Japanese nuclear weapons program

Lise Meitner and Otto Hahn discovered nuclear fission in December 1938. Physicists around the world immediately noticed that chain reactions could be produced and notified their governments of the possibility of developing nuclear weapons. The Japanese atomic program was led by Dr. Yoshio Nishina, who also was a friend of Niels Bohr, and a close associate of Albert Einstein. Dr. Nishina was a highly skilled world class scientist with excellent leadership qualities. He also co-authored the Klein-Nishina Formula, and the Nishina crater on the moon is named after him.

Dr. Nishina had established his own Laboratory at the Riken (the Institute for Physical and Chemical Research) in 1931 to study high-energy physics. He built his first 26 inch cyclotron in 1936, and another 60 inch 220 ton cyclotron in 1937. In 1938 Japan also purchased a cyclotron from the University of California, Berkeley.

In 1939 Dr. 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. Indeed, in 1939, President Franklin D. Roosevelt started the first investigations into fission weapons in the United States, which eventually evolved into the massive Manhattan Project (the very laboratory from which Japan purchased its own cyclotron would become one of the major sites for weapons research). Dr. Nishina tried to match the U.S. research, and promoted the development of a nuclear weapon. In October 1940, Lt. General Takeo Yasuda of the Japanese army finally decided that such a weapon was feasible and practical, and the Japanese atomic program started in July 1941 under the guidance of Dr. Nishina.

Atomic program of the Imperial Japanese Navy

A separate atomic program of the Imperial Japanese Navy was also in progress in 1942 [http://www.fas.org/nuke/guide/japan/nuke/] . This project, called F-Go, was headed by Prof. Bunsaku Arakatsu, a lecturer at the Kyoto University, who studied under Albert Einstein [http://www.skycitygallery.com/japan/japan.html#a-bomb] . Arakatsu built his own cyclotron. His team included Hideki Yukawa, the first Japanese physicist to receive a Nobel Prize in 1949.

The program of the Navy initially aimed only to harness nuclear energy as an energy source to reduce the dependence on oil and to relieve the permanent shortage thereof, as it was thought that a weapon would not be able to be developed for wartime use (in this respect, it was very similar to the German nuclear energy project going on at the same time). However, as the tide of the war turned against Japan, the goal of making a nuclear weapon became a priority. The Japanese Navy launched a search for uranium throughout the dwindling empire. The Japanese military took what Nishina had learned and expanded the program, for instance, building five improved gaseous diffusion separators based on the smaller, single unit developed in Nishina’s effort. What happened to the separators, described by Col. Tatsusaburo Suzuki, who coordinated the effort for the army, is not known. But the Navy lacked time and material, and despite paying huge amounts for uranium on the Chinese black market and arranging for Nazi uranium to be shipped by submarine, it is generally assumed that they failed to produce a nuclear weapon. Exactly how far the Navy project got is a matter of debate. There have been some who contend that a prototype was developed, perhaps using Nazi supplied uranium or plutonium, and was detonatedFact|date=September 2007 on a small island off the coast of what is today North Korea.Fact|date=September 2007, only weeks prior to the bombing of Hiroshima. This conclusion has been disregarded by mainstream scholars (see below).


The Japanese programs' major source of uranium ore according to "Japan's Secret War" by author Robert K Wilcox, was Korea, but other sources included Burma and shipments by U-boat from France in 1944. Most famous of these was the failed voyage of U-234. Korea, known to the Japanese as Chosen, had been under Japanese control since 1910.

Dr. Nishina investigated a number of methods for enrichment of uranium, and decided that the gaseous diffusion method would be most worth pursuing. However there is no evidence that production plants of the size used by the Manhattan Project were ever constructed, and the Manhattan Project plants, for all of their vastness, were only able to produce enough material for five atomic devices by the war's end.

