South Korea developing its own nuclear weapons, a topic long relegated to fringe advocacy, is now being discussed openly, including by its president. There are growing demands from the South Korean populace, the conservative media, and the ruling party for greater nuclear autonomy from Washington, redeployment of U.S. tactical nuclear weapons that were removed in the 1990s, or a nuclear-sharing arrangement with Washington similar to the arrangements that some North Atlantic Treaty Organization (NATO) allies have.

The recent upsurge in widespread mainstream debate over nuclear options is driven by a perfect storm of concerns driven by the deteriorating regional security environment, growing doubts of the reliability of the United States security guarantee, the vicissitudes of American policies, and South Korean national pride.

It is unclear if President Yoon Suk Yeol’s comments in January were missteps when discussing complex policy options, were playing to strong public support for nuclear options, or were deliberate attempts to pressure the U.S. to go beyond previous nuclear restrictions.

The South Korean government is not currently advocating either U.S. nuclear redeployment or an indigenous weapons program. Instead, Seoul is pushing for more tangible signs of U.S. commitment to the defense of South Korea, greater involvement in U.S. planning for potential use of nuclear weapons in Korean contingencies, and a role in nuclear decision-making during a crisis. However, government support for that approach may be conditional on progress in talks with Washington and the extent of future North Korean provocations.

The United States has responded by taking steps to strengthen its extended deterrence policy which is comprised of nuclear weapons, conventional forces, and missile defense. Washington recently resumed large-scale combined military exercises and rotational deployment of U.S. nuclear-capable strategic assets after a four-year hiatus. Presidents Joe Biden and Yoon reactivated the Extended Deterrence Strategy and Consultation Group (EDSCG) to provide a venue for exploring additional reassurance measures.

The Biden and Yoon administrations should continue behind-the-scenes discussions while refraining from public statements that could complicate an agreement or exacerbate bilateral tensions. Washington seems willing to be more forthcoming in revising the highly sensitive nuclear relationship but retains clear red lines. Any agreement will need an energetic and sustained strategic messaging program to gain public support in South Korea.

Even if the Yoon administration is eventually satisfied with the results of bilateral discussions, U.S. efforts may be insufficient to overcome declining South Korean confidence in American credibility and to prevent strains in the bilateral relationship. South Korean political elements and the populace may remain resentful of perceived American constrictions on South Korean national security as compared to nuclear-sharing options available to U.S. allies in Europe.

Catalysts for Nuclear Advocacy

South Korea’s new nuclear advocacy is propelled by several factors: North Korea’s escalating nuclear and missile threats, increasing doubts about whether the U.S. would risk nuclear attacks on its cities by North Korean intercontinental ballistic missiles (ICBMs) in defense of South Korea, concern that the 2024 U.S. presidential election could result in degradation or abandonment of the bilateral alliance, and injured national pride due to not being allowed the nuclear status of some U.S. allies in Europe.

North Korea’s Escalating Nuclear and Missile Threat. Pyongyang has steadily improved both the quality and quantity of its missile and nuclear arsenals in recent years.REF Pyongyang has unveiled tactical and strategic missile systems that pose an ever-greater risk to the United States and its allies. North Korea is producing a new generation of advanced mobile missiles that are more accurate, more mobile, and more difficult to detect and target than the previous generation and have an enhanced ability to evade allied missile defenses.

In September 2022, Pyongyang passed a new law that lowered the threshold for its use of nuclear weapons including pre-emptive strikes with strategic, tactical, and battlefield nuclear weapons. The regime declared that it would use nuclear weapons in response to even perceived preparations for a U.S. or South Korean nuclear or non-nuclear attack on regime leadership, nuclear command structure, or important strategic targets.REF On January 1, 2023, Kim Jong-un vowed to “exponentially” increase his stockpile of nuclear warheads.REF By 2027, Pyongyang could have 200 nuclear weapons.REF

Pyongyang has successfully tested several ICBMs capable of targeting the continental United States with nuclear weapons. The Hwasong-17 ICBM, which had its first successful test flight in 2022, will have three to four nuclear warheads and risks overwhelming America’s limited missile defenses of the homeland. During its February 2023 parade, North Korea revealed at least 11 of the multiple warhead missiles along with a new solid-fuel ICBM. The regime’s ability to hold numerous American cities at risk of attack by hydrogen bombs has aggravated allies’ concerns about U.S. capability, resolve, and willingness to defend their countries.

Growing Doubts About U.S. Reliability. South Koreans increasingly question the strength and commitment of the U.S. extended deterrence guarantee, wondering whether the U.S. would be “willing to trade San Francisco for Seoul” or would instead abandon its ally. Yet, the U.S. was willing to risk its cities in a nuclear exchange with the Soviet Union, a far greater nuclear threat than North Korea, during the Cold War, in essence risking San Francisco, New York, and Washington, DC, for Bonn, Paris, and London.

