Japanese nuclear weapons program

Yoshio Nishina

The Japanese atomic program was a program by the Empire of Japan to develop a genzai bakudan, an atomic bomb during World War II. The program started around the same time as the U.S. Manhattan Project. Most experts believe that the program was small, and managed neither to refine enough uranium-235 nor to breed enough plutonium needed to make a workable device. The surrender of Japan on August 15, 1945 halted all developments before Japan could finish developing the weapon.

Atomic program of the Japanese Army Air Force

During the 1930s, the scientific community in the world started to understand the power of nuclear energy, and the Empire of Japan, like many other governments, was made aware of the possibility of developing a weapon which utilized nuclear fission as the source of its energy. The central figure of the Japanese atomic program is 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 well-known Klein-Nishina Formula, and the Nishina crater on the moon is named after him.

Dr. Nishina 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.

Dr. Nishida knew and understood the military potential of nuclear weapons, and was worried that the Americans were working on a nuclear weapon, which may be—and eventually was—used against Japan. About the same time, in 1939, President Franklin 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 from would become one of the major sites for weapons research). Dr. Nishina, a patriot for his country, 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. Yoshio Nishina.

Atomic program of the Japanese Navy

A separate atomic program of the Japanese navy was also in progress in 1942. This project, called F-Go, was headed by Prof. Bunsaku Arakatsu, a lecturer at the Kyoto University, who also studied under Albert Einstein. Arakatsu also built his own cyclotron. His team also included Hideki Yukawa, the first Japanese physicist to receive a Nobel Prize in 1949.

File:Hideki yukawa.jpg

Hideki Yukawa

The program of the Navy initially aimed only to harness the 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 a nuclear weapon seemed more desireable. Yet the atomic program of the Japanese Navy lacked both time and material, and the leadership also frequently changed its priorities.

Dr. Nishina worked on combining the atomic program of the Japanese Navy with the atomic program of the Japanese Army Air Force in order to utilize the scarce resources and to pool the knowledge. This was a difficult task due to the rivalry of the Japanese Navy and Army, and the Navy program did not produce tangible results.

At least that is one version. But after the Riken was bombed in early 1945, the navy program, led by Arakatsu and without Nishina, gained momentum. Short on ships and planes, the Japanese Navy put more emphasis on win-the-war weapons hoping, among other measures, to develop an atomic bomb to use in suicide planes and submarines against a probable invasion of Japan proper. Col. Tatsusaburo Suzuki, who had been Nishina’s army liaison, took, by order of the Japanese hierarchy, Nishina’s work to the navy project and helped produce six larger and improved (from Nishina’s smaller machine) thermal diffusion uranium gas separators. These, he has said in a memoir, were built by Hokushine Electric and Tokyo Keiki. What happened to the separators is not known. But in conjunction with the stepped up priority, Arakatsu was given 100 kilograms of uranium oxide for experiments in the spring of 1945, according to Lt. Comdr. Tetsugo Kitagawa, his navy liaison, in interviews which can be found in the National Archives, and, according to Lt. Comdr. Tetsuya Takao, a navy supply officer, 100 million yen was spent in collecting uranium from ceramic stocks in Shanghai alone (Record Group 333, Box 2, SCAP 1947-1951). This was much more than Nishina had ever been given. Following the American bombing of Hiroshima, American intercepts and decryptions of Japanese military messages indicated the navy program was still a hope. One decrypt in the National Archives, Magic Far East Summary SRS 508, dated August 10, 1945, says in part: “At (place missing), about five months ago, research was made into the (practical) application of Uranium 234, but no announcements have been made since. However, it is believed that research into the (word missing) of the atom has been completed and (words missing) research into this is considered to be of considerable value. It is believed that it is essential that his be completed immediately.”

Development

The Japanese programs' source of uranium ore was Korea, which had been under Japanese control since 1905. 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 three bombs by the war's end.

Japan disclosed its program to its ally Germany, and requested assistance. It is not known how much material Japan received from Germany, but at least one shipment that was sent to Japan by a German submarine was intercepted.

This submarine, Unterseeboot 234 (U-234) was sent to Japan in 1945 to deliver 560kg of uranium for the Japanese program, as well as a disassembled Me-262 jet fighter and V-2 rocket parts (which would have been of little use for a primitive nuclear weapon). 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 560kg 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 crude atomic bombs of their own with great ease. It is more likely that the uranium was un- or partially-enriched uranium oxide (which naturally has over 99% uranium 238). The submarine 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.

Some reports claim that the 560 kg of uranium oxide was enough to build two atomic bombs, but this would mean that it was substantially enriched (and would have also meant that Germany could have developed its own bomb with it, which it did not). That amount of unenriched uranium, if enriched to around the 90% needed for an atomic bomb, would provide around 4kg of bomb-grade material, far less than needed for an atomic bomb (the "Little Boy" uranium weapon dropped on Hiroshima used over 60kg of uranium-235). If put into a reactor, however, it could have potentially been used to breed plutonium, perhaps enough to use for a weapon if the program had been larger.

