Prime Minister Yukio Kishida announced on August 14th that he would not run for his re-election as leader of the governing Liberal Democratic Party (LDP). Shigeru Ishiba stands as one of the top contenders for Kishida’s succession. Ishiba is an LDP heavyweight, a former Defense Minister with three unsuccessful bids in past elections for the leadership of the LDP.
Describing himself as a “gun-taku” (a portmanteau for “gunji otaku” or military geek), Ishiba is known for his interest in military issues and his propensity to advocate strong defense measures. Ishiba made the headlines in 2011, when he argued against then Prime Minister Naoto Kan’s pledge to gear the country towards reduced dependence on nuclear energy, which had become a sensitive topic in the wake of the Fukushima nuclear disaster. Ishiba opposed the decision on the grounds that abandoning nuclear energy would deprive Japan of a deterrence capability. His plea essentially referred to what is commonly known as “virtual nuclear arsenals.”

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What is a “virtual nuclear arsenal?” The idea is simple. A “virtual nuclear arsenal,” or “nuclear latency,” refers to a nation’s capability to quickly develop nuclear weapons despite not currently possessing them. It requires a highly advanced and relatively autonomous civil nuclear industry because it involves several key components, such as advanced nuclear technology infrastructure, scientific expertise, and the production capacity for fissile materials. Such a state is called a “nuclear threshold state,” or a “paranuclear state.”
Virtual nuclear arsenals supposedly have several benefits. First, a state’s capacity to rapidly assemble nuclear weapons signals its ability to escalate beyond conventional means, or at least its ability to threaten to do so if needed. As such, virtual nuclear arsenals are often depicted as a less potent version of nuclear deterrence, with many – but importantly, not all – of the strategic and diplomatic benefits that are usually associated with it. Second, virtual nuclear arsenals are also said to be very cost efficient. Because nuclear power is a “dual-use” technology (i.e., it can be used for civilian and military purposes), proponents argue that virtual nuclear arsenals needn’t much more than the expenses already allocated to the civil nuclear industry. In comparison, “real” nuclear arsenals are far more costly. For instance, France is set to spend €52 billion (≈ 8,3兆円, current rate) for the upkeep of its nuclear deterrence over the 2024-2030 period, which will siphon off around 13% of the total budget allocated in France’s Military Programming Act (軍事計画法) Third, it also often stated that virtual nuclear arsenals garner less attention from domestic and foreign audiences, reducing pressure on the government and minimizing the risks of actual escalation.

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But arguments in support of virtual nuclear arsenals are often misleading. States may decide to develop an efficient civil nuclear industry for peaceful purposes, unintendedly leading to the constitution of a virtual nuclear arsenal. States may also purposefully build nuclear arsenals, pursuing more or less covert military goals such as the ability to construct nuclear weapons in the future, under the guise of civil nuclear programs. This is called “nuclear hedging.” Some indicators may help other countries assess whether or not a nation’s civil nuclear program acts as a cover for the purposeful development of a virtual nuclear arsenal, and countermeasures exist to discourage such behavior (e.g., IAEA inspections, etc.). But due to the nature of international politics, neighboring countries remain uncertain about a state’s true intentions. Furthermore, it is possible for states to evade international scrutiny. Depending on its relations with neighboring countries, a state’s virtual nuclear arsenal, even if intended exclusively for peaceful use, may also incentivize regional competitors to develop virtual (or even actual) nuclear arsenals of their own, leading to a security dilemma.
In strategic terms, the real benefits of virtual nuclear arsenals are also dubious. Virtual nuclear arsenals can only be seriously considered in the context of nuclear deterrence. Nuclear deterrence not only relies on a nation’s first-strike capability (i.e., the ability to launch a nuclear attack and disarm an adversary’s retaliatory power) but also on its second-strike capability (i.e., the ability to retaliate to a nuclear attack with one’s own nuclear strike). Civilian nuclear facilities such as power generation plants often do not benefit from the same degree of protection as other common counterforce targets such as launch silos do. In case of a nuclear attack, their survivability is not as guaranteed as, say, strategic nuclear-powered ballistic missile submarines concealed in the oceans.
Even worse, this vulnerability to missile strikes – or perhaps even infiltrated groups of saboteurs – paints a target on the back of civilian nuclear power plants. An enemy state would not even need nuclear weapons to inflict nuclear damage.

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Back to Japan. Japan is not a nuclear-weapon state. Its nuclear policy is guided by the Three Non-Nuclear Principles (非核三原則): non-possession (of nuclear weapons), non-production, and non-introduction (on Japanese territory). Yet, aside from nuclear-weapon states recognized by the NPT, Japan is the only country allowed to extract plutonium, an essential component in the production of nuclear weapons. In 2023, Japan’s plutonium stockpile was approximately 45.1 tons (with 9.3 tons held domestically, 21.8 tons in the UK, and 14.1 in France). Although Japan’s total stockpile has been decreasing over the last few years, proliferation observers worry that this quantity remains sufficient to manufacture roughly 5,000 nuclear weapons. The question of plutonium stockpile is further compounded by doubts expressed in Japan regarding the credibility of the US nuclear umbrella and Washington’s commitment to Japanese national security.
In this context, statements such as Ishiba’s are dangerous. They attract the attention of foreign audiences on the potential dual-use nature of Japan’s civil nuclear industry and they cast doubt on Japan’s intentions in the minds of foreign leaders. Disseminating the belief (in Japan and abroad) that Japan possesses a virtual nuclear arsenal capable of deterring aggression may simply incentivize its neighbors to react in ways that are detrimental to Japan’s security.
This is regrettable because, as explained above, such statements are misleading and portray an inaccurate picture of Japan’s capabilities. Granted, under optimal conditions, Japan may rapidly assemble a nuclear weapon if it chooses to do so. But in times of nuclear crisis, conditions are rarely optimal, especially when Japan’s civil nuclear infrastructure has yet to prove its survivability. Additionally, the wider public should not forget that at present, Japan also does not possess any meaningful delivery systems that have been reliably tested.