It is also important to think of the circumstances under which a U.S. President would be faced with such a decision. At such a time, the U.S. would have suffered extensive military and civilian casualties on the Korean Peninsula. Faced with more casualties than Pearl Harbor, 9/11, and possibly the entire 1950–1953 Korean War combined, it is hard to imagine any U.S. President walking away, or the U.S. Congress or the American public allowing a U.S. leader to do so.

Potential U.S. Election Results. Widespread South Korean concerns about the reliability of the U.S. and fear of abandonment are widely cited as a major factor for recent escalating calls for an indigenous nuclear program by advocates, including former senior military officers, non-government experts, and academics. Current and former South Korean officials privately express concern that the 2024 U.S. presidential election could lead to an isolationist administration that downgrades America’s alliance commitments, perceives the military relationship in transactional terms, and again threatens to reduce or remove U.S. forces from the Korean Peninsula while unilaterally terminating combined military exercises and rotational deployment of U.S. strategic assets.REF

National (Wounded) Pride. South Korean nuclear advocates point to French and British possession of nuclear weapons as justification for Seoul to have similar capabilities. These two countries, the advocates argue, also questioned the viability of the U.S. extended deterrence guarantee and the United States eventually accepted them as members of the nuclear club. Many South Koreans question why their nation is being treated less diffidently than European allies, or why India received exemptions from the International Atomic Energy Agency and the Nuclear Suppliers Group (NSG) despite developing nuclear weapons.

South Korean nuclear advocates believe that Seoul should have responsibilities commensurate to that of the NATO Nuclear Planning Group (NPG). The NPG provides a forum in which NATO member countries can participate in the development of the Alliance’s nuclear policy and in decisions on its nuclear posture.REF The NPG does not, however, give European allies a role in U.S. nuclear targeting, operations planning, or any say in U.S. nuclear employment decision-making.

The United States currently has nuclear-sharing arrangements with Belgium, Germany, Italy, the Netherlands, and Turkey, which have dual-capable aircraft (DCA) to deliver U.S. nuclear weapons. Each of these countries also hosts U.S. nuclear weapons, though Washington retains absolute control of the weapons nor do any of the five nations have input on nuclear targeting.

The U.S. has no similar arrangement with South Korea. The United States does not station nuclear weapons in South Korea, nor is there an NPG to allow South Korea to participate in nuclear policy, as exists in NATO.

A Chicago Council on Global Affairs poll showed that 26 percent of South Korean respondents ranked increasing South Korea’s prestige in the international community as the main reason for their support of nuclear weapons, similar in number to countering the North Korean threat (23 percent).REF

South Korean Presidential Statements Cause Controversy

In January 2023, President Yoon made a number of public nuclear-related statements that were at odds with his previous positions, U.S. policy, and the status of ongoing bilateral discussions. Yoon’s comments—subsequently walked back by his administration—triggered widespread media speculation of shifts in South Korean policy.

On January 2, Yoon appeared to deride U.S. extended deterrence as “the U.S. telling us not to worry because it will take care of everything. But now, it’s difficult to convince our people with just that.” He asserted that “we’re in talks with the U.S. about the concept of joint planning and joint exercises in terms of nuclear capabilities, and the U.S. is quite positive about it.” Yoon assessed that joint operation of nuclear forces would be “as good as nuclear sharing.”REF

President Biden, however, denied that a joint nuclear exercise was planned, since such exercises only occur between nuclear nations. The White House downplayed the misunderstanding but emphasized that Washington was looking at “enhanced information sharing, expanded contingencies and an eventual tabletop exercise” with Seoul.REF

Yoon has repeatedly claimed U.S. agreement to joint planning and joint execution of U.S. nuclear forces. However, during the November 2022 Security Consultative Meeting, the U.S. and South Korea agreed only to “strengthen the Alliance’s capabilities, information sharing, and consultation process, as well as joint planning and execution” without specifying that that applied to nuclear execution.REF The phrase was deliberately kept vague.

During a January 11 policy briefing, Yoon made his most explicit statement calling for the U.S. to return nuclear weapons to South Korea—the U.S. withdrew its arsenal in 1991—or for Seoul to develop its own weapons. Yoon remarked: “It’s possible that the [North Korean nuclear] problem gets worse and our country will introduce [U.S.] tactical nuclear weapons or build them on our own. If that’s the case, we can have our own nuclear weapons pretty quickly, given our scientific and technological capabilities.”REF

Yoon added that South Korea’s current policy was not to build nuclear weapons and that for now South Korea remained committed to the Non-Proliferation Treaty (NPT) and would deal with North Korea’s nuclear threat by strengthening its alliance with the United States.REF (Emphasis added.) The inherent conditionality of Yoon’s support for extended deterrence was also reflected in private discussions in Seoul.

