Japan Considers Nuclear-Powered Submarines as China and Russia Increase Pacific Naval Pressure.

Japan has formally included nuclear-powered submarines in its defense posture review, opening the way for Tokyo to assess a future SSN capability alongside its conventional fleet. Such a move could extend Japanese undersea operations across the Western Pacific while requiring new nuclear infrastructure, expertise and deeper technological cooperation with allied states.

Nuclear propulsion would allow Japanese submarines to remain submerged for longer periods, sustain higher speeds and operate at greater distances than the diesel-electric Taigei class, which displaces about 3,000 tonnes and uses lithium-ion batteries. Any future program would require decisions on reactor technology, shipyard and basing infrastructure, crew training and foreign cooperation, with the United States emerging as the most likely partner and the United Kingdom or France representing other possible sources of expertise.

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A Japan Maritime Self-Defense Force Taigei-class submarine. Japan is examining nuclear propulsion as a possible option for the future development of its undersea fleet. (Picture source: Japan MoD)

The Japanese government is not presenting the possibility as a procurement decision. Nuclear propulsion remains one of several options under review as Tokyo prepares an early revision of its three main strategic documents. The debate is therefore focused less on the immediate creation of a new submarine class than on the performance needed to maintain a sustained presence at long range, reduce the energy constraints of conventional platforms, and respond to evolving Chinese and Russian naval capabilities in waters surrounding Japan.

During his press conference on September 11, 2026, Defense Minister Shinjiro Koizumi confirmed that nuclear-powered submarines had not been excluded from the ongoing review. He cited their ability to remain submerged for extended periods, conduct longer deployments, and sustain higher speeds. Koizumi also highlighted the constraints associated with such an architecture, including cost, vessel size, the need for nuclear expertise, and factors related to acoustic discretion.

The discussion comes as the Japan Maritime Self-Defense Force already operates an advanced conventional submarine fleet. Taigei-class submarines have a standard displacement of about 3,000 tonnes and a length of roughly 84 meters. They use lithium-ion batteries, which provide greater energy capacity and longer submerged endurance than older lead-acid batteries. The class is also fitted with six 533 mm torpedo tubes and can exceed 20 knots while submerged. Its diesel-electric propulsion, however, retains an inherent limitation because available energy remains dependent on battery capacity and requires periodic recharging.

A nuclear-powered attack submarine would change that equation. Unlike a diesel-electric boat, it could maintain high submerged speeds for prolonged periods without having to return regularly to periscope depth to operate its generators. The operational impact would be particularly relevant in the Pacific, where distances between bases, straits, and patrol areas can extend over hundreds or even thousands of kilometers. Nuclear propulsion could therefore allow Japan to reach distant sectors more quickly and maintain a longer undersea presence once deployed.

That endurance would give Japanese commanders greater freedom to track a carrier strike group, intercept an opposing submarine, or reposition a platform discreetly between the East China Sea and the Philippine Sea. It could also reduce some of the vulnerabilities associated with snorkeling by conventional submarines, a phase during which exposed masts and related emissions can increase the risk of detection. Sustained speed would further improve the ability to reposition a submarine in response to intelligence from maritime patrol aircraft, surface vessels, acoustic networks, or other allied undersea surveillance assets.

The trade-offs would be considerable. Japan would need either an indigenous naval reactor or access to foreign technology, along with port and industrial infrastructure adapted to nuclear propulsion, specialized crews, maintenance systems, radiological safety procedures, and incident management mechanisms. These requirements would also affect shipyards, basing arrangements, technical training, and the national regulatory framework. They would introduce an additional political dimension in a country where nuclear-related issues remain sensitive.

The comparison with AUKUS therefore emerges naturally, although the model is not directly transferable. Australia is set to receive nuclear-powered but conventionally armed submarines through close cooperation with the United States and the United Kingdom. Japan is not part of the nuclear-submarine component of AUKUS. A comparable move would therefore require new political and technological decisions, most likely accompanied by a deeper level of cooperation with Washington.

If Tokyo ultimately decided to proceed, the United States would be the most likely partner because of the bilateral alliance, its experience in naval nuclear propulsion, and the precedent established with Australia under AUKUS. The United Kingdom could play a complementary role through its experience with the Astute and Dreadnought classes and its participation in the future SSN-AUKUS program. France represents another technically credible option through its experience with the Suffren class, although such a path would be less likely politically given the absence of a French precedent for exporting naval nuclear propulsion. Another possible approach would be for Japan to retain domestic construction of the hull and much of the combat architecture through companies such as Mitsubishi Heavy Industries and Kawasaki Heavy Industries, while seeking reactor technology, technical assistance, and training from abroad.

For Tokyo, the issue extends beyond fleet modernization. The introduction of nuclear-powered submarines would allow Japan to operate for longer periods and at greater distances across the Western Pacific while increasing its contribution to allied surveillance and maritime denial missions. It could also deepen defense technology cooperation with Washington and gradually affect the regional undersea balance, drawing close attention from Beijing, Moscow, and Pyongyang. No acquisition has been approved, but the formal inclusion of this option in Japan’s defense planning process already broadens the strategic debate in the Indo-Pacific.

Written By Erwan Halna du Fretay - Defense Analyst, Army Recognition Group
Erwan Halna du Fretay holds a Master’s degree in International Relations and has experience studying conflicts and global arms transfers. His research interests lie in Security and strategic studies, particularly the dynamics of the defense industry, the evolution of military technologies, and the strategic transformation of armed forces.