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Overview Last updated: September, 2013

Japan's 1947 constitution, which renounces the right to use force or the threat of force to resolve international disputes, sets important limits on Japanese security policy. As a result, the U.S.-Japan alliance is the cornerstone of Japan's security policy. Japan does not possess any programs for the development of weapons of mass destruction (WMD) or their delivery systems, though experts widely believe that Japan has the technical capability to produce such weapons in a short period of time should it make the political decision to do so.

While Tokyo unsuccessfully attempted to develop nuclear weapons during World War II, its experiences during that war as the only country to have been attacked using nuclear weapons precipitated a strong commitment to nonproliferation and disarmament. Japan is a party to all relevant multilateral nonproliferation treaties and regimes. Tokyo ratified the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) in 1976 and the Comprehensive Nuclear Test Ban Treaty (CTBT) in 1997. While Japan developed and employed both chemical and biological weapons prior to 1945, Tokyo is now a state party to both the Chemical Weapons Convention (CWC) and the Biological and Toxin Weapons Convention (BTWC). Japan is also a member of the Australia Group, the Nuclear Suppliers Group, the Missile Technology Control Regime (MTCR), and the Zangger Committee.


Japan's commitment to nuclear disarmament and nonproliferation and its support for the NPT have remained unchanged since it acceded to the treaty in 1976. Domestically, Japan's "Atomic Energy Basic Law" allows only peaceful nuclear activities, [1] and its "Three Non-Nuclear Principles" pledge that Japan will not possess, produce, or permit the introduction of nuclear weapons into the country. [2] Despite Japan's long-standing stance against nuclear weapons, the domestic debate occasionally re-opens. For example, there was an internal debate in the early 1970s about whether Japan should sign the NPT. Moreover, Japan's "nuclearization" debate resurfaces periodically in response to the regional security environment, and especially the North Korean threat. The Japanese public's deep aversion to nuclear weapons and Tokyo's strong commitment to international nonproliferation regimes make any move in this direction improbable. However, Japan is the only NPT non- nuclear weapon state that possesses full-scale nuclear fuel cycle facilities. This has generated significant controversy domestically, regionally, and globally. Japan's neighbors are especially concerned about its significant plutonium stocks, as they are perceived to provide the country with a latent nuclear weapons capability. Before the March 2011 accident at the Fukushima Daiichi Nuclear Power Station, Japan increasingly relied on nuclear power for its electricity needs.

With almost no indigenous energy sources, nuclear energy has accounted for over 30% of the country's total electricity production, and Japan planned to increase this to at least 40% in 2017, and 50% by 2030. [3] Before the Great East Japan Earthquake and Tsunami on 11 March 2011, Japan had 54 nuclear power reactors in operation across the country (the third largest number in the world, after the United States and France). [4] On 15 September 2013, Japan's last operating nuclear power reactor shut down due to safety reviews. [5] Between July 2012 and September 2013, only two of the 50 nuclear reactors were operating. Units 1, 2, 3, and 4 at the Fukushima Daiichi Station are subject to decommissioning. This is the second time that the country is experiencing zero nuclear power generation since the Fukushima crisis started in March 2011. [5] Between May and July 2012, no nuclear power reactor in Japan was operating. [6]

On 11 March 2011, a 9.0-magnitude earthquake and subsequent aftershocks and tsunami waves precipitated power failures at the six-reactor Fukushima Daiichi Nuclear Power Station—since that time, Japanese personnel have been attempting to manage escalating crises involving loss of coolant and possible partial core meltdowns in units 1, 2, and 3, and dangerously low levels of water in the spent-fuel ponds at units 3 and 4. [7] All three units experienced core meltdown. The accident was the first level 7 accident, as defined by the International Nuclear Event Scale (INES) standard, since Chernobyl. It is unclear how much radiation has been or will be released into the environment. According to Japanese governmental officials, the emission of radioactive substances from Fukushima Daiichi is approximately 10% of the amount that had been detected at Chernobyl. [8] On 16 December 2011, the Japanese government announced that the three reactors that suffered meltdowns had officially reached cold shutdown. However, the nuclear crisis is far from over. [9] As of September 2013, one of the most serious concerns related to the Fukushima crisis is the leakage of radiation-contaminated water from the power plant. [10]