After Yoon’s comments caused considerable angst among the South Korean public and U.S. government, the South Korean presidential office affirmed that there had been no change in South Korean policy.REF U.S. White House National Security Council spokesperson John Kirby responded that “the Republic of Korea has made clear that they are [sic] not seeking nuclear weapons” and that the two countries remained committed to strengthening extended deterrence capabilities.REF

Realizing the impact of his statements, Yoon backtracked on January 19 and reiterated that South Korea’s “realistic and rational option is to fully respect the NPT regime,” and that he is “fully confident about the U.S.’s extended deterrence.” He repeated that Seoul was planning “stronger joint planning and joint execution in operating the U.S. nuclear assets on the Korean Peninsula.”REF

Affirming the message, Minister of Unification Kwon Young-se commented on January 29 that discussing a South Korean nuclear program was “inappropriate,” as was questioning the U.S. commitment to defend South Korea. He warned of the economic consequences for South Korea if it breached the NPT. Kwon also downplayed redeploying U.S. nuclear weapons to South Korea since, regardless of “wherever the [U.S.] nuclear weapons are on the peninsula or anywhere nearby using such a weapon to punish [North Korea] won’t take much time.”REF

Foreign Minister Park Jin similarly affirmed that Seoul was seeking to strengthen U.S. extended deterrence to ease public concerns. Park emphasized that it was necessary to “establish a mechanism for a more tangible U.S. extended nuclear deterrence” by discussing implementation plans “in more detail [and] in close coordination with us.”REF

Yoon Has a History of Contradictory Nuclear Policy Remarks

Yoon Suk Yeol, as both candidate and president, has been inconsistent on South Korea’s nuclear policies, repeatedly jumping back and forth between both sides of the fence. In September 2021, during the presidential campaign, Yoon said he would demand that the United States redeploy its tactical nuclear weapons to South Korea and agree to a nuclear-sharing program, though he would not push for a South Korean nuclear armament.REF He subsequently said that he opposed redeploying U.S. tactical nuclear weapons and a nuclear-sharing agreement with the U.S.REF

After becoming president, Yoon commented in October 2022 that he was “weighing the option” of redeploying U.S. tactical nuclear weapons. Later that month, senior Yoon administration officials reiterated that redeployment of U.S. tactical nuclear weapons and a NATO-style nuclear-sharing agreement were off the table.

Defense Minister Lee Jong-sup, Unification Minister Kwon Young-se, and Foreign Minister Park Jin all indicated that the Yoon administration was not considering any of the nuclear options. Minister Kwon, a four-term National Assembly member, emphasized that South Korea’s “nuclear armament, the redeployment of U.S. tactical nuclear weapons and nuclear sharing arrangements do not represent the ruling party’s official stance.”REF

Discerning Yoon’s Motives. U.S. experts and officials debate whether President Yoon has simply repeatedly misspoken, is playing to domestic constituencies and public opinion, or is deliberately trying to pressure the United States to be more forthcoming in nuclear support to South Korea.

Yoon has a free-wheeling speaking style when giving unscripted remarks. He has often made comments that had to be subsequently corrected by South Korean officials. His impromptu informal press briefings were canceled after they repeatedly led to faux pas and caused problems for his administration.

Yoon is not well-versed in military or foreign policy issues, having spent his career as a prosecutor. Yoon may have overstated consensus in bilateral behind-the-scenes discussions or misused nuclear terms that have very precise meanings in the U.S. government lexicon. Some comments by the president during media interviews were in a vague hypothetical future context.

Yoon has also played to public opinion on other issues, which led to remarks that are at odds with stated South Korean policy. He could be seeking to send strong signals to North Korea and China while mollifying strong public demand that Seoul pursue a more independent nuclear course from Washington.

Yoon may also be deliberately taking provocative policy stances as an implicit threat to force the United States to accept greater South Korean involvement in U.S. nuclear planning, decision-making, or even delivery of U.S. nuclear weapons. He could also be laying the marker for future changes in South Korean policy if the security situation deteriorates further or Washington is not perceived as sufficiently strengthening extended deterrence.

Former South Korean officials, non-government experts, and the general public are far more adamant about advocating nuclear options than the Yoon administration, though private discussions in Seoul suggest a range of views within government.

