In 2021, the RAND Corporation and the Asan Institute produced a report, Countering the Risks of North Korean Nuclear Weapons (Bennett et al., 2021). One of the major counters to the risks mentioned in the title has been the U.S. nuclear umbrella, which is designed to assure the Republic of Korea (ROK) that the United States will handle North Korean nuclear weapon threats and relieve the ROK of a need for its own nuclear weapons. However, as the North Korean nuclear weapon threat has grown, polls in the ROK (Kim, Kang, and Ham, 2022) show that much of the ROK population is not feeling assured by the U.S. nuclear umbrella and instead favors the ROK developing its own nuclear weapons. In this report, we describe and evaluate options that the ROK and the United States could take to strengthen ROK nuclear assurance.
North Korea has been vastly expanding its nuclear weapon threat over the past ten years or so and apparently plans to accelerate this process in the future. North Korea has also adopted an extremely hostile campaign of threatening the ROK and the United States with nuclear attacks. China is also vastly expanding its nuclear weapon capabilities and is no longer trusted by most people in the ROK (“Koreans Distrust Chinese More Than Russians, Japanese,” 2022).
To counter these threats, the United States provides extended deterrence for the ROK and promises a nuclear umbrella to cover the ROK so that the ROK does not need its own nuclear weapons, the development of which could imperil the Nuclear Non-Proliferation Treaty. This treaty is the foundation of U.S. nuclear nonproliferation policy. The United States has based this nuclear umbrella on a high degree of strategic ambiguity in the belief that this ambiguity will achieve the most-effective deterrence of North Korean aggression.
For nearly seven decades, the U.S. nuclear umbrella was very assuring to the ROK. Now that North Korea poses a serious nuclear weapon threat to both the ROK and the United States, however, and as concerns have risen that the United States could abandon the ROK, many in the ROK are doubting the existing U.S. commitment and seeking more-concrete assurance (Yang, 2023). After all, the United States has not even formally defined the nuclear umbrella.
In short, a U.S. status quo approach to the ROK might lead to ROK development of nuclear weapons, which the United States clearly does not want. Avoiding this outcome could require the United States to face stark choices in changing policies to provide the ROK with nuclear assurance while still providing nuclear assurance to other allies and partners and dealing with the high-priority threats to the United States posed by China and Russia. Those trade-offs are beyond the scope of this report.
Thus, in this report, we take a descriptive approach to identifying the options that are available to both the ROK and the United States to adjust their policies and measures to enhance the strategic clarity of the U.S. nuclear umbrella. Doing so should reassure the ROK that the North Korean nuclear weapon threat can be managed without the ROK having to field its own nuclear weapons at potentially serious costs to the ROK, the United States, and the nonproliferation regime. The report identifies and provides some evaluation of strategy and policy options, force employment options, and nuclear force posture options for both today and in the coming decades. The potential implementation of some of these options has been included in the April 2023 Washington Declaration of U.S. President Joe Biden and ROK President Yoon Suk Yeol.
This report is a combined effort of the RAND Corporation and the Asan Institute. We start by looking at the nature of the North Korean and Chinese nuclear weapon threats and how North Korea and China might employ those threats. We do so using open literature that describes the quantities and qualities of the nuclear weapons, North Korean and Chinese statements, and previous RAND and Asan research.
We then develop the options for strengthening ROK assurance using our expertise that draws on statements of ROK and U.S. national security experts; knowledge of planned modernization efforts; and knowledge of nuclear forces, nuclear strategy, and nuclear force employment. We describe the feasibility and desirability of these options using open-source information.
We do not seek to be prescriptive but instead to describe options and their relative advantages and disadvantages. Only when an option has substantially greater disadvantages than advantages is that option dismissed.
Our examination of the North Korean and Chinese nuclear weapon threats to the ROK and United States lead us to conclude the following:
• North Korea has already established a nuclear weapon force that could pose an existential threat to the ROK and is on the verge of posing a serious threat to the United States. The North hopes to use its nuclear weapon threat to the United States to help break the ROK-U.S. alliance.1 The North also hopes to dominate the ROK without having to invade it.2
• China also poses very serious nuclear weapon threats to the ROK and the United States and will likely use its nuclear weapons as one means for influencing both countries.
