Japanese nuclear weapons program

building in Taisho period In 1934, Tohoku University professor Hikosaka Tadayoshi's "atomic physics theory" was released. Hikosaka pointed out the huge energy contained by nuclei and the possibility that both nuclear power generation and weapons could be created. In December 1938, the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to Naturwissenschaften reporting that they had detected the element barium after bombarding uranium with neutrons; simultaneously, they communicated these results to Lise Meitner. Meitner, and her nephew Otto Robert Frisch, correctly interpreted these results as being nuclear fission and Frisch confirmed this experimentally on 13 January 1939. Physicists around the world immediately realized that chain reactions could be produced and notified their governments of the possibility of developing nuclear weapons. ==World War II==

Masatoshi Okochi submitted a report on "Possibility of Uranium Bomb Manufacturing" in May 1941. The leading figure in the Japanese atomic program was Yoshio Nishina, a close associate of Niels Bohr and a contemporary of Albert Einstein. Nishina had co-authored the Klein–Nishina formula. Nishina had established his own Nuclear Research Laboratory to study high-energy physics in 1931 at RIKEN Institute (the Institute for Physical and Chemical Research), which had been established in 1917 in Tokyo to promote basic research. Nishina had built his first cyclotron in 1936, and another , 220-ton cyclotron in 1937. In 1938 Japan also purchased a cyclotron from the University of California, Berkeley. In 1939, Nishina recognized the military potential of nuclear fission, and was worried that the Americans were working on a nuclear weapon which might be used against Japan. In August 1939, Hungarian-born physicists Leo Szilard and Eugene Wigner drafted the Einstein–Szilard letter, which warned of the potential development of "extremely powerful bombs of a new type". The United States started the investigations into fission weapons in the United States, which eventually evolved into the massive Manhattan Project, and the laboratory from which Japan purchased a cyclotron became one of the major sites for weapons research. In the early summer of 1940, Nishina met Lieutenant-General Takeo Yasuda on a train. Yasuda was at the time director of the Army Aeronautical Department's Technical Research Institute. Nishina told Yasuda about the possibility of building nuclear weapons. However, the Japanese fission project did not formally begin until April 1941 when Yasuda acted on Army Minister Hideki Tōjō's order to investigate the possibilities of nuclear weapons. Yasuda passed the order down the chain of command to Viscount Masatoshi Ōkōchi, director of the RIKEN Institute, who in turn passed it to Nishina, whose Nuclear Research Laboratory by 1941 had over 100 researchers. B-Research Meanwhile, the Imperial Japanese Navy's Technology Research Institute had been pursuing its own separate investigations, and had engaged professors from the Imperial University, Tokyo, for advice on nuclear weapons. Before the Attack on Pearl Harbor in 1941, Captain Yoji Ito of the Naval Technical Research Institution of Japan initiated a study that would allow for the Japanese Navy to use nuclear fission. After consulting with Professor Sagane at Tokyo Imperial University, his research showed that nuclear fission would be a potential power source for the Navy. The attack also effectively destroyed the Clusius tube and any chances of the Japanese producing an atomic bomb in time to influence the war in their favor and rival the West in nuclear weaponry. F-Go Project In 1943, a different Japanese naval command began a nuclear research program, the F-Go Project (lit. "The F Project"), under Bunsaku Arakatsu at the Imperial University, Kyoto. Arakatsu had spent some years studying abroad including at the Cavendish Laboratory at Cambridge under Ernest Rutherford and at Berlin University under Albert Einstein. Next to Nishina, Arakatsu was the most notable nuclear physicist in Japan. His team included Hideki Yukawa, who would become in 1949 the first Japanese physicist to receive a Nobel Prize. Early on in the war Commander Kitagawa, head of the Navy Research Institute's Chemical Section, had requested Arakatsu to carry out work on the separation of Uranium-235. The work went slowly, but shortly before the end of the war he had designed an ultracentrifuge (to spin at 60,000 rpm) which he was hopeful would achieve the required results. Only the design of the machinery was completed before the Japanese surrender. 