A February 2022 survey by the Chicago Council on Global Affairs reported that 71 percent of South Korean respondents supported the development of a domestic nuclear weapons program.REF A Gallup Korea poll conducted in late 2022 showed that 76.6 percent of respondents favor South Korea developing nuclear weapons. Only 51.3 percent of those polled believed that the United States will demonstrate extended deterrence to defend Seoul in case of contingencies on the Korean Peninsula.REF

Other polls, however, show reduced public support when additional information is provided, including potential costs and risks of U.S. redeployment of tactical nuclear weapons or of obtaining nuclear capabilities.REF

Yoon’s statements are unhelpful to ongoing bilateral discussions and relations with Washington. By playing to populist sentiments to pressure the U.S., Yoon is inciting the public to expect more than Washington may be willing to deliver. U.S. policymakers are faced with the dilemma of whether to dispute Yoon’s misstatements, which could reinforce national resentment against Washington for constraining its ally.

Consequences of a South Korean Nuclear Program

South Korea developing nuclear weapons could have devasting economic effects on its civilian nuclear industry and national economy. During the presidential campaign, Yoon had vowed to reverse predecessor Moon Jae-in’s policy to move away from nuclear energy in response to the 2011 nuclear disaster in Japan. Yoon instead promised to “reinvigorate the nuclear-energy industry by reactivating suspended atomic power plants and resuming building new ones.”REF

South Korean nuclear weapons would violate the NPT or require Seoul to withdraw from the agreement. Either action would require the NSG to curtail supply of fissile material to South Korea’s civilian nuclear energy program,REF which accounts for 30 percent of the country’s electricity. The NSG could also request the return of all previously provided fissile material. A weapons program would likely end South Korea’s export of civilian nuclear reactors. Seoul is nearing completion of a $20 billion civilian nuclear deal with the United Arab Emirates and recently signed an agreement for further nuclear cooperation.REF

South Korea imports all the uranium used for its civilian nuclear reactors and depends on other countries for enrichment services. It does not have a stockpile of uranium or weapons-grade plutonium nor fissile material enrichment or reprocessing facilities. Building nuclear weapons would require using existing civilian reactor fissile material and converting some of its reactors to produce weapons fuel, a process that could take at least two years to produce even a few bombs, let alone a credible nuclear deterrent.REF

An indigenous nuclear weapons program would violate the U.S.–South Korea bilateral nuclear cooperation agreementREF as well as the Atomic Energy ActREF and would strain relations with Washington. The U.S. provides its extended deterrence guarantee in return for South Korea not seeking its own nuclear weapons and remaining a signatory to the NPT.

To provide a viable deterrent against North Korea, Seoul would need to test a completed nuclear weapon to prove its design and fabrication and build a nuclear arsenal. The national government would likely face fierce resistance from local constituencies to hosting a nuclear test site. A nuclear test would also trigger the U.S. Glenn Amendment sanctions, which include prohibitions on foreign assistance; munitions sales and licenses; foreign military financing; government credits, guarantees, and financial assistance; U.S. support for multilateral financial assistance; private bank lending to the affected government; and exports of certain specific controlled goods and technology.

Nuclear weapons advocates have not yet addressed whether South Korean nuclear weapons would be integrated into the U.S.–South Korean Combined Forces Command (CFC) and Operations Plan 5015 (the allied strategic plan for a major conflict with North Korea). If so, South Korean nuclear weapons would still be subject to the National Command Authorities of both countries.

Seoul keeping its nuclear force separate from the integrated command structure would raise U.S. concerns about South Korea’s military concept of employment. South Korea developing nuclear weapons could lead to calls in Washington for the withdrawal of U.S. forces either due to anxiety of being drawn into South Korean escalatory actions or perceptions that Seoul could now go it alone since it no longer trusted the American commitment.

South Korean development of nuclear weapons mounted on offensive missiles that would be able to reach China would likely cause Beijing to retaliate with far more devastating economic sanctions than those imposed after Seoul’s 2016 decision to deploy the Terminal High Altitude Area Defense (THAAD) ballistic missile defense system. South Korean manufacturers suffered at least $7.5 billion in economic losses, and the South Korean tourism industry may have suffered as much as $15 billion in losses. Seoul could declare that its nuclear weapons were directed only at North Korea, as it did with THAAD, but Beijing would likely interpret it as part of a U.S.-led anti-China coalition.

South Korean boldness in defying China to build nuclear weapons would be at odds with Seoul’s past and ongoing timidity in refraining from criticizing Beijing’s human rights violations and sovereignty transgressions in the East and South China Seas. In joint statements with the United States, South Korea was willing to criticize Chinese actions but, unlike Japan and Australia, refrained from identifying Beijing as the perpetrator.REF

Similarly, South Korea’s Indo–Pacific Strategy released in December 2022 contained only one reference to China, and that was a positive depiction. By contrast, Japan’s National Security and Defense Strategies released the same month harshly and repeatedly criticized China.