• ROK assurance in the U.S. nuclear umbrella has faltered because of these growing threats and ambiguity in the U.S. commitment to ROK security, leading to increased calls for the ROK to develop its own nuclear weapons.
• Because of these developments, the level of strategic ambiguity of the U.S. nuclear umbrella is no longer appropriate for either deterrence or ROK assurance.
• President Biden responded to ROK concerns, in part those voiced by ROK President Yoon, by announcing the Washington Declaration with President Yoon in April 2023; the declaration promises greater strategic clarity. However, the Washington Declaration lacks the implementation details that are needed to truly increase ROK nuclear assurance. The declaration especially lacks details related to the creation of the Nuclear Consultative Group, which would be key to nuclear assurance.
• The United States could pursue strategic clarity akin to the efforts taken by the United States in NATO in the 1960s (McNamara, 1962).
• The United States could commit nuclear weapons to establish some level of parity against the growing, likely existential, North Korean nuclear weapon threat to the ROK. Doing so might avoid a future ROK government decision to produce its own nuclear weapon force.
• ROK nuclear weapon production could lead to international sanctions on the ROK that would seriously damage the ROK economy, cause tremendous political controversy and instability in the ROK and Northeast Asia, and increase global nuclear weapon proliferation, which would be problematic for both the ROK and the United States.
Options to Strengthen ROK Nuclear Assurance
The main function of this report is to present options to be considered for strengthening ROK nuclear assurance. The ROK and United States could implement the following options, which we list from those that would be the easiest to implement to those that would likely be more difficult to implement but have the greatest impact:
1. Implement a dynamic and capable NCG, which could be assisted by a team of strategic advisors, to bring strategic clarity to the U.S. nuclear umbrella extended to the ROK.3
2. Educate ROK and U.S. national security personnel on the implications of the North Korean nuclear weapon threat and what can be done about it.
3. Develop more ROK public awareness of the North Korean nuclear weapon threat and the actions that are being taken to counter it. This option could also better explain the serious risks and potential downsides of ROK nuclear weapon development.
4. Shift the focus of conflict planning in the Combined Forces Command to dynamic planning with conventional-nuclear force integration. The Combined Forces Command could use regular tabletop exercises to assist in strategy formulation, which would enhance both defensive and offensive efforts against North Korean nuclear weapon use and thereby strengthen deterrence of that use and ROK nuclear assurance.
5. Establish ROK and U.S. nuclear weapon employment guidelines, exploit the regular tabletop exercises, and seek ROK and U.S. National Command Authority approval of the guidelines.
6. Use a full variety of information, economic, and military coercive measures to induce a North Korean nuclear weapon and critical nuclear material production freeze.
7. Commit some U.S. nuclear weapons to support ROK security. The ROK and United States could use an approach with a four-step, sequential process to establish a degree of parity with the North Korean nuclear weapon threat and seek a North Korean nuclear weapon production freeze.4 This family of options is designed to political turmoil that might otherwise accompany U.S. nuclear weapon deployments in the ROK.5 The process involves the following four steps:
a. Modernize or build new U.S. tactical nuclear weapon storage in the ROK.
b. Dedicate all or part of the nuclear weapons on a U.S. ballistic missile submarine
operating in the Pacific to targeting North Korea.
c. Modernize approximately 100 U.S. tactical nuclear weapons—which the United States
otherwise plans to dismantle—at ROK expense. These weapons could then be stored
in the United States but would be committed to supporting the ROK
and rapidly deployable to the ROK.
d. Deploy a limited number of U.S. tactical nuclear weapons to the ROK to be stored
in the prepared nuclear weapon storage facilities.
