East Asia is undergoing fundamental shifts in the maritime balance of power amid intensifying strategic competition and growing regional polarization. South Korea’s announcement of an unprecedented defense agreement with the United States to develop nuclear-powered submarines marks a qualitative transformation in its defense policy and broader military posture. The significance of this move extends well beyond reinforcing deterrence against North Korea. It recalibrates Seoul’s position within the regional security architecture and reshapes the dynamics of its alliance with Washington. It also accelerates the regional arms competition and influences the broader balance of power among major actors in the international system.

Key Motivations

South Korea's pursuit of nuclear submarines is linked to its presence in a highly threatening environment. This stems from the deep-seated historical animosity with North Korea, Pyongyang's possession of nuclear weapons and ballistic missiles capable of threatening its security. Relations between Seoul and China (a North Korean ally) are also strained, amid an intensifying regional polarization in East Asia. The main motivations behind South Korea's acquisition of nuclear submarines are as follows:

1- Implementing a policy of defense autonomy: South Korea has long pursued a policy of maximizing its self-reliance in defense and reducing its dependence on allies. This stems from a loss of confidence in defense commitments within alliances, a consequence of the ‘America First’ U.S. defense doctrine under President Donald Trump, which places the responsibility for the security of allies on the United States. Furthermore, the U.S. National Defense Strategy 2026 prioritized the Western Hemisphere, declining the importance of the Indo-Pacific region.

The key pillars of South Korea’s defense autonomy policy include the continuous increase in military spending, focusing on missile defense systems and the development of the domestically produced KF-21 fighter jet to bolster the national defense industry. Seoul has also developed long-range surface-to-air missile (L-SAM) systems as part of a multi-layered national air defense system. Additionally, the South Korean military has strengthened its command and control capabilities and expanded its arms exports as part of a strategy to elevate Seoul's ranking to fourth place among the world's arms exporters.

2- Maintaining the Cohesion of the South Korea-US Alliance: U.S. calls for South Korea to become more self-reliant have intensified, most recently in the former’s National Defense Strategy issued in January 2026. This strategy included indications that South Korea should assume responsibility for deterring external threats instead of relying entirely on the United States. The U.S. strategy did not explicitly state that North Korean denuclearization was a goal of U.S. defense policy. Instead, it focused on a shift in the balance of responsibility for security on the Korean Peninsula. This has reflected changes in the nature of the long-standing alliance between Washington and Seoul and the defense commitments within it. In response, South Korean President Lee Jae-myung emphasized a "self-reliant national defense" in an unstable security environment.

From this perspective, the nuclear submarine deal represents a South Korean effort to balance building its own capabilities with maintaining a minimum level of U.S. involvement. These deals also send a message to the Trump administration that Seoul is committed to responding to U.S. demands for greater defense responsibility within a broader strategic vision that preserves the defense partnership between the two countries.

3- Shifting to a Heavily Armed "Smart" Forces Model: South Korea is striving to transition from a manpower-intensive army to a heavily equipped, technologically advanced force. This is through relying on advanced and sophisticated weapons systems to counter the decline in its number of troops. In this context, President Lee Jae-myung announced in October 2025 that the South Korean army would transform into a "smart, elite force" by increasing defense spending and investing in strategic armaments, which explains South Korea's pursuit of nuclear submarines.

This is linked to changes in the structure of the South Korean military, with troop numbers expected to decrease to 450,000 according to reports issued by the South Korean Ministry of Defense in August 2025. The number of those eligible for military service is projected to decline to 140,000 by 2040, a trend associated with declining population growth and birth rates. This further exacerbates the numerical imbalance in defense capabilities with North Korea, which has at least 1.28 million active-duty military personnel, a number that rises to 5.7 million when including reservists, gendarmerie, and paramilitary forces.