Finally, an indigenous nuclear program of sufficient size to be a deterrent to North Korea would divert an enormous amount of South Korea’s defense budget away from critical requirements to duplicate an existing capability that the U.S. currently provides. Those defense funds would be better spent augmenting conventional force requirements and the bilateral plan for the transition of wartime operational command.

Redeploying U.S. Nuclear Weapons Does Not Enhance Deterrence

The redeployment of U.S. nuclear weapons to South Korean soil is counter-productive to deterrence. The ground-based weapons removed in the 1990s no longer exist in the U.S. military inventory. Today’s tactical nuclear weapons are mounted on mobile air-based and sea-based platforms, making them difficult for North Korea to find and target. To place them in a static underground bunker would degrade deterrence and heighten the risk of a North Korean pre-emptive attack on such high-value targets. Pyongyang has more weapons that could target nuclear storage sites in South Korea than if they were deployed further away. The difference in delivery time would be negligible.

Some have suggested that, if tensions on the peninsula should rise, the missiles could always be moved back to their mobile-launch platforms. But South Korean or U.S. officials might deem doing so during a crisis as “too escalatory” and, therefore, prevent it, thus increasing risk to the population.

Deployment of U.S. offensive nuclear weapons would likely trigger greater South Korean domestic protests and Chinese economic retaliation than the deployment of the U.S. THAAD missile defense system.

Washington’s Extended Deterrence Reassurance. As a sign of its unwavering commitment to its South Korean ally, the United States has a mutual defense treaty, an extended deterrence guarantee, years of presidential and senior officials’ pledges to fulfill its obligations, an integrated bilateral CFC, rotational deployments of strategic nuclear-capable assets to the peninsula, and 28,500 sons and daughters in uniform stationed in harm’s way.

This year marks the 70th anniversary of the creation of the U.S.–South Korean alliance. Washington can point to the names of 36,000 Americans carved into the Wall of Remembrance at the Korean War Memorial in Washington, DC, and the alliance forged in blood during the crucible of war as tangible symbols of America’s pledge to defend South Korea. Similarly, South Korea helped America in Afghanistan, Iraq, and Vietnam.

In response to the recent growing South Korean doubts over the extended deterrence guarantee, the U.S. has taken additional steps of reassurance. During the 54th bilateral Security Consultative Meeting between the U.S. and South Korean military leaders in November 2022, Secretary of Defense Lloyd Austin affirmed that the United States is prepared to use “the full range of its defense capabilities,” including nuclear, conventional, and missile defense capabilities and advanced non-nuclear capabilities, and that any nuclear attack against the United States or its allies and partners, including the use of non-strategic nuclear weapons, would result in the end of the Kim regime.REF

Secretary Austin highlighted the resumption of rotational deployments of U.S. nuclear-capable strategic assets to the Korean Peninsula, including the USS Ronald Reagan aircraft carrier and B-52 bombers, for the first time in four years. Washington pledged to further enhance these deployments in a timely, coordinated, and routine manner.REF

In line with this pledge, the U.S. Nuclear Posture Review (NPR) affirmed in October 2022 the modernization of the U.S. nuclear forces, tailored regional strategies, and enhanced consultative mechanisms. The NPR called for fielding flexible nuclear forces, including the capability to forward deploy strategic bombers, dual-capable fighter aircraft, and nuclear weapons to the region.REF

Secretary Austin and Minister of National Defense Lee pledged to further strengthen the alliance’s capabilities and readiness through information sharing, training, exercises, and consultation, as well as through joint planning and execution, to deter and respond to North Korea’s advancing nuclear and missile threats.REF

The two military leaders agreed to review existing bilateral coordination mechanisms, such as the Korea–U.S. Integrated Defense Dialogue (KIDD), the recently resurrected Extended Deterrence Strategy and Consultation Group (EDSCG), and the Deterrence Strategy Committee (DSC) to further strengthen extended deterrence.

The two countries have been revising the Tailored Deterrence Strategy (TDS) in response to North Korea’s growing nuclear weapons and missiles threats. To support this revision, the U.S. and South Korea will conduct tabletop exercises (TTX) in February and May 2023 to include a North Korean nuclear-use scenario. The results will be reflected in the new TDS to be completed by the end of the year. Defense Minister Lee assessed that South Korea will have a much larger say in how U.S. extended deterrence functions in the region than in the past.REF

The two TTX will examine specifics of U.S. strategy and strategic asset responses to the North Korean nuclear threat, imminent nuclear attack, and nuclear attack scenarios. The TTX in May will be held at the military-division level for the first time and “while the previous tabletop exercises were more of a strategic, policy-level framework, the one we are planning to hold in May will be far more concrete and substantive than the February programs.”REF

What Washington Should Do to Strengthen Extended Deterrence

The U.S. extended deterrence guarantee serves both to dissuade opponents and reassure allies. To be successful, it requires credible capabilities and unquestioned commitment, as well as convincing communication of that resolve. Effective reassurance requires unending and relentless effort, which can be undermined by either increased opponent threat or by declining allied confidence.

