In last April’s Washington Declaration, South Korea and the United States agreed to strengthen extended deterrence by creating the NCG (Nuclear Consultative Group). Regular port calls of American nuclear-powered ballistic missile submarines (SSBN) in Korea were also guaranteed on the condition that Seoul complies with the NPT (Non-proliferation Treaty). Subsequently, Yoon Suk Yeol became the first South Korean president to visit the American SSBN U.S.S. Kentucky in person.

Nonetheless, North Korea is now immune to U.S. power projection in the Korean Peninsula. When the U.S. aircraft carriers visited this year, Pyongyang fired ballistic missiles. The next day the U.S.S. Kentucky docked in the southern port city of Busan. The North signaled its disapproval by firing ballistic missiles, matching the distance between its firing point and Busan. Additionally, after the French and South Korean air forces conducted a combined exercise, Pyongyang released an aggressive statement blaming France.

Indeed, South Koreans’ unprecedentedly strong pro-nuclear sentiment amid escalating North Korean and Chinese security threats brought Washington Declaration. However, observing the recent case showing that a third party’s involvement in a foreign conflict might not necessarily happen, non-nuclear states realize that paper-based security commitment is not always reassuring. Similarly, South Korea is ready for a difficult situation where it needs powerful denial capabilities with conventional weapons against nuclear-armed neighbors without violating the NPT.

Realistically, the method of bypassing the NPT involves the acquisition of Korean nuclear-powered submarines through the modification of the ROK-U.S. nuclear agreement. With a limited defense budget, Seoul must prioritize acquiring its own nuclear-powered attack submarines (SSN) as an asymmetric strategic asset. From the United States’ perspective, this could even contribute to curbing Seoul’s mainstream opinion favoring nuclear.

Shackled non-nuclear South Korea amid regional insecurity

Only armed with conventional forces and without a nuclear arsenal, South Korea desperately needs a game changer against North Korean nuclear threats and Chinese maritime rise. Seoul’s dilemma of facing nuclear-armed nations without going nuclear can be offset by speedily acquiring nuclear submarines. Still, their development has been recognized as the last security shackle for Koreans after the termination of the missile guidelines that capped Seoul’s firepower.

In 2003, the Roh Moo-Hyun administration launched a clandestine defense project, dubbed the 362 Initiative, to develop and deploy its own SSN by 2020. However, the program failed as it attracted the scrutiny of the International Atomic Energy Agency (IAEA). In 2017, the same agenda gained momentum as President Moon Jae-In, who had worked closely with Roh, announced his intention to develop SSNs by the early-2030s by revising the ROK-U.S. nuclear agreement. He pledged to build nine new submarines in batches of three by 2030. Despite the strong willingness of Moon’s National Security Office, however, Seoul was frustrated by Washington’s non-proliferation policy. It has not made further progress since then, as even the current Yoon administration, conscious of its declared NPT compliance, does not consider the SSN a viable priority.

What makes nuclear-powered submarines better than diesel submarines?

If South Korea chooses nuclear submarines, it will not risk exposing itself during operations at sea. The best strategic advantage of SSNs lies in their stealthiness for covert operations and superior offensive capabilities compared to diesel submarines. Theoretically, a nuclear-powered submarine could stay submerged for extended periods. Operating undetected for several months holds greater strategic significance than diesel submarines' week-long missions.

SSNs that do not need to surface during mission-critical operations can conduct unlimited underwater maneuvers as much as crews can tolerate. South Korean nuclear submarines could monitor and track enemy submarines equipped with SLBMs for months and, if necessary, remain in the vicinity of North Korean waters or sea lines of communication and exit after precisely striking hostile nuclear facilities and command centers.

The Falklands War in 1982 is an example of the comparison between the strategic differences between the two types of submarines. The British Royal Navy’s nuclear-powered submarines traveled to the Falklands region, approximately 14,000 km, in ten days, contributing to the defeat of the Argentine Navy and securing the rule of the sea. In contrast, diesel submarines that departed simultaneously took five weeks to reach the theatre of operations.

The construction of SSNs could also contribute to addressing one of the prevalent issues in the Korean Navy: the poor working environments. In addition to inadequate government support for improving their working conditions, the main reasons for leaving the Navy include the low quality of life resulting from the confined space of small submarines. Currently, the South Korean Navy’s conventional submarines are cramped because of the space occupied by engines and equipment. Larger nuclear submarines would allow more available space for crew facilities and supplies.

