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World War II

Prelude to WW II: Isolationism, Refugee Policy and the Roosevelt Administration
Pearl Harbor and Mobilization
Internment Policy
Pacific Theatre
European Theatre
Wartime Refugee Policy
The Atomic Bomb

The Atomic Bomb

Atomic bomb
Photo of first test of the atomic bomb at Almagordo, New Mexico.

When Harry Truman assumed the presidency upon the death of Franklin D. Roosevelt on April 12, 1945, he had no knowledge of The Manhattan Project, the program to develop an atomic bomb. The potential of developing a nuclear weapon had been first suggested to President Roosevelt in a letter from Albert Einstein delivered to the President in 1939, well before the U.S. entry into World War II. The letter was based primarily on information provided to Einstein by his fellow physicist Leo Szilard, and may indeed have been drafted by Szilard for Einstein's signature:

...In the course of the last four months it has been made probable--through the work of Joliot in France as well as Fermi and Szilard in America--that it may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.

This new phenomenon would also lead to the construction of bombs, and it is conceivable--though much less certain--that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory. However, such bombs might very well prove to be too heavy for transportation by air....

Excerpts from letter dated August 2, 1939, from Albert Einstein to President Roosevelt

Source: U.S. Army Trinity Site

While research continued at scattered university sites, the concentrated effort to develop an atomic weapon escalated after the entry of the U.S. into the War following Pearl Harbor. The work also gained urgency when American scientists learned that the Nazis also were pursuing atomic weapons research. In 1941, the Manhattan Project was formally organized, and the next year General Leslie Groves of the Army Corps of Engineers was appointed to manage the overall program, with physicist J. Robert Oppenheimer named to head the nuclear research laboratories that were constructed at Los Alamos, New Mexico. When Roosevelt died, the scientists were optimistic that they would soon be ready for their first test of a bomb.

At his first Cabinet meeting on April 12, the day of Roosevelt's death, President Truman was advised briefly of the project's existence by Secretary of War Henry L. Stimson. Stimson later followed this up with a much more extensive session at the White House on April 25 at which a memorandum was given the President projecting that the bomb would be ready for use within four months and suggesting that the President appoint a committee to review the options for possible use of the weapon. Soon, with the surrender of Germany in May, any fear that the Nazi atomic research would produce a weapon was removed.

President Truman's account of his first Cabinet meeting as president, April 12, 1945, the day of President Roosevelt's death

That first cabinet meeting was short, and when it adjourned, the members rose silently and made their way from the room--except for Secretary Stimson.

He asked to speak to me about a most urgent matter. Stimson told me that he wanted me to know about an immense project that was underway--a project looking to the development of a new explosive of almost unbelievable destructive power. That was all he felt free to say at the time, and his statement left me puzzled. It was the first bit of information that had come to me about the atomic bomb, but he gave me no details.... The next day Jimmy Byrnes, who until shortly before had been Director of War Mobilization for President Roosevelt, came to see me, and even he told me a few details, though with great solemnity he said that we were perfecting an explosive great enough to destroy the whole world.

Source: Memoirs by Harry S. Truman, 1945: Year of Decisions (New York: Smithmark, 1995), pp. 10-11, published online by Nuclear Age Peace Foundation

President Truman accepted Stimson's recommendations, and named Stimson to chair what would become known as the Interim Committee. At the Committee's June 1, 1945 meeting, they reviewed options for the bomb's use, as reported in the Committee meeting notes, " Mr. [James] Byrnes recommended, and the Committee agreed, that... the [atomic] bomb should be used against Japan as soon as possible; that it be used on a war plant surrounded by workers' homes; and that it be used without prior warning."

On June 18, the President met at the White House with the Joint Chiefs of Staff to review the military situation and to seek estimates on the potential casualties that would result from an invasion of the Japanese home islands. During the meeting, he expressed concern that the action could produce a rate of loss similar to that suffered in the fighting for Okinawa, when over a third of Amercan troops were casualties, with more than 25,000 killed and 55,000 wounded. A joint army and navy war plans committee estimated that 25,000 men would be killed in an invasion of the Japanese island of Kyushu on two fronts; 40,000 might die if an invasion on a single front was followed by invasion of the island of Honshu, where Tokyo was located; and 46,000 deaths were projected from a two-front invasion of Kyushu followed by an invasion of Honshu.

