Japan certainly had able physicists before the Second World War. Yoshio Nishina had worked with Rutherford at the Cavendish and Bohr in Copenhagen for five years during the 1920s, and he was friendly with Ernest Lawrence of the University of California, who advised Nishina on the building of a Japanese cyclotron—a particle accelerator—in 1937 and provided the machine with a 60-inch magnet. Nagaoka Hantaro anticipated by several years Rutherford’s description of a ‘Saturnian’ atom, and Hideki Yukawa predicted an atomic particle called a meson—much heavier than an electron and a carrier of nuclear strong force—in 1934. By that time, the Institute of Physical and Chemical Research, called the Riken, had been open in Tokyo for nearly two decades. Like the Europeans and Americans, the Japanese had been convinced by the experience of the First World War that science must be supported by the government if their nation was to compete economically with the West. Nishina started the Nuclear Research Lab at Riken in 1935. His younger colleagues called him Oyabun, the old man, though he was a sprightly 52. An admirer of the West, Nishina kept Webster’s International Dictionary on a stand near his desk so he could polish his English.9
Japanese physicists also knew what was meant by a chain reaction. Bunsaku Arakatsu, who had been apprenticed to Rutherford and Einstein, built a particle accelerator and by 1936 was bombarding nuclei. In October 1939, less than a year after Hahn and Strassmann had announced their discovery of fission, Arakatsu and a colleague published an article estimating with good accuracy the number of neutrons liberated each time the fissioned nucleus broke apart. Arakatsu understood, as did Nishina and many others, that a successful chain reaction could in theory produce a big explosion. But Japanese scientists in general seem to have been little interested in pursuing a nuclear weapon—or, if they were, their path to its pursuit was so thickly littered with obstacles as to make a Japanese bomb unlikely.10
One obstacle was the scientists’ own uncertainty that a nuclear bomb could be built. Nishina and the others knew, in the first place, that an atomic bomb was a good deal more than a laboratory exercise in making fissions. It would require close organization, coordination of science and engineering, an enormous commitment of financial resources, a solution to problems like fuses and initiators and fin design, that had not been broached, and a substantial amount—no one knew how much; an educated guess was 100 tons—of fissionable uranium 235, to be derived from uranium ore that Japan appeared not to have. Scientists lacked heavy water and pure graphite, predicted moderators of a chain reaction. Japan at peace was a country whose economic health depended on a vigorous foreign trade and careful management of scarce land, oil, and minerals. Japan at war would have its natural scarcities exaggerated, its priorities recast, and its services stretched to breaking point. Its immediate needs—for fighting the war, and for keeping the population sufficiently well fed to prevent domestic uprising—could not be served by an expensive and probably quixotic quest for a nuclear weapon. Japanese popular fantasies about atomic bombs were certainly no less vivid than European ones. As John Dower has noted, just before Pearl Harbor a Japanese scientist who was a member of the House of Councillors spoke openly of an overwhelmingly powerful bomb the size of a matchbox. (This boast was repeated by another scientist-politician in the House of Peers a year and a half later.) During the war, a magazine for boys ran a story called ‘Atomic Bomb’. But these visions of grandeur did not change scientists’ skepticism concerning the likelihood of building a nuclear weapon. After the war, one eminent physicist pointed out that the Japanese research effort ‘might have looked very well on paper, but [it] really amounted to very little’ in practice. The United States would spend $2 billion to build its atomic bombs. The total outlay for nuclear weapons research in Japan during the war was no more than $11.2 million, and perhaps as little as $650,000.11
A second obstacle to a successful nuclear weapons program in Japan was a general lack of enthusiasm for it among scientists. It is comforting to believe that Japanese physicists (and German ones) were reluctant for moral reasons to build weapons, especially nuclear weapons. It is also true that after the war scientists in defeated nations had an interest in underplaying their contributions to making weapons viewed with horror by much of the world. It is nevertheless plausible that Japanese scientists held themselves back from developing a weapon about which they had serious practical—not ethical—doubt. The widely held perception that a bomb was beyond Japan’s capacity to build would have contributed to a disinclination to work on the project: scientists may have asked themselves whether the bomb should be built on the discouraging assumption that it probably could not be. Dower has noted that Nishina, ordered by the military to undertake the bomb project, never by his behavior seemed to endorse the task. Nishina often seemed unresponsive to the military’s entreaties to work faster, privately expressed doubts about whether Japan could win the war under any circumstance, and ultimately put in charge of the project two scientists who were not among the luminaries in the field of nuclear physics. One of them, Masashi Takeuchi, who was to supervise the delicate task of uranium separation, later described himself as a ‘blank page’ where atomic research was concerned. There is some evidence that Nishina and Arakatsu requisitioned young scientists for nuclear projects they regarded, not unhappily, as hopeless, with the chief intent of keeping their most prominent charges out of the military and away from the front.12
Insofar as the Japanese state took notice of the atomic bomb, it made little effort to mobilize scientists into a cohesive unit to work on it. Here was the third and most important obstacle that stood in the way of a successful program. The military, which held predominant influence in the government, was interested in obtaining any weapon that might prove decisive against the Americans, particularly after confidence waned following the Japanese naval defeat at Midway in June 1942. But the military’s effort on this score was hampered (again) by scientists’ skepticism that a bomb was a practical possibility, the prospect of other winning weapons—rockets, so-called ‘death rays,’ and suicide planes or torpedoes— competing with nuclear weapons for budgetary favor, and above all a lack of coordinated thinking by the military branches that might have set the priorities for scientific projects and directed funds to those that seemed most likely to succeed in the shortest possible time. That the Japanese state during the Pacific War was authoritarian did not mean that its scientific and technological planning was fully coordinated. Japan’s pursuit, such as it was, of an atomic bomb ran on at least two tracks at once, one sponsored by the army, the other by the navy.
