Joint Statement: Japan Should Not Possess Nuclear-Powered Submarines

Members of Japan's ruling coalition and government expert panels have issued proposals for Japan to possess nuclear-powered submarines, in a highly dangerous development. Nuclear-powered submarines are designed for long-distance submerged operations and attacks, which grossly deviates from the principle of "exclusively defense-oriented policy" (Senshu Boei) that the Japanese government has long maintained under the peace constitution. Furthermore, using nuclear energy for military purposes runs counter to international efforts aiming for a world without nuclear weapons.

On July 14, Peace Boat, in joint cooperation with the Citizens' Nuclear Information Center and the Japan Campaign to Abolish Nuclear Weapons, released a statement titled "Japan Should Not Possess Nuclear-Powered Submarines." Peace Boat's Kawasaki was a joint initiator of this statement, while Watanabe Rika spoke at the press conference held on the same day.

Emphasising the importance of Article 9 of the Constitution, Watanabe appealed that possessing nuclear-powered submarines is "inappropriate for Japan's defense posture, which proclaims an exclusively defense-oriented policy." Furthermore, she pointed out that if Japan were to amend the Atomic Energy Basic Act to acquire nuclear submarines, "the way countries around the world view Japan would change drastically, sparking suspicion that nuclear armament is the next step," and thereby damaging Japan's credibility within the international community.

This joint statement is co-signed by 15 organizations, including Peace Boat, and 115 individuals. The full text of the statement is as follows in English, or can be dowloaded as a PDF here (click).

Access the original Japanese here.

Joint Statement: Japan Should Not Possess Nuclear-Powered Submarines

On June 24, 2026, Nippon Ishin no Kai (Japan Innovation Party) released its "Recommendation: National Security Strategy in the Era of the 'Thirty Years' Crisis.'" Alongside a review of the Three Non-Nuclear Principles and consideration of nuclear sharing, the recommendation places significant weight on the possession of nuclear-powered submarines, devoting 16 of its 124 pages to nuclear submarines and 13 to nuclear strategy. The same possibility already surfaced in two earlier documents, in both cases under the euphemism of "next-generation propulsion." The Ministry of Defense's Expert Panel on the Fundamental Reinforcement of Defense Capabilities signaled it in its September 2025 report, as did the Liberal Democratic Party in its "Recommendation Toward the Formulation of a New National Security Strategy and Related Documents," released the same day as the Ishin recommendation. We believe Japan should not possess nuclear-powered submarines, and we view these developments with grave concern.

First, the very necessity of such submarines is questionable. Generally, the roles of nuclear-powered submarines are considered to be, in the case of attack submarines, engaging enemy vessels, escorting aircraft carriers, and conducting surveillance; and in the case of strategic submarines, nuclear deterrence (second strike). Much of the recent argument for possessing nuclear submarines presumes deployment across wide-ranging maritime areas, which exceeds the bounds of Japan's national policy of maintaining an exclusively defense-oriented posture (Senshu Boei). Moreover, as a non-nuclear-weapon state, Japan has no role to play as the operator of the nuclear second strike that strategic submarines exist to deliver. There are also significant practical barriers. Beyond construction costs said to reach ¥1 trillion (roughly US$6.5 billion at current exchange rates) per submarine, operational challenges abound, including securing a home port and building a crewing structure capable of sustaining extended submerged patrols. There are safety concerns as well, foremost the risk of radiological accidents. Development would also take considerable time, since the concept differs markedly from that of conventional submarines. Given how fast battery technology has advanced in recent years, nuclear submarines may well have lost their competitive advantage before they ever enter service.

The gravest problem is the serious blow it would deal to the nuclear non-proliferation regime. The Comprehensive Safeguards Agreement (paragraph 14), concluded under Article III of the Nuclear Non-Proliferation Treaty (NPT), provides for the non-application of International Atomic Energy Agency (IAEA) safeguards (inspections) while nuclear material is being used in non-proscribed military activity. This is why the use of nuclear material aboard nuclear-powered submarines is widely regarded as a potential "loophole" in the NPT. So long as only nuclear-weapon states possessed nuclear-powered military vessels, the problem remained theoretical. Moves by non-nuclear-weapon states such as Australia and South Korea to acquire nuclear submarines, however, will require the special and specific safeguards arrangement stipulated in that paragraph. No such arrangement has ever been concluded, so its terms remain opaque, and the prospect is already placing serious strain on the non-proliferation regime. Some argue that using low-enriched uranium would ease these concerns, yet the underlying structure, in which nuclear material falls temporarily outside safeguards coverage regardless of enrichment level, remains unchanged. For Japan to join this trend would complicate the safeguards system and drive the further weakening of the non-proliferation regime. At a time when the line between the military and civilian uses of nuclear energy is growing ever more blurred, for a non-nuclear-weapon state with Japan's advanced nuclear capabilities to acquire nuclear-powered submarines would risk entrenching that ambiguity as a fait accompli.

Japan has long declared its responsibility, as the only nation to have suffered atomic bombings in wartime, to lead the effort toward the abolition of nuclear weapons, and under Article 2 of the Atomic Energy Basic Act it has confined the use of nuclear energy solely to peaceful purposes. To possess nuclear-powered submarines would be for Japan itself to disavow that very position. A Japan that upholds an exclusively defense-oriented posture as a matter of national policy has no need for nuclear-powered submarines. The political and financial resources that would otherwise be spent on this debate should instead be directed toward easing tensions through diplomacy. We strongly urge the government to rule out the acquisition of nuclear-powered submarines.

14 July 2026

Jointly issued by 15 organizations and 115 individuals, including Citizens’ Nuclear Information Center (CNIC), Japan Campaign to Abolish Nuclear Weapons and Peace Boat.