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Hanford plutonium begins reprocessing in preparation for weaponization.

U.S. scientists and physicians begin secret experiments on plutonium toxicity by injecting plutonium into patients and prisoners, without their knowledge or consent. A civilian consultant to Department of War, Jack Madigan, summarizes his findings on the efficacy of the Manhattan Project: "If the project succeeds there won’t be any investigation. If it doesn’t, they won’t investigate anything else."

The first batch of Uranium 235 is successfully separated at Oak Ridge National Laboratory in Tennessee.

Soviet Army liberates Auschwitz.

Roosevelt , Churchill, and Stalin hold a Conference at Yalta. They agree upon occupation zones for postwar Germany, a plan to set up a new government for Poland, and "a general international organization to maintain peace and security."

Massive Allied bombing of Dresden creates a firestorm for the second time in history. American author, Kurt Vonnegut, was present in Dresden and wrote about it in Slaughterhouse Five .

Head of the War Mobilization Board and future Secretary of State, James Byrnes, sends a memo to Franklin Roosevelt warning that if there is no "product" before the end of the war, then "there would be serious consequences for the Democratic Party." He also states, "I understand that the expenditures for the Manhattan Project are approaching two billion dollars with no definite assurance yet of production. We have succeeded to date in obtaining the co-operation of congressional committees in secret hearings. Perhaps we can continue to do so while the war lasts."

At the urging of Leo Szilard, Albert Einstein signs a letter of introduction of Szilard to President Roosevelt. Szilard wishes to warn Roosevelt of the post-war dangers of a nuclear arms race if the atomic bomb is used against Japan. The letter states: "The terms of secrecy under which Dr. Szilard is working at present do not permit him to give me information about his work; however, I understand that he now is greatly concerned about the lack of adequate contact between scientists who are doing this work and those members of your Cabinet who are responsible for formulating policy." In the memorandum accompanying the letter, Szilard wrote: "our ’demonstration’ of atomic bombs will precipitate a race in the production of these devices between the United States and Russia and that if we continue to pursue the present course, our initial advantage may be lost very quickly in such a race."

Eleanor Roosevelt, who received a copy of Szilard’s letter to President Roosevelt, replies to Szilard proposing a meeting in her Manhattan apartment on May 8. President Roosevelt’s death, however, prevents this from happening. 

As part of the Manhattan Project, an injured motorcyclist named Ebb Cade was injected with 4.7 micrograms of plutonium without his knowledge. 

Franklin Roosevelt dies. Harry Truman becomes the 33rd President of the United States. In his last prepared speech he writes:

"We are faced with the preeminent fact that if civilization is to survive we must cultivate the science of human relationship-- the ability of peoples of all kinds to live together and work together in the same world, at peace. We have learned and paid an awful price to learn, that living and working together can be done in only one way only -- under law. There is now truer and simpler idea in the world today. Unless it prevails, and unless by common struggle we are capable of new ways of thinking, mankind is doomed."

Secretary of War Stimson and General Groves brief President Truman on the bomb. In this briefing, Groves insists that Japan had always been the target of the bomb’s use. Joint Chief Planners advise Joint Chiefs of Staff that "unless a definition of unconditional surrender can be given which is acceptable to the Japanese, there is no alternative to annihilation and no prospect that the threat of absolute defeat will bring about capitulation."

Soviet and U.S. troops meet at Torqau on the Elbe.

The Target Committee meets for the first time in order to decide which Japanese cities to target with the atomic bomb. By the end of May, the following cities are selected: Kyoto, Hiroshima, Kokura and Niigata. Eventually, Kyoto is replaced by Nagasaki, and the listed cities are spared further conventional bombing by the American Army Air Force.

In a report entitled, "Unconditional Surrender," the Joint Intelligence Committee informs the Joint Chiefs of Staff that "numbers of informed Japanese, both military and civilian, already realize the inevitability of absolute defeat."

Hitler commits suicide.

Manhattan Project experiments continue in Chicago on three cancer patients. Each patient is injected with a different level of plutonium. Patients were informed, but consent was obtained with an implication that the injections may help their condition.

Jimmy Byrnes is chosen as President Truman’s personal representative on the Interim Committee.

War in Europe ends.

