TOKYO/WASHINGTON -- Some experts in Washington, including a U.S. Navy official, are growing receptive to the idea of Japan acquiring nuclear-powered submarines, arguing that the vessels would enable the Japan Self-Defense Forces to deter China more effectively.

During a parliamentary hearing on Oct. 23, Japanese Defense Minister Shinjiro Koizumi said "a wide range of options should be discussed" regarding propulsion systems for next-generation submarines, signaling a positive view of nuclear-powered vessels. Japan looks to revise its three main security documents by the end of the year, and any policy changes could be included in the new versions.

Nuclear submarines can remain submerged much longer than the diesel-electric vessels operated by the Japan Maritime Self-Defense Force. This reduces the risk of detection by adversaries and allows for higher sustained speeds. Koizumi also cited enhanced crew safety as another benefit. The idea has some support among lawmakers from the Japan Innovation Party (JIP), the junior member of the ruling coalition.

In the U.S., some think Japanese nuclear submarines would contribute to security in the Indo-Pacific region. A U.S. Navy official told Nikkei and other media in September that Tokyo should consider acquiring them.

Japan's security policy emphasizes China, and Tokyo's threat perception aligns closely with that of the U.S. military. This creates favorable conditions for deeper cooperation with U.S. forces monitoring Chinese activities across Asia.

A report by the American Enterprise Institute think tank argued that nuclear submarines could let Japan "take on a greater role in countering the expansion and modernization" of the Chinese navy.

The report said nuclear submarines "will likely be increasingly important for Japan as the [Chinese navy] will likely transition toward a largely nuclear-powered submarine fleet in the next decade and is set to significantly expand its surface warfare capabilities." Beijing is thought to be expanding submarine operations in the Western Pacific beyond the so-called first island chain, which stretches from Taiwan and Okinawa to the Philippines. Some vessels may carry submarine-launched ballistic missiles capable of reaching the U.S. mainland. Monitoring the Western Pacific for Chinese submarine activity is difficult for American forces alone.

JIP's support for the idea also is rooted in China's growing military presence in the Western Pacific. In a policy proposal released in June, the party argued that Japan needs to shift its thinking toward "submarines capable of defending the entire Western Pacific." The party said diesel-electric submarines are insufficient for that mission and emphasized that "nuclear-powered submarines are the only option." Japanese nuclear submarines based at Yokosuka could remain active in the Philippine Sea for 85 days, Brent Sadler of U.S.-based think tank Heritage Foundation estimates, more than twice as long as diesel-powered vessels. In the South China Sea, they would be able to operate over four times longer.

If Japan decides to acquire nuclear submarines, cooperation from the U.S. will be critical. To date, Washington has limited sharing of submarine nuclear propulsion technology to close partners such as the U.K. and Australia. The challenges are formidable.

"The question of 'should Japan have nuclear submarines' should be considered separately from 'can Japan operate them safely,'" said Naoto Sekimura, professor emeritus at Tokyo University and an expert on nuclear safety and nuclear fuel. "Both questions require thorough discussion." Introducing nuclear submarines would require an independent regulatory and oversight framework based on nuclear safety standards. Japan also would need to train personnel capable of carrying out those regulatory functions, as well as specialists for operation, maintenance and repairs.

Japan's security policy is premised on an exclusively defense-oriented posture, prioritizing protection of areas near Japanese territory. A broad debate is needed over whether limited defense resources should be allocated to nuclear submarines designated for wide-ranging operations. The American Enterprise Institute report also identified funding, including maintenance and sustainment costs, as a major challenge.

Sekimura noted that nuclear submarines would raise issues related to international nuclear nonproliferation treaties, saying "diplomatic issues should also be addressed." Even if Japan opted for low-enriched uranium fuel, enrichment levels likely would be substantially higher than the roughly 5% typically used in civilian nuclear power. Neighboring Asian countries could express concerns about Japan acquiring such vessels.

Within the government, some propose incorporating language into the revised security documents calling for "investigations" and "research" into whether Japan should obtain nuclear-powered submarines.