- Lessons from Iran’s nuclear latency strategy are forcing a strategic rethink in Tokyo and Seoul amid doubts about the credibility of the US nuclear umbrella.
The war involving Iran has delivered a stark and unsettling verdict on one of the most debated strategies in modern nuclear politics: nuclear latency. The concept—maintaining the technological capability to develop nuclear weapons without actually building them—was long seen as a way for states to balance deterrence with international legitimacy.
But the latest conflict suggests that this delicate balancing act may not work as intended.
Instead of deterring adversaries, nuclear latency may invite preventive strikes, leaving states trapped in what analysts call a dangerous strategic gray zone. The implications are already rippling far beyond the Middle East, particularly in Northeast Asia, where both Japan and South Korea have quietly pursued their own forms of nuclear hedging for decades.
For policymakers in Tokyo and Seoul, the lessons from Iran are profound: possessing the capability to build nuclear weapons without actually doing so may not guarantee security. In fact, it may increase the likelihood of conflict.
Nuclear latency refers to a country’s ability to quickly produce nuclear weapons if needed. This means having the fissile material required to build a bomb, the technical knowledge to construct a warhead, and the delivery systems—such as missiles or aircraft—to deploy it.
The theory has long been attractive.
By remaining just below the nuclear threshold, countries can avoid the diplomatic and economic consequences of openly becoming nuclear powers while still signaling to adversaries that they could cross that threshold rapidly in a crisis.
For Iran, this strategy seemed particularly appealing.
According to nuclear expert Ankit Panda of the Carnegie Endowment for International Peace, Tehran’s approach allowed it to preserve multiple strategic advantages simultaneously. Iran could maintain the technical infrastructure required for a nuclear program, keep open the possibility of negotiations with Western powers, and uphold the religious decree by Supreme Leader Ali Khamenei prohibiting nuclear weapons.
But the strategy carried inherent risks.
Panda argues that Iran ultimately adopted what may have been the worst possible nuclear posture—one that placed it dangerously close to acquiring nuclear weapons but stopped short of doing so.
That proximity made the country appear threatening enough to justify preventive military action by adversaries, yet not threatening enough to deter them outright.
For nuclear latency to work as a credible deterrent, two conditions must hold.
First, adversaries must believe that the country can quickly produce nuclear weapons if attacked. Second, there must be diplomatic alternatives available that make war less attractive.
In Iran’s case, both conditions were shaky.
The war involving Iran and regional rivals—particularly Israel and the United States—demonstrated how quickly that fragile balance could collapse.
Instead of deterring conflict, Iran’s nuclear proximity became a justification for military pressure aimed at destroying its nuclear infrastructure before weaponization occurred.
For strategic analysts, the result is a sobering lesson: nuclear latency may create what experts describe as a “window of vulnerability”—a period during which a country is clearly moving toward nuclear capability but has not yet achieved a fully operational deterrent.
During this window, adversaries may feel compelled to strike.
The implications of that lesson are resonating loudly in Northeast Asia.
Both Japan and South Korea possess sophisticated civilian nuclear programs, advanced technological bases and modern military capabilities. These elements together create what many experts describe as latent nuclear capabilities.
Japan, in particular, has maintained one of the world’s most significant stockpiles of plutonium.
Despite being the only country ever attacked with nuclear weapons—during the Atomic bombings of Hiroshima and Nagasaki in 1945—Tokyo has quietly built the technical capacity to develop nuclear arms relatively quickly if its security environment deteriorates.
Japan currently holds about 45 tons of weapons-usable plutonium, though most of it is stored overseas. The country also possesses advanced uranium enrichment technology, ballistic missile expertise derived from its space-launch programs, and modern fighter aircraft capable of carrying nuclear payloads.
A recent assessment by the International Atomic Energy Agency suggested that Japan’s nuclear infrastructure functions as a strategic hedge against regional threats.
At the same time, it serves another purpose: diplomatic leverage.
The existence of this latent capability sends a subtle signal to Washington that weakening security guarantees could eventually trigger nuclear proliferation.
South Korea’s path toward nuclear latency has been more complicated.
For decades, Seoul has sought capabilities similar to Japan’s but has faced significant restrictions due to its civil nuclear cooperation agreement with the United States, commonly known as the “123 Agreement.”
That pact limits South Korea’s ability to enrich uranium or reprocess spent nuclear fuel—two key steps in producing fissile material.
Yet the issue is becoming increasingly prominent in South Korean politics.
The government of Lee Jae-myung has begun negotiations with Washington to revise aspects of the agreement, particularly to allow uranium enrichment that could support nuclear-powered submarines.
What once appeared to be a niche position among conservative policymakers has now spread across the political spectrum in South Korea.
Public opinion surveys increasingly show support for developing an independent nuclear deterrent, driven by growing concerns about regional threats.
Underlying these debates is a deeper strategic anxiety: doubts about the reliability of US extended deterrence.
For decades, the United States has promised to defend allies under its “nuclear umbrella,” meaning that American nuclear forces would be used to protect partner countries if necessary.
But shifts in global politics are raising questions about whether that guarantee will remain credible.
A joint report released in February 2026 by the Center for Strategic and International Studies and the Asan Institute for Policy Studies argues that the international role of the United States is undergoing fundamental change.
