Preparing for and countering limited nuclear attacks in East Asia: Guardian Tiger III

Considering biases in cases of limited nuclear attack

Limited nuclear attack is a topic uniquely vulnerable to bias. Project research trips and the tabletop exercise both revealed deep-seated organizational and cognitive biases that obstruct or distort preparation for an LNA, particularly in the North Korea case. There isn’t even an agreed-upon definition of an LNA, and there is a lack of consensus on the appropriate response to one. Biases thrive in this type of probabilistic, low-information environment where it is necessary to rely on inference and heuristics to make time-sensitive judgments under pressure. The resulting biases lead to preparations, policies, and postures that might be reassuring to the United States and its allies but are suboptimal operationally, generate risk, and could constrain options. Bias might therefore be the biggest obstacle to preparing for and responding to an LNA effectively. The following are three key effects.

• • Participants in the TTX generally neglected the potential advantages and viability of damage mitigation and consequence management in preparing for an LNA. This might be due, in part, to the effects of biases such as hyperbolic discounting (the tendency to prefer immediate payoffs relative to later payoffs) and availability heuristic (the tendency to overestimate the likelihood of events that are more accessible in memory).
  • Participants in the TTX misinterpreted adversary beliefs, perceptions, and risk-reward assessments and their change over time. This might be due, in part, to biases such as mirror imaging (projecting one’s own values when striving to understand another’s behavior), confirmation bias (the tendency to focus on information in a way that confirms one’s preconceptions), and a failure to understand loss aversion (people are more motivated to avoid losses than to acquire gains).
  • Cultural and organizational biases such as plan continuation bias (failure to recognize that the original plan of action is no longer appropriate for a changing situation) and anchoring bias (the tendency to rely too heavily on one trait or piece of information when making decisions) undermine analysis and exacerbate preexisting cognitive bias. For example, even when briefed with authoritative assessments of nuclear effects or adversary nuclear policy that contradict assumptions, leaders might not change their beliefs, plans, or intentions.

Another major finding from the TTX was that it was uncommon for one bias to operate in isolation. Instead, the effects of individual biases were often lumped together. This had the effect of compounding, and sometimes even disguising, their unwelcome influence on analytic and decision processes.

Recognizing that cognitive and organizational biases exist, and accounting for them when developing and executing actions, can be key for enabling preparation for an LNA. Mitigating the effects of said biases related to LNA can help analysts and leaders: better identify advantages of mitigation and consequence management; improve understanding of adversary risk and reward calculus; and devise better countermeasures to an LNA.

Many key findings from this report react to and compensate for biases discussed in this appendix. For example, overcoming normalcy bias is essential for developing a deeper and broader understanding of the risks of LNA (see Key Finding 1). Additionally, overcoming confirmation bias is a necessary precursor for increasing resilience to the psychological and political effects of an LNA (see Key Finding 2). Finally, overcoming hyperbolic discounting and zero-risk biases is needed to prioritize damage mitigation and disaster response (see Key Finding 4). This is not a comprehensive list; a more detailed discussion follows below.

The remainder of this appendix contains background on how bias affects national security considerations and proceeds to spotlight three key areas that emerged as bias vulnerabilities for LNAs, including: neglect of risk management, misinterpretation of adversary assessment of risk and reward, and organizational and cultural bias.

Background on bias

Cognitive bias is caused by heuristics, which are mental shortcuts that help us make sense of a messy and complicated world. These mental shortcuts are usually helpful and almost always invisible. They are most frequently associated with subconscious cognitions and snap judgments, but they can also affect slow, deliberate, and effortful cognition.¹Tess M. S. Neal, Pascal Lienert, and Emily Denne, “A General Model of Cognitive Bias in Human Judgment and Systematic Review Specific to Forensic Mental Health,” Law and Human Behavior 46, 2 (2022), 99–120, https://psycnet.apa.org/doiLanding?doi=10.1037%2Flhb0000482. Awareness of the bias does not necessarily help with mitigating the effects. Even top specialists, including medical and forensic experts, are subject to the effects of bias. However, empirical studies have proven that a few tradecraft techniques make a meaningful difference.

Biases are relevant for national security because no matter what the strategic objective is—from a de-escalation approach to an overwhelming kinetic response—success ultimately boils down to the adversary’s interpretation. For example, if the goal is to restore deterrence, it is worth emphasizing that deterrence is essentially a psychological state within the adversary’s mind: a belief that the cost of a given action outweighs its benefits. Similarly, restraint and proportionality will only succeed if the enemy agrees that the given response is indeed proportional and restrained. Last, an overwhelming and decisive response will only send the appropriate signal if the adversary’s perception aligns with the intention.

Critically, the adversary might view threat, risk, and reward differently than the observer. And biases do not discriminate. They impact perceptions, judgments, and decisions for all players throughout the decision space, including analysts, officials, political leaders, and the general public in all the relevant countries, including one’s own country, allies, and adversaries.

