“A Very Pleasant Way to Die”: Radiation Effects and the Decision to Use the Atomic Bomb against Japan



  • This article grew out of research presented at the June 2008 conference of the Society for Historians of American Foreign Relations (SHAFR) in Columbus, OH, and the March 2009 “Symposium on Nuclear Histories in Japan and Korea” at the Tokyo Institute of Technology. I would like to thank my all fellow panelists for their feedback and comments. Alex Wellerstein was particularly helpful in pointing me toward documents at the Nuclear Testing Archive in Nevada that proved to be crucial to illuminating the pre-Hiroshima understanding of radiation effects in the United States. I have also benefited from exchanges on this subject with Barton J. Bernstein, Michael R. Gordin, Gregg Herken, Robert S. Norris, M. Susan Lindee, Masakatsu Yamazaki, Shiho Nakazawa, Jacob Darwin Hamblin, and Campbell Craig, as well as the comments of two anonymous reviewers for Diplomatic History.


One of the distinguishing characteristics of the atomic bombs used against Hiroshima and Nagasaki was their accompanying radiation effects. The effects of ionizing radiation on the bomb's survivors have been the subject of intense study and discussion since August 1945. This article examines a related question that has received surprisingly little scholarly attention: what did American scientists and policy makers know about radiation effects prior to the use of the bomb? In making the decision, did American leaders understand that the atomic bombs used against Japanese cities and civilians would have lingering and deadly effects in some ways analogous to chemical or biological weapons?

A careful study of pre-Hiroshima knowledge of radiation effects in the United States makes it clear that most of the immediate and long term biological effects of radiation on the victims of the bomb were, in fact, predictable at the time of the A-bomb decision. While the pre-Hiroshima understanding of radiation among Manhattan Project scientists was far from perfect, that the bomb would produce lingering and lethal effects was suggested as early as 1940. Extensive research carried out by Manhattan Project scientists and physicians during World War II, including both human and animal experiments, greatly expanded knowledge of the biological effects of ionizing radiation.

Despite the intense wartime study of radiation effects in the United States, this knowledge played little or no role in the decision to use the atomic bomb. The policy of compartmentalization and secrecy enforced by Manhattan Project director General Leslie R. Groves, combined with the single-minded drive at Los Alamos to build a working bomb, meant that few even inside the Manhattan Project itself were aware of, or interested in, the emerging body of knowledge on radiation effects generated during the war. The high-level American leaders who made the final decisions about the bomb, including President Harry S. Truman, Secretary of State James F. Byrnes, and Secretary of War Henry L. Stimson, were never informed that the weapon would continue to sicken and kill its victims long after use.

For all of the outstanding technical successes of the Manhattan Project, the policy of wartime compartmentalization and postwar denial with respect to radiation effects ultimately served neither American leaders nor the many victims of the bomb in Japan. In addition to analyzing the evidence of pre-Hiroshima knowledge of radiation effects in the United States, this article explores the disconnect between scientific knowledge and political decision making with respect to the atomic bomb that would continue into the Cold War.