Option 7, which we characterize as being the most difficult to implement but likely having the greatest impact on ROK nuclear assurance, could be implemented slightly differently from what is proposed here depending on specific ROK and U.S. government requirements. But, if implemented roughly as described, this option could commit up to about 180 U.S. nuclear weapons to ROK security in the next few years; perhaps eight to 12 B61 nuclear bombs could be deployed in the ROK for both symbolic and operational purposes. If ROK and U.S. threats to implement these steps fail to lead to a North Korean nuclear weapon production freeze—failure that we unfortunately expect—further commitments of U.S. nuclear forces in future years could sustain the appearance of nuclear weapon parity with North Korea and avoid the appearance that the ROK needs to produce its own nuclear weapons.
About This Report
Figure and Tables
CHAPTER 1. Introduction
The U.S. Nuclear Umbrella for the ROK
Contrasting Nuclear Deterrence and Nuclear Assurance
Some Issues for Assurance and Deterrence
Organization of This Report
CHAPTER 2. Why the ROK Needs Greater Nuclear Assurance
The North Korean Threat
The Chinese Threat
ROK Interest in Strong Assurance
Other Issues That Challenge ROK Assurance
CHAPTER 3. Policy and Strategy Options
Organizing the Nuclear Consultative Group
Preparing the ROK and United States: Education on Nuclear Weapon Issues
Reassuring the ROK on U.S. Extended Deterrence
Reining In the North Korea Nuclear Weapon Program
CHAPTER 4. Employment Planning and Execution Assurance Options
Developing a Common View of the North Korean Threat
Improving the Nonnuclear Force Balance, Countering the North’s Nuclear Shadow
Creating Defenses Against North Korean Nuclear Weapon Use Nuclear Warfighting
Obtaining ROK Government Approval of U.S. Nuclear Weapon Employment
Improve ROK and Japanese Defense Cooperation and Planning
CHAPTER 5. Nuclear Weapon Force Assurance Options
Potential Nuclear Weapon Commitment Options
Deploying U.S. Strategic Weapon Systems to the Peninsula
Explaining U.S. Nuclear Weapon Availability and Safety
CHAPTER 6. ROK Nuclear Assurance in Changing Conditions
Strengthening ROK Nuclear Assurance Before North Korea Creates a Large Nuclear
Nuclear Weapon Force Commitments to the ROK Against a Large North Korean Nuclear
Conclusions on the Future Nuclear Weapon Force Options
APPENDIX. Nuclear Damage Assessment
Calculating Potential Fatalities and Serious Casualties
The Report is a product of joint research between the Asan Institute for Policy Studies and RAND Corporation.
- 1. As described in the report, North Korea apparently hopes to undermine the U.S. nuclear umbrella by threatening nuclear attacks on the United States if the United States uses its nuclear weapons to retaliate against North Korean nuclear weapon attacks on the ROK.
- 2. A 2023 ROK poll indicates that, when nuclear weapons are included, a significant plurality find North Korea to be militarily superior to the ROK (Lee et al., 2023, pp. 56–58). A 2023 U.S. National Intelligence Estimate argues that the North is highly likely to use this superiority for coercion to “yield political, economic, or military benefits” (National Intelligence Council, 2023). Thus, this dominance would take the form of the ability to coerce the ROK into actions wanted by North Korea rather than North Korean occupation and strong control of the ROK.
- 3. President Yoon has been very clear that he thinks strategic clarity is needed to strengthen ROK nuclear assurance. In early 2023, he argued that the “nuclear weapons belong to the U.S., but the planning, information sharing, exercises and training should be carried out jointly by South Korea and the U.S.” (Lee H., 2023a).
- 4. This four-step process uses some of the principles the United States used to prevent North Atlantic Treaty Organization nuclear proliferation beyond the United Kingdom and France and adds some new ideas.
- 5. For example, rather than the United States immediately deploying tactical nuclear weapons in the ROK, this stepwise approach is designed to demonstrate, especially to the Chinese and to ROK progressives, the rationales for countering the North Korean nuclear weapon buildup and the patience and moderation being shown by the ROK and United States.