The mental models of many, if not most, practitioners of deterrence rely on states acting rationally under conditions of immense pressure and stress.²Bradley A. Thayer, “Thinking about Nuclear Deterrence Theory: Why Evolutionary Psychology Undermines Its Rational Actor Assumptions,” Comparative Strategy 26, 4 (2007), 311–323, https://www.tandfonline.com/doi/full/10.1080/01495930701598573?needAccess=true. This conception is increasingly at odds with the evidence. The important insights that come out of social psychology are that humans are not always rational actors and rationality cannot be understood apart from the quirks of human psychology.³Robert Jervis, Perception and Misperception in International Politics: New Edition (Princeton, NJ: Princeton University Press, 2017), https://press.princeton.edu/books/hardcover/9780691177434/perception-and-misperception-in-international-politics?srsltid=AfmBOoojQ3CdKvK__nmgcnlL3bOdJ85ejcNFRBrD8cbfE0tBAq9aqf_Q. And while there are scholars and practitioners seeking to use these insights to retool the conceptual foundations of deterrence dynamics, there are no agreed-upon systemic solutions to integrate a more nuanced understanding of human psychology.⁴Beyza Unal, Yasmin Afina, and Patricia Lewis, “Perspectives on Nuclear Deterrence in the 21st Century,” Chatham House, April 20, 2020, https://www.chathamhouse.org/2020/04/perspectives-nuclear-deterrence-21st-century-0/human-rationality-and-nuclear-deterrence. The fallout is that careful, systematic, and anticipatory review is needed to shine a light on the areas most affected. This appendix is one such effort.

A prior Defense Threat Reduction Agency-sponsored study in this series found a variety of cognitive and organizational biases that inhibit US and allied assessment of Chinese intervention in Korean Peninsula contingencies.⁵Jonathan Corrado, “Biases Blind Us to the Risk of Chinese Military Intervention in Korea,” Atlantic Council, August 12, 2023, https://www.atlanticcouncil.org/in-depth-research-reports/issue-brief/biases-blind-us-to-the-risk-of-chinese-military-intervention-in-korea/. Findings from that study include the following.

• Mirror imaging prevents US analysts from understanding Beijing’s beliefs, threat perception, and risk tolerance when it comes to Korea. The United States and China both find the status quo in Korea to be an uncomfortable yet ultimately tolerable compromise, but any tip in the balance could prompt Chinese policymakers to take a risk by interceding (loss aversion and prospect theory).
• Some analysts suspect that conflict with China over Korea is unlikely because it has not happened since the Korean War (availability heuristic and oversensitivity to consistency).
• Organizational barriers between the conventional and strategic domains, and between regional combatant commands, lead analysts to overlook vertical and horizontal escalation risks (law of the instrument bias: using readily available tools rather than designing a solution based on the specifics of the situation). Finally, some biases work at cross purposes but are nonetheless simultaneously held by different parts of the US government. For example, while some believe that China can or will intervene and solve the problem on terms acceptable to the United States (optimism bias), others believe that no Chinese role can be acceptable (hostile attribution bias).

Biases contributing to the neglect of risk management

One major finding of the TTX is that participants generally neglected the importance of damage mitigation and disaster response in responding to and preparing for LNAs. Discussions about retaliatory strikes and alliance politics overshadowed efforts to prepare and modify military installations and posture to add resilience against further attacks and improve the ability to protect and assist the civilian population dealing with a nuclear threat. A few cognitive biases created misconceptions that pushed the conversation in this direction.

• Hyperbolic discounting is the tendency to prefer immediate payoffs relative to later payoffs. In the TTX, participants seemed to derive greater psychological satisfaction from extracting a pound of flesh via retaliatory strikes compared to the relatively unsatisfying process of damage mitigation and disaster response. These less flashy and more internal-facing measures are not immediately gratifying because the urgency of their need is not immediately apparent. There is also a political cost associated because these measures could look like a policy failure and it takes time to recognize success.
• Availability heuristic is the tendency to overestimate the likelihood of events with greater availability in memory. Because an LNA has never happened before, participants underplayed the likelihood of an additional LNA after the first one. They therefore focused more on restoring deterrence rather than preparing for a protracted conflict (this also displayed normalcy bias, optimism bias, and plan continuation bias).
• Zero-risk bias is the preference for reducing a small risk to zero over a greater reduction in a larger risk. Participants framed the discussion in such a way as to avoid confronting the larger risk of escalation via additional nuclear attacks. Instead of prioritizing the escalation potential and taking appropriate immediate actions to mitigate and reduce harm and damage, participants reframed the problem to reduce risk potential by projecting confidence in the success of their countermeasures to achieve the restoration of deterrence. This naturally led them to de-emphasize the importance of more immediate measures in their considerations.
• Scope insensitivity is the tendency to misinterpret the size of the problem. As mentioned in Key Finding 2, even national security experts and officials are subjected to exaggerated fatalism about nuclear escalation and nuclear effects. In the aftermath of an LNA, confirmation bias and scope insensitivity could undercut efforts to analyze the effects, and framing effect and plan continuation bias could undermine the response.

Misinterpreting adversary assessment of risk and reward

Participants in the TTX demonstrated a misunderstanding about how the situation and adversaries’ risk profiles were actively developing over time.

People perceive risk differently depending upon the situation. Any sports fan or gambler will tell you that people tend to take more risks when they are suffering losses. This flows from a bias called loss aversion. The pain of a loss is felt more acutely than the thrill of a gain. In matters of war and peace, this means that states facing losses—be they political, territorial, economic, or personal—could be more willing to embrace risky solutions. This might not be intuitively obvious to partners and adversaries, who might even assume the opposite: that a loss-fraught environment will induce more cautious decision-making.