's accelerator demolition by GHQ, 24 November 1945. After Arakatsu and Nishina's meeting, in spring 1944, the Army-Navy Technology Enforcement Committee formed due to lack of progress in the development of Japanese nuclear weapons. This led to the only meeting of the leaders of the F-Go Project scientists, on 21 July 1945. After the meeting, nuclear weaponry research ended as a result of the destruction of the facility that housed isotope separation research, known as Building 49. This was done on 24 November; the Riken's cyclotrons were taken apart and thrown into Tokyo Bay. In a letter of protest against this destruction Nishina wrote that the cyclotrons at the Riken had had nothing to do with the production of nuclear weapons, however the large cyclotron had officially been a part of the Ni-Go Project. Nishina had placed it within the Project by suggesting that the cyclotron could serve basic research for the use of nuclear power, simply so that he could continue working on the device; the military nature of the Project gave him access to funding and kept his researchers from being drafted into the armed forces. He felt no qualms about this because he saw no possibility of producing nuclear weapons in Japan before the end of the war. who had been an investigator with the 24th Criminal Investigation Detachment in Korea after the war, which alleged that the Japanese had successfully tested a nuclear weapon near Hungnam (Konan) before the town was captured by the Soviets. He said that he had received his information at Seoul in September 1945 from a Japanese officer to whom he gave the pseudonym of Captain Wakabayashi, who had been in charge of counter-intelligence at Hungnam. SCAP officials, who were responsible for strict censorship of all information about Japan's wartime interest in nuclear physics, were dismissive of Snell's report. Under the 1947–1948 investigation, comments were sought from Japanese scientists who would or should have known about such a project. Further doubt is cast on Snell's story by the lack of evidence of large numbers of Japanese scientists leaving Japan for Korea and never returning. These specific reports were dismissed in a review of the book by Department of Energy employee Roger M. Anders which was published in the journal Military Affairs, an article written by two historians of science in the journal Isis, and another article in the journal Intelligence and National Security. ==Postwar==

Since the bombing of Hiroshima and Nagasaki, Japan has been a staunch upholder of antinuclear sentiments. Its postwar Constitution forbids the establishment of offensive military forces, and in 1967 it adopted the Three Non-Nuclear Principles, ruling out the production, possession, or introduction of nuclear weapons. Despite this, the idea that Japan might become a nuclear power has persisted. After China's first nuclear test in 1964, Japanese Prime Minister Eisaku Satō said to President Lyndon Johnson when they met in January 1965, that if the Chinese Communists had nuclear weapons, the Japanese should also have them. This shocked Johnson's administration, especially when Sato added that "Japanese public opinion will not permit this at present, but I believe that the public, especially the younger generation, can be 'educated'." Throughout Sato's administration Japan continued to discuss the nuclear option. It was suggested that tactical nuclear weapons, as opposed to larger strategic weapons, could be defined as defensive, and therefore be allowed by the Japanese Constitution. A White Paper commissioned by future Prime Minister Yasuhiro Nakasone opined that it would be possible that possessing small-yield, purely defensive nuclear weapons would not violate the Constitution, but that in view of the danger of adverse foreign reaction and possible war, a policy would be followed of not acquiring nuclear weapons "at present". In 1969, a policy planning study for Japan's Foreign Ministry concluded that Japan should, even if it signed the NPT, maintain the economic and technical ability to develop and produce nuclear weapons in case it should ever become necessary, for example due to the international situation. Japan finally signed the NPT in 1970 and ratified it in 1976, but only after West Germany became a signatory and the US promised "not to interfere with Tokyo's pursuit of independent reprocessing capabilities in its civilian nuclear power program". For this reason Japan is often said to be a "screwdriver's turn" away from possessing nuclear weapons, or to possess a "bomb in the basement". The United States stored extensive nuclear assets in Okinawa prefecture when it was under American administration until the 1970s. There were approximately 1,200 nuclear warheads in Okinawa. Significant amounts of reactor-grade plutonium are created as a by-product of the nuclear energy industry. During the 1970s, the Japanese government made several appeals to the United States to use reprocessed plutonium in forming a "plutonium economy" for peaceful commercial use. This began a significant debate within the Carter administration about the risk of proliferation associated with reprocessing while also acknowledging Japan's need for energy and right to the use of peaceful nuclear technology. Ultimately, an agreement was reached that allowed Japan to repurpose the byproducts of nuclear power-related activities; however their efforts regarding fast-breeding plutonium reactors were largely unsuccessful. In 2012, Japan was reported to have 9 tonnes of plutonium stored in Japan, which would