Although the technological details are simplified in the movie, its strategic intuition is right on point. A ballistic missile —possibly a Submarine Launched Ballistic Missile (SLBM) attributable to North Korea—creates a uniquely destabilizing crisis. The alert time is compressed, attribution gets ambiguous, and U.S. homeland missile defense becomes both the first and last line of defense. However, such a situation should not be a U.S. only issue especially in a West Pacific launch scenario, originating from the Sea of Japan or an adjacent maritime area. Both Japan and South Korean alliances present capabilities already in place or being actively pursued which could change the outcome.

Why SLBMs Create a Distinct Crisis?

SLBMs raise more profound challenges for interception than a land-based missile launched deep inside North Korean territory. The launch location is uncertain, early warning alerts could be delayed, while a credible trajectory may only be acquired after the boost phase. This compresses the U.S. leader’s decision-making cycle and complicates attribution at precisely the moment when clarity matters most.

Japan’s Role: Forward Maritime-Based Defense

Japan already fields many of the relevant capabilities to address . The Japanese Maritime SDF operates Aegis destroyers that are armed with SM-3 interceptors, including the SM-3 Block IIA variant that is co-developed with the United States. Under controlled experimental conditions, this interceptor has verified its ability to intercept ICBM-class targets, indicating that its strategic relevance goes beyond regional missile defense.

More importantly, Japan is moving towards a maritime-oriented ballistic missile defense posture. The planned Aegis System Equipped Vessels (ASEVs)—built around the SPY-7 radar—are designed to provide continuous BMD coverage without diverting multi-mission destroyers. Expected to be deployed in the late 2020s, these vessels would function as constant BMD platforms.

In an SLBM launch scenario in the Sea of Japan, such vessels could be ideally poised to detect, track, and intercept an SLBM that is transiting the Northern Hemisphere. Such forward deployment expands the interception theater, creating an opportunity for an early engagement before activating the missile defense situated in the continental United States. Therefore, Japan’s contribution is geometrical, not symbolic, shortening the initial time of engagement. 

South Korea’s Emerging Contribution

Similarly, South Korea is preparing to add the second crucial defense layer. Seoul is proceeding with the procurement of SM-3 missiles, reflecting the understanding that missile defense can no longer be restricted to terminal-phase defense on the Korean Peninsula. While South Korea’s existing air and missile defense system is centered on short- and medium-range threats, SM-3 introduces a new mission: sea-based midcourse interception.

South Korea’s Aegis destroyers equipped with SM-3s can operate in partnership with the Japanese defense forces in a complementary manner, creating azimuth diversity in intercept geometry. Multiple engagement opportunities from different angles to complicate an opponent’s countermeasures and lower the dependency on a single interception attempt. This is not mere redundancy, but resilience under uncertainty.

Another important element is South Korea’s push for a nuclear-powered submarine (SSN). Although an SSN does not intercept a missile, it influences the very unstable factor in this scenario: The North Korean submarine itself. While diesel-electric submarines rely on limited endurance and predictable operational patterns, SSNs can loiter, sprint, and conduct continuous operations across vast maritime areas. This makes it extremely difficult for North Korean submarines to reach actual launch areas undetected. In that sense, South Korea’s SSN ambition represents a denial strategy that could prevent the crisis from emerging, rather than serving as mere prestige or a symbol of a blue-water navy.

A Trilateral Layered Response

Pre-crisis posture is decisive. Japan’s ASEVs or Aegis destroyers should maintain BMD patrol points somewhere in the Sea of Japan, while South Korean Aegis destroyers could be operated near Korean waters in complementary sectors. Real-time information sharing through trilateral missile alert mechanisms should be a standing arrangement rather than an ad hoc measure.

At launch, forward sensors and shipborne radars could track earlier than what is portrayed in the movie—and if geometric conditions are met, Japanese naval vessels could attempt the first interception through SM-3 during early midcourse. Sequentially, South Korean destroyers could conduct a second round of engagement from different azimuths. To be sure, these attempts do not guarantee interception. Nevertheless, they reshape the problem from a terminal-phase gamble into a layered contest.

Only when these attempts fail would the engagement fall back to U.S. homeland defense; in this case, GBIs serve as the last line of defense rather than the sole response. At that juncture—when the U.S. must launch its GBIs—decision-makers would have more information, higher attribution credibility, and greater room for diplomacy to manage further escalation. The objective is not interception certainty, but the expansion of decision space under extreme uncertainty.

