Japan's Koizumi says nuclear-powered submarines not ruled out in defense review

September 15, 2026 at 10:54 AM2 min

This digest was compiled by AI from multiple sources — links to the originals are below.

Japan's Defense Minister Shinjiro Koizumi said on September 11 that Tokyo will not rule out nuclear-powered submarines as it revises its three key national security documents by year-end. The remarks came two days after a U.S. Navy official reportedly expressed a positive view of Japan considering SSNs. Koizumi stressed no decision has been made and the government is not working toward a predetermined conclusion.

Key Facts

Japan's Defense Minister Shinjiro Koizumi said on September 11 that Tokyo will not rule out nuclear-powered submarines as an option in its defense review.
Japan's three key national security documents — the National Security Strategy, National Defense Strategy and Defense Buildup Program — are expected to be revised by year-end.
A U.S. Navy official reportedly told journalists at Joint Base Pearl Harbor-Hickam on September 9 that Japan operates nuclear power plants and possesses relevant nuclear technology.
Koizumi 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 conventionally powered submarines.
Koizumi cited high cost, larger hulls, and specialized technical expertise as disadvantages of nuclear-powered submarines.

Defense Review Options

Koizumi said the option of nuclear-powered submarines 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 are expected to be revised by year-end. Koizumi stressed that no decision had been made and that the government was not working toward a predetermined conclusion.

SSN Capabilities and Costs

Koizumi 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. He said these characteristics make it possible to conduct required activities while ensuring a higher level of safety for the crew. Koizumi also acknowledged significant disadvantages, including that nuclear-powered submarines are said to be less quiet underwater than conventionally powered submarines. He 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.

U.S. Navy Signal

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.