It is time to restation nuclear weapons in South Korea. The United States must modernize extended deterrence and strengthen the assurance of allies across the Indo-Pacific region. While the United States and South Korea previously agreed to station weapons from 1958 until the end of 1991, that agreement was part of an earlier nuclear posture centered on the Soviet Union. Now though, both North Korea and China have surged their numbers of nuclear weapons and delivery systems, adding a worsening complexity to the region for the United States and its allies.
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.