• US participants split into three Blue Cells: interagency, national military and defense, and theater military. Allied participants split into three Green Cells: South Korea, Japan, and United Nations Command (UNC) key sending states. A Red Cell represented North Korea, and two Orange Cells represented China and Russia.
• There was disagreement within and among the Blue and Green Cells about how facing losses would affect Kim’s calculus. Loss aversion bias and prospect theory suggest that individuals facing losses become more risk acceptant. Perhaps due to this, some Blue and Green Cells’ recommendations that were designed to escalate to de-escalate, such as a strike on Kim’s Wonsan Villa, ended up exacerbating the problem. This was a particularly stubborn bias. Early in the TTX, members of the control team alerted the participants to the effect of loss aversion bias; nonetheless, this did not seem to affect the discussion.
• As the TTX continued, Blue Cell participants struggled with Red and Orange Cell intentions. Blue Cell recommendations were designed to entice Pyongyang and Beijing with a return to the status quo. A Red Cell participant noted the United States was mistaken because establishing a new normal had become more attractive and attainable. Blue Cell participants therefore demonstrated mirror imaging bias, illusion of asymmetric insight, illusion of transparency, and optimism bias.
• At times, Blue, Green, Red and Orange Cells interpreted the same events very differently, leading to more divergent perceptions that exacerbated the challenge of understanding adversary intentions, signals, and behaviors. The Blue Cell based some of its proposed countermeasures on faulty projections of Red Cell perceptions and beliefs. For example, the strike on Kim’s villa and other threats to induce capitulation showed evidence of mirror imaging, confirmation bias, and hot-cold empathy gap.

Institutional and cultural biases

In the TTX, the Blue Cells all identified the restoration of deterrence as a key objective. However, they struggled to break out of a reactive, tit-for-tat posture that prioritized retaliation over consequence management, risk reduction, and assurance. There is a uniquely US version of action bias discussed by Richard Neustadt and Ernest May in their seminal work Thinking in Time: “Americans in public life have been habituated by national history . . . to ‘can do’ beliefs. Anything we seek we can accomplish; implementation follows automatically from decision, assuming enough will.”⁶Richard E. Neustadt and Ernest R. May, Thinking in Time: The Uses of History for Decision-makers (New York: First Free Press, 1988). In the TTX, this bias inspired confidence in a can-do attitude and prioritized solutions that came from US initiative rather than that of adversaries. In the TTX, it contributed to a retaliation-centric strategy that sought the restoration of deterrence but ended up degrading it. Hyperbolic discounting (valuing short-term gains over longer-term ones) might have also played a role. The Blue Cell participants’ unwillingness to communicate and compromise with Red and Orange Cell participants might have stemmed from hostile attribution bias. Red and Orange Cell participants said the Blue Cell rejected their proposals out of hand and refused to negotiate in good faith even when presented with solutions that reduced risk. Zero-risk bias might have also played a role.

• Multiple participants attested to the fact that the declaratory policy shrunk the analysis within constraints that obscured ideal solutions. This is an example of framing bias and anchoring bias. Similarly, one Blue Cell participant said the tendency to fall back on a framework of high-, medium-, and low-risk damage assessment options obscured a more assessment-grounded analytic process.
• Last, one Blue Cell participant said that the TTX revealed how the United States is struggling to cope with the fact that the US–South Korea alliance might no longer have escalation dominance in Korea. This is perhaps a form of plan continuation bias (continuing to apply an old framework after it loses its relevance).

In addition to the top priority recommendations identified above, the following are additional actions we recommend to address the key findings.

• Additional hardened in-theater aircraft shelters: The DTRA—supported by USSTRATCOM and in concert with USPACOM, USFK and USFJ—should identify viable options for adding additional hardened in-theater aircraft shelters that can accommodate dual-capable fighter aircraft to enhance resilience during a conflict​. Distributing the additional hardened aircraft shelters across multiple in-theater air bases would add greater agility and complicate adversary planning and targeting, while also enhancing deterrence.
  • Such shelters would provide additional options to policymakers and military commanders for either rotational deployments during peacetime or contingencies during a crisis or conflict. The various options—such as hardened aircraft shelters for F-35A aircraft carrying B61-12 bombs—would depend on threat perceptions and political considerations, but the political considerations for hardened aircraft shelters in allied countries would likely be less significant than for dual-capable aircraft themselves—and likely less than for actual nuclear weapons.
• In-depth study of implications of modified or newly fielded weapons systems: US Pacific Command—supported by DTRA—should lead an in-depth study regarding the potential implications of modified or newly fielded weapons systems in the Indo-Pacific, such as an SLCM-N or a modified version of the F-35B aircraft to internally carry B61-12 bombs. This would include assessing how such systems could provide additional options to policymakers and military commanders during an LNA-related crisis or conflict.
  • For SLCM-N, this would involve how it could provide in-theater LNA-related options, given the stealth of its launch platform, without the political considerations of positioning more visible nuclear attack platforms such as in-theater dual-capable aircraft. It would also provide messaging options regarding what (and how much) information to publicly reveal regarding such capabilities being positioned in theater.
  • For the “B” variant of the F-35 aircraft, its short take-off and vertical landing (STOVL) capability would provide additional positioning options for dual-capable aircraft in theater beyond the limitations of air bases with traditional-length runways, which would complicate adversary targeting of US DCA and reduce their perceived vulnerability to LNA.
• Improve US and allied interoperable missile and anti-drone defenses: The United States should work with allies to develop and field improved capabilities to defend against missile and drone attacks, to include new technologies, expanded force structure, improved posture, interoperability of systems, and magazine depth of interceptors.
• Partner with allies regarding declaratory policy: The United States should work with allies to develop frameworks and terminology for assessing LNA and considering parameters of response and how these relate to declaratory policy, to include potentially adjusting declaratory policy to focus on holding individuals accountable rather than the whole regime.
• Model nuclear effects: DTRA should lead an effort to ensure releasable capability to rapidly characterize and model nuclear effects in the immediate aftermath of an LNA sufficient to inform US and allied political leaders and publics.
• Understand effects perceptions: Designated US government-supported or contracted organizations should conduct surveys to better measure shortfalls and misperceptions in US and allied civilian and military personnel’s understanding of nuclear weapons effects and their fears, to better focus psychological preparation and resilience measures.
• Encourage allied activities: US government and military organizations conducting activities to prepare and train for LNA should include allied participants or observers as much as possible, and should enable and encourage allies to repeatedly include nuclear attack scenarios (or at least radiological threats) and civilian consequence management in their own tabletop exercises, civil defense drills, and military and civil exercises.
• Build allied capacity: The State Department should lead an effort to encourage and enable allied capacity building and international cooperative measures that would be applicable in disaster scenarios and LNA consequence management.​
• Work with Republic of Korea (ROK) STRATCOM: Led by USFK, the United States should work with ROKSTRATCOM to integrate its capabilities into future alliance exercises and response approaches, even outside of nuclear attack scenarios.
• Leverage training for multiple adversaries: US military and government organizations should leverage training and preparation for a North Korean LNA as opportunities to also enhance preparedness and deterrence against an LNA by China or Russia, and vice versa.
• Ensure preparations: US military and government organizations should ensure that preparations for nuclear consequence management and risk mitigation are already in place or require little additional decision-making and analysis during crisis—ideally pre-delegated authorities to execute preparations once conflict begins or nuclear escalation appears imminent.
• Work with allies on consequence management: Led by the State Department and the United Nations Command (UNC), US government and military organizations should coordinate with South Korean and Japanese counterparts to prepare, exercise, and plan rapid international interagency, local government, and nongovernmental organization contributions, particularly from United Nations Sending States, to support consequence management in the event of an LNA.

