Japan to Study Acquiring Nuclear-Powered Subs in Security Review

Talks between the ruling Liberal Democratic Party and its coalition partner, Nippon Ishin (the Japan Innovation Party), began Nov. 10, and nuclear-powered submarines are set to be a central item as Tokyo rewrites its three national security documents, last updated in 2022. The package includes the National Security Strategy, the National Defense Strategy and the Defense Buildup Program.

According to government and ruling coalition sources cited by Asahi Shimbun on Nov. 11, the revised documents are expected to say Japan will consider adding nuclear-powered submarines to its fleet. Options under discussion include a pledge to begin “research and studies” toward introduction, or language that the government will “consider the matter and reach a conclusion.” The sources said a definitive decision to field the boats will not be written into the documents. Tokyo would first weigh the advantages, drawbacks and costs.

Prime Minister Sanae Takaichi, who has taken a hawkish line on national security, ordered the review amid China’s growing maritime activity, Russia’s war in Ukraine and North Korea’s nuclear and missile programs. A government expert panel is due to report in early December, and the Cabinet is expected to approve the revised documents later that month. The coalition plans to meet about once a week, with the hardest issues — nuclear-powered submarines, a possible review of the Three Non-Nuclear Principles and the size of the defense budget — reserved for December.

The two parties are not starting from the same place. In June recommendations, Ishin called for the early introduction of nuclear-powered submarines, while the LDP spoke only of considering “next-generation propulsion” for boats fitted with vertical launch systems for long-range missiles. Defense Minister Shinjiro Koizumi has already said Tokyo will not rule the option out.

Proponents argue that nuclear propulsion would let submarines stay submerged longer, travel farther and faster than Japan’s diesel-electric fleet, and support patrols and counterstrike missiles as China pushes into the Pacific. Continuous operations would reportedly require at least three boats, each estimated at about 1 trillion yen ($6.33 billion) to build, plus heavy maintenance costs, a timeline of more than a decade, and specialized crews. Japan’s Atomic Energy Basic Law limits nuclear energy to peaceful purposes, and past governments have said it cannot be used to power Self-Defense Forces submarines. Tokyo is separately wrestling with how to pay for a much larger defense buildup.

The LDP’s Research Commission on Security, chaired by former Defense Minister Yasukazu Hamada, met Nov. 11. Taro Honda, the commission’s secretary general, said there were calls to consider introducing nuclear-powered submarines and “nuclear sharing,” under which the United States would deploy nuclear weapons in Japan for joint operation, Kyodo News reported. Nuclear sharing would sit in tension with the Three Non-Nuclear Principles, which ban the possession, production or introduction of nuclear weapons. That debate is separate from nuclear propulsion, which would not by itself arm the boats with nuclear weapons.

Only six nuclear-armed states — the United States, Russia, China, Britain, France and India — currently operate nuclear-powered submarines. North Korea is also believed to be building one. The United States approved South Korean construction of nuclear-powered submarines in October 2025, and Australia is moving ahead with its own plans. Japan’s conventional undersea fleet is already being renewed, including the Taigei class.