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Japan’s Defense Minister: Nuclear-Powered Submarines Will Not Be Ruled Out

NAVAL NEWS, 15/09/2026, By Kosuke Takahashi

Speaking at a press conference on September 11, Koizumi was asked about reports that a U.S. Navy official had expressed a positive view of Japan potentially acquiring nuclear-powered submarines. While declining to comment directly on individual media reports, Koizumi said the option would be considered as part of the government’s planned revision of Japan’s three key national security documents: the National Security Strategy, National Defense Strategy and Defense Buildup Program. The three documents are expected to be revised by year-end.

As I have said before, in the course of revising the three documents, we will consider all options without ruling anything out,”
“Of course, we will also proceed with our consideration without ruling out nuclear-powered submarines as an option.”Japan’s Defense Minister Shinjiro Koizumi

Koizumi stressed that no decision had been made and that the government was not working toward a predetermined conclusion.

Asked about the strategic advantages of nuclear-powered submarines and the challenges Japan would face if it decided to acquire them, Koizumi offered one of his most detailed public assessments of SSNs to date. Speaking in general terms, he said nuclear-powered submarines can remain submerged for long periods, conduct extended operations, and are said to be capable of speeds several times higher than those of conventionally powered submarines.

“These characteristics make it possible to conduct the required activities while ensuring a higher level of safety for the crew,” Koizumi said.

At the same time, he acknowledged significant disadvantages. He said nuclear-powered submarines are said to be less quiet underwater than conventionally powered submarines. He also cited the high cost of nuclear propulsion systems, the need for larger hulls, and the specialized technical expertise required to operate, maintain, and service nuclear propulsion plants.

“In an increasingly rapidly changing security environment across various fields, we will examine the measures necessary to improve deterrence and response capabilities without ruling out any options,” Koizumi said.

U.S. Navy Official Voices Support for Japan Considering SSNs

Koizumi’s remarks came two days after a U.S. Navy official reportedly expressed a positive view of Japan considering nuclear-powered submarines.

The unnamed U.S. Navy official spoke to Japanese, South Korean, and other Asia-Pacific journalists at Joint Base Pearl Harbor-Hickam in Hawaii on September 9.

According to Japanese media reports, when asked whether Japan should consider acquiring nuclear-powered submarines, the official responded positively, pointing out that Japan operates nuclear power plants and possesses relevant nuclear technology. The same official also drew attention in South Korea by saying Seoul needed a “valid reason” for acquiring nuclear-powered submarines and warning against pursuing them merely as a “status symbol.”

Japan currently operates only conventionally powered diesel-electric submarines, but the debate over nuclear propulsion has accelerated over the past year…………………………….

Major obstacles remain, however. Nuclear-powered submarines would be far more expensive than Japan’s current conventional boats and would require an entirely new infrastructure for naval nuclear propulsion, including reactor maintenance, nuclear fuel management, and specialized personnel. There are also legal and political questions. Japan’s Atomic Energy Basic Act restricts the use of nuclear energy to peaceful purposes, raising longstanding questions about the compatibility of nuclear-powered warships with the existing legal framework.

Koizumi’s September 11 remarks do not mean Japan has decided to acquire SSNs. But his explicit statement that nuclear-powered submarines will not be excluded from consideration, combined with his detailed public assessment of their advantages and disadvantages, suggests that the issue is moving from a largely theoretical debate toward a concrete defense policy discussion. https://www.navalnews.com/naval-news/2026/09/japan-defense-minister-nuclear-powered-submarines/

September 17, 2026 - Posted by Christina Macpherson | Japan, weapons and war