Does Japan Need Nuclear Subs? The Debate Is Bigger Than China

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Seiji Maehara, a senior JIP lawmaker responsible for its national security discussions, has argued that China's expanding naval operations into the Pacific make greater underwater endurance increasingly important.

His view reflects a wider concern that Japan must prepare for a maritime environment extending well beyond its immediate coastal approaches.

The Liberal Democratic Party (LDP), however, has not embraced the idea as explicitly, at least not yet. Although both coalition partners support strengthening Japan's defenses, their June security proposals diverged over nuclear propulsion.

The government's later willingness to consider a study has moved the issue closer to formal policy deliberation without resolving the disagreement. Reports on October 13 indicated that some lawmakers remained unconvinced that the military purpose of acquiring nuclear submarines had been adequately defined.

This is the first test of political reality. Takaichi must reconcile a junior partner seeking a firm commitment with a senior party that remains cautious. Defense Minister Shinjiro Koizumi has kept the option open but has also acknowledged the trade-offs.

Nuclear-powered submarines offer long endurance and high sustained speeds, yet they are expensive and require specialized expertise to maintain and operate. Conventional submarines, meanwhile, can retain important advantages in underwater quietness.

China's naval buildup explains why the debate has gained traction, but does not establish that nuclear propulsion is Tokyo's only credible response. Takaichi's government must thus distinguish between agreeing on the need to strengthen deterrence and agreeing on how to do it.

Japan already operates 23 diesel-electric attack submarines. That is a substantial foundation, not an absence of underwater capability. The relevant question is what additional missions nuclear propulsion would make possible, and whether those missions justify the investment.

Japan's defense budget sharpens the question. Japan allocated 9 trillion yen (US$57.3 billion) for defense-related spending in fiscal 2026, up 3.8% from the previous year.

The higher budget includes 120.8 billion yen to build a tenth Taigei-class submarine, 16 billion yen for submarine-launched missiles and 100 billion yen for the SHIELD coastal defense program, which combines unmanned systems into a layered defensive network.

Those line items show the alternatives competing for budget outlays. Japan must fund submarines, missiles, surveillance systems, unmanned platforms, personnel and supporting infrastructure.

A nuclear-powered fleet would add requirements for reactor engineering, specialized maintenance facilities, safety systems and highly trained crews. The costs would extend well beyond the price of the vessels themselves.

The government should therefore weigh nuclear propulsion against a portfolio of alternatives, including improved conventional submarines, underwater sensors, maritime patrol aircraft and anti-submarine warfare systems.

The goal should be the greatest operational gain for the money, not an assumption that the most sophisticated platform necessarily yields the greatest strategic return.

The legal dimension is just as important. Japan's Atomic Energy Basic Act limits nuclear development and use of nuclear energy to peaceful purposes, raising questions about the legal framework for acquiring military nuclear propulsion.

The government would need a defensible interpretation of the law, together with appropriate arrangements for reactor safety, fuel management and institutional oversight.

Japan's three non-nuclear principles prohibit possessing, producing or permitting the introduction of nuclear weapons, but they do not automatically prohibit nuclear-powered vessels. The two issues should not be conflated.

Nor can Japan move straight from political approval to operational deployment. Nuclear propulsion requires a specialized industrial ecosystem, including reactor engineering, testing, maintenance and safety capabilities.