Hailed as an example of the success of the international non-proliferation regime, Japan has consistently taken principled stands on non-proliferation and disarmament issues. Today, Japanese officials and experts remain remarkably uniform in their consensus that Japan is unlikely to move toward nuclear status in the short-to-medium term. North Korea's test of a nuclear device in 2006 and China's military modernization have altered the strategic dynamics in the region, and any signs of stress in the U.S.-Japan alliance raises questions among some about the robustness of the U.S. security guarantee. All of these factors together increase the still unlikely possibility that Japan will reconsider its position on nuclear weapons. Any reconsideration of Japan's policy of nuclear weapons abstention would have significant implications for U.S. policy in East Asia. Globally, Japan's withdrawal from the Nuclear Non-Proliferation Treaty (NPT) could damage the most durable international non-proliferation regime. Regionally, Japan "going nuclear" could set off a nuclear arms race with China, South Korea, and Taiwan and, in turn, India, and Pakistan may feel compelled to further strengthen their own nuclear weapons capability. Bilaterally, assuming that Japan made the decision without U.S. support, the move could indicate Tokyo's lack of trust in the American commitment to defend Japan. An erosion in the U.S.-Japan alliance could upset the geopolitical balance in East Asia, a shift that could indicate a further strengthening of China's position as an emerging hegemonic power. These ramifications would likely be deeply destabilizing for the security of the Asia Pacific region and beyond. The rejection of nuclear weapons by the Japanese public appears to be overwhelmingly driven by moral, rather than pragmatic, considerations, but Japan's leaders have based their policy of forswearing nuclear weapons on protection by the U.S. nuclear arsenal. An Evolving Security Environment in Asia

Since the end of the Cold War, and particularly in the past decade, developments in the region have increased Japan's sense of vulnerability and caused some in the policy community to rethink Japan's policy of forswearing nuclear weapons development. Producing nuclear weapons would require expertise on bomb design including metallurgists and chemists; while a reliable deterrent capability may also require reliable delivery vehicles, an intelligence program to protect and conceal assets from a first-strike, and a system for the protection of classified information. Japanese Legal and Political Restraints

		Domestic Factors

			Public Opinion

In general, public opinion on defense issues in Japan appears to be shifting somewhat, but pacifist sentiment remains significant.
Japan, traditionally one of the most prominent advocates of the international non-proliferation regime, has consistently pledged to forswear nuclear weapons. Nevertheless, evolving circumstances in Northeast Asia, particularly North Korea's nuclear test in October 2006 and China's ongoing military modernization drive, have raised new questions about Japan's vulnerability to potential adversaries and, therefore, the appeal of developing an independent nuclear deterrent. The previous taboo within the Japanese political community of discussing a nuclear weapons capability appears to have been broken, as several officials and opinion leaders have urged an open debate on the topic. Despite these factors, a strong consensus—both in Japan and among Japan watchers—remains that Japan will not pursue the nuclear option in the short-to-medium term.
This paper examines the prospects for Japan pursuing a nuclear weapons capability by assessing the existing technical infrastructure of its extensive civilian nuclear energy program. It explores the range of challenges that Japan would have to overcome to transform its current program into a military program. Presently, Japan appears to lack several of the prerequisites for a full-scale nuclear weapons deterrent: expertise on bomb design, reliable delivery vehicles, an intelligence program to protect and conceal assets, and sites for nuclear testing. In addition, a range of legal and political restraints on Japan's development of nuclear weapons, including averse public and elite opinion, restrictive domestic laws and practices, and the negative diplomatic consequences of abandoning its traditional approach is analyzed.
Any reconsideration and/or shift of Japan's policy of nuclear abstention would have significant implications for U.S. policy in East Asia. In this report, an examination of the factors driving Japan's decision-making—most prominently, the strength of the U.S. security guarantee—analyzes how the nuclear debate in Japan affects U.S. security interests in the region. Globally, Japan's withdrawal from the Nuclear Non-Proliferation Treaty (NPT) would damage the world's most durable international non-proliferation regime. Regionally, Japan "going nuclear" could set off an arms race with China, South Korea, and Taiwan. India and/or Pakistan may then feel compelled to further expand or modernize their own nuclear weapons capabilities. Bilaterally, assuming that Japan made the decision without U.S. support, the move could indicate a lack of trust in the U.S. commitment to defend Japan. An erosion in the U.S.-Japan alliance could upset the geopolitical balance in East Asia, a shift that could strengthen China's position as an emerging hegemonic power. All of these ramifications would likely be deeply destabilizing for the security of the Asia Pacific region and beyond.
This report will be updated as circumstances warrant.