A post-Fukushima nuclear energy policy review was completed in September 2012 under the then ruling Democratic Party of Japan (DPJ). The DPJ ousted the Liberal Democratic Party (LDP) in 2009; the latter had been in power for almost half a century. The policy document issued on 14 September 2012 stated that Japan would phase out nuclear energy by the end of the 2030s. [11] However, following the DPJ's three-year rule, at the first nationwide election (Lower House) after the Fukushima accident, the LDP won a landslide victory over the DPJ, mainly because of the electorate's dissatisfaction with the DPJ's economic policy. The LDP is more pro-nuclear energy, and is advocating a more conservative approach to reducing Japan's nuclear energy dependence. As such, the LDP will review the DPJ's decision to phase out nuclear energy by the end of 2030s. [12] With the LDP's decisive victory over the DPJ again in the July 2013 Upper House Election, the ruling coalition of the LDP and the New Komei Party is the dominant power in both the Lower and Upper houses, it is generally perceived that the government will accelerate the revival of the country's nuclear energy program. [13] However, the LDP's junior coalition partner, the New Komei Party, supports the phase-out of nuclear power as soon as possible, and a review of Japan's fuel cycle policy. Therefore, how far and how fast the new government will reduce nuclear energy's share of Japan's total energy generation still remains to be seen.


Japan had an active biological warfare (BW) program prior to 1945. The focal point of the program was the now infamous Unit 731, based at a laboratory complex in northeastern China during the Japanese occupation. Unit 731 experimented on Chinese civilians and Allied prisoners of war with various biological agents, including plague, cholera, and hemorrhagic fever. Additionally, the Japanese military used biological weapons against China. Most of the data that the Japanese military accumulated during WWII was confiscated by the U.S. military. After World War II, the Japanese government abandoned its BW program. Japan signed the BTWC in 1972 and ratified it in 1982, and has actively supported negotiation of a protocol to strengthen the treaty's provisions. Since the 1995 Aum Shinrikyo sarin (chemical weapons) attack and failed attempt to disperse anthrax, Japan has increased its focus on bio-terrorism defenses. Although Japan has a growing biotechnology industry, it is still small in comparison with its chemical industry. As a member of the Australia Group, Japan's biotech industry is subject to a comprehensive set of export controls.


Japanese scientists began developing a chemical warfare (CW) capability as early as 1917. The Japanese Army used chemical weapons after invading China in 1937, conducting an estimated 1,000 to 3,000 attacks. Japan reportedly produced five to seven million munitions containing agents such as phosgene, mustard, lewisite, hydrogen cyanide, and diphenyl cyanarsine. [14] Although Japanese forces used many of these munitions between 1937 and 1945, they abandoned a considerable amount of the munitions while retreating. After World War II, Japan pledged it would not produce chemical weapons and participated in the negotiation of the Chemical Weapons Convention (CWC), which Japan signed in 1993 and ratified in 1995. Japan's CWC obligations include responsibility for the disposal of its abandoned chemical weapons in China. To that end, the Japanese government established the Abandoned Chemical Weapons Office under the Prime Minister's Office (now the Cabinet Office) on 1 April 1999. Between 300,000 and 400,000 munitions remain in China's Jilin Province. [15] The deadline for completion of the clean-up was 2007, but Tokyo and Beijing requested a five-year extension from the Organization for the Prohibition of Chemical Weapons (OPCW). Japan's chemical industry is the world's third largest after the United States and China. [16] As a member of the Australia Group, Japan has developed comprehensive and well-enforced export controls on chemical weapons precursors and dual-use items. Since the 1995 Aum Shinrikyo sarin attack, Japanese spending on CW defense has increased.