These theoretical and historical references provided foundational background for this study.

Gerald Brown, “Conflict and Competition: Limited Nuclear Warfare and the New Face of Deterrence,” Global Security Review, December 16, 2019, https://globalsecurityreview.com/conflict-competition-limited-nuclear-warfare-new-face-deterrence/.

Michael E. Brown, “Deterrence Failures and Deterrence Strategies,” RAND, 1977, https://www.rand.org/pubs/papers/P5842.html.

Kai He and Huiyun Feng, Prospect Theory and Foreign Policy Analysis in the Asia Pacific (London: Routledge, 2017), https://www.routledge.com/Prospect-Theory-and-Foreign-Policy-Analysis-in-the-Asia-Pacific-Rational/He-Feng/p/book/9781138107939.

Van Jackson, Rival Reputations: Coercion and Credibility in US-North Korea Relations (Cambridge: Cambridge University Press, 2016), https://www.cambridge.org/core/books/rival-reputations/F8A225F88C98E9B93670622EA3BC95A1.

Robert Jervis, “Deterrence Theory Revisited,” World Politics 31, 2 (1979), 289–324, https://www.jstor.org/stable/2009945.

Daniel Kahneman and Amos Tversky, “Prospect Theory: An Analysis of Decision under Risk,” Econometrica 47, 2 (1979), 263–292, https://www.jstor.org/stable/1914185.

Jeffrey A. Larsen and Kerry M. Kartchner, eds., On Limited Nuclear War in the 21st Century (Palo Alto, CA: Stanford Security Studies, 2014), https://www.sup.org/books/politics/limited-nuclear-war-21st-century.

Antoine Levesques, Desmond Bowen, and John H. Gill, “Nuclear Deterrence and Stability in South Asia: Perceptions and Realities,” International Institute for Strategic Studies, May 2021, https://www.iiss.org/globalassets/media-library—content–migration/files/research-papers/nuclear-deterrence-and-stability-in-south-asia—perceptions-and-realities.pdf.

Jack S. Levy, “When Do Deterrent Threats Work?” British Journal of Political Science 18, 4 (1988), 485–512, https://www.jstor.org/stable/193882.

Keir A. Lieber and Daryl G. Press, “Coercive Nuclear Campaigns in the 21st Century: Understanding Adversary Incentives and Options for Nuclear Escalation,” US Naval Postgraduate School, January 2013, https://calhoun.nps.edu/bitstream/handle/10945/34337/nps08-040813-01.pdf.

John J. Mearsheimer, Conventional Deterrence (Ithaca, NY: Cornell University Press, 1985), https://www.cornellpress.cornell.edu/book/9780801493461/conventional-deterrence/#bookTabs=4.

Jerry Meyerle, “Nuclear Weapons and Coercive Escalation in Regional Conflicts: Lessons from North Korea and Pakistan,” Center for Naval Analyses, November 2014, https://apps.dtic.mil/sti/tr/pdf/ADA614958.pdf.

Vipin Narang, Nuclear Strategy in the Modern Era: Regional Powers and International Conflict (Princeton, NJ: Princeton University Press, 2014), https://press.princeton.edu/books/paperback/9780691159836/nuclear-strategy-in-the-modern-era.

T. V. Paul, Asymmetric Conflicts: War Initiation by Weaker Powers (Cambridge: Cambridge University Press, 2011), https://www.cambridge.org/core/books/asymmetric-conflicts/3A02638851E475FC15F2C6C608638A0B.