To augment deterrence against the growing North Korean threat and enhance reassurance to America’s allies, Washington must implement a comprehensive strategy of pragmatic nuclear policies, new nuclear coordination initiatives with its allies, robust military capabilities, and improved trilateral security coordination with Seoul and Tokyo. As part of this comprehensive strategy, Washington should:

Refuse to Abandon Denuclearization Policy. Eleven U.N. resolutions require North Korea to relinquish its weapons of mass destruction programs in a complete, verifiable, irreversible manner. U.S. renunciation of complete denuclearization as a policy objective, or formal recognition of North Korea as a nuclear state, would remove the legal authority for Washington and other nations to impose and enforce sanctions for Pyongyang’s violations of international agreements.

Such a policy shift would also undermine the NPT and contradict decades of U.S. nonproliferation policy as well as send a dangerous signal to other nuclear weapons aspirants that they can violate agreements and outlast international resolve to uphold them.

Were the U.S. to seek only to constrain rather than eliminate North Korean nuclear weapons, that would exacerbate allied concerns about the viability of the U.S. commitment to their defense, as would U.S. adoption of a “no first use” nuclear policy. Allies would worry that Washington might only seek to limit Pyongyang’s ICBMs that are capable of hitting the American homeland while allowing Pyongyang to retain hundreds of nuclear-capable short- and medium-range missiles. These concerns could increase calls in South Korea for an indigenous nuclear weapons program and greater reliance on pre-emption strategies.

Enhance Bilateral U.S.–South Korean Consultations on Nuclear Planning. While the U.S. has been forthcoming in bilateral discussions to allay South Korean concerns, Washington will need to be even more flexible to reassure its ally and to forestall Seoul from taking drastic measures. Seoul, however, must also understand the limits of what Washington is willing or able to do as well as the downsides of South Korean nuclearization.

Washington should discern which additional measures would enhance reassurance, pressing for detailed recommendations from South Korea. To date, Seoul has not articulated specific measures that would allay its concerns. U.S. officials should privately emphasize that South Korea abrogation of the NPT would have severe consequences, including for the alliance.

Initially, the U.S. will need to engage in nuclear education by providing more details on U.S. nuclear policy and strategy. Washington should also forthrightly describe the parameters and responsibilities of the NATO NPG, which are likely less than South Korea perceives them to be. The NPG does not engage in nuclear operations planning or nuclear targeting.

Establish a Bilateral Nuclear Planning Group. The U.S. and South Korea should create a bilateral mechanism to coordinate on extended deterrence policies, including nuclear planning, options, contingencies, combined exercises, and deployment of U.S. strategic assets. Washington should delineate procedures for including South Korea in crisis decision-making related to potential use of U.S. nuclear weapons.

While the U.S. could designate and empower an existing bilateral group as a nuclear consultative group, it seems that South Korea would perceive anything less than creating a new body with the NPG moniker—commensurate with the existing NATO entity—as insufficient.

Increasing South Korean involvement would be consistent with the U.S. Nuclear Posture Review, which pledged “stronger extended deterrence consultation emphasizing a cooperative approach between the United States and Allies in decision-making related to nuclear deterrence policy, strategic messaging, and activities that reinforce collective regional security.”REF

The U.S. is understandably reluctant to divulge information on highly sensitive nuclear topics. However, the U.S.–South Korean CFC is America’s most integrated command in the world and will someday be under the command of a South Korean general. It is subordinate to the Military Committee comprised of the National Command Authorities of both countries, including both presidents. The CFC has detailed operations and contingency plans, incorporating extensive South Korean forces, which presumably envisions North Korean nuclear weapons use and potential U.S. nuclear responses. Seoul should be aware of those scenarios.

Subsequently Multilateralize the U.S.–South Korea Nuclear Planning Group. Following creation of a bilateral NPG with South Korea, Washington should invite Australia and Japan to join as an additional means to incorporate U.S. allies in collectively addressing common threats to the Indo–Pacific region. Creating a new quadrilateral defense coordinating group would emphasize a cooperative approach between the U.S. and security partners in nuclear deterrence decision-making.

The U.S. might instead prefer initially to create a quadrilateral nuclear coordination group rather than a two-step process. However, given the far greater existing integration of U.S. and South Korean forces in the CFC, the more urgent requests from Seoul, and South Korean national pride, it would be better to first establish the bilateral group.

