The Atomic Bomb: “The Year of Decisions”

Teacher Notes:

Introduction to Case:

This case begins with a quote from President Harry Truman’s personal diary only months after taking the oath of office on April 12, 1945. He writes, “I have to decide Japanese strategy—shall we invade Japan proper or shall we bomb and blockade?...”. While some classroom examinations of this time period opt to put Truman “on trial” for crimes against humanity or to second guess his decisions in the summer of 1945, this case examines whether Truman, in fact, actually made a decision or if the decision was not to drop the bomb but to stop what seemed to be an inevitability at the time.

Due to the global nature of the case and the number of “players” involved, this case is necessarily complicated. To assist teachers, we created a “Usual Suspects” guide to assist students in understanding the role of each document author and the people they describe within the document. Further, instead of focusing on sourcing the documents (although an important skill), the “detective’s log” focuses on organizing the documents to argue the case in either direction. For example, on the left side of the graphic organizer students are asked to put quotes from documents that could be used to argue that the dropping of the bomb was inevitable. On the right side of the graphic organizer, students are asked to find quotes and documents that support that Truman did, in fact, make a decision and to categorize those documents under the following headings: Geopolitical, Economic and Military as a way to scaffold their argument.

In terms of documents, it was difficult to limit the scope but we found that this is necessary in order for teachers to keep it to a one or two day exercise. Further, we truncated several of the documents (including Truman’s Potsdam diary) and excerpted others (e.g. Truman by David McCullough) to make the case more manageable for the typical high school student.

While many of the cases on the site are well suited for a variety of age groups (5-12th grade), this one is most appropriate for high school students as the documents require a broader understanding of history and a reading level not typically found in younger students.

Purpose of the Case:

To this day, many historians still consider this as one of the most critical decisions made in the 20th Century. After 33 years, in 1978, Truman’s handwritten diary from the days at the Potsdam conference (July 16th through 30th, 1945) was discovered and were made available to the public. This diary, along with other first person documents from the time and afterwards, allows us to examine the crucial period leading up to and after the dropping of both bombs through the eyes of the decision maker himself, Truman.

It is important to note that teachers could bring out others issue of historical construction by discussing the dates of the documents. For example, in Document F, Truman corresponds with a reporter and provides a rationale for the dropping of the bomb. One question that it raises is how is history remembered almost twenty years after the event. To what extent can we rely on this document in light of a President’s concern of his own legacy?

Other questions that arise within this case involve the use of historical scholarship as a source in classroom inquiry. For example, we used an excerpt from McCollugh’s Pulitzer Prize winning biography on Truman as an “efficient” telling of this event but also because we hoped students might ask questions of the document in terms of McCullough’s point of view—and more broadly, a historian’s point of view.



This exercise was funded by the Library of Congress through a grant from the Teaching with Primary Source Program (TPS) Eastern Region at Waynesburg University. The Year of Decisions case was designed by Dr. Kathy Swan (University of Kentucky) in consultation with Dr. David Locascio (Longwood University), Dr. Mark Hofer (College of William and Mary), and Julie Bray, M.Ed (Toano Middle School).


NCSS Theme II: Time, Continuity and Change
Focus on reading and reconstructing the past to:
1. include various perspectives on historical events;
2.draw upon historical knowledge during the examination of social issues;
3. develop the habits of mind that historians and schalors employ.



Becoming a Detective

On June 17th, 1945, President Truman writes in his personal diary, “I have to decide Japanese strategy – shall we invade Japan proper or shall we bomb and blockade? That is my hardest decision to date. But I’ll make it when I have all the facts.” To this day, many historians consider this “decision” as one of the most momentous of the 20th century.

Given the context of Truman’s recent ascension to the Presidency on April 12, 1945, and the fact that he had not been aware of the Manhattan Project prior to this time, would it have been realistic to expect him to stop the momentum underway or in fact offer an alternative Japanese strategy? In other words, did Truman decide to drop the bomb, or was the use of the atomic bomb inevitable?


Investigating the Evidence

  • Document A: Excerpts from Truman’s diary from the Potsdam conference (Dated entries from July 17 to August 10, 1945)
  • Document B: Excerpt from document produced during June 6, 1945 meeting of Japanese Supreme War Council entitled The Fundamental Policy to be Followed Henceforth in the Conduct of the War.
  • Document C: Excerpt from diary of Secretary of War Henry Stimson regarding meeting of General Staff (Dated entry from June 11, 1945)
  • Document D: Memorandum by Manhattan Project scientist J. R. Oppenheimer, "Recommendations on the Immediate Use of Nuclear Weapons," (June 16, 1945)
  • Document E: General George C. Marshall(November 2, 1959)
  • Document F: Correspondence between Irv Kupcinet and Harry S. Truman, including draft copies of Truman’s letter, July 30 and August 5, 1963, responding to Mr. Kupcinet’s column in the Chicago Sun-Times about the dropping of the atomic bomb on Japan.
  • Document G: Excerpt from autobiography of Admiral William D. Leahy, I Was There (1979).
  • Document H: Richard G. Hewlett and Oscar E. Anderson, Jr., The New World: A History of the United States Atomic Energy Commission, Volume 1, 1939/1946 (1972).
  • Document I: Excerpt from David McCullough’s Truman, pages 400-401.

Searching for Clues

Please answer the following questions in the formatted case log (PDF Format, Word Format) about each primary source document to help you understand their meaning.



Cracking the Case

Based on your analysis of the documents and citing evidence to support you answer, please write a paragraph or two answering the following questions: Did Truman decide to drop the bomb, or was the use of the atomic bomb inevitable? Within your analysis, please indicate whether you were satisfied with the evidence and list any additional questions that have been left unanswered through your investigation.