Japan and weapons of mass destruction
| Weapons of mass destruction |
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| Non-state |
| Biological weapons by country |
| Chemical weapons by country |
| Nuclear weapons by country |
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The Empire of Japan extensively used and researched chemical and biological weapons (CBW) during the Second Sino-Japanese War as part of Japanese war crimes. Japan is the only country ever attacked with nuclear weapons, by the United States' 1945 atomic bombings of Hiroshima and Nagasaki at the end of World War II. During the Cold War, the United States stationed chemical and nuclear weapons in Japan from the early 1950s to early 1970s. Postwar Japan ratified the Nuclear Non-Proliferation Treaty, Biological Weapons Convention, and Chemical Weapons Convention. The US provides a nuclear umbrella to Japan.
Beginning in the mid-1930s, Japan conducted numerous attempts to acquire, develop and use weapons of mass destruction. Japan's biological warfare is estimated to have killed between 200,000 and 500,000 people in China. Biological warfare units, led by Unit 731, operated across the Japanese colonial empire, dispersing anthrax, cholera, dysentery, typhoid, plague, and others. In the Japanese puppet state of Manchukuo, Unit 731 and Unit 516 were centers of CBW research, including human experimentation. CBW was used at the Battle of Changde, the Battle of Wuhan, the Ningbo plague attack, and elsewhere. The Imperial Japanese Navy planned a weaponized plague attack against California. Unit 731 members provided information to the Soviet and United States biological weapons programs, twelve of whom were found guilty in the Khabarovsk war crimes trials. From 1940 to 1945, Japan conducted a nuclear weapons program which did not progress past laboratory experiments. The US covered up Japan's biological warfare, and the Japanese government first acknowledged the program in 2002.
The US atomic bombings, the culmination of the Manhattan Project, devastated Hiroshima and Nagasaki, killing between 150,000 and 246,000 people within four months. The ethics and role of the attacks in the unconditional surrender of Japan and end of the Pacific War are the subject of continued debate. The attacks had a strong influence on Cold War's nuclear arms race and in popular culture.
From 1954 until 1972, the US stationed a range of strategic and tactical nuclear weapons, especially in the US-administered Ryukyu Islands. These included nuclear tactical ballistic missiles, cruise missiles, artillery, anti-air, anti-submarine weapons, and strategic bombers. Following the 1954 US Castle Bravo thermonuclear test, one Japanese fisherman died when all 23 crew aboard the Daigo Fukuryū Maru suffered acute radiation syndrome. The US stockpiled thousands of tons of chemical weapons in Okinawa, including mustard gas, sarin, and VX, which were removed in 1971.
Article 9 of the Constitution of Japan has been interpreted to prohibit the country from weapons of mass destruction and long-range delivery systems. Under the Three Non-Nuclear Principles established in 1971, Japan rejects possessing, producing, and introducing into its territory nuclear weapons. However, postwar Japan is an exemplar of nuclear latency: possessing the materials and technical capacity for an indigenous nuclear weapons program. This includes an advanced civil nuclear program, reprocessing, and stockpile of plutonium. Some 21st century politicians have supported a role for US nuclear weapons in Japan.
The Japanese religious cult Aum Shinrikiyo carried out the first chemical terrorist attacks to use nerve agents. Members perpetrated at least 10 such attacks, notably using sarin in Matsumoto in 1994 and on the Tokyo subway in 1995, as well as some of the first attacks to use VX. The group also unsuccessfully attempted bioterrorist attacks with anthrax and botulinum toxin, which remains the most extensive non-state biological weapons program to date.