Shane Praiswater, “Strategies of Limited Nuclear War with Modern Authoritarians” in Sarah Minot Asrar, ed., “On the Horizon: A Collection of Papers from the Next Generation,” Center for Strategic and International Studies, February 1, 2019, http://www.jstor.org/stable/resrep22545.16.

Manpreet Sethi, “The Idea of ‘Limited Nuclear War’: As Impractical and Dangerous Now, as It Was Then,” Indian Foreign Affairs Journal 14, 3 (2019), 235–247, https://www.jstor.org/stable/48636729.

Glenn H. Snyder, Deterrence and Defense (Princeton, NJ: Princeton University Press, 2016), https://press.princeton.edu/books/hardcover/9780691652092/deterrence-and-defense.

John K. Warden, “Limited Nuclear War: The 21st Century Challenge for the United States,” Center for Global Security Research, Lawrence Livermore National Laboratory, July 2018, https://cgsr.llnl.gov/content/assets/docs/CGSR_LP4-FINAL.pdf.

These unclassified government documents provided authoritative information relevant to the study.

Ross Buchanan, et al., “Extended Deterrence in the Indo-Pacific: A Regional Track 1.5 Dialogue,” Center for Global Security Research Report, Lawrence Livermore National Laboratory, September 2024, https://cgsr.llnl.gov/sites/cgsr/files/2024-11/event_report_-_extended_deterrence_in_the_indo-pacific.pdf.

Daniel R. Coats, “2019 Worldwide Threat Assessment of the US Intelligence Community,” Senate Select Committee on Intelligence, January 29, 2019, https://www.intelligence.gov/assets/documents/archive/2019-ATA-SFR—SSCI.pdf.

Madelyn R. Creedon, “America’s Strategic Posture: The Final Report of the Congressional Commission on the Strategic Posture of the United States,” October 2023, https://www.armed-services.senate.gov/imo/media/doc/americas_strategic_posture_the_final_report_of_the_congressional_commission_on_the_strategic_posture_of_the_united_states.pdf. This report warns that adversaries might employ limited nuclear strikes to shock US decision-makers and recommends posture changes.

“Defense Primer: Strategic Nuclear Forces,” Congressional Research Service, May 1, 2025, https://www.congress.gov/crs-product/IF10519. This is a concise overview of US strategic and low-yield nuclear force elements that underpin limited-attack response options.

“Nuclear-Armed Sea-Launched Cruise Missile (SLCM-N),” Congressional Research Service, February 12, 2025, https://www.congress.gov/crs-product/IF12084. This explains why a low-yield, theater-range cruise missile is being pursued to deter or respond to limited nuclear attacks.

“U.S. Extended Deterrence and Regional Nuclear Capabilities,” Congressional Research Service, August 8, 2024, https://sgp.fas.org/crs/nuke/IF12735.pdf. This details US commitments to allies and the forces available for countering limited nuclear coercion.

“U.S. Strategic Nuclear Forces: Background, Development, and Issues,” Congressional Research Service, December 14, 2021, https://sgp.fas.org/crs/nuke/RL33640.pdf.

“Guidance on the North Korean Cyber Threat,” Cybersecurity and Infrastructure Security Agency, last updated June 23, 2020, https://www.cisa.gov/uscert/ncas/alerts/aa20-106a.

China Military Power: Modernizing a Force to Fight and Win (Washington, DC: Defense Intelligence Agency, 2019), https://www.dia.mil/Portals/110/Images/News/Military_Powers_Publications/China_Military_Power_FINAL_5MB_20190103.pdf.

“North Korea Military Power: A Growing Regional and Global Threat,” Defense Intelligence Agency, September 2021, https://www.dia.mil/Portals/110/Documents/News/NKMP.pdf.

“Nuclear Challenges: The Growing Capabilities of Strategic Competitors and Regional Rivals,” Defense Intelligence Agency, August 2024, https://www.dia.mil/Portals/110/Images/News/Military_Powers_Publications/Nuclear_Challenges_2024.pdf.

Ben Frohman, Emma Rafaelof, and Alexis Dale-Huang, “The China-North Korea Strategic Rift: Background and Implications for the United States,” US-China Economic and Security Review Commission, January 24, 2022, https://www.uscc.gov/sites/default/files/2022-01/China-North_Korea_Strategic_Rift.pdf.

“National Security Strategy,” White House, October 2022, https://bidenwhitehouse.archives.gov/wp-content/uploads/2022/10/Biden-Harris-Administrations-National-Security-Strategy-10.2022.pdf.

“China’s Evolving North Korea Strategy,” US-China Economic and Security Review Commission, September 2019, https://www.uscc.gov/sites/default/files/2019-09/Chapter%203%20Section%205-%20China%27s%20Evolving%20North%20Korea%20Strategy_0.pdf.

“2022 Nuclear Posture Review” in “National Defense Strategy,” US Department of Defense, October 2022, https://media.defense.gov/2022/Oct/27/2003103845/-1/-1/1/2022-NATIONAL-DEFENSE-STRATEGY-NPR-MDR.pdf. This review sets current policy on low-yield warheads and “flexible, limited-nuclear-employment” options to deter regional aggression without large-scale escalation.

“Joint Publication 3-72: Nuclear Operations,” US Department of Defense, June 11, 2019, https://irp.fas.org/doddir/dod/jp3_72.pdf. This foundational joint-doctrine text defines “limited” nuclear employment options, escalation-control concepts, and tailored strike planning.

