By Yuan Yue

Japan's right-wing forces have been continuously seeking to break through the long-standing Three Non-Nuclear Principles upheld by the Japanese government in recent time, a trend that warrants close attention. According to the research report jointly released by China Arms Control and Disarmament Association (CACDA) and China Institute of Nuclear Industry Strategy (CINIS) titled Nuclear Ambitions of Japan's Right-Wing Forces: A Serious Threat to World Peace, Japan's nuclear capabilities are not in their infancy. Rather, the country has already accumulated sizable reserves of sensitive nuclear materials and developed a relatively comprehensive nuclear technology system.

In terms of plutonium, Japan possesses the world's fifth-largest stockpile. As of the end of 2024, Japan held approximately 44.4 tons of unirradiated separated plutonium. With regard to uranium, according to compilations of publicly available information by James  Martin Center for Nonproliferation Studies, Japan's civilian stockpile of highly enriched uranium ranks among the highest among non-nuclear-weapon states, at an estimated 1.8 tons.

Under safeguards assessment of the International Atomic Energy Agency (IAEA), eight kilograms of plutonium or 25 kilograms of uranium-235 equivalent constitute a significant quantity, that is, the approximate amount of material required to manufacture a rudimentary nuclear device. Based on this standard, Japan's domestic plutonium stockpile could theoretically produce about 1,075 nuclear device equivalents, while its total separated plutonium corresponds to roughly 5,550 equivalents. Its civilian highly enriched uranium reserves could also be converted into several dozen nuclear devices. Even after accounting for material losses, the potential yield of Japan's sensitive nuclear materials still far exceeds the requirements of a medium-sized nuclear arsenal.

Japan possesses multiple forms of nuclear materials, and the difficulty and time required for weaponization both fall within the critical window of crisis escalation. This is sufficient to drive latent capabilities toward actualization and exert pressure on regional security. In the short term, under extreme scenario assumptions, Japan could rely on its existing scientific and industrial base to produce a rudimentary, detonable nuclear device within six to twelve months. To reduce sanctions-related and political costs, Japan may rely on computer simulations and existing data to avoid conducting public nuclear tests, adopting an ambiguous strategy of assembly without declaration.

In the medium term, multiple assessments suggest that transforming Japan's latent capabilities into an initial nuclear arsenal would require three to five years. During this period, Japan could achieve warhead miniaturization and integration with delivery platforms, develop a warhead inventory on the order of two digits, and establish a basic nuclear command-and-control system as well as a specialized force structure. Compared with France's trajectory in the 1960s, when it took roughly seven years to progress from its first nuclear test to the gradual development of air- and sea-based nuclear capabilities, Japan starts from a higher baseline and possesses a more complete technological and institutional foundation. Once constraints are loosened, the pace of its nuclear advancement should not be underestimated.

Overall, Japan faces no major technical bottlenecks across the key stages of nuclear weapons development. The primary limiting factors lie in political will and international pressure, rather than in capability itself. Once Japan decides to break the long-standing taboo, its industrial and technological reserves would enable a rapid leap from zero to operational capacity within a very short period of time. Accordingly, the recent stream of statements by Japan's right-wing political forces that undermine the domestic consensus on non-nuclear principles represents a deliberate, step-by-step attempt to challenge, erode, and redefine the postwar international order and the nuclear restraint regime. Such moves warrant the highest vigilance and firm opposition.

Should Japan's latent nuclear weapons capability be translated into reality, it would fundamentally reshape the regional security landscape and weaken the global non-proliferation regime. The international community must not take this lightly. Instead, it must respond with a strong sense of crisis awareness and necessary collective action and remain alert to the specter of nuclearization haunting East Asia.

(The author is from the Institute of International Relations at China Foreign Affairs University.)

Editor's note: Originally published on china.com.cn, this article is translated from Chinese into English and edited by the China Military Online. The information and opinions in this article do not necessarily reflect the views of eng.chinamil.com.cn.