Policy Implications

If The House of Dynamite is a warning, the response should be concrete. Japan should recognize ASEVs as the backbone of regional BMD rather than as a peripheral capability. Meanwhile, South Korea should invest in the training, doctrine, and readiness required for sustained SM-3 operations. To be sure, together with the U.S., the three countries should institutionalize exercises that explicitly rehearse ICBM-class scenarios.

Although The House of Dynamite is a compelling drama, it is not destiny. The decisive factor is not technology itself, but alliance design, specifically whether Tokyo and Seoul are already in the fight when the crisis begins.

Dr. Ju Hyung Kim currently serves as a President at the Security Management Institute, in the South Korean National Assembly. He holds a doctoral degree in international relations from the National Graduate Institute for Policy Studies (GRIPS) in Japan, a master’s degree in conflict management from the Johns Hopkins University School of Advanced International Studies (SAIS), and a degree in public policy from Seoul National University’s Graduate School of Public Administration (GSPA). The views of the author are his own.

Fixing the House of Dynamite – An SLBM Crisis in East Asia was originally published on Global Security Review.

The EAR Report is a must read for National security professionals to stay informed about rapidly evolving global threats and the strategic implications for U.S. defense policy.

This report addresses critical developments in nuclear deterrence, missile defense, and geopolitical trends, and equips professionals with actionable insights to navigate the complexities of modern security challenges effectively.

Commentary and Quotes of the Week

• Defense Secretary Lloyd Austin: Reaffirmed the U.S.-ROK alliance and the strengthening of extended deterrence through the Nuclear Consultative Group.
  Peter Huessy: Detailed the financial and strategic implications of eliminating the ICBM leg of the U.S. nuclear triad, emphasizing the costs of alternative measures for maintaining current deterrence levels.
  Jon Finer, Deputy National Security Adviser: Highlighted Pakistan’s emerging threat with the development of long-range ballistic missile capabilities.
  Bill Gertz: Revealed China’s rapid nuclear buildup and the expansion of its missile capabilities.
  Russian Leaders: Asserted advancements in missile systems and dismissed arms control as a relic of the past.
  Rep. Chuck Fleischmann: Stressed the urgency of modernizing the U.S. nuclear deterrent, citing contributions from Tennessee’s Oak Ridge Lab.

Strategic Developments of the Week

• China’s Military Build-Up: The Pentagon report highlighted Beijing’s dramatic advancements in hypersonic missile technology, nuclear warheads, and ‘intelligentized warfare.’
  Russia’s Strategic Actions: Russia’s legislative shift regarding the Taliban and progress in missile systems underlined its geopolitical maneuvers.
  U.S. Missile Defense Challenges: Reports emphasized the lag in U.S. hypersonic missile capabilities compared to China, pressing the need for enhanced missile defense systems.
  Space and Drone Developments: New legislation and technological advances highlight the increasing role of space and drones in modern warfare.

Important Reports of the Week

1. “President Trump Must Put the Nuclear Enterprise on a Wartime Footing” by Robert Peters:
   • Advocates for accelerating nuclear arsenal modernization to restore deterrence credibility.
     Calls for a stronger commitment to stockpile stewardship and missile defense.
2. “Importance of Building Homeland Missile Defense” by Robert Joseph:
   • Reiterates the vision of a comprehensive missile defense system to counter emerging threats.
     Proposes leveraging space-based systems for more robust and efficient protection.
3. “What Happens if the United States Eliminates the ICBM Leg of the Triad?”:
   • Examines the repercussions of removing the ICBM leg, including massive financial costs for alternative deterrence methods and strategic vulnerabilities.

Download the Full Report

ICBM EAR Report for December 20th was originally published on Global Security Review.

North Korea continues to increase its weapons production while advancing its intercontinental ballistic missile (ICBM) and nascent submarine-launched ballistic missile (SLBM) legs of an emerging nuclear dyad. At the same time, China increased its numbers and types of nuclear weapons and dual-capable delivery systems. It has built multiple fast breeder reactors and reprocessing facilities to produce and separate plutonium. Moreover, China’s fielding of a dual-capable fractional orbital bombardment system (FOBS) and hypersonic glide vehicle raises questions about its commitment to its long-standing policy of no-first-use of nuclear weapons.

