🌊 Japan does not have nuclear weapons. It has long held to three non-nuclear principles: not possessing them, not producing them and not permitting their introduction. Now a proposal has surfaced to write a study of nuclear-powered submarines for the Self-Defense Forces into the security documents the government plans to revise by the end of 2026.

The "nuclear" in a nuclear submarine describes what turns the propeller, not what sits in the launch tubes. And when Japan's government has explained why owning one would be "difficult," it has pointed not to the non-nuclear principles but to its reading of a law passed in 1955.

What Actually Surfaced

Kyodo News reported the plan on October 6, 2026, and the Yomiuri Shimbun followed on October 7, both citing multiple government and ruling-party sources. The "three security documents" are Japan's top-level defense blueprints: the National Security Strategy, the National Defense Strategy and the Defense Buildup Program. They were last revised in December 2022.

The two reports differ in tone. Kyodo said the text may stop at language that supports research and debate, without presupposing ownership. The Yomiuri described a proposal to state that the government will begin studying the idea; if that is written in, research could start, and a decision on ownership would be expected to take several years. The Yomiuri also cited an assessment that, with China expanding its maritime activity into the Pacific, long-endurance nuclear submarines are essential to maintaining deterrence.

At a September 11 press conference, Defense Minister Shinjiro Koizumi said the government would "consider all options without ruling anything out," nuclear submarines included. The Japan Innovation Party (Ishin), the Liberal Democratic Party's coalition partner, called in June for early introduction, arguing that nuclear power is the only option for a submarine that fires missiles from vertical launch tubes underwater. The LDP's own proposal to Prime Minister Sanae Takaichi called for "next-generation propulsion" for such submarines without naming the type. For how far Japan's defense posture has already moved, see our pieces on the first Tomahawk live fire and the LDP's draft defense proposal.

Conventional vs. Nuclear: What Changes

All of Japan's submarines are conventionally powered. The newest, the Taigei class, displaces about 3,000 tons and runs on a diesel-electric system with lithium-ion batteries. It is regarded as one of the most capable conventional submarines in the world, and one boat cost about 114 billion yen (about $721 million) in the fiscal 2025 budget. Dollar figures in this article use exchange rates as of October 7, 2026.

The limit is the battery. Once it runs low, the boat has to come up near the surface and draw in air to run its diesel engines and recharge, and during that time it is easier to detect. A reactor needs no air. A nuclear boat can stay down far longer, and Koizumi said it can reach several times the speed of a conventional one.

Why now? A Defense Ministry expert panel report on September 19, 2025 said submarines should carry long-range missiles and be able to travel far and stay submerged for long periods, including by studying next-generation propulsion. The ministry began research on a submarine vertical launch system (VLS) in fiscal 2025, and as of July 2025 planned to evaluate the results by fiscal 2029.

"Nuclear" Does Not Mean Nuclear Weapons

An attack submarine (SSN) carries conventional weapons such as torpedoes and cruise missiles. It is a different animal from a ballistic missile submarine (SSBN), which carries nuclear-tipped missiles. Australia's program with the US and UK is officially described as "conventionally armed, nuclear-powered submarines."

Japan's three non-nuclear principles are about nuclear weapons. They say nothing about how a ship is propelled. Prime Minister Takaichi told the Diet in November 2025 that she "firmly maintains" them "as a policy."

The hurdle has been the Atomic Energy Basic Act of 1955, whose Article 2 limits nuclear research, development and use to peaceful purposes. On April 14, 1965, Kiichi Aichi, then director-general of the Science and Technology Agency, told the Diet that even using nuclear power to propel SDF ships was not permitted while nuclear propulsion had not become common for ships. In 1980 the government said "common" meant a situation in which nuclear-powered merchant ships had become common. A cabinet answer to a lawmaker's question on November 14, 2025 said the 1965 view was unchanged and that no specific propulsion type was under study. In September 2024, Yoshimasa Hayashi, then chief cabinet secretary, said that under the current reading of the law it would be "difficult" for Japan to own nuclear submarines.

Owning one would mean changing either that interpretation or the law itself. Separately, a debate about nuclear weapons has also surfaced. In July 2026, Koizumi said on an online program that the nuclear weapons question could not be avoided, and a Chinese Foreign Ministry deputy spokesperson called the remark provocative and dangerous. At the expert panel on the security documents, one proposal called for reviewing the "no introduction" principle. The two debates are running at the same time, but they are separate questions.

How Australia, South Korea and Brazil Are Doing It

Under AUKUS, the pact with the US and UK launched in 2021, Australia plans to operate eight such submarines. Under the plan as of June 2026, US and UK boats will rotate through Western Australia from 2027, giving Australian crews hands-on experience. A 2023 estimate put the cost at A$268 billion to A$368 billion (about $187 billion to $256 billion) through the mid-2050s. On non-proliferation, the key mechanism is Article 14 of Australia's safeguards agreement with the International Atomic Energy Agency (IAEA), the provision that lets nuclear material be used for naval propulsion within the inspection framework. Consultations on that arrangement were still under way as of June 2026. China has repeatedly raised the program at the IAEA board, and in September 2026 the UK replied that the Nuclear Non-Proliferation Treaty (NPT) lets nuclear material be transferred whatever its enrichment level, as long as the transfer is not for weapons and stays within safeguards.

South Korea published a basic plan on May 26, 2026. It will build its submarines at home, fuel them with low-enriched uranium (generally meaning below 20 percent enrichment) and aim to launch the first boat in the mid-2030s. Because its nuclear agreement with the US covers only civil use, Seoul says a separate deal will be needed for the fuel.

Brazil is building the Álvaro Alberto. Originally due in 2025, it is now delayed to at least 2038 for lack of funds.

A US Navy official, speaking on September 9, 2026, said Japan already has the technical base from its nuclear power plants. Discussing South Korea, he cited a naval officer's view that a navy that doesn't plan to leave the waters near Korea doesn't need nuclear submarines, and said buying them as a status symbol would be a mistake.

Money and People

According to the Yomiuri, a nuclear submarine would cost several times as much as a conventional boat to build. Maintaining a reactor at sea takes specialized skills, and training those people is another hurdle. At the June 8, 2026 expert panel meeting, Noriko Endo, a senior researcher with professor rank at Waseda University, argued that nuclear submarines would give Japan "the ultimate counterstrike capability." Several other members doubted that crews could be secured over the long term as Japan's population shrinks, and some said procurement priorities needed to be clearer.

Naval News notes that Japan would need an entirely new infrastructure, from reactor maintenance to nuclear fuel management.

Still Only a Proposal

As of October 2026, what is settled is the schedule: the documents are due to be revised by the end of the year. How much they say about nuclear submarines will depend on the expert panel's recommendations and debate within the ruling parties, and caution runs deep inside the LDP. Even if the word "study" makes it in, research would come first, and any decision on ownership would follow years later.

Does your country's navy operate nuclear-powered submarines? If not, is anyone arguing that it should, or that it shouldn't?

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