As a result, it is often cited as a primary example of a latent or threshold nuclear state, capable of developing weapons in a very short timespan should its government decide to do so.

[2] 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;[3] simultaneously, they communicated these results to Lise Meitner.

The leading figure in the Japanese atomic program was Yoshio Nishina, a close associate of Niels Bohr and a contemporary of Albert Einstein.

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".

[11] 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.

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.

[9] This resulted in the formation of the Committee on Research in the Application of Nuclear Physics, chaired by Nishina, that met ten times between July 1942 and March 1943.

The uranium oxide was reportedly labeled as "U-235", which may have been a mislabeling of the submarine's name and its exact characteristics remain unknown; some sources believe that it was not weapons-grade material and was intended for use as a catalyst in the production of synthetic methanol to be used for aviation fuel.

[13][14] 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.

[9] According to the historian Williams, "The same lack of sufficient high quality uranium that had impeded the German atomic project had also, as it turned out, obstructed Japanese attempts to make a bomb."

Arakatsu had spent some years studying abroad including at the Cavendish Laboratory at Cambridge under Ernest Rutherford and at Berlin University under Albert Einstein.

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.

[12][17] 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.

In 1926, Noguchi founded the Korean Hydro Electric Company at Konan (now known as Hungnam) in north-eastern Korea: this became the site of an industrial complex producing ammonia for fertilizer production.

However, despite the availability of a heavy-water production facility whose output could potentially have rivalled that of Norsk Hydro at Vemork in Norway, it appears that the Japanese did not carry out neutron-multiplication studies using heavy water as a moderator at Kyoto.

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.

[29] The Johnson administration became anxious about Sato's intentions and made securing Japan's signature to the Nuclear Non-Proliferation Treaty (NPT) one of its top priorities.

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".

[29] The second event was the August 1998 launch of a North Korean Taepodong-1 missile over Japan which caused a public outcry and led some to call for remilitarization or the development of nuclear weapons.

Fukushiro Nukaga, head of the Japan Defense Agency, said that his government would be justified in mounting pre-emptive strikes against North Korean missile bases.

However, it is thought that Prime Minister Junichiro Koizumi implied he agreed that Japan had the right to possess nuclear weapons when he added, "it is significant that although we could have them, we don't".

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.

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.

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.

It's a tacit nuclear deterrent"[42]On 24 March 2014, Japan agreed to turn over more than 700 pounds (320 kg) of weapons grade plutonium and highly enriched uranium to the US,[44] which started to be returned in 2016.

[46] 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.

[51] 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.