The U.S. atomic bombings of Hiroshima and Nagasaki killed large numbers of civilians and left long-term radiation effects. These attacks became the central historical reference point for Japan’s postwar anti-nuclear identity and activism.
Japan’s postwar Constitution entered into force with Article 9 renouncing war. While not a nuclear policy document, it strongly shaped postwar security debates and helped create political space for anti-nuclear norms in Japan.
The tuna boat Daigo Fukuryū Maru (Lucky Dragon No. 5) was contaminated by radioactive fallout from the U.S. Castle Bravo hydrogen bomb test at Bikini Atoll. The incident triggered nationwide alarm over radiation exposure and catalyzed Japan’s mass anti-nuclear movement.
Kuboyama Aikichi, the Lucky Dragon’s chief radioman, died after suffering acute radiation effects. His death became a symbol of the dangers of nuclear testing and strengthened anti–H-bomb public mobilization in Japan.
The First World Conference against Atomic and Hydrogen Bombs convened in Hiroshima, linking Japanese grassroots activism with emerging international anti-nuclear networks and establishing an annual focal point for anti-nuclear organizing.
Japan enacted the Atomic Energy Basic Law, establishing guiding principles for nuclear development, including the stated limitation of atomic energy to peaceful purposes and under democratic management with public disclosure of results.
Following the Atomic Energy Basic Law, Japan established the Atomic Energy Commission to plan and coordinate nuclear research and development policy, embedding civilian nuclear governance structures within the cabinet system.
Atomic-bomb survivors (hibakusha) organized nationally as Nihon Hidankyo, strengthening the moral and political force of Japan’s anti-nuclear movement through testimony, relief advocacy, and international outreach.
Japan’s first research reactor, JRR-1, achieved criticality, marking a major milestone in the institutionalization of civilian nuclear science in the postwar period and intensifying debates about nuclear technology’s risks and purposes.
Japan and the United States signed the revised Treaty of Mutual Cooperation and Security. The treaty’s ratification process provoked the massive Anpo protests, with nuclear war fears and U.S. base issues intertwined in public opposition.
Prime Minister Eisaku Satō articulated Japan’s Three Non-Nuclear Principles—not possessing, not producing, and not permitting the introduction of nuclear weapons—providing a clear political benchmark for Japan’s postwar nuclear restraint and for anti-nuclear advocacy.
Japan signed the NPT, aligning its formal international commitments with its domestic non-nuclear stance while continuing to rely on the U.S. security alliance for extended deterrence.
Japan’s Diet formally adopted a resolution endorsing the Three Non-Nuclear Principles. Although not enacted as statutory law, the resolution strengthened their status as enduring national policy and a rallying point for anti-nuclear movements.
Okinawa reverted to Japanese administration, an event closely tied to domestic nuclear politics and public insistence on a nuclear-free status for the territory amid debates over the U.S. nuclear posture in the region.
The Daigo Fukuryū Maru was preserved as a museum ship in Tokyo, institutionalizing public memory of nuclear testing’s human impacts and providing a durable educational site for Japan’s anti-nuclear movement.
Japan deposited its instrument of ratification of the NPT, completing accession and reinforcing its postwar non-nuclear policy architecture while expanding international safeguards coverage over Japanese nuclear facilities.
Nuclear Policy and Anti-Nuclear Movements in Postwar Japan (1945–1976)
