This issue is not new. In his 1957 book Nuclear Weapons and Foreign Policy, Henry Kissinger made a controversial, yet analytically compelling, argument for the possible utility of tactical nuclear weapons in limited wars. He warned that massive retaliation was neither credible nor effective for deterring limited aggression and that a rigid dichotomy between conventional and strategic nuclear responses risked inviting coercion at the lower rungs of the escalation ladder. For Kissinger, introducing the possibility of limited nuclear use was not a call to war, but a recognition of strategic reality; the ability to escalate with restraint could deter adversaries from escalating first.

Fast forward to the 2030 scenarios modeled in Guardian Tiger I and II, and Kissinger’s insights remain disturbingly relevant. In the exercise, North Korea carried out a low-yield nuclear strike targeting South Korean naval vessels. American decision-makers, faced with the risk of horizontal escalation with China and the lack of consensus among allies, struggled to identify a proportional yet credible response. The idea of a retaliatory tactical nuclear strike was floated, but the simulated American leadership hesitated, reflecting both doctrinal ambiguity and an operational gap in American nuclear capabilities.

The risks of such hesitation are manifold. First, American restraint may be misinterpreted as indecision or weakness, particularly by allies like South Korea and Japan, who are directly exposed to North Korean and Chinese threats. Second, it creates an opening for adversaries to believe they can escalate to the nuclear level without inviting proportional retaliation. Third, it undermines the entire architecture of extended deterrence that underpins regional security.

Critics will rightly point out the perils of normalizing nuclear use. Introducing tactical nuclear weapons into a conflict zone invites moral hazards, increases the risk of miscalculation, and breaks long-standing nuclear taboos. It also challenges existing declaratory policies, such as the 2022 P5 Joint Statement affirming that “a nuclear war cannot be won and must never be fought.”

But these arguments, while valid in principle, must be weighed against the operational reality that a low-yield nuclear strike by an adversary may not be deterred by threats of massive retaliation. As the Atlantic Council report noted, North Korea’s nuclear doctrine increasingly incorporates elements of pre-delegated authority, tactical nuclear use, and efforts toward a more survivable second-strike posture. If the United States signals that it will not respond proportionally to a limited nuclear attack, North Korea may calculate that it can use nuclear weapons to coerce the South or constrain American action without triggering regime-ending consequences.

Moreover, the credibility problem is not confined to North Korea. China, observing Washington’s reluctance to respond in kind, may also be emboldened to engage in horizontal escalation, confident that the United States’s nuclear threshold is politically—and perhaps operationally—immobile. This perception could unravel the strategic coherence of integrated deterrence.

To address these challenges, US Forces Korea (USFK) and Indo-Pacific Command should adopt a more robust approach across multiple dimensions. First, the United States should consider forward-deploying platforms capable of delivering low-yield nuclear weapons. This could include the reintroduction of dual-capable aircraft or sea-based assets positioned in or near the Korean Peninsula. Such deployments must be both survivable and possess the ability to clearly signal an adversary of will, while being fully integrated into bilateral operational planning with the Republic of Korea (ROK).

Second, escalation options must be clarified through updates to American declaratory policy. This does not mean issuing public ultimatums or fixed thresholds but rather ensuring that adversaries understand the United States is willing to conduct proportional nuclear responses if deterrence fails. Strategic ambiguity must not become strategic paralysis.

Third, while the US and South Korea launched the Nuclear Consultative Group (NCG) in 2023 to enhance extended deterrence coordination, further institutionalization is needed. A structure modeled more closely on the North Atlantic Treaty Organization’s (NATO) Nuclear Planning Group would help deepen transparency, signal unity of purpose, and reduce the risk of fragmented responses during crises.

Fourth, both US and ROK forces must be equipped and trained to operate in the aftermath of a limited nuclear strike. This includes rehearsals and exercises focused on base survivability, radiological detection and decontamination, logistics continuity, and the resilience of command-and-control (C2) systems.

Fifth, strategic communication must be strengthened. Clear and consistent messaging to both adversaries and allies is critical. Deterrence depends not only on military capabilities, but also on the perceived credibility of those capabilities and the intentions behind them.

Ultimately, the goal of these measures is not to normalize the use of nuclear weapons, but to reinforce the threshold against their use by making deterrence more credible and responsive.

If that threshold is ever crossed and the United States fails to respond proportionately, the credibility of its extended deterrence architecture could unravel. The Guardian Tiger exercises highlight this grim possibility and should serve as a clarion call to action for policy and defense leaders alike.

As Kissinger warned in 1957, the danger of total war arises not so much from a deliberate decision to embark on it as from a series of actions which, though rational in themselves, cumulatively lead to disaster. The United States must ensure that its rational desire to avoid nuclear escalation does not lead to an irrational loss of deterrence. Tactical nuclear flexibility, responsibly exercised and credibly signaled, may be the painful but necessary insurance policy to uphold peace in East Asia.

Dr. Ju Hyung Kim, President of the Security Management Institute, a defense think tank affiliated with the South Korean National Assembly, is currently adapting his doctoral dissertation, “Japan’s Security Contribution to South Korea, 1950 to 2023,” into a book.