“2023 Congressional Posture Statement,” Senate Armed Services Committee, March 9, 2023, https://www.armed-services.senate.gov/imo/media/doc/2023%20USSTRATCOM%20Congressional%20Posture%20Statement%20-%20SASC.pdf. US Strategic Command’s commander provided unclassified testimony on how the United States would respond if an adversary attempted a “limited nuclear strike” in Europe or the Indo-Pacific.

“2021 Annual Threat Assessment of the US Intelligence Community,” US Office of the Director of National Intelligence, April 9, 2021, https://www.dni.gov/index.php/newsroom/reports-publications/reports-publications-2021/3532-2021-annual-threat-assessment-of-the-u-s-intelligence-community.

“2022 Annual Threat Assessment of the US Intelligence Community,” US Office of the Director of National Intelligence, February 7, 2022, https://www.odni.gov/files/ODNI/documents/assessments/ATA-2022-Unclassified-Report.pdf.

“2023 Annual Threat Assessment of the US Intelligence Community,” US Office of the Director of National Intelligence, February 6, 2023, https://www.odni.gov/files/ODNI/documents/assessments/ATA-2023-Unclassified-Report.pdf.

“2024 Annual Threat Assessment of the US Intelligence Community,” US Office of the Director of National Intelligence, March 11, 2024, https://www.dni.gov/index.php/newsroom/reports-publications/reports-publications-2024/3787-2024-annual-threat-assessment-of-the-u-s-intelligence-community.

“National Intelligence Estimate. North Korea: Scenarios for Leveraging Nuclear Weapons through 2030,” US Office of the Director of National Intelligence, June 15, 2023, https://www.dni.gov/files/ODNI/documents/assessments/NIC-Declassified-NIE-North-Korea-Scenarios-For-Leveraging-Nuclear-Weapons-June2023.pdf.

“Military and Security Developments Involving the People’s Republic of China 2021: Annual Report to Congress,” US Office of the Secretary of Defense, 2021, https://media.defense.gov/2021/Nov/03/2002885874/-1/-1/0/2021-CMPR-FINAL.PDF.

These books and articles from nongovernment sources also contributed significant insights, perspectives, and data points that informed the study.

Vincent K. Brooks and John S. Park, “Micro Deterrence Signaling,” Belfer Center for Science and International Affairs, Harvard Kennedy School, April 4, 2022, https://www.belfercenter.org/publication/micro-deterrence-signaling.

Sungmin Cho and Oriana Skylar Mastro, “North Korea Is Becoming an Asset for China: Pyongyang’s Missiles Could Fracture America’s Alliances,” Foreign Affairs, February 3, 2022, https://www.foreignaffairs.com/articles/north-korea/2022-02-03/north-korea-becoming-asset-china.

Collin Clark, “North Korea Welcomes Trump Back with ‘Strategic’ Cruise Missile Test: What’s Next?” Breaking Defense, February 4, 2025, https://breakingdefense.com/2025/02/north-korea-welcomes-trump-back-with-strategic-cruise-missile-test-whats-next/.

Ellie Cook, “What Is HAEIL-5-23? North Korea’s Underwater Nuke System Test Raises Alarm,” Newsweek, January 19, 2024, https://www.newsweek.com/north-korea-nuclear-drone-test-haeil-1862120.

Patrick M. Cronin, “Fear and Insecurity: Addressing North Korean Threat Perceptions,” Hudson Institute, March 2021, https://s3.amazonaws.com/media.hudson.org/Cronin_Fear%20and%20Insecurity%20Addressing%20North%20Korean%20Threat%20Perceptions.pdf.

Paul K. Davis and Bruce W. Bennett, “Nuclear-Use Cases for Contemplating Crisis and Conflict on the Korean Peninsula,” Journal for Peace and Nuclear Disarmament 5, 1 (2022), 24–49, https://www.tandfonline.com/doi/full/10.1080/25751654.2022.2053426.

Michael Elleman, “North Korea’s New Short-Range Missiles: A Technical Evaluation,” 38 North, October 9, 2019, https://www.38north.org/2019/10/melleman100919/.

Max Fisher and Jugal K. Patel, “What One Photo Tells US about North Korea’s Nuclear Program,” New York Times, February 24, 2017, https://www.nytimes.com/interactive/2017/02/24/world/asia/north-korea-propaganda-photo.html.

Markus V. Garlauskas, Ken E. Gause, and Elizabeth Yang, “North Korea’s Arena of Asymmetric Advantage: Why We Should Prepare for a Crisis in the Yellow Sea,” Center for Naval Analyses, October 2021, https://www.cna.org/analyses/2021/10/north-korea-asymmetric-advantage-in-yellow-sea.

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Overview

The Guardian Tiger III tabletop exercise was designed to synthesize and develop new insights on the project’s key research question: “How should the Pentagon—in concert with key US allies—prepare for and respond to the risk of a limited nuclear attack in East Asia over the coming decade?” It was designed to address a series of questions.

• Is the threat of LNA credible?
• What are the thresholds and drivers for initiating an LNA?
• How do we define and assess LNA?
• Are the effects of LNA considered manageable or catastrophic?
• What are the psychological, political, and operational effects of an LNA or threat of LNA, and how can they be mitigated?
• What are the trade-offs of preparing for an LNA versus other priorities prior to and during a conflict?
• What are the key political-military factors for LNA deterrence, preparation, and response options?