According to declassified Magic transcripts of signals to Japan's embassy in Berlin, General Toranosuke Kawaishima first requested Czechoslovakian Uranium on 7 July 1943. In an exchange of queries from the Germans up to November 1943 questioning its intended use, Kawashima gave very guarded answers that it was for an experimental jet fuel project. A handful of Japanese I-class submarines collected Uranium oxide from French ports, but none made it all the way back to Japan. Italian transport submarines in German service numbered UIT-24 and UIT-25 are thought to have transported early shipments, but no precise proof exists. It is not known how much material Japan received from Germany, but at least one shipment, 560 kg of Uranium Oxide which was sent to Japan by a German Unterseeboot U-234 was intercepted after surrender at sea in 1945 [http://vikingphoenix.com/public/JapanIncorporated/1895-1945/nzisub4j.htm] .

Unterseeboot 234 (U-234) was sent to Japan in April 1945 to deliver 560 kg of unprocessed uranium oxide for the Japanese program, as well as a disassembled Me-262 jet fighter and assorted German military technology. Earlier in 1944, U-219 and U-195 had reached Djakarta with 12 broken down components for the V-2 rocket. Two Japanese military officials and a number of German experts were also on board. The nuclear cargo was labeled "U-235," perhaps as a mislabeling of the submarine name, or perhaps in reference to the fissile isotope of uranium, uranium-235. It is extremely unlikely, though, that it was truly 560 kg of uranium-235—this would have been some eight times more of the rare element than was produced by the entire U.S. effort, and enough for Nazi Germany to have built many atomic bombs of their own with great ease.

The U-boat was ordered to surrender on May 10, 1945, two days after the overall German surrender, by Admiral Dönitz. To avoid capture, the two Japanese officials, Lieutenant Commander Hideo Tomonaga and Lieutenant Commander Genzo Shoji, committed suicide and were buried at sea the next day. The submarine was boarded by US forces on May 14 and the cargo fell into U.S. hands [http://vikingphoenix.com/public/JapanIncorporated/1895-1945/nzisub4j.htm] .

The US Navy records that they only recovered 560 kg of un-enriched Uranium oxide. There is however a significant discrepancy in U-234's cargo manifest upon leaving Germany and the manifest drawn up by the US Navy according to "Japan's Secret War" by Robert K Wilcox.

Others claim the quantity of uranium was enough to build two atomic bombs, but this would require that it was already substantially enriched. It would have also meant that Germany could have developed its own bomb, which it did not. That amount of uranium, if enriched to around the 90% needed for an atomic bomb, would only provide around 3.92 kg of bomb-grade material, far less than needed for an atomic bomb (the "Little Boy" uranium weapon dropped on Hiroshima used over 60 kg of uranium-235).


After the war, the U.S. occupation forces found a total of four cyclotrons, which they judged to be part of the weapons programs. (Some have mistakenly claimed there were five cyclotrons, but one was actually a mass spectrometer and referred to by some Japanese scientists at the time as "the baby cyclotron".) Cyclotrons can be used for electromagnetic uranium enrichment as mass spectrometers, but by themselves would not be useful as production facilities. In the United States, large cyclotrons at the Berkeley Radiation Laboratory were used to develop even more massive Calutron machines at the Oak Ridge facility, which were used for the bulk of the electromagnetic enrichment, but the Japanese cyclotrons would have been much smaller than even the prototype American machines. The Japanese cyclotrons were then dumped into Tokyo harbor by the U.S. Army, and many American scientists protested this act after the fact, insisting that the cyclotrons by themselves couldn't be used to make atomic weapons.

In many ways, the Japanese program is more similar to the abortive German atomic program than it was to the massive Allied bomb program. It is worth noting that by comparison, the Manhattan Project was one of the largest expenditures for the American side in World War II ($1.8 billion in 1945 dollars, with radar R&D costing some $3 billion), involved over 30 different research and production sites, and employed 150,000 employees, including numerous Nobel Laureates. Even with this investment, the USA was only able to produce five atomic devices ( the Trinity device, one Little Boy, and three Fat Man ) by August 1945.