The Interim Committee meets for the first time. Its purpose is "to study and report on the whole problem of temporary war controls and later publicity, and to survey and make recommendations on post war research, development and controls, as well as legislation necessary to effectuate them." Members of the Interim Committee are, Jimmy Byrnes, the President’s personal representative; Ralph Bard, an undersecretary of the Navy; William Clayton, an assistant secretary at the State Department; Vannevar Bush, Director of the US Office of Scientific Research and Development and a former Dean of Engineering at MIT; James Conant, president of Harvard University and a distinguished chemist; and Karl Compton, president of MIT and a noted physicist.

William Donovan, Director of the Office of Strategic Services, reports to President Truman that Japan’s minister to Switzerland, Shunichi Kase, wished "to help arrange for a cessation of hostilities."

Leo Szilard visits the White House with a letter of introduction from Albert Einstein to warn President Truman of the dangers that atomic weapons pose for the post-War world and to urge him not to authorize use of atomic weapons against Japan. Szilard is referred by Matthew J. Connelly, Truman’s appointments secretary, to James Byrnes in Spartanburg, South Carolina.

Assistant Secretary of War John J. McCloy argues to Secretary of War Stimson that the term "unconditional surrender" should be dropped, arguing that "unconditional surrender is a phrase which means loss of face, and I wonder whether we cannot accomplish everything we want to accomplish in regard to Japan without the use of that term."

Leo Szilard
, along with Walter Bartky, and Harold Urey, meet with Jimmy Byrnes at his home in Spartanburg, South Carolina. Szilard attempts to persuade Byrnes to demonstrate the bomb’s power, rather than using it on Japan. Byrnes asks Szilard, "How would you get Congress to appropriate money for atomic energy research if you do not show results for the money which has been spent already?" Reflecting on this meeting later, Szilard writes, "I thought to myself how much better off the world might be had I been born in America and become influential in American politics, and had Byrnes been born in Hungary and studied physics. In all probability there would then have been no atomic bomb and no danger of an arms race between America and Russia."In a State Department Memorandum of Conversation, Acting Secretary of State Joseph Grew describes a meeting with President Truman that day. Grew writes, "The greatest obstacle to unconditional surrender by the Japanese is their belief that this would entail the destruction or permanent removal of the Emperor and the institution of the Throne. If some indication can now be given the Japanese that they themselves, when once thoroughly defeated and rendered impotent to wage war in the future will be permitted to determine their own future political structure, they will be afforded a method of saving face without which surrender will be highly unlikely."

Wanting to influence the Interim Committee, Szilard arranges a meeting with Oppenheimer in Groves’ office. Oppenheimer tells Szilard, "this is a weapon with no military significance. It will make a big bang--a very big bang--but it is not a weapon which is useful in war."

The Interim Committee agrees that "the most desirable target would be a vital war plant employing a large number of workers and closely surrounded by workers’ houses." Among those agreeing is James Conant, the president of Harvard University. The Office of Strategic Services (OSS) reports on receiving a Japanese peace feeler through a Japanese diplomat stationed in Portugal. The Japanese diplomat says that the actual terms are unimportant so long as the term "unconditional surrender" is not used.

Interim Committee makes a formal decision not to warn the civilian populations of the targeted cities. The minutes for the Interim Committee meeting state: "Mr. Byrnes recommended and the Committee agreed, that the Secretary of War should be advised that, while recognizing that the final selection of the target was essentially a military decision, the present view of the Committee was that the bomb 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."

Chief of Staff General George Marshall, in a memo to Secretary of War Stimson, writes, "We should cease talking about unconditional surrender of Japan and begin to define our true objective in terms of defeat and disarmament."

The Franck Committee, headed by Nobel Laureate James Franck, issues a report advising against a surprise atomic bombing of Japan. The report states, "If we consider international agreement on total prevention of nuclear warfare as the paramount objective, this kind of introduction of atomic weapons to the world may easily destroy all our chances of success." The report correctly predicts that dropping an atomic bomb "will mean a flying start toward an unlimited armaments race."

The Franck Committee Report--with its recommendation that the bomb be demonstrated to Japan before being used on civilians--is taken by Compton to Los Alamos and copies were given to Fermi, Lawrence, and Oppenheimer.

Joint War Plans Committee (JWPC), an advisory committee to the Joint Chiefs of Staff, concludes that about 40,000 Americans would die in the planned two stage assault on Japan.

Compton, Fermi, Lawrence, and Oppenheimer conclude, "We can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use."

Assistant Secretary of War McCloy tells Secretary of War Stimson that "there were no more cities to bomb, no more carriers to sink or battleships to shell; we had difficulty finding targets."