American bombing raids disrupted the development of the genzai bakudan, and both raw material and equipment was destroyed at the Institute for Physical and Chemical Research. To avoid further bombing, the development was relocated to Konan (now called Hungnam, in North Korea) early in 1945. This region was close to the source of ore, in less danger of attack than mainland Japan, and also a major industrial area in Asia. However, the move delayed the development by critical three months. Konan was captured by the Russian army in August 1945, and belongs currently to North Korea. The atomic bombings of Hiroshima and Nagasaki on August 6 and 9 led to the Japanese surrender on August 12, 1945.

Aftermath

After the war, the U.S. occupation forces found a total of five cyclotrons, which they judged to be part of the weapons programs. 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 have been dumped into Tokyo harbor by the U.S. Army, though many American scientists tried to intervene, insisting that the cyclotrons by themselves they 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 the single largest expenditure for the American side on World War II ($1.8 billion in 1945 dollars), 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 three crude atomic devices 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. However, Japan does 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. 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.

Disputed reports about the nuclear program in Konan in 1945

Very little is known about the size of the atomic program in Konan though it is conventionally thought to have been quite small in comparison with the successful U.S. effort. In 1946, a journalist named David Snell, working for the Atlanta Constitution, wrote a sensational story which claimed that Japan had in fact successfully developed and tested a nuclear weapon in Konan. Snell had served in the military during the war and was assigned to the 24th Criminal Investigation Detachment in Korea. During this time in Korea he interviewed "a Japanese officer, who said he was in charge of counter intelligence at the Konan project before the fall of Japan", known under the pseudonym Capt. Tsetusuo Wakabayashi.

According to Snell, 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 100 m (the first American bomb, "Trinity", 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 (a suspiciously common cliché about nuclear testing). Snell then claimed that the Russian Army captured Konan shortly thereafter, imprisoned the scientists and seized the remaining materials (and for some reason kept the entire thing a secret).

Even in its own time, Snell's story was viewed with suspicion. A New York Times article published the day after noted that US Army Intelligence officers found Snell's tale amusing, and both American and Japanese scientists found it to be spurious. The paper quoted an MIT scientist working for the army as having dismissed it completely: "There is no information here to justify such a story."

Mainstream historians dispute that the Japanese program ever came anywhere close to developing an atomic bomb, and cite the massive amounts of evidence that the Japanese program was small and insubstantial (compared to the dearth of evidence that it was in any way successful).

A 1985 book by Robert Wilcox repeated many of Snell's claims, and was critically panned. 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 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."

While the above, at the beginning, is accurate in its discussion of how much is known about Konan and that the mainstream do not believe the Japanese got close to a bomb, it is one-sided and biased regarding Snell and Wilcox. The forward to Wilcox’s book, Japan’s Secret War, was written by Professor Derek deSolla Price, head of Yale’s history of science department and a giant in the field, a fact that is left out of the above discussion. Price wholeheartedly endorsed it, as did other historians and reviewers. James L. Stockesbury, author of A Short History of World War II, called it “Fascinating. I had no idea the Japanese were working as seriously on an atomic bomb as the book indicates, and this has to modify our perception of one of the crucial issues of the war.” There were controversial aspects of the book that were attacked. But the book was published at a time, 1985, when practically no one outside of a few select scientists knew the Japanese even had an atomic bomb project. Most thought they were solely victims of the bomb and this was used to attack America. Except for the controversial part - the possibility that Japan had moved their program to Korea and possibly gotten farther than science had known - the book accurately portrayed what had happened on the mainland predominately through interviews with Japanese who had been part of the program and formerly top secret documents that had not been seen or used by historians prior.

Whoever wrote the above, has not read Japan’s Secret War. The book does not repeat many of Snell’s claims. Snell’s article had long been buried when it was recounted at the start of Japan’s Secret War. It was only used to launch into research about what happened at Konan, which is known as Hungnam in Korean. The basis for the possibility that Konan housed an atomic project came primarily from formerly top secret US intelligence documents, like this army G-2 summary of May 1-15, 1946, written by Col. Cecil W. Nist, which can be found in the National Archives (Record Group 319, Box 739): “Of increasing interest have been recent reports about an apparent undercover research laboratory operated by the Japanese at...Hungnam. Many of the reports are from Japanese who formerly held positions in this company. And these reports, received separately, are surprisingly uniform as to content...All reports agree that research and experiments on atomic energy were being conducted in a section of the Hungnam plant...Further reports state that the actual experiments on atomic energy were conducted in Japan, and the Hungnam plant was opened for the development of the practical application of atomic energy to a bomb or other military use...It is felt that a great deal of credence should be attached to these reports...”

The book’s main premise is that there is more to be found out about what the Japanese did regarding their atomic project than has so far come to light and to be fair these facts should be included in any discussion of disputed reports about Konan/Hungnam.

References

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

Disputed references

Robert K. Wilcox, Japan's Secret War: Japan's Race Against Time to Build Its Own Atomic Bomb (New York: Morrow, 1985).
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

FAS: Nuclear Weapons Program: Japan - Federation of American Scientist's
Japan's Atomic Bomb - page about Japan's motivations
Japan's A-Bomb - site claiming that Japan detonated an atomic bomb