As North Korea continues to expand and refine its nuclear arsenal—through warhead miniaturization, long-range missile development, and advances in MIRV (multiple independently targetable reentry vehicle) technology—public and elite concerns in South Korea about the credibility of U.S. extended deterrence have intensified. Although the United States and South Korea have taken steps to strengthen deterrence through strategic dialogues, expanded exercises, and nuclear consultation mechanisms, doubts remain.
This article does not advocate for South Korea to develop nuclear weapons. Rather, it explores a hypothetical scenario: What would a credible South Korean nuclear deterrent look like if the alliance framework eroded and public pressure for nuclear armament became politically irresistible? Modeling such a scenario can clarify the risks, requirements, and regional consequences that policymakers and alliance managers must consider now—before such a decision point arises.
Why Talk About This Now?
The nuclear debate in South Korea is no longer confined to fringe voices. A 2024 Korea Institute for National Unification survey found that 66 percent of South Koreans support acquiring an indigenous nuclear arsenal. Prominent policymakers and scholars increasingly argue that U.S. extended deterrence may not be sufficient to counter North Korea’s growing capabilities and threats of decoupling the alliance in a crisis.
Despite positive developments such as the Nuclear Consultative Group (NCG) launched under the Biden-Yoon administration, lingering doubts remain about whether the United States would risk a nuclear exchange with North Korea in defense of Seoul. In this strategic context, modeling a South Korean nuclear force is no longer an abstract exercise. It is a necessary tool to understand how deterrence dynamics may shift, and how regional actors might respond.
What Would a South Korean Nuclear Force Look Like?
A credible South Korean nuclear force would prioritize survivability, second-strike capability, and the ability to inflict unacceptable damage in retaliation. This logic mirrors the “minimum deterrence” models pursued by countries such as China and, to some extent, India.
To achieve a survivable second-strike posture, South Korea would likely need between 20 and 30 nuclear warheads. This estimate reflects the need to absorb a potential first strike and retain the capacity to retaliate against critical North Korean leadership and military infrastructure. With North Korea estimated to possess around 50 warheads, the goal would not be numerical parity, but assured retaliation.
South Korea’s potential delivery systems may comprise:
F-35A and F-15K fighter aircraft adapted for nuclear delivery; Hyunmoo-4 medium-range ballistic missiles with enhanced payload integration; and Future nuclear-powered ballistic missile submarines (SSBNs), which could offer the most survivable component of a nuclear triad—though such a capability remains at least a decade from realization.
Warhead yields in the 100 to 300 kiloton range would likely be optimal to strike hardened targets and leadership bunkers. This is significantly higher than most tactical warheads and reflects a shift toward strategic deterrence rather than battlefield use.
South Korea’s existing Three Axis System—Kill Chain (preemption), KAMD (missile defense), and KMPR (retaliatory punishment)—would play a supporting role. Kill Chain and KAMD would be especially critical in limiting damage from a North Korean first strike, enhancing the survivability and credibility of South Korea’s retaliatory capabilities.
Risks and Red Lines
Meanwhile, any pursuit of nuclear weapons by South Korea would have severe international, legal, and alliance repercussions.
First, South Korea is a signatory to the Nuclear Non-Proliferation Treaty (NPT) and would face global condemnation and likely sanctions for violating it. Such a move would erode global nonproliferation norms and could trigger a domino effect in the region.
Second, it could strain the U.S.-ROK alliance. Historically, Washington has opposed allied nuclear armament, as seen in its pressure on South Korea and Taiwan in the 1970s. A nuclear-armed South Korea could be interpreted as a loss of confidence in U.S. extended deterrence, potentially leading to a rupture in strategic cooperation.
Third, regional backlash would be swift. China might respond with economic retaliation or increased military deployments. Japan could reassess its own nuclear posture, possibly leading to a Northeast Asian arms race. ASEAN states and Australia might view the development as destabilizing and escalate their own defense postures.
Domestic constraints are also significant. While public opinion is shifting, legal barriers such as South Korea’s Atomic Energy Act and political resistance from civil society and opposition parties could stall or derail any attempt at nuclearization.
Policy Implications and What to Watch
Even if South Korea never chooses to pursue nuclear weapons, the growing support for such a move is a warning signal. To avoid a strategic rupture, the United States and South Korea should deepen nuclear consultation, increase transparency in deterrence planning, and accelerate interoperability in missile defense and counterforce capabilities.
At the same time, policymakers should quietly begin preparing for extreme contingencies. That includes scenario planning for alliance adaptation, command and control integration, crisis escalation management, and early warning systems. Planners should also consider how to communicate with regional actors to avoid misperception and accidental escalation.
Modeling a South Korean nuclear deterrent is not a prediction, nor is it a prescription. But in a region where strategic dynamics are rapidly evolving and nuclear threats are no longer theoretical, it is prudent to think the unthinkable. By doing so, the U.S.-ROK alliance can better prepare for the decisions it hopes never to face—and strengthen the deterrence architecture needed to prevent them.
Ultimately, the best way to ensure that South Korea never needs to consider a nuclear path is to address the underlying fears driving the debate. That means reinforcing the credibility of extended deterrence, improving regional crisis management mechanisms, and investing in conventional and missile defense capabilities that make nuclear options less attractive. Strategic imagination now can prevent strategic failure later.
[Photo by DALL·E]
The views and opinions expressed in this article are those of the author.
Dr. Ju Hyung Kim currently serves as the president at the Security Management Institute, a defense think tank affiliated with the South Korean National Assembly. He has been involved in numerous defense projects and has provided consultation to several key organizations, including the Republic of Korea Joint Chiefs of Staff, the Defense Acquisition Program Administration, the Ministry of National Defense, the Korea Institute for Defense Analysis, the Agency for Defense Development, and the Korea Research Institute for Defense Technology Planning and Advancement. He holds a doctoral degree in international relations from the National Graduate Institute for Policy Studies (GRIPS) in Japan, a master’s degree in conflict management from the Johns Hopkins University School of Advanced International Studies (SAIS), and a degree in public policy from Seoul National University’s Graduate School of Public Administration (GSPA).
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