Additionally, South Korea can use its nuclear submarines as multi-purpose strategic assets. A nuclear-powered submarine can improve speed and onboard living conditions and be equipped with more missile tubes and torpedo launchers, enhancing the striking power. Also, installing a special force delivery vehicle for transportation on SSNs is a method adopted by the U.S. and UK Royal Navies. Seoul can adopt this to enhance the versatility of its nuclear-powered submarines.

In other words, the most suitable means of deterring opponents’ nuclear assets is nuclear-powered attack submarines without thermonuclear missiles. Considering the capable nuclear technology accrued over time, the world’s top shipbuilding capacity, and an increasing defense budget, it is financially feasible for Seoul to invest in more R&D for nuclear submarine construction, provided the political will exists.

How to use South Korean nuclear-powered submarines

South Korea’s acquisition of nuclear-powered submarines would enable better mission flexibility to address regional security problems. They could play a crucial role in deterring Pyongyang’s future submarines and ballistic missiles while serving as a deterrent against provocations from China. For instance, South Korean SSNs stationed near their naval base could pressure Chinese fleets in the East China Sea.

Such preparation for firepower delivery would reduce the lead time required to develop counter-offensive strategies in the worst scenarios, which would also be an essential element of South Korean nuclear potential. Based on the SSN platform, increasing their size to integrate possessing missile launch tubes could enable South Korea to convert them into ballistic missile submarines (SSBN) or guided missile submarines (SSGN) with heavier conventional payloads. This would make opponents uncertain and force them to reconsider their offensive actions. If Seoul goes nuclear, with Washington’s consent, its indigenous SSBN or SSGN will ensure second-strike capability as a part of the nuclear triad.

Introducing Korean SSNs would consolidate Seoul’s position as a vital U.S. ally in East Asia, effectively keeping the Chinese Navy in check in the western Pacific. Furthermore, simultaneous coordinated actions between Russia, China, and North Korea are concerning. Korean nuclear submarines would restrain North Korea’s escalatory actions in case of a Chinese attempt to annex Taiwan. Consequently, the ROK-U.S. agreement on nuclear-powered submarines would be a powerful warning to Chinese president Xi Jinping and North Korean dictator Kim Jong Un.

Without nuclear submarines, South Korea’s support for the United States would be limited, as Seoul would be solely focused on Pyongyang. The United States will likely struggle to deal with the new Cold War in the region. China’s navy already outnumbers America’s, and Russia is keen on checking American submarines. The U.S. Navy has fifty nuclear-powered submarines, but less than half are reportedly available for regular duties due to maintenance and training schedules. They need to confront almost thirty Russian and Chinese nuclear submarines, and the number is increasing. It is why the United States abandoned its non-proliferation principle to provide Australia with eight SSNs through AUKUS, but Canberra’s SSNs will be available only after 2042. There is room for South Korea to step into this for support and cooperation.

Depending on how the Russo-Ukrainian War and potential conflict around Taiwan Strait proceed, a proxy war between the West and its adversaries makes the United States ill-positioned to mindlessly impose its non-proliferation rules on Asian allies.

As former officials and security experts have noted, South Korea already possesses the necessary capacity to develop Korean nuclear submarines. Within thirty years, it has developed infrastructure, submarine design, and shipbuilding capabilities comparable to major submarine powers like Germany and Japan. Seoul has also acquired technology for producing small nuclear reactors used in nuclear submarines, along with agreed technical cooperation with Washington.

Opposing Perspectives

A significant problem for nuclear-powered engines is noise. But advancements in noise reduction technology have mitigated this concern. American Virginia-class attack submarines (SSN) and Ohio-class ballistic missile submarines (SSBN) have also significantly reduced noise since the 2000s. Such improvements provide them with less risky mobility and better combat readiness against anti-submarine weapons like torpedoes than diesel submarines.

Some argue that South Korea’s development of SSNs is tantamount to nuclear armament because the country signed and ratified the NPT. The fact that South Korean nuclear submarines would be platforms without nukes addresses the concern. They would only track hostile nuclear submarines or carry conventional warheads for SLBMs and guided missiles. Nuclear-powered submarines do not violate the NPT if they are conventionally armed.