Excerpt of minutes of meeting held at the White House on June 18, 1945. Source: Harry S. Truman Presidential Museum & Library

Despite the recommmendation, there continued to be debate within the government, as well as among the scientists working on the bomb's development, over the moral and military issues relating to its use. Leo Szilard, the physicist whose work led to Einstein's contacts to Roosevelt that ultimately produced the Manhattan Project, became a leading spokesman for restraint in the use of the weapon. In March, Szilard had drafted another letter for Einstein to send to Roosevelt asking the President to hear Szilard's concerns, but the letter failed to reach Roosevelt prior to his death on April 12. Szilard also attempted to organize support from other scientists urging that the U.S. not act alone in the use of the weapons.

...the way in which nuclear weapons, now secretly developed in this country, will first be revealed to the world appears of great, perhaps fateful importance.

Nevertheless, it is not at all certain that the American public opinion, if it could be enlightened as to the effect of atomic explosives, would support the first introduction by our own country of such an indiscriminate method of wholesale destruction of civilian life.

Thus, from the "optimistic" point of view - looking forward to an international agreement on prevention of nuclear warfare - the military advantages and the saving of American lives, achieved by the sudden use of atomic bombs against Japan, may be outweighed by the ensuing loss of confidence and wave of horror and repulsion, sweeping over the rest of the world, and perhaps dividing even the public opinion at home....

"The Franck Report" (Report of the Committee on Political and Social Problems of the Manhattan Project chaired by James Franck and including Leo Szilard) dated June 11, 1945

Source: Atomic Bomb: Documents on the Decision to use Atomic Bombs on the Cities of Hiroshima and Nagasaki, Gene Dannen

On June 27, Undersecretary of the Navy Ralph A. Bard wrote to Secretary of War Stimson that use of the bomb without warning was contrary to "the position of the United States as a great humanitarian nation," especially since Japan seemed close to surrender. Others argued, however, that the Japanese military, as illustrated by the suicide kamikaze campaigns launched late in the war against U.S. ships, would never accept a surrender.

On July 16, 1945, the first atomic bomb was tested at the Trinity site near Los Alamos. The heat of the explosion on exposed skin was felt up to 20 miles from the site.

The explosion took place at about 5:30 A.M. I had my face protected by a large board in which a piece of dark welding glass had been inserted. My first impression of the explosion was the very intense flash of light, and a sensation of heat on the parts of my body that were exposed. Although I did not look directly towards the object, I had the impression that suddenly the countryside became brighter than in full daylight. I subsequently looked in the direction of the explosion through the dark glass and could see something that looked like a conglomeration of flames that promptly started rising. After a few seconds the rising flames lost their brightness and appeared as a huge pillar of smoke with an expanded head like a gigantic mushroom that rose rapidly beyond the clouds probably to a height of 30,000 feet. After reaching its full height, the smoke stayed stationary for a while before the wind started dissipating it....

Enrico Fermi eyewitness account of first test of bomb on July 16, 1945

Source: Atomic Bomb: Documents on the Decision to use Atomic Bombs on the Cities of Hiroshima and Nagasaki, Gene Dannen

On the day following the successful test, Leo Szilard forwarded a petition to the President from himself and 69 others working on the bomb program:

We, the undersigned scientists, have been working in the field of atomic power. Until recently, we have had to fear that the United States might be attacked by atomic bombs during this war and that her only defense might lie in a counterattack by the same means. Today, with the defeat of Germany, this danger is averted and we feel impelled to say what follows:

The war has to be brought speedily to a successful conclusion and attacks by atomic bombs may very well be an effective method of warfare. We feel, however, that such attacks on Japan could not be justified, at least not unless the terms which will be imposed after the war on Japan were made public in detail and Japan were given an opportunity to surrender.

If such public announcement gave assurance to the Japanese that they could look forward to a life devoted to peaceful pursuits in their homeland and if Japan still refused to surrender our nation might then, in certain circumstances, find itself forced to resort to the use of atomic bombs. Such a step, however, ought not to be made at any time without seriously considering the moral responsibilities which are involved.