4- Countering North Korea's Rising Naval Capabilities: South Korea is striving to counter the rapid development of North Korea's naval capabilities, particularly in the areas of submarines and frigates, by modernizing its fleet and enhancing its combat effectiveness. Pyongyang's commissioning of modern frigates equipped with vertical launch cells and long-range missiles has raised concerns in Seoul about the potential use of these advanced offensive naval capabilities against it. This has prompted South Korea to expedite the commissioning of its Chungnam-class frigates, which are equipped with advanced air defense and anti-submarine warfare systems. North Korea's announcement of the development of an attack submarine capable of carrying tactical nuclear missiles has further heightened Seoul's concerns about the threat to its maritime security. In response, South Korea has strengthened its domestically developed KSS-3 class submarine program, which boasts advanced missile capabilities, while simultaneously pursuing the acquisition of nuclear-powered submarines to bolster its deterrent capabilities and extend its endurance at sea.

5- Elevating Seoul’s Position in Defense Manufacturing: The deal to manufacture nuclear-powered submarines in South Korea is expected to enhance its portfolio in advanced defense manufacturing capabilities, particularly in precision defense industries. The production of nuclear-powered submarines demands meticulous precision at every stage, from reactor design and construction to the development and testing of operating systems under various exceptional conditions, including handling emergency scenarios such as radioactive leaks.

In this context, South Korea ranked among the top ten arms exporters between 2020 and 2024, accounting for 2.2% of total global arms exports, according to data from the Stockholm International Peace Research Institute (SIPRI). South Korea aims to become the world's fourth-largest arms exporter by 2027, after Russia, the United States, and China. It has successfully developed an attractive model based on short delivery times, competitive pricing, and favorable technology transfer terms compared to other exporting countries. This can be illustrated by the fact that Hanwha Group, a leading South Korean arms manufacturer, achieved export profits exceeding its domestic sales in 2024.

6- Confronting Escalating Maritime Security Threats: South Korea faces escalating threats to its maritime security, particularly in the Yellow Sea, where its exclusive economic zone intersects with that of China. Seoul confronts illegal fishing operations and repeated incursions by the Chinese coast guard into its territorial waters. Beijing employs "grey zone" tactics, expanding its maritime presence through coast guard vessel movements in the Yellow Sea, constructing artificial installations and platforms, and frequently announcing maritime restrictions for training purposes. This is inextricably linked to the South Korean-Japanese dispute in the Sea of Japan over the ownership of the islands known as Dokdo in South Korea and Takeshima in Japan. Seoul routinely rejects any Japanese claims of sovereignty over these disputed islands.

The acquisition of nuclear-powered submarines is part of a policy to deter China and North Korea, and to a lesser extent Japan, as well as to raise the cost of naval confrontations with these countries over disputed territories. In this regard, U.S. Chief of Naval Operations Admiral Daryl Caudle stated in remarks published in November 2025 that the use of these new nuclear submarines was a likely course of action for the United States to counter what he described as the most significant threat: China.

Intricate Repercussions

The North Korean nuclear submarine deal is expected to have multiple domestic and regional repercussions due to its political and economic costs. The most prominent of these repercussions are:

1- Containing hardline pressures toward Pyongyang: South Korean President Lee Jae-myung faced mounting pressure from conservative factions who accused him and the Democratic Progressive Party of being ‘too soft’ with North Korea. On February 11, 2025, the Ministry of Unification faced criticism for adopting a "submissive" position after Unification Minister Chung Dong-young criticized the incursion of a drone into North Korean airspace from South Korea. Similarly, on February 10, 2025, Prime Minister Kim Min-seok was criticised by some members of parliament for failing to take appropriate measures to counter perceived threats from North Korea’s alleged possession of nuclear submarines.

2- Increasing military burden on the South Korean economy: The allocation of additional financial resources to defense expenditure is expected to exert further pressure on the South Korean economy. A member of the South Korean parliament pointed to a budget deficit caused by increased defense spending. In this context, the Ministry of National Defense faced an unprecedented crisis in implementing the defense budget in late 2025, reducing the planned increase and delaying crucial payments, particularly to the procurement agency, amounting to 1.3 trillion won. This impacted soldiers' salaries and allowances, as well as key armament programs such as the development of the KF-21 fighter jet. This situation raised concerns within the military establishment about an unusual fragility in defense budget management and instability in military funding.

