Hypersonic weapons, capable of exceeding Mach 5 with unpredictable flight paths, shatter the bedrock principles of conventional missile defense. Their ability to glide and maneuver within the atmosphere allows them to evade radar detection and interceptor systems, compressing warning times to mere minutes. This drastic reduction in reaction time amplifies the risk of miscalculations and accidental escalation, particularly in moments of crisis.

The global balance of power is being fundamentally altered, not merely adjusted, by the aggressive pursuit of maneuverable hypersonic weapon capabilities. China’s DF-17 hypersonic missile, coupled with its reported testing of a fractional orbital bombardment system (FOBS) with a hypersonic payload, demonstrates a clear intent to achieve global strike capabilities with minimal warning. Russia’s deployment of the Avangard HGV on its SS-19 intercontinental ballistic missiles and the operational status of the Zircon hypersonic anti-ship missile further highlight the growing proliferation of these advanced weapons. North Korea’s claim of successful hypersonic missile tests, while requiring verification, signal a potential integration of these weapons into its theater nuclear strategy, adding another layer of complexity to regional security.

The inherent capacity of maneuverable hypersonic weapons to render existing missile defense systems obsolete signifies not just a technological leap, but a deliberate dismantling of established strategic certainties. The unpredictability of their flight paths and the compression of warning times do not just complicate defense planning; they erode the very foundation of strategic stability, where deterrence relies on the certainty of retaliation. The potential for these weapons to carry both conventional and nuclear payloads does not just increase their versatility; it blurs the lines between conventional and nuclear conflict, creating a perilous ambiguity that heightens the risk of miscalculation.

The ability to strike targets with minimal warning does not just enhance offensive capabilities; it creates a coercive tool, enabling states to exert pressure and achieve strategic objectives without resorting to large-scale conventional warfare. The potential for hypersonic weapons to be deployed in a first-strike role does not just raise concerns about escalation; it fundamentally alters the calculus of deterrence, where the threat of retaliation may no longer be sufficient to prevent aggression.

To counter this burgeoning vulnerability, the United States must not merely react, but fundamentally redefine its strategic posture, acknowledging that piecemeal technological solutions are insufficient to address the profound shift hypersonic weapons impose on the security landscape. The rapid development of the glide phase interceptor (GPI) and space-based tracking systems is not just about enhancing missile defense; it is about restoring a sense of strategic stability, reassuring allies and deterring potential adversaries. The expansion of conventional hypersonic programs, such as the AGM-183 ARRW, conventional prompt strike, and the long-range hypersonic weapon, is not just about developing counterforce capabilities; it is about demonstrating a commitment to maintaining a credible deterrent, signaling to potential adversaries that aggression will be met with a swift and decisive response. The integration of hypersonic weapons into existing military doctrines does not just require tactical adjustments; it demands a fundamental reevaluation of strategic thinking, adapting to a new era of high-speed warfare.

The international community’s response to hypersonic weapons must not be limited to national defense initiatives; it must include a concerted effort to promote arms control and transparency. The absence of clear international norms and regulations regarding hypersonic weapons does not just create uncertainty; it fosters a climate of strategic competition, where states are incentivized to develop and deploy these weapons without restraint. The development of transparency and confidence-building measures is not just about reducing the risk of miscalculation; it is about building a foundation for strategic stability, where states can engage in dialogue and cooperation to mitigate the risks posed by these advanced weapons.

Hypersonic weapons represent a paradigm shift in military technology, fundamentally questioning if the world is entering a new era of vulnerability, undermining the foundations of traditional missile defense and reshaping the strategic landscape. Addressing this challenge requires a comprehensive approach that combines technological innovation, strategic adaptation, and international cooperation. Only through a concerted effort can the international community hope to mitigate the risks posed by hypersonic weapons and ensure a more stable and secure future.

Brandon Toliver, PhD, serves on the A4 staff of Headquarters Air Force. The views expressed are those of the author and do not reflect the official guidance or position of the United States government, the Department of Defense, the United States Air Force, or the United States Space Force.

Hypersonic Weapons: Are We Entering a New Era of Vulnerability? 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.