According to a report by The South China Morning Post on October 8th, the Japanese government is considering adding research on maintaining nuclear-powered submarines to three security documents, including the National Security Strategy, which will be revised by the end of this year. The Japanese government has not yet decided on the construction of such submarines, nor have they determined the number, model, or timeline. However, once this is included in the security documents, it will allow the Ministry of Defense to conduct more formal technical and policy research.
On September 11, Japan's Defense Minister Yukio Satō made it very clear: Japan will consider “any option” when revising the three security-related documents, and nuclear-powered submarines will not be excluded either.
What is discussed here is using nuclear reactors to power submarines, rather than equipping submarines with nuclear warheads. However, even so, for Japan, this remains a clear political barrier.
Japan's Atomic Energy Basic Law stipulates that the use of atomic energy should be limited to peaceful purposes. In 1965, the Japanese government even clarified that the use of atomic energy for propulsion in self-defense ships was not allowed until nuclear-powered ships became widespread. The government still reiterated this interpretation in 2017. Now, Tokyo has put military nuclear power back on the agenda, indicating that the policy boundaries that have existed for decades are being challenged.
But what really drove discussions about nuclear submarines in Japan is not a interest in 'nuclear' technology itself, but rather a change in the scope of maritime warfare.
Japan's current main types of submarines are still the Canglong-class and Dajing-class submarines with conventional power systems. Japan has also been at the forefront in using large-capacity lithium-ion batteries for submarines, making it a leader in silent operation and underwater endurance for conventional submarines.
This type of submarine is very suitable for the combat environments that Japan was accustomed to in the past: to guard the seas around the Japanese archipelago and to carry out hidden ambushes near the East China Sea, the Matsushima Strait, and the Southwestern Islands.
The problem is that the Chinese Navy is increasingly using these straits for its operations.
The 2026 edition of Japan’s ‘Defense White Paper’ states that the presence of Chinese vessels in the Pacific has become a frequent occurrence. Their routes include not only the area between Okinawa Island and Miyako Island, but also the Osumi Strait and the direction towards Toktaonu Island. As of the end of May this year, the Liaoning aircraft carrier had entered the Pacific 13 times, while the Shandong aircraft carrier has done so 9 times. The Japan Defense Ministry believes that China’s maritime and air operations in distant waters will continue to expand.
This has created a problem for Japan's conventional submarines that is becoming increasingly difficult to evade:
The true advantage of nuclear-powered submarines is not simply “unlimited range,” but the ability to maintain high-speed operation for extended periods. Naoki Inoue himself acknowledges that compared to conventional submarines, nuclear-powered submarines can operate for longer distances and at higher speeds, with several times greater underwater propulsion. At the same time, their hulls can be designed to be larger, allowing room for more weapons and even long-range missiles.
This means that Japan is discussing the possibility of a bigger change hidden behind discussions about nuclear submarines – one more significant than simply "changing power sources"
The Japan Maritime Self-Defense Force is considering whether future submarines will remain merely underwater forces defending Japan's nearby waters, or whether they will become oceanic combat platforms capable of operating deep into the Philippine Sea and even the Western Pacific.
The former requires extreme quietness and mastery of key straits; the latter demands speed, endurance, long-range maneuverability, and the ability to track continuously.
Of course, Japan still has a long way to go before taking this step. Building nuclear reactors, professional personnel, and maintenance systems from scratch would be extremely costly compared to conventional submarines. Moreover, Japan must also address political issues arising from the Atomic Energy Basic Law and domestic anti-nuclear public opinion. Shinzo Abe himself acknowledges that nuclear submarines are expensive, have large hulls, require specialized maintenance techniques, and their noise reduction capabilities may not be as good as those of conventional submarines.
So in the short term, what really deserves attention is not when Japan will be able to build its first nuclear submarine.
Instead, Tokyo has already begun to consider that the question of whether Japan should have nuclear-powered warships is something that can be discussed on its own.
There is still a long way to go from "not discussing" to "researching", and then to deciding whether to build at all. But this has often been the way Japanese security policies have changed over the past ten years: first breaking political taboos, then turning capacity building into a technical issue.
This time, it might be the same for nuclear-powered submarines as well.
