Last Updated: February, 2017
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,  and its "Three Non-Nuclear Principles" pledge that Japan will not possess, produce, or permit the introduction of nuclear weapons into the country.  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. Japan had 54 nuclear power reactors in operation across the country (the third largest number in the world, after the United States and France).  With almost no indigenous energy sources, nuclear energy accounted for over 30% of the country's total electricity production, and Japan had planned to further increase this. However, the March 2011 accident at the Fukushima Daiichi Nuclear Power Station, caused by the Great East Japan Earthquake and Tsunami significantly impacted the country's nuclear energy policy. The number of nuclear reactors decreased from 54 to 42 due to the damage caused by the Tsunami and the retirement of old reactors.
In April 2014, the government adopted the 4th Basic (or Strategic) Energy Plan, proposed by the Ministry of Economy, Trade and Industry (METI), the first Energy Plan after the Fukushima disaster.  The ruling Liberal Democratic Party (LDP) that returned to power in December 2012 after being an opposition party for three years completely reviewed the decision made by the Democratic Party of Japan (DPJ) that was in power when the Fukushima accident happened.  The plan calls nuclear power "an important base-load power source as a low carbon and quasi-domestic energy source," expresses the Japanese government's commitment to restarting the country's nuclear power plants, and reiterates the need to reduce radioactive waste through reprocessing of spent fuels and effective use of plutonium.  However, anti-nuclear energy sentiment among the general public galvanized by the Fukushima disaster continued to impose uncertainty on Japan's nuclear energy policy.
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.  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. While more than 50,000 chemical weapons have been unearthed from 90 sites around China, the Office's work is far from complete. More weapons are still being discovered today, and construction of weapons destruction sites is slow and expensive, as is destroying the weapons. Director General of the Abandoned Chemical Weapons Office Kenichi Takahashi estimated cumulative costs of these operations at over 1 billion euros ($1.4 billion), with projected future costs difficult to ascertain. The problem is illustrated most vividly by the Haerbaling site, in the northeast province of Jilin, with an estimated 330,000 buried chemical weapons and destruction facilities that are not yet operational. The original deadline for completion of the clean-up was 2007; Tokyo and Beijing requested a five-year extension from the Organization for the Prohibition of Chemical Weapons (OPCW) but failed to meet that deadline as well. 2016 is the current deadline for weapons destroyed in "mobile facilities," and 2022 for the 330,000 weapons at Haerbaling.  The Chinese government urged Japan to expedite the chemical weapon destruction process in July 2015, highlighting the significance of the 70th anniversary of the end of the Second World War. 
Japan's chemical industry is the world's third largest after the United States and China.  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.  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.  Following its landslide victory over the DPJ in the December 2012 Lower House election, the LDP issued new National Defense Program Guidelines in December 2013. The document mentions the need to maintain and enhance ballistic missile defense systems as part of its plan to address the "threat of nuclear weapons." 
 "Atomic Energy Basic Act," Nuclear Safety Commission of Japan Website, www.nsc.go.jp.
 "On the Three Non-Nuclear Principles," Japanese Ministry of Foreign Affairs, www.mofa.go.jp.
 "Nuclear Power in Japan," World Nuclear Association, www.world-nuclear.org.
 Japan retains nuclear in energy mix, World Nuclear News, 11 April 2014, www.world-nuclear-news.org.
 Abe administration puts plans to end nuclear power by 2030s under review, The Mainichi, 27 December 2012, http://mainichi.jp.
 Japan decides new energy policy that supports use of nuclear power, Nikkei Asian Review, 11 April 2014, http://asia.nikkei.com.
 Abandoned Chemical Weapons Office, wwwa.cao.go.jp.
 Nina Notman, "Explosive end for Japan's second world war chemical weapons, Chemistry World," www.rsc.org.
 Statement by Ambassador Chen Xu, the Head of the Chinese Delegation to the 79th session of the Executive Councile of the OPCW, 12 July 2015, www.fmprc.gov.cn.
 Abandoned Chemical Weapons Office, wwwa.cao.go.jp.
 Japanese Ministry of Defense, "Summary of National Defense Program Guidelines," FY2011.
 David S. Cloud, "U.S., Japan agree on new missile-defense site against North Korea," LA Times, 17 September 2012, http://latimesblogs.latimes.com.
 "Document: Japan's 2014 National Defense Program Guidelines," USNI News, 17 December 2013, http://news.usni.org.
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