The Japanese program was initiated by the Army Lieutenant General Takeo Yasuda in the spring of 1940. Yasuda, who was trained as an electrical engineer, had read about fission in science journals, and he requested a fellow officer with slightly more expertise in physics than himself to ‘explore the possibility of an atomic bomb’. The officer’s twenty-page report, which came out that October, expressed optimism that Japan might be able to capture enough uranium to build a bomb. The army contacted the Riken physicists the following April. The institute director handed the problem to Nishina, who, more interested in the performance of his cyclotron than in weapons production, let it languish. Meanwhile the navy, represented by Captain Yoji Ito, whose credentials in physics were somewhat better than those of his army counterparts, opened a discussion of nuclear research, presumably to include work on a bomb. After Midway, Admiral Isoroku Yamamoto ordered his researchers to develop new weapons for the war and provided Ito’s committee with $500 (!) to begin its work. Evidently without knowing that Nishina had some fifteen months earlier been asked to assist with the army’s nuclear project, the navy committee invited Oyabun to serve as its chair. Each project was top secret, but Nishina was functionally in charge of both. While Nishina seems to have found his bureaucratic home thereafter in the navy committee, fission work continued on parallel and compartmentalized courses.
The Ito Committee met some ten times between July 1942 and March 1943. Ito later summarized its conclusions. While it was ‘obviously’ possible theoretically to make an atomic bomb, Japan lacked the uranium necessary to do it, and although there may have been deposits in the ‘wrinkles in the earth’ in Burma, there was no assurance of this. Above all, the committee considered it unlikely that the United States could produce an atomic bomb before the end of the war. This assessment reflected optimism about the limitations of American technology and perhaps pessimism about the duration of the war. Such conclusions discouraged the navy from continued, active pursuit of a nuclear bomb; Yamamoto’s decisive weapon would have to be something else. Nishina now focused his efforts on behalf of the army, and on the separation of uranium 235 from the odd shipments of uranium ore his subordinates managed to find. His lab was handicapped by persistent shortages of materials—his Riken colleague Kunihiko Kigoshi had to plead from the army, and finally steal from his mother, enough rationed sugar to conduct a heating experiment—and his own serious miscalculation of the timing of a chain reaction: he was off by a factor of ten.
The army-sponsored program, called the NI (for Nishina) Project, inched forward from May 1943 on. Located in Riken building number 49, put up the previous year in part as a mess hall, it was dedicated almost exclusively to the separation of U-235 through the time-consuming method of gaseous diffusion, such as Francis Simon had explored at Oxford. (The work was now more sophisticated than Simon’s experiments with the family kitchen strainer. Researchers were to make hexafluoride gas, then force it through a number of baffles, whose tiny holes were to admit the light 235 isotope while blocking the bulkier U-238.) The gas itself proved difficult to produce: much-qualified triumph came in January 1944, with the emergence of a hexafluoride crystal the size of a grain of rice. The entire process remained on a ludicrously small scale. Riken lacked the space, the money, the isotope separators, and even the electricity needed to create the fissionable uranium necessary for a bomb; Walter Grunden estimates that by early 1945 the lab would have needed 10 percent of the electrical power then available in the entire country to be successful. That February, Nishina placed what distillate his researchers had produced into one of his cyclotrons and blasted it with neutrons. No radioactivity resulted. Then, on 13 April, American bombers struck Tokyo. In the pre-dawn chill, hours after the planes had dropped their bombs and flown off, Building No. 49 suddenly burst into flames and was destroyed. That all but put an end to Japan’s atomic quest.
Its destruction was no great surprise, and at the time well down the list of Japanese disappointments and concerns. The Japanese government never expected to have an atomic bomb, and the military branches, working separately from each other, saw nuclear bombs as a prospect more remote than the fabrication of other fantastic weapons. Scientists like Nishina were unenthusiastic about the bomb, and others, including Kigoshi and his colleague Takeuchi, were in over their heads. Theoretical sophistication aside, Japanese scientists lacked the apparatus and materials they needed to do more than dream about an atomic bomb. By 1945, like their countrymen and -women, they were trying desperately to survive. (Dower observes that Kigoshi was finally so weak with hunger that he had trouble holding a test tube steady.) History might have remembered Japan’s pursuit of an atomic bomb as simple folly. In the aftermath of Hiroshima and Nagasaki, it seemed equally a grim irony.13