Japan does not have a ballistic missiles development program, but its space program includes a number of technologies that could potentially be adapted to serve as long-range missiles. Japan lacks sophisticated command-and-control systems, as well as some guidance and warhead technology that would be necessary to develop operational missiles. Japan is a member of the Missile Technology Control Regime (MTCR) and was involved in drafting the Hague Code of Conduct Against Ballistic Missile Proliferation (HCOC). Japan is one of the most active partners with the United States in the field of missile defense. Tokyo has deployed a multi-layered missile defense system consisting of sea-based midcourse missile defense (the Aegis BMD system), and ground-based terminal-phase missile defense (Patriot Advanced Capabilities-3). The December 2010 National Defense Program Guidelines called for further deployment and improvement of Japan's missile defense systems in cooperation with the United States. [17] Under the DPJ government, the United States and Japan agreed to place a new missile defense radar system on Japanese territory to defend against ballistic missile threats from North Korea. [18] Following its landslide victory over the DPJ in the December 2012 Lower House election, the LDP plans to issue new National Defense Program Guidelines by the end of 2013. The LDP is expected to increase spending on missile defense systems. [19]

Additionally, Japan has become more interested in space activities mainly because of North Korea's ballistic missile launches and the accelerating development of China's space program. On 27 August 2008, the Basic Space Law entered into force, lifting the ban on the Japanese government's use of space for defense purposes. [20] Another significant development in furtherance of U.S.-Japan cooperation in missile defense systems was the Japanese government’s decision to relax the three principles on arms exports on 27 December 2011. With this development, Japan can allow the United States to transfer a jointly developed missile defense system to third countries, provided such a transfer contributes to Japan’s national security and international peace and security. [21]

[1] "Atomic Energy Basic Act," Nuclear Safety Commission of Japan Website, www.nsc.go.jp.
[2] "On the Three Non-Nuclear Principles," Japanese Ministry of Foreign Affairs, www.mofa.go.jp.
[3] "Nuclear Power in Japan," World Nuclear Association, www.world-nuclear.org.
[4] "Nuclear Power in Japan," World Nuclear Association, www.world-nuclear.org.
[5] Japan Atomic Industrial Forum, www.jaif.or.jp.
[6] "Nuclear Power in Japan," World Nuclear Association, www.world-nuclear.org.
[7] For more details and future updates on the situation at Fukushima, see "Japan in Focus: A Collection of the Bulletin's Coverage," Bulletin of the Atomic Scientists, retrieved from BAS website 21 March 2011, http://thebulletin.org.
[8] Frank N. von Hippel, "The Radiological and Psychological Consequences of the Fukushima Daiichi Accident," Bulletin of the Atomic Scientists, September/October 2011
[9] Justin McCurry, "Fukushima is in cold shutdown, says Japanese prime minister," The Guardian, 16 December 2011, gurdain.co.uk. Justin McCurry in Tokyo.
[10] Tatsujiro Suzuki, "Suzuki's Fukushima updates," Bulletin of the Atomic Scientists, September 2013, http://thebulletin.org.
[11] The Energy and Environment Council, the Government of Japan, "Innovative Strategy for Energy and Environment," 14 September 2012, www.npu.go.jp.
[12] Abe administration puts plans to end nuclear power by 2030s under review, The Mainichi, 27 December 2012, http://mainichi.jp.
[13] "Abe cements power with LDP's sweeping victory in Upper House race," The Japan Times, 22 July 2013, www.japantimes.co.jp.
[14] Abandoned Chemical Weapons Office, wwwa.cao.go.jp.
[15] Abandoned Chemical Weapons Office, wwwa.cao.go.jp.
[16] Abandoned Chemical Weapons Office, wwwa.cao.go.jp.
[17] Japanese Ministry of Defense, "Summary of National Defense Program Guidelines," FY2011.
[18] David S. Cloud, "U.S., Japan agree on new missile-defense site against North Korea," LA Times, 17, September 2012, http://latimesblogs.latimes.com.
[19] "Defense budget rises after decade of falls," Yomiuri Online, 9 January 2013, www.yomiuri.co.jp.
[20] "Ban lifted on use of space for defense," The Daily Yomiuri, 29 August 2009.
[21] Masami Ito, "Government goes ahead with easing arms export ban," The Japan Times, 28 December 2011, www.japantimes.co.jp.

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This material is produced independently for NTI by the James Martin Center for Nonproliferation Studies at the Monterey Institute of International Studies and does not necessarily reflect the opinions of and has not been independently verified by NTI or its directors, officers, employees, or agents.

Get the Facts on Japan

  • Possesses a reprocessing plant capable of separating eight tons of Pu per year
  • State party to the BWC, but experimented on human subjects with biological agents during WWII
  • Possesses technological capabilities which could be adapted for the production of long-range ballistic missiles