President Truman convenes a meeting of his chief advisers to discuss the military’s contingency plans for the invasion of Japan. The invasion was to begin no earlier than November 1, 1945 and according to Admiral William Leahy, "The invasion itself was never authorized." McCloy is asked to prepare language for what is to become Article 12 of the drafted Potsdam Declaration. It specifies that the post-war Japanese government "may include a constitutional monarchy under the present dynasty." Admiral Leahy makes a diary entry noting, "It is my opinion at the present time that a surrender of Japan can be arranged with terms that can be accepted by Japan and that will make fully satisfactory provision for America’s defense against future trans-Pacific aggression." He also notes that General Marshall believes that an invasion of Kyushu, the southern-most Japanese island, "will not cost us in casualties more than 63,000 of the 190,000 combatant troops estimated as necessary for the operation." This may be compared to later estimates, after the atomic bombings, of 500,000 to 1,000,000 American lives saved.

James Forrestal’s diary describes a top-secret "State-War-Navy Meeting" in which surrender terms are discussed. He writes, "Grew’s proposal, in which Stimson most vigorously agrees that something be done in the very near future to indicate to the Japanese what kind of surrender terms would be imposed upon them and particularly to indicate to them that they would be allowed to retain their own form of government and religious institutions, while at the same time making it clear that we propose to eradicate completely all traces of Japanese militarism."

A meeting of the Supreme War Direction Council before Emperor Hirohito is held on the subject of ending the war. According to the U.S. Strategic Bombing Survey, "the Emperor, supported by the premier foreign minister and Navy minister, declared for peace; the army minister and the two chiefs of staff did not concur."

TheUnited Nations Charter is signed by delegates from fifty nations in San Francisco. Stimson, Forrestal, and Grew agree that a clarification of surrender terms should be issued well before an invasion and with "ample time to permit a national reaction to set in." The three agreed that "Japan is susceptible to reason."

Undersecretary of the Navy Ralph Bard sends a memo to Secretary of War Stimson recommending that "fair play" demanded that the U.S. give the Japanese prior warning of an atomic attack. He recommends that the U.S. give the Japanese "information regarding the proposed use of atomic power."

Leo Szilard begins circulating a petition to President Truman, expressing opposition on moral grounds to using the atomic bomb against Japan.

Secretary of War Henry Stimson advises Truman to offer a definition of "unconditional surrender," and Stimson states, "I think the Japanese nation has the mental intelligence and versatile capacity in such a crisis to recognize the folly of a fight to the finish and to accept the proffer of what will amount to an unconditional surrender."

James Byrnes becomes U.S. Secretary of State.

New York Times reports, "Senator [William] White of Maine, the minority [Republican] leader, declared that the Pacific war might end quickly if President Truman would state, specifically, in the upper chamber just what unconditional surrender means for the Japanese."

Leo Szilard writes to a colleague regarding the petition to the President: "I personally feel it would be a matter of importance if a large number of scientists who have worked in this field went clearly and unmistakably on record as to their opposition on moral grounds to the use of these bombs in the present phase of the war."

Truman leaves for Potsdam on the Augusta, accompanied by Secretary of State Byrnes. They are at sea one day when Byrnes receives a telegram from Acting Secretary of State Joseph Grew describing a peace overture from the Japanese military attaché in Stockholm. The attaché offered a negotiated settlement of the war if the U.S. would guarantee the reign of the Emperor.

At a meeting of the Supreme War Direction Council, Emperor Hirohito urges haste in moves to mediate the peace throughout Russia.

Washington intercepts and decodes a cable from Japanese Foreign Minister Shigenori Togo to his Ambassador in Moscow that states, "Unconditional surrender is the only obstacle to peace.." Secretary of Navy Forrestal writes in his diary: "The first real evidence of a Japanese desire to get out of the war came today through intercepted messages from Togo, Foreign Minister, to Sato, Jap Ambassador in Moscow, instructing the latter to see Molotov if possible before his departure for the Big Three meeting and if not then immediately afterward to lay before him the Emperor’s strong desire to secure a a termination of the war."Farrington Daniels, Director of the Met Lab at the University of Chicago, reported to James Compton that 72 percent of the scientists favored a military demonstration of the bomb in Japan or in the U.S., with Japanese representatives present, before using the weapon on civilians.

President Truman lands at Antwerp on his way to the Potsdam meeting. Byrnes has convinced him to drop Article 12 of the Potsdam Declaration, which had provided assurance that the Emperor would be allowed to retain his throne as a constitutional monarch.