be enough for more than 1,000 nuclear warheads, and an additional 35 tonnes stored in Europe. It has constructed the Rokkasho Reprocessing Plant, which could produce further plutonium. Japan also possesses an indigenous uranium enrichment plant which could hypothetically be used to make highly enriched uranium suitable for weapons use. Japan has also developed the M-V three-stage solid-fuel rocket, somewhat similar in design to the U.S. LGM-118A Peacekeeper ICBM, giving it a missile technology base. It now has an easier-to-launch second generation solid-fuel rocket, Epsilon. Japan has experience in re-entry vehicle technology (OREX, HOPE-X). Toshiyuki Shikata, a Tokyo Metropolitan Government adviser and former lieutenant general, said that part of the rationale for the fifth M-V Hayabusa mission, from 2003 to 2010, was that the re-entry and landing of its return capsule demonstrated "that Japan's ballistic missile capability is credible." A Japanese nuclear deterrent would probably be sea-based with ballistic missile submarines. In 2011, former Minister of Defense Shigeru Ishiba explicitly backed the idea of Japan maintaining the capability of nuclear latency: On 24 March 2014, Japan agreed to turn over more than of weapons grade plutonium and highly enriched uranium to the US, which started to be returned in 2016. It has been pointed out that as long as Japan enjoys the benefits of a "nuclear-ready" status held through surrounding countries, it will see no reason to actually produce nuclear arms, since by remaining below the threshold, although with the capability to cross it at short notice, Japan can expect the support of the US while posing as an equal to China and Russia. Former Mayor and Governor of Osaka Tōru Hashimoto in 2008 argued on several television programs that Japan should possess nuclear weapons, but has since said that this was his private opinion. Former Governor of Tokyo 1999-2012, Shintaro Ishihara was an advocate of Japan having nuclear weapons. On 29 March 2016, then-U.S. presidential candidate Donald Trump suggested that Japan should develop its own nuclear weapons, claiming that it was becoming too expensive for the US to continue to protect Japan from countries such as China, North Korea, and Russia that already have their own nuclear weapons. On 27 February 2022, former prime minister Shinzo Abe proposed that Japan should consider a nuclear sharing arrangement with the US similar to NATO. Although an indigenous nuclear program in Japan is unlikely to develop due to low public support, the existential Chinese and North Korean threats have raised security concerns domestically. The role of public opinion is central, and studies show that threat perceptions—mainly of China’s growing military abilities—have strengthened Japanese public support for a nuclear program. Japan has long held negative views on nuclear weapons, and previously, even discussions of nuclear armament or deterrence in the country was unpopular due to a strong "nuclear taboo". However, this taboo has been breaking, especially because Abe elevated the topic to mainstream politics during his tenure. National identity is an important factor in Japanese nuclear armament. Since World War II, the peace constitution has greatly limited the ability of Japanese military advancement, restricting them from having an active military or waging war with another country. These restrictions and the strong desire of former colonies—especially Korea and China—for apology and reconciliation by Japan for its crimes and atrocities committed under pre-WWII imperialism, coupled with Japan's refusal to make appropriate amends, led to the rise of a conservative branch of the ruling Liberal Democratic Party (LDP) in Japan that encouraged revisions to the Peace Constitution and promoted, under former prime minister Shinzo Abe, "healthy nationalism", which aimed to restore the Japanese public's sense of pride in the country. The revisionists sought to "create a new national identity" that increased national pride, allowed for collective self-defense and removed "institutional limitations on military activities". Since the reliability of U.S. security guarantees shapes Japan's nuclear policy, a strong American nuclear umbrella is necessary to prevent Japan from developing nuclear weapons of its own. Since the 1960s, however, Japanese confidence in U.S. security guarantees has been influenced by American foreign policy shifts, from Nixon's "Guam Doctrine" to Trump's desire for allies to provide more of their own security. Although Japan developing nuclear weapons would violate the Non-Proliferation Treaty (NPT) and potentially decrease U.S. power in East Asia, there is historical precedent for the U.S. to be complacent regarding Japan building nuclear arms: as long as Japan is a democracy, a friend of Washington and has high state capacity, the U.S. alliance would likely be maintained. This was the case for France and the United Kingdom, when they developed their own nuclear weapons after the end of the Second World War despite American deterrence. ==See also==