In view of the foregoing, we, the undersigned, respectfully petition: first, that you exercise your power as Commander-in-Chief, to rule that the United States shall not resort to the use of atomic bombs in this war unless the terms which will be imposed upon Japan have been made public in detail and Japan knowing these terms has refused to surrender; second, that in such an event the question whether or not to use atomic bombs be decided by you in light of the considerations presented in this petition as well as all the other moral responsibilities which are involved.

Excerpts from Petition to the President of the United States dated July 17, 1945, signed by Leo Szilard and 69 co-signers at the Manhattan Project "Metallurgical Laboratory" in Chicago.

At the time of the test, President Truman was in Europe meeting with Stalin and Churchill at the Potsdam Conference. The President had postponed the meeting in hopes that the test would take place, thus giving him leverage with the Soviets in the sensitive negotiations on how the Allies would govern the post-War world.

Went to lunch with F.M. at 1:30, walked around to British headquarters. Met at the gate by Mr. Churchill. Guard of honor drawn up. Fine body of men - Scottish Guards. Band played "Star Spangled Banner." Inspected guard and went in for lunch. P.M. and I ate alone. Discussed Manhattan (it is a success). Decided to tell Stalin about it. Stalin had told F.M. of telegram from Jap emperor asking for peace. Stalin also read his answer to me. It was satisfactory. Believe Japs will fold up before Russia comes in. I am sure they will when Manhattan appears over their homeland. I shall inform Stalin about it at an opportune time.

Harry S. Tuman diary entry for July 18, 1945 during Potsdam Conference with Winston Churchill and Josef Stalin

Truman and the Bomb, a Documentary History, Edited by Robert H. Ferrell, Harry S. Truman Presidential Museum & Library

Stalin showed little visible reaction to the news. Later, however, evidence was disclosed that he promptly directed the Soviet scientists to expedite their existing atomic development schedule.

I was perhaps five yards away, and I watched with the closest attention the momentous talk. I knew what the President was going to do. What was vital to measure was its effect on Stalin. I can see it all as if it were yesterday. He seemed to be delighted. A new bomb! Of extraordinary power! Probably decisive on the whole Japanese war! What a bit of luck! This was my impression at the moment, and I was sure that he had no idea of the significance of what he was being told. Evidently in his immense toils and stresses the atomic bomb had played no part. If he had the slightest idea of the revolution in world affairs which was in progress his reactions would have been obvious. Nothing would have been easier than for him to say, "Thank you so much for telling me about your new bomb. I of course have no technical knowledge. May I send my expert in these nuclear sciences to see your expert tomorrow morning?" But his face remained gay and genial and the talk between these two potentates soon came to an end. As we were waiting for our cars I found myself near Truman. "How did it go?" I asked. "He never asked a question," he replied. I was certain therefore that at that date Stalin had no special knowledge of the vast process of research upon which the United States and Britain had been engaged for so long...

Winston Churchill, Triumph and Tragedy (Boston: Houghton-Mifflin, 1953) pp 669-70


The leaders at Potsdam also issued a Declaration demanding that Japan surrender, but without any mention of the potential for nuclear destruction. During the Potsdam meeting, the President also conferred with his advisers over the options in continuing with the prior plan to invade Japan or to employ the new weapons in an attempt to end the War.

...I called a meeting of the Secretary of State, Mr. Byrnes, the Secretary of War, Mr. Stimson, Admiral Leahy, General Marshall, General Eisenhower, Admiral King and some others, to discuss what should be done with this awful weapon.

I asked General Marshall what it would cost in lives to land on the Tokyo plain and other places in Japan. It was his opinion that such an invasion would cost at a minimum one quarter of a million casualties, and might cost as much as a million, on the American side alone, with an equal number of the enemy. The other military and naval men present agreed.

I asked Secretary Stimson which cities in Japan were devoted exclusively to war production. He promptly named Hiroshima and Nagasaki, among others.

We sent an ultimatum to Japan. It was rejected.

I ordered atomic bombs dropped on the two cities named on the way back from Potsdam, when we were in the middle of the Atlantic Ocean....

....Dropping the bombs ended the war, saved lives, and gave the free nations a chance to face the facts.