Current nuclear activities in Japan

Since the bombing of Hiroshima and Nagasaki, Japan is a staunch opponent of nuclear arms on all government levels. Three Non-Nuclear Principles were adopted as a parliamentary resolution in 1971, stating that Japan shall never manufacture, possess, nor allow the introduction of nuclear weapons into its territory. Though never formally adopted into law, this statement reflects the attitude both of government and general public opinion.

However, Japan does make extensive use of nuclear energy in nuclear reactors, generating a significant percentage of the electricity in Japan. Japan has the third largest nuclear energy production after the U.S. and France, and plans to produce over 40% of its electricity using nuclear power by 2010. Significant amounts of Plutonium are created as a by-product of the energy production, and Japan had 4.7 tons of plutonium in December 1995. Japan also possesses an indigenous uranium enrichment plant [http://www.jnfl.co.jp/english/uranium.html] - the same plant, or a secretly constructed plant using similar technology, could be used to make highly enriched uranium suitable for weapons. Japan has also developed the M-5 three-stage solid fuel rocket, similar in design to the U.S. LGM-118A Peacekeeper ICBM. While there are currently no known plans in Japan to produce nuclear weapons, it has been argued Japan has the technology, raw materials, and the capital to produce nuclear weapons within one year if necessary, and some analysts consider it a "de facto" nuclear state for this reason. [http://www.largeassociates.com/R3126-A1-%20final.pdf]

Some argue that there is little military advantage for Japan to develop nuclear weapons as China, its main potential adversary, has sufficient landmass to easily deter an attack. A few thermonuclear weapons would largely destroy Japan, but China could absorb a similar attack. Japan is safer under the U.S. nuclear umbrella. [http://www.atimes.com/atimes/Japan/HH16Dh02.html] Some analysts, however, fear that Japan may abandon its anti-nuclear arms stance in the face of North Korea's development of nuclear weapons as part of a wider nuclear arms race in eastern Asia, especially after that nation's nuclear test on October 9, 2006.Fact|date=August 2008 Others note that despite the U.S.-Japan alliance, there could be the eventuality the Americans refused to retaliate with nuclear weapons even after an enemy attack with an atom bomb on Japan.Fact|date=August 2008

Disputed reports about the nuclear program in Konan in 1945

Little is known about the size of the alleged atomic program in Konan though it is conventionally thought to have been small in comparison with the successful U.S. effort. In 1946, a journalist named David Snell working for the Atlanta Constitution wrote a sensationalist story which indicated that Japan had in fact successfully developed and tested a nuclear weapon in Konan. Snell was a former reporter, soon to become "Life Magazine" correspondent assigned to the 24th Criminal Investigation Detachment in Korea. He interviewed a Japanese officer who said he had been in charge of counter intelligence at the Konan project before the fall of Japan.

According to the officer, who used a pseudonym in the article because he was afraid of retaliation by occupation forces, the program was able to assemble a complete nuclear weapon in a cave in Konan and detonate it on August 12, 1945 on an unmanned ship nearby. Reportedly, the weapon produced a mushroom shaped cloud with a diameter of about 1000 m (the first American bomb, "the gadget", had a mushroom cloud some three times the size of that), and also destroyed several ships in the test area. To the observers 20 mi (32 km) away, the bomb was brighter than the rising sun. The officer then claimed that the Russian Army, which captured Konan in November 1945 after some of the last fighting in the war, dismantled the Japanese project and shipped it and some of its scientists taken prisoner back to the Soviet Union.

Most mainstream historians dispute that the Japanese program got close to developing an atomic bomb but US intelligence took the possibility very seriously after Snell's article was published and continued to question repatriated Japanese from the Konan area about the project.

A 1985 book by Robert Wilcox reprinted the Snell interview as a basis for investigating the Japanese WWII nuclear efforts. In addition to detailing the known Japanese army and navy efforts, the book cites numerous intelligence reports and interviews which indicated the Japanese might have had an atomic program at Konan. It also gave evidence that the Japanese navy, taking up the atomic project after Nishina’s Riken had been destroyed, increased the Japanese efforts to make a weapon. The book, prefaced by Derek deSolla Price, Avalon professor of the history of science at Yale University, who endorsed it, was both panned and praised. Price wrote, “No longer can we maintain that a Japanese bomb just couldn’t have happened. Obviously it ‘nearly’ did. The only questions are how near and what does it do to our judgment on the one case we have of atomic warfare.” James L. Stokesbury, author of A Short History of World War II, wrote: “I had no idea the Japanese were working as seriously on an atomic bomb...this has to modify our perception of one of the crucial issues of the war.”