Augment the Size, Scope, Frequency, and Type of Combined U.S.–South Korean Military Exercises, Including U.S. Strategic Assets. Cancelling allied military exercises in 2018 led to a four-year degradation of allied deterrence and defense capabilities for no reciprocal North Korean military or diplomatic gestures. The resumption of combined exercises in 2022 was an important reversal to repair the damage. Washington and Seoul have committed to even higher training levels in 2023.

The U.S. and South Korea should consider a return to pre-2018 training levels a minimum requirement. Given the escalating growth in North Korean nuclear and missile forces, as well as the regime’s extensive conventional force provocations in late 2022, Washington should confer with Seoul on the parameters of a training regimen and deployment of U.S. strategic assets—including strategic bombers, dual-capable aircraft, and carrier strike groups—necessary to augment deterrence and reassure South Korea.

Fund the Nuclear Sea-Launched Cruise Missile (SLCM-N) and Its Accompanying Warhead to Accelerate Development of the Program. Fielding the SLCM-N would allow the United States to send a nuclear capability directly to the Indo–Pacific theater of conflict, as it would be deployed on attack submarines or surface ships. Compared to the low-yield submarine-launched ballistic missile, which is deployed on a strategic submarine far out at sea, the SLCM-N could be deployed directly to the region.REF As the United States does not currently base any nuclear weapons in the region, the SLCM-N would help to fill a gap in America’s nuclear deterrence capabilities and allied assurance commitments. Because it is sea-based, the SLCM-N can assure South Korea of the U.S. nuclear commitment without the need for basing nuclear weapons on the peninsula.

Last year, Congress rejected the Biden Administration’s decision to cancel the SLCM-N and provided funding to continue research and development for the program. Congress should now accelerate the program by funding it at the level necessary to move the program into development and field it by the end of the decade.REF The Administration should also be sure to clearly communicate to South Korea that this capability is underway, and that part of its reason for development is to improve extended deterrence.

Enhance Strategic Missile Defense of the American Homeland. If the United States can intercept North Korean missiles aimed at the homeland, it will not have to contemplate risking San Francisco to save Seoul. But North Korea’s growing ICBM force with potential multiple warheads, along with the ability to indigenously produce large transporter-erector-launchers for ICBMs, poses problems for American homeland missile defenses.

The United States currently has only about 44 ground-based interceptors. The Biden Administration currently plans to augment the force by fielding 20 of the Next Generation Interceptor (NGI), which will have advanced capabilities that can address North Korea’s advanced missiles more effectively. However, the Biden Administration should plan to purchase at least 64 NGIs so it can increase the capacity of the current force while replacing all the current ground-based interceptors with this advanced system. These improvements will enhance deterrence by decreasing North Korea’s confidence that its plan would succeed and will also thwart its efforts to decouple the United States from its allies.REF

Augment U.S. Regional Ballistic Missile Defense. Pyongyang’s expansion of tactical and submarine-launched missiles increases the threat to U.S. forces in the Indo–Pacific region that are critical for responding to contingencies on the Korean Peninsula. One way to improve regional missile defense is by building an advanced missile defense system on Guam to bolster the existing THAAD system on the island. Last year, Congress appropriated funds for the Guam Defense System, and the Defense Department began its development. Congress should continue to support this project with the goal of providing an initial capability on the island by 2024. Enhancing U.S. ability to defend the U.S. territory of Guam will further prevent North Korean efforts to decouple the United States from South Korea.

Coordinate Missile Defense with South Korea and Japan. At the November 2022 East Summit, the U.S., South Korea, and Japan agreed to share missile-warning data in real time to improve the identification, tracking, and targeting of North Korean missiles.REF This was a major political agreement that could lead to enhanced interoperability of allied missile defenses.

To date, South Korea has refrained from integrating its Korea Air and Missile Defense System with that of the U.S.–Japanese system due to lingering tensions with Tokyo over Japan’s occupation of the Korean Peninsula from 1910 to 1945. Depending on the manner and scope of implementing the recent political agreement, it could enable quicker, more efficient allied tracking, targeting, and intercepting of North Korean ballistic missiles.

Minimize Public Disagreement with Seoul. Any U.S. differences with South Korea over nuclear policies should be conveyed in private discussions. It would be counter-productive to the alliance to strongly refute President Yoon’s misstatements or to publicly warn of the penalties if Seoul were to develop nuclear weapons. It is not in the U.S. interest to have a bilateral rift with South Korea when the two countries are in alignment on a wide array of foreign and security policies.