According to the report, Washington appears to be stepping away from the rules-based order it helped build after the World War II, raising new uncertainties about long-term alliance commitments.
Historically, two forces constrained nuclear ambitions in Japan and South Korea.
The first was the credibility of the American nuclear umbrella. The second was Washington’s strict opposition to nuclear proliferation among its allies.
Both of those constraints now appear less certain.
Within Japan’s strategic community, skepticism about extended deterrence has been simmering for years.
According to Richard Samuels, a professor at the Massachusetts Institute of Technology who has studied Japanese security policy extensively, Tokyo has never been fully comfortable relying entirely on American protection.
Japanese officials have repeatedly sought stronger assurances from Washington over the decades.
Samuels warns that it would be naïve to assume that Japan is not reconsidering its long-standing nuclear restraint.
He notes that similar debates are unfolding in Europe, particularly in countries such as Germany and France, where policymakers are also questioning the long-term reliability of American security guarantees.
Former Japanese defense official Noboru Yamaguchi goes even further.
Deterrence, he argues, ultimately depends on perception rather than proof.
“It is impossible to prove extended deterrence is valid,” Yamaguchi has said. “Deterrence is about how we feel.”
During the Cold War, he suggests, faith in nuclear deterrence was already uncertain. Today, he says, it is even less convincing.
Another factor shaping the debate is the evolving stance of the United States toward allied nuclear programs.
Former US president Donald Trump has previously suggested that American allies might need to take greater responsibility for their own defense—including potentially developing nuclear weapons.
If Washington were to abandon its traditional opposition to allied nuclearization, the diplomatic barriers facing Tokyo and Seoul would be significantly reduced.
According to Siegfried Hecker, former director of the Los Alamos National Laboratory, the absence of US opposition would remove one of the biggest obstacles to nuclear latency strategies in Northeast Asia.
Without American pushback, he says, the political costs of pursuing such capabilities would decline sharply.
Yet the lessons from Iran raise a troubling possibility.
If Japan or South Korea begin moving closer to nuclear weaponization, adversaries might attempt to destroy their nuclear infrastructure before they reach the threshold.
The countries most likely to react strongly would be China and Russia.
Samuels emphasizes that the crucial audience for nuclear signaling is not domestic publics or even allies.
Instead, the real test lies in convincing potential adversaries that crossing the nuclear threshold is both possible and imminent if necessary.
Nuclear strategist Panda believes that China and Russia might initially rely on “gray-zone” tactics to slow any move toward nuclear weapons.
These could include cyberattacks similar to those previously launched against Iranian nuclear infrastructure.
Such measures could disrupt nuclear programs without triggering a full-scale military confrontation.
The most dangerous period in any nuclear latency strategy is the gap between a country’s decision to move toward weaponization and the moment it actually deploys nuclear weapons.
Analysts call this the “window of vulnerability.”
During this time, a state may appear threatening enough to provoke attack but not strong enough to deter it.
Building a credible nuclear deterrent requires more than just constructing a bomb.
Countries must also develop secure delivery systems and survivable arsenals capable of withstanding a first strike. For many analysts, this means deploying submarine-launched ballistic missiles.
Such capabilities can take years to develop.
Among potential latent nuclear powers, Japan holds a significant technological advantage.
Hecker estimates that Japan could assemble a uranium-based nuclear weapon within six months to a year if it decided to do so.
Producing a plutonium-based weapon might take up to two years.
South Korea’s timeline would likely be longer, particularly because it lacks domestic fissile material production capabilities.
Hecker believes Seoul would require more than two years just to produce the necessary nuclear material.
However, Panda notes that South Korea may be further ahead in certain aspects of nuclear weapons engineering.
One unusual scenario discussed among analysts involves cooperation between Japan and South Korea.
In such an arrangement, South Korea could contribute expertise in weapon design while Japan provides fissile material from its plutonium reserves.
Panda describes the idea as a theoretical “marriage made in heaven.”
Yet such a partnership would carry enormous political risks and would likely provoke intense reactions from neighboring powers.
If either Japan or South Korea moved decisively toward nuclear weapons, regional tensions could escalate rapidly.
North Korea—already a nuclear-armed state—might respond aggressively.
Hecker suggests that Pyongyang could attempt to involve Russia in countermeasures.
China, meanwhile, would likely react with particular anger to any Japanese nuclear program.
Historical memories and geopolitical rivalry make the idea of a nuclear-armed Japan especially sensitive in Beijing.
“If there is one thing that gets the Chinese exercised,” Hecker notes, “it’s Japan and a potential nuclear program.”
The war involving Iran may ultimately force policymakers in Tokyo and Seoul to confront a difficult choice.
They can interpret Iran’s experience as a warning about the dangers of nuclear latency, reinforcing the case for remaining firmly within the nonproliferation regime.
Or they may conclude that deteriorating security conditions—and uncertain alliance guarantees—leave them with few alternatives.
Either way, the debate over nuclear latency is entering a new phase.
For decades, the strategy was seen as a clever compromise between deterrence and restraint.
Now, the lessons of Iran suggest that it may be something far more dangerous: a temporary state that invites conflict rather than preventing it.
For Japan and South Korea, the question is no longer theoretical.
