In what could represent a significant enhancement to its deterrence capabilities, the Japan Maritime Self-Defense Force (JMSDF) is reported to have received a recommendation from a group of analysts to move forward with the acquisition of new nuclear-powered submarines — a proposal that responds to rising tensions in the Indo-Pacific and the growing naval power of China. Specifically, this recommendation came from a panel of experts established in February to assess the progress of the JMSDF in meeting Japan’s national defense strategies. The panel also indicated that it will be crucial for Tokyo’s future defense posture to include submarines capable of deploying long-range missiles launched vertically.
According to local reports, the document in question was presented to Japan’s Ministry of Defense last month, with the issue of submarines as its central focus. Among other things, the report highlights the need for the JMSDF’s future submarines to possess greater attack capabilities and remain at sea for longer periods. To achieve the latter, the experts suggested that their “next-generation” propulsion system should not be limited to conventional designs — a statement that sparked speculation regarding a potential nuclear component.
Explaining the rationale behind this recommendation, the panel argued that Japan must begin to conceive its defense strategy beyond its national borders, adopting instead a regional approach that takes the Chinese threat into account. Moreover, speculation has emerged in Japan that the government may be considering changes to the legislation governing the Self-Defense Forces since the end of World War II — particularly regarding the loosening of the strict limitations placed on their capabilities. Additionally, any potential decision to develop nuclear-powered submarines would also have to address the Basic Atomic Energy Law, which currently prohibits the country from engaging in nuclear research or development for military purposes.
This latter point holds special relevance in Japan’s political debates regarding the future, as differing views exist between the current administration and prominent figures within the incoming government. A clear example of this divide lies in the statements made by Chief Cabinet Secretary Yoshimasa Hayashi, who remarked a year ago that Japan would face major obstacles in acquiring nuclear-powered submarines under current law. Conversely, potential future Prime Minister Sanae Takaichi has stated that she would support the JMSDF possessing nuclear-powered submarines, arguing that such a move would not be unconstitutional.
It is also worth noting that the aforementioned improvements — particularly the inclusion of a Vertical Launch System (VLS) — have already been considered by Japan’s Ministry of Defense, as well as by Kawasaki Heavy Industries. In 2023, the company presented a new submarine design featuring such systems positioned between the bow and the sail, intended as a successor to the Taigei-class submarines currently being incorporated into the JMSDF fleet.
In line with this, local media have discussed potential weapons that could be integrated into these future systems — notably a new variant of the domestically produced Type 12 missile or the U.S.-made Tomahawk, which is already set to equip the JMSDF’s surface fleet. In both cases, future Japanese submarine designs would require larger hulls to accommodate these systems, which would in turn necessitate more powerful propulsion solutions.
However, while the acquisition of nuclear-powered submarines remains a possibility, there are numerous obstacles — beyond the legal ones — that make it a complex endeavor. Experts noted that developing such capabilities domestically would take nearly a decade before the first submarine could enter service. Leasing vessels from allies such as the United States would also be difficult, as those nations already face heavy operational demands on their existing fleets. Furthermore, like many other armed forces around the world, Japan faces a shortage of military personnel — particularly for submarine crews.
In this context, analysts suggest two possible alternatives to developing nuclear-powered submarines: first, acquiring them under a framework similar to Australia’s AUKUS agreement; or second, pursuing designs that combine multiple propulsion sources to achieve greater power output. Following the latter approach, Japan could look to South Korea’s example — its new submarines integrate lithium-ion batteries, diesel engines, and an Air-Independent Propulsion (AIP) system. Finally, another still underexplored possibility lies in the field of unmanned underwater systems, such as the U.S. Orca and Australia’s Ghost Shark, which could directly address several of the challenges mentioned above.
*Images used for illustrative purposes
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