The Trinity test, a plutonium implosion device, takes place at 5:29:45 a.m. mountain war time at Alamogordo, New Mexico. It is the world’s first atomic detonation. The device has a yield of 19 kilotons, which is equivalent to 19,000 tons of TNT. J. Robert Oppenheimer recalls a quote from the Bhagavad Gita, a Hindu text, which states, "I am become death, the destroyer of worlds." Brigadier General T.F. Farrell, General Groves ’ deputy commander, describes the explosion in this way: "The effects could well be called unprecedented, magnificent, beautiful, stupendous, and terrifying. The lighting effects beggared description. The whole country was lighted by a searing light with the intensity many times that of the midday sun. It was golden, purple, violet, gray, and blue. It lighted every peak, crevasse and ridge of the nearby mountain range with a clarity and beauty that cannot be described but must be seen to be imagined..."

President Truman at Potsdam writes in his diary, "Just spend [sic] a couple of hours with Stalin .. He’ll be in the Jap War on August 15th. Fini Japs when that comes about." Secretary of War Stimson records in his diary, "Byrnes was opposed to a prompt and early warning to Japan which I first suggested. He outlined a timetable on the subject [of] warning which apparently had been agreed to by the president, so I pressed it no further." Leo Szilard, unaware of the Trinity test, prepares final draft of Petition to the President of the United States, calling on the President to "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 the light of the considerations presented in this petition as well as all other moral responsibilities which are involved." The petition was signed by 155 Manhattan Project scientists.

President Truman writes in his diary, "P.M. [Churchill] & I ate alone. Discussed Manhattan (it is a success). Decided to tell Stalin about it. Stalin had told P.M. of telegram from Jap Emperor asking for peace. Stalin also read his answer to me. It was satisfactory. Believe the Japs will fold up before Russia comes in. I am sure they will when Manhattan [reference to Manhattan Project] appears over their homeland. I shall inform about it at an opportune time."

President Truman approves order for atomic bombs to be used.

Assistant Secretary of War McCloy writes in diary, in Potsdam, "Throughout it all the ’big bomb’ is playing its part--it has stiffened both the Prime Minister and the President. After getting Groves’ report they went to the next meeting like little boys with a big red apple secreted on their persons."

UK Prime Minister Winston Churchill remarks, "[I]t is quite clear that the United States do not at the present time desire Russian participation in the war against Japan."

Walter Brown, special assistant to Secretary of State Byrnes, writes in his journal that Byrnes was now "hoping for time, believing after atomic bomb Japan will surrender and Russia will not get in so much on the kill, thereby being in a position to press claims against China." Secretary of War Henry Stimson passes on orders for atomic attack.

President Truman writes in his diary: "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 Mexican desert was startling - to put it mildly..." "This weapon is to be used against Japan between now and August 10. I have told the secretary of war, Mr. Stimson , to use it so that military objectives and soldiers 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 this 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." General Carl Spatz, commander of the United States Army Strategic Air Forces, receives the only written order on the use of atomic weapons from acting Chief of Staff General Thomas Handy .

Secretary of Defense Forrestal's secret diary states: "In the past days Sato in Moscow has been sending the strongest language to the Foreign Office at Tokyo his urgent advice for Japan to surrender unconditionally. Each time the Foreign Minister, Togo, responds by saying that they want Sato to arrange for the Russians to receive Prince Konoye as a special representative of the Emperor to Moscow. Sato’s persistent reply to these messages was that this is a futile hope, that there is no possibility of splitting the concert of action now existing between Great Britain, the United States and Russia."

The Potsdam Declaration calls upon the Japanese government "to proclaim now the unconditional surrender of all Japanese armed forces." The alternative, the Declaration states, is "prompt and utter destruction."

U.S. Senate approves the U.N. Charter by a vote of 98 to 2. Japan rejects Potsdam Declaration.

President Truman, while aboard Augusta, receives a new report that Japan is seeking peace. Walter Brown, special assistant to Secretary of State Byrnes, writes in his diary, "Aboard Augusta - President, Leahy, JFB agreed Japs looking for peace. (Leahy had another report from Pacific.) President afraid they will sue for peace through Russia instead of some country like Sweden."

The world’s second atomic bomb, Little Boy, a gun-type uranium bomb, is detonated 1,900 feet above Hiroshima, Japan. It has a yield of approximately 15 kilotons TNT. Some 90,000 to 100,000 persons are killed immediately; about 145,000 persons would perish from the bombing by the end of 1945. Upon hearing the news of the atomic bombing of Japan on his way home from Potsdam, President Truman remarked that this was "the greatest thing in history." Leo Szilard, the atomic scientist who had worked so hard to prevent the use of the bomb, writes to a friend, "Using atomic bombs against Japan is one of the greatest blunders of history."