Letter dated January 12, 1953, of President Truman to Professor James L. Cate responding to Cate's inquiry for information on the decision reached following the Potsdam Conference to use the atomic bomb against Japan

The Decision to Drop the Atomic Bomb: Truman and the Bomb, a Documentary History

Robert H. Ferrell, Harry S. Truman Presidential Library & Museum

Despite the dissent within the government and the scientific community over the need and morality of the bomb's use, the President decided to use the weapon on Japan, although there remains controversy over whether there was full appreciation of the high civilian populations in both the initial target--Hiroshima and Nagasaki.

We have discovered the most terrible bomb in the history of the world. It may be the fire destruction prophesied in the Euphrates Valley Era, after Noah and his fabulous Ark.

Anyway we "think" we have found the way to cause a disintegration of the atom. An experiment in the New Mexico desert was startling - to put it mildly. Thirteen pounds of the explosive caused the complete disintegration of a steel tower 60 feet high, created a crater 6 feet deep and 1,200 feet in diameter, knocked over a steel tower 1/2 mile away and knocked men down 10,000 yards away. The explosion was visible for more than 200 miles and audible for 40 miles and more.

This weapon is to be used against Japan between now and August 10th. I have told the Sec. of War, Mr. Stimson, to use it so that military objectives and soldiers and sailors are the target and not women and children. Even if the Japs are savages, ruthless, merciless and fanatic, we as the leader of the world for the common welfare cannot drop that terrible bomb on the old capital or the new.

He and I are in accord. The target will be a purely military one and we will issue a warning statement asking the Japs to surrender and save lives. I'm sure they will not do that, but we will have given them the chance. It is certainly a good thing for the world that Hitler's crowd or Stalin's did not discover this atomic bomb. It seems to be the most terrible thing ever discovered, but it can be made the most useful...

Truman diary entry on July 25, 1945, quoted in The Decision to Drop the Atomic Bomb: Truman and the Bomb, a Documentary History >>Robert H. Ferrell, Harry S. Truman Presidential Library & Museum

Twenty-one days after the Los Alamos test, on August 6, 1945, the B-29 bomber Enola Gay dropped the bomb on Hiroshima. Three days later, a more powerful bomb was used to bomb Nagasaki.

Destruction following bombing of Hiroshima. Image Source: US Army/A-Bomb WWW Museum

Subsequent studies have estimated the deaths occurring as a result of the bombings either immediately or through radiation exposure as ranging between 90,000 to 140,000 of Hiroshima's then population of 310,000 and 60,000 to 80,000 of Nagasaki's population of 250,000. See Radiation Effects Research Foundation. On the day after the bombing of Nagasaki, the Japanese government offered to surrender on the condition that the role of the Emperor be maintained. After further exchanges between the State Department and the Japanese government, Japan agreed to an unconditional surrender on August 15, 1945, bringing an end to World War II. In addition to the six million Jews and other civilians who died in the Holocaust, total estimates of deaths toll attributable to the war for military and civilian casualties have ranged upward to 60 million. See Casualties in World War II: Jason McDonald.


The Decision to Drop the Atomic Bomb: Truman and the Bomb, a Documentary History >>Robert H. Ferrell, Harry S. Truman Presidential Library & Museum

President Harry Truman and the Decision to Drop the Atomic Bomb >>The National Archives (U.K.) Learning Curve

Atomic Bomb: Documents on the Decision to use Atomic Bombs on the Cities of Hiroshima and Nagasaki >> Gene Dannen

Fifty Years from Trinity >> The Seattle Times

Hiroshima Archive

A-Bomb WWW Museum

World War II History Info

Franklin D. Roosevelt Presidential Library and Museum

Suggestions for the Classroom: The Holocaust, anti-Semitism, U.S. immigration policy, Franklin Delano Roosevelt, World War II,

Winston Churchill and Dresden, The National Archives (U.K.) Learning Curve

Educational Tools:

Lesson Plans: The Manhattan Project >> The History Teaching Institute, The Ohio State University

Student Activity: Atomic Bomb-Truman Press Release-August 6, 1945 >> Harry S. Truman Presidential Library & Museum

Lesson Plans: Nuclear Science: Understanding the Development and Control of Nuclear Energy >> Harry S. Truman Presidential Library & Museum

Ending the War Against Japan: Science, Morality, and the Atomic Bomb >> Choices for the 21st Century Education Program, Watson Institute for International Studies, Brown University

Contemporary History of Civilization, Professor Joseph V. O'Brien, John Jay College of Criminal Justice