South Korea’s Nuclear-Powered Submarine Deal: Strategic Shift in East Asia
East Asia is witnessing profound changes in naval power balances due to increasing strategic competition and regional polarization. South Korea recently announced an unprecedented defense agreement with the United States to build nuclear-powered submarines, marking a qualitative leap in its defense policy and national armament capabilities. The implications extend beyond strengthening deterrence against North Korea; they also include repositioning Seoul within regional security equations, altering its alliance with Washington, accelerating the Asian arms race, and affecting the major power balance in the international system.
Drivers Behind the Deal
South Korea’s pursuit of nuclear-powered submarines is rooted in a high-threat environment, stemming from its longstanding enmity with North Korea, Pyongyang’s nuclear arsenal and ballistic missile capabilities, fluctuating relations with China (North Korea’s supporter), and intensifying regional competition. Key motivations include:
- Implementing Defense Self-Reliance Policy:
South Korea has long pursued a policy of maximizing its own defense capabilities and reducing reliance on allies, driven by waning confidence in alliance commitments. This reflects the U.S. “America First” doctrine under President Trump, which shifted defense responsibility toward allied nations. The 2026 U.S. National Defense Strategy prioritized the Western Hemisphere, reducing emphasis on the Indo-Pacific.
South Korea’s policy has manifested in increasing military spending, advancing domestic weapons systems like the KF-21 fighter, developing multi-layered long-range missile defense systems (L-SAM), enhancing military command capabilities, and expanding arms exports. These efforts aim to elevate Seoul to the world’s fourth-largest arms exporter.
- Maintaining the U.S.-South Korea Alliance:
U.S. policy documents, including the January 2026 National Defense Strategy, increasingly urge South Korea to assume primary responsibility for deterring external threats. While denuclearizing North Korea is not explicitly stated as a U.S. defense goal, the focus is on “rebalancing security responsibilities” on the peninsula. President Yoon Jae-Myung has emphasized that “in an unstable security environment, self-reliance in national defense is essential.”
The nuclear submarine deal represents a balance between building independent capabilities and preserving minimal U.S. engagement through major arms purchases—signaling Seoul’s strategic commitment to shared defense responsibilities with Washington.
- Transition to a “Smart, Well-Armed Military”:
South Korea aims to move from a numerically large force to a “smart, technologically advanced military,” relying on high-tech weaponry to offset decreasing troop numbers. In October 2025, President Yoon announced the transformation into an “elite smart force” via increased defense spending and strategic weapons investment.
South Korea’s active military strength is projected at 450,000 troops (as of August 2025), with the eligible conscript pool expected to shrink to 140,000 by 2040 due to declining birth rates. This numerical gap contrasts sharply with North Korea’s 1.28 million active-duty troops, expanding to 5.7 million when including reserves, paramilitary, and militia forces.
- Countering North Korea’s Rapid Naval Expansion:
South Korea aims to counter Pyongyang’s rapidly advancing naval capabilities, including new frigates equipped with vertical launch systems and long-range missiles, which raise concerns about offensive maritime threats. North Korea’s introduction of a tactical nuclear-capable attack submarine further escalates Seoul’s naval security concerns, prompting upgrades to its KSS-3 submarine program and the pursuit of nuclear-powered submarines for extended sea endurance and credible deterrence. - Enhancing South Korea’s Advanced Defense Manufacturing:
The nuclear submarine program will elevate South Korea’s position in high-precision defense manufacturing. Producing nuclear submarines requires exacting standards in reactor design, construction, operational systems, and emergency scenario testing, including radiation containment.
Between 2020–2024, South Korea ranked among the top ten global arms exporters, accounting for 2.2% of total global arms exports (SIPRI data). Seoul aims to reach fourth place globally by 2027, leveraging short delivery times, competitive pricing, and technology transfer incentives. Hanwha Group, leading South Korean arms manufacturing, earned more from exports in 2024 than from domestic sales, highlighting the effectiveness of this model.
- Addressing Escalating Maritime Security Threats:
South Korea faces rising maritime security threats, particularly in the Yellow Sea, where its exclusive economic zone overlaps with China. These include illegal fishing, repeated Chinese coast guard incursions, and gray-zone tactics (incremental maritime expansion via platforms, artificial islands, and restricted navigation zones). Disputes with Japan over the Dokdo/Takeshima islands further complicate maritime security.
The nuclear submarine deal serves as a deterrent against China, North Korea, and, to a lesser extent, Japan, raising the cost of maritime confrontation. U.S. Navy Admiral Daryl Caudle noted in November 2025 that deploying nuclear submarines to counter China’s maritime threat is a likely U.S. response.
Complex Implications
The nuclear submarine deal carries multiple domestic and regional consequences:
- Domestic Pressure to Take a Hard Line on North Korea:
President Yoon and the Democratic Party have faced criticism from conservatives for perceived leniency toward Pyongyang, including accusations of failing to respond adequately to North Korea’s military provocations in February 2025. - Increased Military Spending Burden on the Economy:
Allocating more resources to defense strains the South Korean economy. Delays in budget execution, including a 1.3 trillion won shortfall in procurement payments, have affected salaries, key programs like the KF-21 fighter, and overall military financial stability. The 2026 defense budget increase was reduced from 8.2% to 7.5%, lowering total spending from 66.29 trillion to 65.86 trillion won. - Need for Advanced Training:
Operating nuclear submarines requires highly skilled personnel, yet a significant portion of South Korea’s equipment dates back to the 1960s–1970s. Modern aircraft constitute 60% of the Air Force, while older F-5s and F-4s make up 40%, with replacement planned over ten years—a situation mirrored across military branches. - Risk of North Korean Sabotage:
South Korea fears North Korea may attempt preemptive sabotage or espionage on the nuclear submarine program. Past cyberattacks, including in 2016 targeting defense, semiconductor, and automotive sectors, underscore these risks. - Expansion of the Regional Nuclear Arms Race:
North Korea and China are likely to use South Korea’s nuclear submarine acquisition to accelerate their own nuclear programs. Satellite imagery in February 2026 showed China constructing new 095-class nuclear attack submarines. Japan has also indicated potential interest in nuclear submarines, marking a doctrinal shift in regional defense. - Potential Reduction of U.S. Nuclear Umbrella:
The deal may signal a long-term trend toward South Korean defense autonomy, possibly reducing reliance on U.S. extended nuclear deterrence in line with U.S. policy to limit overseas commitments and focus on threats in the Western Hemisphere. While South Korea continues to affirm U.S. protection, nuclear submarines represent a step toward independent deterrence.
Conclusion
South Korea’s nuclear-powered submarine acquisition represents a profound strategic shift from dependence on the U.S. nuclear umbrella toward a more autonomous deterrence posture. While the initiative strengthens deterrence, maritime security, and industrial capabilities, it also complicates the regional security environment, intensifies the East Asian arms race, and imposes significant domestic economic and technological challenges. Balancing deterrence effectiveness with economic sustainability will be critical in navigating this new era of East Asian security dynamics.