This is related to the South Korean Ministry of National Defense's announcement in December 2026 of a reduction in the planned increase in the 2026 defense budget to 7.5%, down from the 8.2% proposed by the government in October 2025. The total defense budget was initially set at 66.29 trillion won, but difficulties in securing funding led to a reduction to only 65.86 trillion won.

3- The Need for Advanced Military Skills Training: Operating nuclear submarines requires advanced military skills to handle highly sophisticated and complex weapons systems. For example, in the military aviation sector, modern imported and domestically produced fighter jets constitute 60% of the air force's combat armament structure, while older F-5 and F-4 fighters make up 40% of the fleet, with a plan to replace them within 10 years. This pattern is similar across the rest of the South Korean military, where approximately 50% of the equipment dates back to the 1960s and 1970s. This situation highlights the gap between the skill level of South Korean military personnel and the costly training required to operate advanced nuclear submarines.

4- Growing Concerns About North Korean Sabotage: South Korea fears that Pyongyang might launch preemptive clandestine operations to disrupt the nuclear submarine program or, at the very least, conduct espionage to uncover the submarines' technical secrets. South Korea has previously accused its northern neighbor of launching cyberattacks targeting government institutions in the defense, semiconductor, and automotive sectors. Among the most prominent accusations is the 2016 cyberattack aimed at obtaining sensitive information about the South Korean military.

5- Intensifying the Nuclear Arms Race in Asia: North Korea and China are expected to exploit the recent nuclear submarine deal to expand their nuclear weapons development programs, disregarding demands from the United States, South Korea, and Japan for nuclear reduction, which they perceive as contradicting Seoul's current actions. In this regard, the North Korean news agency stated that South Korea's acquisition of nuclear submarines will trigger a "nuclear domino effect" in the region and an arms race, prompting Pyongyang to take more realistic countermeasures.

China is expected to accelerate its nuclear attack submarine program. Satellite imagery from February 9, 2026, revealed the construction of a prototype of China's new-generation Type 095 nuclear attack submarine. This is expected to coincide with an expansion of anti-submarine operations against China in the Yellow Sea and the East China Sea to counter the potential deployment of South Korean nuclear submarines in areas of Chinese influence. In a similar vein, Japanese Defense Minister Shinjiro Koizumi called in November 2025 for a study on acquiring nuclear submarines, representing a shift in Japanese military doctrine given its historical aversion to nuclear weapons. The Japanese Defense Minister emphasized that most of Japan's neighboring countries are now moving towards acquiring nuclear submarines.

6- The Possibility of Reducing U.S. Nuclear Protection for South Korea: The recent deal between Washington and Seoul may be a prelude to reducing the scope of the U.S. nuclear umbrella for South Korea as part of a policy of limiting U.S. military commitments abroad and focusing on the "Western Hemisphere". Despite repeated South Korean assurances that the U.S. nuclear umbrella will not be withdrawn and that U.S. defense commitments remain unchanged, South Korea’s acquisition of nuclear submarines may mark the beginning of a shift toward greater Korean defense autonomy. This could be part of President Trump’s plans to scale back on extended deterrence and focus on Chinese threats to U.S. interests.

Ultimately, the nuclear submarine deal represents a profound strategic shift in North Korea's defense doctrine, reflecting a move from traditional reliance on the U.S. defense umbrella to a more independent path based on building qualitative and unconventional deterrent capabilities. While this shift is expected to yield benefits, it also complicates the regional security environment and intensifies the arms race in East Asia. It further imposes significant domestic economic and technological burdens that require careful management to avoid an imbalance between deterrence requirements and economic sustainability.

Implications of South Korea’s Pursuit of Nuclear-Powered Submarines