The decision is made to drop warning pamphlets on Japanese cities.

The Soviet Union informs Japan that it is entering the war. The decision is made to set up International Tribunal at Nuremburg.

At 9:44 a.m., Bockscar, a B-29 carrying Fat Man, the world’s third atomic bomb, arrives at its primary target, Kokura. The city is covered in haze and smoke from an American bombing raid on a nearby city. Bockscar turns to its secondary target Nagasaki. At 11:02 a.m. the world’s third atomic bomb explosion devastates Nagasaki, the intense heat and blast indiscriminately slaughters its inhabitants. President Truman speaks to the American people via radio broadcast. He states, "The world will note that the first atomic bomb was dropped on Hiroshima, a military base. That was because we wished in the first instance to avoid, in so far as possible, the killing of civilians." [The official Bombing Survey Report stated: "Hiroshima and Nagasaki were chosen as targets because of their concentration of activities and population." More than 95 percent of those killed at Hiroshima and Nagasaki were civilians.] Soviet Union begins its offensive against Japan in Manchuria.

The U.S. drops warning leaflets on Nagasaki on the day after the bombing.

Manhattan Project releases report, "Atomic Energy for Military Purposes," written by physicist Henry DeWolf Smyth. The report, known as the "Smyth Report," discusses the workings of the Manhattan Project, the basics of nuclear physics, and some of the technologies used in producing plutonium and enriching uranium.

Japanese physicists, investigating the epicenter of the Hiroshima bomb burst, start noticing high levels of radioactivity.

Japan surrenders.

Emperor Hirohito of Japan, in a radio broadcast to his nation, announces that Japan has lost the war. The Emperor’s announcement is hard to understand because he speaks in archaic court Japanese, but one fact is understood: "Moreover, the enemy has begun to employ a new and most cruel bomb, the power of which to damage is indeed incalculable, taking the toll of many innocent lives." The New York Times reports, "Russia’s entry into the Japanese war was the decisive factor in speeding its end and would have been so, even if no atomic bombs had been dropped, is the opinion of Major-General Claire Chennault .."

Soviet Union announces that the Japanese Manchurian Army has surrendered.

22 patients in Rochester with minor medical complications are injected with plutonium. No evidence suggests these patients knew they were part of an experiment.

Japan formally signs documents of surrender.

The Trinity test site is opened to the press for the first time. General Groves and J. Robert Oppenheimer dispel rumors of lingering high radiation levels there.

The U.S. Joint Chiefs of Staff embrace "first strike" atomic warfare policy.

Robert Oppenheimer refuses to participate in a full-fledged effort to build a hydrogen bomb when approached by Edward Teller.

Top-secret documents from the Los Alamos National Laboratory reach the desk of Lavrenty Beria, head of the Soviet secret police and director of the Soviet nuclear program.

Albert Einstein makes a plea to the world government. He states, "Since I do not foresee that atomic energy is to be a great boon for a long time, I have to say that for the present, it is a menace."

President Harry Truman and Prime Ministers Clement Attlee of Great Britain and Mackenzie King of Canada call for a UN Atomic Energy Commission

Judge Robert H. Jackson makes the opening statement on behalf of the United States at the International Military Tribunal of Nazi war criminals at Nuremberg. Jackson states: "We must never forget that the record on which we judge these defendants today is the record on which history will judge us tomorrow. To pass these defendants a poisoned chalice is to put it to our own lips as well. We must summon such detachment and intellectual integrity to our task that this trial will commend itself to posterity as fulfilling humanity’s aspiration to do justice."

In a secret agreement between the USSR and the Czech-Slovak Social Republic (CSSR), the Soviet Union secures exclusive rights to all uranium mined within Czechoslovakia.

As part of the Manhattan Project, uranium injections are made in Rochester on six patients without their knowledge or consent. Doses are raised in each consecutive patient until kidney damage was detected.

As part of the Manhattan Project, three human test subjects at the University of Chicago are injected with Plutonium. 

Eugene Rabinowitch and Hyman Goldsmith publish first issue of The Bulletin of the Atomic Scientist.

Nuclear research begins in India with establishment of Tata Institute of Fundamental Research (TIFR) with Homi Jehangir Bhabha as its first director.

The U.S. Embassy in Moscow warns of an all-out Soviet effort to build atomic bomb.

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