Japan Keeps Nuclear Submarine Option on Table as Security Debate Deepens

Overview

• Defense Minister Shinjiro Koizumi said Japan will not rule out nuclear-powered submarines when revising three core security documents, a position he reiterated on Sept. 11.
• A U.S. Navy official and the U.S. Pacific Fleet signaled support for Japan studying nuclear propulsion, making allied input a key factor in Tokyo’s review.
• Tokyo’s move to fund submarine-launched hypersonic weapons in the FY2027 budget increases the operational appeal of longer-range, longer-endurance platforms and links the propulsion question to concrete weapons plans.
• Major hurdles remain: legal limits in the Atomic Energy Basic Act, much higher costs per SSN compared with diesel-electric boats, and shortages of specially trained personnel and shore infrastructure.
• The debate responds to regional shifts in undersea power, including U.S. ONI testimony about China’s rapid move to a largely nuclear submarine force, which has altered Japan’s strategic calculations.