A review by a Department of Energy employee in the journal "Military Affairs" degraded it::Journalist Wilcox' book describes the Japanese wartime atomic energy projects. This is a laudable, in that it illuminates a little-known episode; nevertheless, the work is marred by Wilcox' seeming eagerness to show that Japan created an atomic bomb. Tales of Japanese atomic explosions, one a fictional attack on Los Angeles, the other an unsubstantiated account of a post-Hiroshima test, begin the book. (Wilcox accepts the test story because the author [Snell] , "was a distinguished journalist"). The tales, combined with Wilcox' failure to discuss the difficulty of translating scientific theory into a workable bomb, obscure the actual story of the Japanese effort: uncoordinated laboratory-scale projects which took paths least likely to produce a bomb.

In the historical journal "Isis", two historians of science said only of Wilcox's work that his thesis stood "on the flimsiest and most unconvincing of grounds," and surmised that the hidden agenda of such conspiracy theories was "to furnish a new exculpation for America's dropping of atomic bombs on Hiroshima and Nagasaki."

An article published in the journal "Intelligence and National Security" in 1998, based on a review of many of the same documents used by Wilcox, and more, came to a similar conclusion. The article cites several US military intelligence documents and Japanese corporate records of the Nitchitsu firm that ran most of the industry in Hungnam and found no substantive evidence of any nuclear research program existing there during the war. [William Yenne, "Not Just a Target: Japan's Bomb," "Secret Weapons of World War II: The Techno-Military Breakthroughs That Changed History" (New York: Berkley Books, 2003), 13-15.]

See also

*Nuclear weapon
*History of nuclear weapons
*List of countries with nuclear weapons
*List of nuclear weapons
*Nuclear testing
*Norwegian heavy water sabotage


*Richard Rhodes, "The Making of the Atomic Bomb" (New York, Simon and Schuster, 1986).

*Walter E. Grunden, "Secret Weapons & World War II: Japan in the Shadow of Big Science" (Lawrence: University Press of Kansas, 2005).

*Walter E. Grunden, "Hungnam and the Japanese Atomic Bomb: Historiography of a Postwar Myth," "Intelligence and National Security" [Great Britain] 1998 13(2): 32-60.

Disputed references

*Robert K. Wilcox, "Japan's Secret War: Japan's Race Against Time to Build Its Own Atomic Bomb" (New York: Morrow, 1985; reprinted with new information by Marlowe, New York, 1995).
*David Snell, "Japan Developed Atom Bomb; Russia Grabbed Scientists," "Atlanta Constitution" (2 Oct 1946), available online at a conspiracy-theory website, [http://www.reformation.org/atlanta-constitution.html] .

Criticism cited

*Roger M. Anders, Review of "Japan's Secret War", in "Military Affairs" 50:1 (Jan 1986): 56-57, quote from 57.
*R.W. Home and Morris F. Low, "Postwar Scientific Intelligence Missions to Japan," "Isis" 84:3 (Sep 1993): 527-537, quote from 528fn3.
*"Newsman Says Japanese Had Atom Bomb and Russians Now Hold the Inventors," "New York Times" (3 Oct 1946), 22.

External links

* [http://www.fas.org/nuke/guide/japan/nuke/ FAS: Nuclear Weapons Program: Japan] - Federation of American Scientists
* [http://39th.org/39th/hc/hc_japan_a_bomb.html Japan's A-Bomb] - site claiming that Japan detonated an atomic bomb
* [http://store.aetv.com/html/product/index.jhtml?id=74425 Japan's atomic bomb] History Channel International documentary

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