What South Korea Should Do to Enhance Its Defense

As part of a comprehensive strategy Seoul should:

Develop a Strategic Messaging Strategy. President Yoon should choose his words more carefully when discussing extended deterrence and nuclear policy as well as refrain from comment on ongoing bilateral discussions. Yoon’s misstatements inadvertently suggested major shifts in South Korean defense policy and required both Seoul and Washington to address the resulting controversy.

After conclusion of a bilateral nuclear coordination agreement, the Yoon administration will need to play an active role in convincing the South Korean populace that Washington sufficiently strengthened extended deterrence so that an indigenous nuclear program or redeployment of U.S. nuclear weapons are unnecessary.

The Yoon administration should extensively engage with the National Assembly, media, non-government experts, and the public to explain the parameters of any new nuclear agreement. Seoul should also underscore the extent of existing alliance capabilities and coordination supporting South Korean national security, as well as the consequences of an indigenous South Korean nuclear program.

Upgrade Information Security. Before the U.S. shares extremely sensitive nuclear information, South Korea will need to improve its cybersecurity infrastructure, update its technology, and improve its practices. South Korea’s systems are perceived by U.S. officials as below NATO standards and more vulnerable to penetration.

In the past, North Korean cyberattacks have successfully targeted the U.S.–South Korean CFC, the South Korean Joint Chiefs of Staff, the Ministry of Defense, and the Defense Integrated Data Center where all South Korean defense information is stored.REF

Continue Enhancement of Missile Defenses. Seoul should continue deployment of its Cheongung II medium-range surface-to-air missile (SAM) and development of its long-range SAM (L-SAM) programs to augment existing Patriot and THAAD land-based missile defenses. The L-SAM successfully intercepted a ballistic missile for the first time in November 2022.REF Seoul should carry through on plans to deploy SM-6 missiles on its Aegis-equipped KDX-III destroyers to defend the country against North Korean submarine-launched ballistic missiles.

Strengthen Offensive Capabilities. Seoul should maintain ongoing efforts to procure additional advanced attack aircraft and develop missiles with larger payloads and ranges. President Yoon pledged to strengthen South Korean capabilities to implement the Kill Chain pre-emptive-attack strategy and the Massive Punishment and Retaliation strategy against North Korea. The Ministry of Defense announced plans to increase its inventory of land-, sea-, and air-based precision missiles, augment penetration and strike capabilities of special forces, and procure additional F-35 stealth fighter jets.REF

Affirm the Importance of Security Cooperation with Japan. President Yoon should continue his efforts to improve strained bilateral relations with Tokyo. Even absent resolution of contentious history issues, South Korea should expand military coordination with Japan to enable more effective responses to the North Korean military threat. In 2022, the U.S., South Korean, and Japanese navies conducted their first trilateral anti-submarine drills in five years as well as trilateral naval defense exercises to detect, track, and intercept North Korean ballistic missiles.

Washington, Seoul, and Tokyo should institute a “2+2+2” meeting of their defense and foreign ministers to address common security threats from North Korea and China. They should hold periodic trilateral meetings to facilitate greater coordination on foreign and security policies.

Seoul should also accept the necessity of Japan developing counter-strike capabilities to protect its territory and people. Being able to hold enemy targets at risk increases the price of any attack on Japan, thereby enhancing allied deterrence and regional stability while degrading an opponent’s attempts at coercion. A Japanese ability to “shoot the archer,” rather than intercepting all incoming arrows, would enhance allied capabilities to disrupt an opponent’s ability to conduct follow-on attacks and thereby reduce additional casualties and destruction.

Conclusion

The divergence between the U.S. and South Korea on extended deterrence mars what had been a near-complete alignment of policies following President Yoon’s inauguration. U.S. officials and Korea watchers in Washington had welcomed the change in South Korean administrations since Yoon brought pragmatic thinking on foreign and security policies. Yoon had declared that a strong alliance with the United States would be the basis for South Korea’s foreign relations with North Korea, Japan, and China.

The nuclear issue requires deft management by both sides. The U.S. must intensify trust-building efforts to assuage South Korean concerns. South Korea, in return, needs to manage public expectations about what is possible. If North Korea continues its provocative actions, President Yoon will face greater pressure to build an independent nuclear deterrent. Dissatisfaction with U.S. efforts to strengthen extended deterrence or any perceived wavering in America’s commitment to defend South Korea would intensify South Korean advocates’ calls for indigenous nuclear options.

If not handled well by both sides, the nuclear dispute risks causing tension in the alliance at a time when the two countries, along with other allies and partners in the Indo–Pacific region, need to be working closely together to address the growing North Korean and Chinese threats.

Bruce Klingner is Senior Research Fellow in the Asian Studies Center at The Heritage Foundation.