter and counter China is the insufficient number of U.S. submarines available for the Pacific theater. This gap has driven initiatives like AUKUS — particularly its submarine pillar — but U.S. submarine production has stagnated, leaving a critical vulnerability in undersea warfare capabilities. In this context, supporting South Korea’s nuclear-powered submarine program would align with U.S. strategic interests by strengthening allied maritime power in the region. South Korea’s ability to conduct extended-range submarine operations would complement U.S. efforts to deter Chinese aggression without requiring additional American deployments.

The Trump administration previously took a hardline stance on China, emphasizing the need for allies to play a greater role in counterbalancing Beijing. South Korea’s nuclear-powered submarines would fit into this strategy, providing a crucial capability that enhances regional deterrence while allowing the United States to mitigate its submarine shortfall. Even if the Trump administration prioritizes deterring North Korea over its broader Indo-Pacific objectives, the nuclear-powered submarine program would contribute to both goals, ensuring greater stability while addressing a pressing gap in allied naval forces.

Managing Costs, Public Perception, and Political Dynamics

Developing and maintaining nuclear-powered submarines is a costly endeavor, and South Korea’s defense budget is already under strain due to the need to counter immediate threats from North Korea. Some may argue that the Trump administration’s insistence on greater burden-sharing could create financial pressures that limit Seoul’s ability to invest in nuclear-powered submarines while also meeting U.S. financial demands for hosting American forces.

However, this challenge also presents an opportunity. By committing to a nuclear submarine program, South Korea is demonstrating its willingness to invest in high-end capabilities rather than simply increasing financial contributions for U.S. troop presence. This shifts the burden-sharing debate from a transactional “cost-sharing” model to one of strategic investment, reinforcing South Korea’s role as a proactive security partner rather than a dependent ally.

Public perception in South Korea remains an important factor. The first Trump administration generated concerns about the perceived imbalance in the alliance, with many South Koreans viewing his financial demands as undermining partnership equality. The nuclear-powered submarine program could counter this narrative by showcasing South Korea’s independent military capabilities while still maintaining strong U.S. ties. If the United States actively supports the program — particularly by facilitating nuclear fuel access — it would strengthen public confidence in the alliance and mitigate concerns about American commitment.

Conclusion: A Strategic Investment in the Future of the U.S.-South Korean Alliance

Despite concerns about South Korea’s shifting political landscape and the Trump administration’s potential lack of enthusiasm for regional engagement, the nuclear-powered submarine program presents a unique opportunity to reinforce the U.S.-South Korean alliance in a way that aligns with Trump’s strategic priorities.

By investing in nuclear-powered submarines, South Korea is directly addressing Trump’s calls for allies to take on a greater share of their defense burden. These submarines would enhance deterrence against North Korea, complement America’s Indo-Pacific strategy, and reduce the need for additional American naval deployments. Moreover, U.S. support for the program — whether through nuclear fuel cooperation or strategic alignment — would reinforce the alliance’s credibility and modernization.

In a renewed Trump era, the success of the U.S.-South Korean alliance will depend not just on policies, but on both nations’ ability to adapt to evolving security challenges. If managed effectively, South Korea’s nuclear-powered submarine program could serve as a cornerstone of alliance modernization, ensuring that burden-sharing is not just a financial demand but a strategic investment in regional stability.

Rather than viewing the nuclear-powered submarine program as a marginal issue, the Trump administration should recognize it as an opportunity to achieve its broader objectives — reducing U.S. military commitments, strengthening allied deterrence capabilities, and reinforcing a more balanced and resilient security partnership.

Jihoon Yu, Ph.D., is director of external relations and associate research fellow at the Korea Institute for Defense Analyses. He is the principal author of the South Korean navy’s Navy Vision 2045. The views here are those of the author and do not reflect those of any state institution in South Korea.

Image: Petty Officer 1st Class Desmond Parks via Wikimedia Commons

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