The Case for US Low-Yield Nuclear Options in Korea was originally published on Global Security Review.

The international system is now firmly bipolar, with China’s global power rapidly increasing at a time when Russia regularly threatens to use nuclear weapons against the North Atlantic Treaty Organization (NATO), influencing the administration of President Donald Trump. The combined Chinese and Russian threats are leading President Trump to warn of a possible World War III.

American power is increasingly contested, bringing new operational challenges to extended deterrence. A fundamental question is now in play—should the US abandon the Nuclear Non-Proliferation Treaty (NPT) it created in 1960s and instead push its allies to field nuclear weapons?

Allies are already reconsidering their nuclear stance. In the Asia-Pacific, American ally Australia provides useful historical insights.

From the late 1940s to the early 1970s, Australia sought to acquire nuclear weapons in response to an unstable international order where it felt threatened by China. In 1967, Secretary of US Defense Robert McNamara said it would be “entirely natural” and “an obvious thing to happen” for Australia to acquire nuclear weapons in response to China developing them. He also expressed interest in establishing a collective nuclear organization for the Far East, “starting with Australia and the Philippines.”

Indeed, Secretary of State Dean Rusk earlier suggested a “US-supplied Far Eastern nuclear stockpile” open to Japan and India. In 1958, others proposed the US could base intercontinental ballistic missiles (ICBMs) in Australia, in the event the US decided to keep tight control of nuclear weapons in its own hands and actively worked to push its allies to agree to the NPT treaty.

There were similar debates around friendly nuclear proliferation in Europe around the same time. Aiming to regain leadership in Europe, the US proposed a multilateral nuclear force within NATO. While there were doubts over its military utility, the diplomatic discussions that started around sharing nuclear hardware and control did allow time to develop a European non-proliferation solution. In 1966, the NATO nuclear planning group was established, allowing some European allies to be involved in how and under which circumstances American weapons might be used.

The structural changes in the international system that prompted these earlier ideas are happening again. It is time to start thinking seriously about the next steps to take. The nuclear history noted suggests three broad approaches.

First, allies might build their own nuclear forces. The logic is that in a high-intensity conflict between the US and a nuclear power, the adversary may target American allies with nuclear weapons. Such an escalation demonstrates an adversary’s willingness to coerce allies into ceasing support for the United States.

This is the worst-case scenario that extended deterrence was created to prevent. If allies seriously doubt American credibility, fielding independent nuclear forces is a solution.  Indeed, economically challenged Pakistan and North Korea took this path already. For America’s allies, acquiring nuclear forces may be a lower cost option than growing their conventional forces.

Second, allies might work together to devise a modern multilateral nuclear force as considered in 1960s Europe. In the Pacific, Australia considered working with Britain on nuclear weapons in the late 1940s and 1950s; some still favor this effort. In that regard, Japan and Australia have recently acquired Tomahawk cruise missiles, which the US armed with nuclear warheads to deter Russia in the 1980s. Such weapons might be a starting point for an allied nuclear force in the eastern Pacific. As noted, the US considered deploying ICBMs in the Australian outback.

Third, another option, arguably better for American global leadership, is to address the allies’ deepening concerns over extended deterrence. This would involve the current administration actively reassuring allies that it still places importance on existing security treaties, increasing nuclear sharing and including more nations in nuclear planning, especially in the Pacific. Such steps would be at marginal cost to the US.

The most important might be nuclear sharing as this appears a tangible example of commitment. Of course, nuclear sharing is actually a misnomer since the US shares in the employment of certain nuclear weapons. It retains full control of the weapons prior to an authorization to strike a target.

The US could increase nuclear sharing with Pacific allies, such as Australia, Japan, and South Korea, and broaden out to other NATO nations like Poland and the Scandinavian nations, which appear to be Russia’s next target after Ukraine. These nations could then reciprocate in hosting US nuclear weapons as Belgium, Germany, Italy, and the Netherlands do now.

This discussion hinges on American ambitions for global leadership. As the Trump administration pushes allies to bare a greater share of their own security while attempting to close a $2 trillion annual deficit, the US must necessarily cut costs everywhere. Thus, American allies must take a realistic look at what President Trump is seeking to accomplish with the federal budget and understand that they must step into the breach while the US sets its house in order.

Sometimes, a great power must admit that it may be in its interests to change direction and push its allies down a new, different path. In that case, the Trump administration might declare the NPT finished and instead encourage its allies to go nuclear.

Dr. Christine Leah is a Fellow at the US National Institute for Deterrence Studies and has worked on nuclear issues at Yale, MIT, and RAND and in London, Singapore, and Canberra. She is the author of The Consequences of American Nuclear Disarmament and Australia and the Bomb. Dr. Peter Layton is Visiting Fellow at the Griffith Asia Institute and an Associate Fellow at the Royal United Services Institute. He is author of Grand Strategy and coauthor of Warfare in the Robotic Age.

Time to Proliferate Nuclear Weapons (or Not?) was originally published on Global Security Review.