The participants were organized into a Blue (US) Team, Green (allies) Team, Red and Orange (adversaries) Team, and Control Team, together totaling more than one hundred participants—primarily government and military, with a handful of nongovernment experts—from seven countries: the United States, South Korea, Japan, select UNC Sending States (Australia, France, and the United Kingdom), and Sweden. The Blue Team consisted of three cells of up to twenty members each, representing different echelons: a National Interagency Cell (approximating National Security Council processes), a National Defense and Military Cell (addressing considerations for the Pentagon and relevant Joint Combatant Commands), and a Korean Theater Military Cell. The Green Team consisted of three allied cells to represent South Korea, Japan, and key UN Command Sending States, including participation from those respective countries. The Red and Orange Team included three adversary cells—North Korea (Red), and China and Russia (Orange)—with current and former US government experts on these adversaries.

The scenario was set in 2032 in the context of an ongoing conflict that North Korea did not appear to be winning, and was therefore designed to provide North Korea with plausible conditions to initiate some form of LNA in the context of ongoing conflict, at the start of each of four turns.

Scenario background

By 2032, North Korea’s military capabilities had continued to increase, but at a price. The domestic situation had grown strained due to the regime’s lost grip on the information environment, amid rumors of preparation to name a successor to Kim. Other elements of the scenario were as follows.

• • Russia, despite a pause in the war in Ukraine, enabled North Korea’s qualitative and quantitative military growth; China bolstered North Korea’s economy and diplomacy; China has grown more assertive and capable militarily in both the Yellow (West) Sea and the Taiwan Strait.
  • South Korea’s military capabilities improved, but it remained non-nuclear and allied to the United States, with adjustments to Combined Forces Command wartime operational control. The South Korean population had a low tolerance for North Korean aggression and Chinese economic coercion; ROKSTRATCOM was fully mission capable with precision strike capabilities against mobile and hardened targets.
  • Japan’s Joint Operations Command was fully operational, closely coordinating with USJAPANCOM (former United States Forces Japan with a warfighting mission and capability) for defense of Japan and area; South Korea–Japan–US trilateral cooperation continued, but with no major breakthrough; Japan reinforced defenses around UNC rear bases and developed liaison with UNC staff.
  • It was an election year in the United States. US capabilities and posture in the Pacific had improved overall but were primarily focused on China. National (and theater) missile defense improved dramatically but did not outpace the growth of the North Korean threat. USKORCOM (former USFK) remained small, with qualitative upgrades for fires, command, control, communications, computers, intelligence, surveillance, and reconnaissance (C4ISR), missile defense, and aircraft enabling US combat operations, but primarily enabled wartime force provider to CFC.
  • UNC staff and training strengthened; Australia, France, and the United Kingdom (UK) played leading roles.
    • Australia’s military cooperation expanded with South Korea and Japan; an Australian three-star served as the deputy commander (DCDR) of UNC. The trilateral Australia–US–UK submarine program remained on track with Submarine Rotational Force-West operating with US and UK submarines, including Australian officers.
    • France grew and modernized its military, expanding its role not only in European security, but also in the Indo-Pacific and on the UNC staff.
    • UK force modernization continued, maintaining strong NATO engagement while the UK remained outside the European Union, and expanded its presence in the Indo-Pacific and on the UNC staff.

Key elements of North Korea’s military capabilities had been on a path of improvement for more than a decade, including serial production and employment of systems first tested in 2019–2025. These capabilities were enabled by Russian support and technology transfer, domestic development, and espionage, along with sanctions evasion to obtain commercial dual-use technologies and materials, particularly from China.

• Growing numbers of new mobile close-, short-, and medium-range ballistic missiles with mobile launchers, along with maneuvering (hypersonic) re-entry vehicles and cruise missile systems, increasing the capability to evade or overwhelm defense and the accuracy to hit targets with conventional, chemical, or nuclear warheads.
• An increasing number and sophistication of unmanned aerial systems, including various types for tactical, operational, and strategic reconnaissance and targeting, as well as attack capability, including possible nuclear armament.
• Unmanned underwater vehicles, including extended-range nuclear-capable platforms.
• A small ballistic missile submarine capability, sufficient to reinforce North Korea’s second-strike nuclear capability against targets in Northeast Asia and expand attack vectors to challenge South Korea’s missile defenses.
• Mobile liquid- and solid-fuel intermediate-range ballistic missiles and intercontinental ballistic missiles, with multiple re-entry vehicles and defense evasion measures to pose a credible second-strike nuclear threat in the region and to the continental United States.
• Enhanced cyberattack capabilities to achieve disruptive and destructive effects, particularly against civilian targets.
• A growing stockpile of fissile material and nuclear warheads, including previously tested fission and thermonuclear warheads, as well as tested low-yield, small tactical nuclear warheads.
• New mobile surface-to-air and anti-ship missile systems to boost the defense of North Korea’s airspace and coastline.

TTX flow highlights

Prior to the start of the TTX, North Korea had launched a limited attack against South Korea’s northwest islands, and the conflict escalated beyond North Korea’s original intent. See Figure 1 below.

Figure 1. Road to war visual summary

Turn one initiated the exercise when a North Korean autonomous torpedo sank a South Korean warship off the east coast in international waters, with an underwater nuclear detonation of a disco ball fission warhead.

In turn two, after South Korean-US forces destroyed the Kim family villa complex at Wonsan in response, North Korea conducted a thermonuclear (peanut) nuclear airburst over the island of Dokdo (Liancourt Rocks) with an intermediate-range hypersonic glide vehicle, while launching non-nuclear strikes with drones and missiles against ROKSTRATCOM HQ on the south edge of Seoul. Alliance counterstrikes against North Korean forces continued. See Figure 2 below.