As Matthew Kroenig notes, the more nuclear weapons a state has, the more assertive and coercive it tends to become to achieve its goals. This fits China’s pattern of behavior and is consistent with North Korea’s modus operandi. These developments threaten vital American security interests by undermining extended deterrence—placing the United States and mutual defense treaty allies at increased risk.

To counter this situation, while preserving strategic options for use during periods of acute crisis, “nuclear castling” would involve the restationing of nuclear weapons in South Korea. In chess, castling involves the simultaneous moving of the king and rook in a protective maneuver that preserves capabilities and opens new possibilities across the board.

Repositioning American nuclear weapons to South Korea would help close an emergent theater deterrence gap and modernize extended deterrence for all Indo-Pacific allies. The following proposal addresses how these weapons would serve an even greater imperative than in the past, even if only to provide the president of the United States options for use in extremis.

The United States should restation B61-3, 4, and/or 12 nuclear gravity bomb variants in South Korea for delivery of low-yield weapons by dual-capable F-35A, F-15E, or F16C/D. New START Treaty limitations only apply to heavy bombers, ICBMs, and SLBMs, as opposed to these lower yield warheads and fighter aircraft. Additionally, the South Korean Air Force should train to perform conventional support for nuclear operations (CSNO), similar to how the air forces of some North Atlantic Treaty Organization (NATO) allies in Europe operate. The United States should also use this opportunity to invite the Japanese Air Force to participate in CSNO training and operations.

Skeptics will likely say the April 2023 Washington Declaration between the United States and South Korea should have a chance to strengthen deterrence and assurance. Part of the agreement commits America to reintroducing periodic ballistic missile submarine patrols in the vicinity of South Korea. In addition to South Korea reaffirming its pledge not to seek its own nuclear weapons and commitment to the Non-Proliferation Treaty (NPT), the Washington Declaration clears the way for America and South Korea to establish a nuclear consultative group modeled on NATO’s Nuclear Planning Group.

In fact, within six months of the Washington Declaration, the USS Kentucky made the first visit of an American ballistic missile submarine to South Korea since the 1980s. The visible gesture of deterrence accompanied the inaugural meeting of the American and South Korean Nuclear Consultative Group meeting on the same day in July 2023.

In parallel, an April 2024 display of combined air operations with the South Korean and Japanese Air Forces further contributes to theater deterrence. But, while the Washington Declaration is an important step in the right direction, more is needed to deter North Korea or China and to assure our regional allies.

Others will also argue that reintroducing small numbers of nuclear weapons to South Korea will not make an appreciable difference in North Korea or China’s perception of risk or the credibility of America’s nuclear deterrent. However, repositioning weapons within the theater to deter two nuclear arms–racing aggressors and assure allies creates options for the United States that do not require employment of strategic weapons. For allies that rely on extended deterrence, reintroducing nuclear weapons to South Korea would renew confidence in America’s nuclear umbrella.

While some observers may also view any reintroduction of nuclear weapons to South Korea in this manner as a contravention of the NPT, the United States would rely on custodial control to align with the NPT. Though fundamentally different than long-standing NATO arrangements that pre-date the NPT, restationing nuclear weapons in South Korea is a comparable approach that involves a treaty ally of the United States. Most importantly, there is a historic precedent between both countries.

At a relatively low cost and risk, restationing nuclear gravity bombs in South Korea has a high return on investment if agreed to by the South Korean government. Additionally, considering production delays for the American Columbia-class ballistic missile submarines to replace the current Ohio-class submarines and the similarly lengthy timeline for fielding a nuclear sea-launched cruise missile, this recommendation is a timely option for strengthening overall American nuclear deterrence.

The Indo-Pacific chess board has strategically shifted since the United States last stationed weapons there. The longer America maintains a regional nuclear status quo in the face of egregious North Korean and Chinese nuclear arms racing, the less credible and more overstretched America’s nuclear deterrent may appear. Nuclear castling offers an approach to close the emergent deterrence gap and to provide a forceful example of interoperability for treaty allies, complementing bold integrated deterrence moves and magnifying a new sense of integrated assurance.

COL Michael R. DeMarco serves in the United States Army Reserve. Disclaimer: The views expressed in this article are those of the author and do not reflect the official policy or position of the National Defense University, the Department of Defense, or the US government.

Nuclear Castling in the Indo-Pacific was originally published on Global Security Review.