Japan must consider acquiring nuclear-powered submarines, the nation’s defense minister said.
“The environment surrounding Japan is truly becoming so severe that we must debate whether to continue with diesel [propulsion systems] as we have, or to opt for nuclear-powered submarines,” Shinjiro Koizumi said in November 2025.
Japan is not the only United States ally in the Indo-Pacific looking to strengthen its maritime security with nuclear-powered submarines, which traditionally are faster and have greater endurance than conventional diesel-electric subs.
South Korea and the U.S. recently agreed to cooperate on Seoul’s efforts to build nuclear-powered, conventionally armed submarines amid increasing threats posed by the Chinese Communist Party and North Korea. Australia also is set to replace its diesel submarines with nuclear-powered vessels under its AUKUS security partnership with the United Kingdom and the U.S.
“This is a new development, and all the surrounding countries have them,” Koizumi said.
The Japan Maritime Self-Defense Force fleet includes Taigei-class submarines powered by diesel engines and lithium-ion battery technology, which allows for longer, quieter submerged operations, the Australian Naval Institute reported in October 2025.
In September 2025, Japan’s Defense Ministry recommended studying the use of a “next-generation power source” for submarines equipped with vertical launch systems for counterstrike capabilities, The Asahi Shimbun newspaper reported.
The government agreed in October 2025 to promote such an acquisition based on the Defense Ministry recommendation. Neither document mentioned nuclear power. Japan’s Atomic Energy Basic Act, which stipulates that nuclear power must be used for peaceful purposes, may need to be modified, The Japan Times newspaper reported.
“At this point, nothing has been decided regarding the next generation of propulsion systems for submarines,” Koizumi said, according to the website Naval News.
Sentry is a professional military magazine published by U.S. Strategic Command to provide a forum for national security personnel.