Figure 2. Turn two summary

Turn three saw increased US nuclear force posture and deployed dual-capable aircraft (no warheads) to Kunsan Air Force Base. North Korea conducted a large, complex missile and drone attack on Osan Air Force Base, included a single very low-yield (1.5-kiloton notional warhead design) airburst from a submarine-launched cruise missile with minimal fallout and collateral damage, rendering the base non-mission capable. See Figure 3 below.

Figure 3: Turn three summary

In turn four, in an attempt to stabilize the situation, China began to establish a no-fly zone over North Korea, even as Russia withdrew its air defense forces. Despite the no-fly zone, the alliance responded to North Korean nuclear escalation with a limited South Korean–US conventional nuclear counterattack in southeast North Korea, paired with an ultimatum to the North Korean regime to cease hostilities. See Figure 4 below.

Figure 4: Limited US–South Korean conventional-nuclear integrated strikes in turn four

North Korea launched an attack with multiple nuclear short-range ballistic missiles (SRBM) armed with Hwasan-31 tactical warheads on Kunsan Air Force Base, destroying dual-capable aircraft that had been repositioned there, reasoning that this was a proportional response to a nuclear attack on its nuclear-capable SRBMs. See Figure 5 below.

Figure 5: Turn four North Korean LNA on Kunsan Air Force Base

Pyongyang rejected the alliance ultimatum, leading to South Korean–US conventional and nuclear strikes on North Korean nuclear command and control (NC2) and nuclear forces to end the regime and to neutralize North Korea’s nuclear employment capabilities. This led to combat with Chinese forces attempting to impose a no-fly zone over North Korea. See Figure 6 below.

Figure 6: US–South Korean strikes against North Korean nuclear command and control and missile forces

This triggered North Korean pre-planned and pre-delegated nuclear retaliation, which was not adjudicated, but which passed beyond the scope of how the study defined limited nuclear attack and brought an end to the TTX. See Figure 7 below for the Red Cell’s assessment of what notional pre-delegated orders for retaliation would be in such an eventuality.

Figure 7: Assessment of incoming North Korean counterstrike at the end of the exercise

Overall TTX insights: Principal investigator’s perspective

Overall, Garlauskas noted a new insight that TTX participants’ focus on developing a response to the last nuclear event drowned out the bandwidth to discuss preparation for future nuclear attacks. It is plausible that a similar phenomenon would occur in the event of an actual LNA, making advance preparation of societal and military resilience and consequence management vital, as little leadership or staff time would be available to make new plans, decisions, or resource reallocations.

Player discussions suggested that LNA situations bring to the forefront potential differing measurements on escalation between the Red and Blue and Green teams, as well as the lack of a linear escalation ladder in such situations. For example, the destructive non-nuclear strikes proposed by the US and South Korean cells on the Kim family’s Wonsan villa complex, in response to an underwater nuclear attack on a military target, appeared more escalatory and disproportionate to the Red Cell than intended (despite the clear message that it was not intended to hit Kim personally), while also showing fear of nuclear escalation. Ironically, a nuclear strike on a North Korean vessel or port would have been viewed as less escalatory but more resolute.

Even after what was clearly determined to be a limited nuclear attack on Osan Air Force Base, player discussions suggested the imperative to apply previously stated declaratory policy to end the regime (i.e., the Washington Declaration) might not necessarily be clear and a last chance could be offered. US and South Korean participants, after much debate, proposed a limited conventional-nuclear counterattack while still offering a final ultimatum that, if accepted, could have left the North Korean regime in power after such a clear nuclear attack.

Insights from the analytic cell

Unclear criteria and response parameters for an LNA: Even late in the TTX, the Blue Cell continued to struggle to determine whether an action taken by North Korea was an LNA. Pre-establishing criteria for LNA and parameters for a response would help senior policymakers more efficiently and quickly determine whether an event should be considered an LNA.

Too much focus on immediate military retaliation: The Blue Cell’s primary and immediate focus on military retaliation resulted in less consideration of using other tools of national power (such as economic tools), as well as the resulting psychological and strategic effects, including the role of domestic political considerations and the necessary preparations to ensure resilience in the face of additional nuclear attacks.

Prioritized preventing escalation rather than preparing for it: The Blue Cell responded to a North Korean LNA by threatening to impose unacceptable costs on North Korea to attempt to prevent escalation (both vertical and horizontal), rather than prioritizing preparing to be targeted by additional attacks, including attacks on the US homeland.

Conceptualizing relationship of LNA, CNI, and proportionality

Table 1. Relationships among LNA, CNI, and proportionality

“LNA is plausible, and we need to prepare for it. We need to figure out how to deter LNA.”—Markus Garlauskas, Guardian Tiger III principal investigator

North Korea’s employment of an LNA is the key feature of the “failure of deterrence” stage and marks the beginning of key actors’ efforts to calibrate on what CNI and proportionality denote. In the “vacuum of deterrence” stage, all actors first focus on an LNA response but quickly expand to CNI responses in an effort to re-establish deterrence in a proportionate manner. However, in practice, their employment of CNI exacerbates the fast-emerging gaps as the exchange rate of nuclear versus non-nuclear measures shifts rapidly in the aftermath of the initial LNA. This dynamic feeds into the “escalate to de-escalate” stage, in which each actor’s effort to now establish dominance outpaces prior attempts to establish proportionality. All the actors become locked in a cycle in which reaction feeds into reaction with higher levels of escalation.

Key takeaways: What were the top insights from the Guardian Tiger III TTX to inform the best military advice?

Table 2. Key takeaways