The Manhattan Project: Making the Atomic Bomb

Manhattan Project Chronology

Ernest Rutherford discovers the proton by artificially transmuting an element (nitrogen into oxygen).
Ernest O. Lawrence builds the first cyclotron in Berkeley.
Robert J. Van de Graaff develops the electrostatic generator.
James Chadwick discovers the neutron.
J. D. Cockroft and E. T. S. Walton first split the atom.
Lawrence, M. Stanley Livingston, and Milton White operate the first cyclotron.
Enrico Fermi produces fission.
December 1938
Otto Hahn and Fritz Strassmann discover the process of fission in uranium.
December 1938
Lise Meitner and Otto Frisch confirm the Hahn-Strassmann discovery and communicate their findings to Niels Bohr.
January 26, 1939
Bohr reports on the Hahn-Strassman results at a meeting on theoretical physics in Washington, D. C.
August 2, 1939
Albert Einstein writes President Franklin D. Roosevelt, alerting the President to the importance of research on chain reactions and the possibility that research might lead to developing powerful bombs.
September 1, 1939
Germany invades Poland.
October 11-12, 1939
Alexander Sachs discusses Einstein's letter with President Roosevelt. Roosevelt decides to act and appoints Lyman J. Briggs head of the Advisory Committee on Uranium.
October 19, 1939
Roosevelt informs Einstein that he has set up a committee to study uranium.
October 21, 1939
The Uranium Committee meets for the first time.
November 1, 1939
The Uranium Committee recommends that the government purchase graphite and uranium oxide for fission research.
March 1940
John R. Dunning and his colleagues demonstrate that fission is more readily produced in the rare uranium-235 isotope, not the more plentiful uranium-238.
Spring-Summer 1940
Isotope separation methods are investigated.
June 1940
Vannevar Bush is named head of the National Defense Research Committee. The Uranium Committee becomes a scientific subcommittee of Bush's organization.
February 24, 1941
Glenn T. Seaborg's research group discovers plutonium.
March 28, 1941
Seaborg's group demonstrates that plutonium is fissionable.
May 3, 1941
Seaborg proves plutonium is more fissionable than uranium-235.
May 17, 1941
A National Academy of Sciences report emphasizes the necessity of further research.
June 22, 1941
Germany invades the Soviet Union.
June 28, 1941
Bush is named head of the Office of scientific Research and Development. James B. Conant replaces Bush at the National Defense Research Committee, which becomes an advisory body to the Office of Scientific Research and Development.
July 2, 1941
The British MAUD report concludes that an atomic bomb is feasible.
July 11, 1941
A second National Academy of Sciences report confirms the findings of the first.
July 14, 3941
Bush and Conant receive the MAUD report.
October 9, 1941
Bush briefs Roosevelt and Vice President Henry A. Wallace on the state of atomic bomb research. Roosevelt instructs Bush to find out if a bomb can be built and at what cost. Bush receives permission to explore construction needs with the Army.
November 9, 1941
A third National Academy of sciences report agrees with the MAUD report that an atomic bomb is feasible,
November 27, 1941
Bush forwards the third National Academy of sciences report to the President.
December 7, 1941
The Japanese attack Pearl Harbor.
December 10, 1941
Germany and Italy declare war on the United States.
December 16, 1941
The Top Policy Committee becomes primarily responsible for making broad policy decisions relating to uranium research.
December 18, 1941
The S-1 Executive committee (which replaced the Uranium Committee in the Office of Scientific and Research Development) gives Lawrence $400,000 to continue electromagnetic research.
January 19, 1942
Roosevelt responds to Bush's November 27 report and approves production of the atomic bomb.
March 9, 1942
Bush gives Roosevelt an optimistic report on the possibility of producing a bomb.
May 23, 1942
The S-1 Executive Committee recommends that the project move to the pilot plant stage and build one or two piles (reactors) to produce plutonium and electromagnetic, centrifuge, and gaseous diffusion plants to produce uranium-235.
June 1942
Production pile designs are developed at the Metallurgical Laboratory in Chicago.
June 17 1943
President Roosevelt approves the S-1 Executive Committee recommendation to proceed to the pilot plant stage and instructs that plant construction be the responsibility of the Army. The Office of Scientific Research and Development continues to direct nuclear research, while the Army delegates the task of plant construction to the Corps of Engineers.
July 1942
Kenneth Cole establishes the health division at the Metallurgical Laboratory.
August 7, 1942
The American island-hopping campaign in the Pacific begins with the landing at Guadalcanal.
August 13, 1942
The Manhattan Engineer District is established in New York City, Colonel James C. Marshall commanding.
August 1942
Seaborg produces a microscopic sample of pure plutonium.
September 13, 1942
The S-1 Executive Committee visits Lawrence's Berkeley laboratory and recommends building an electromagnetic pilot plant and a section of a full scale plant in Tennessee.
September 17, 1942
Colonel Leslie R. Groves is appointed head of the Manhattan Engineer District. He is promoted to Brigadier General six days later.
September 19, 1942
Groves selects the Oak Ridge, Tennessee site for the pilot plant.
September 23, 1942
Secretary of War Henry Stimson creates a Military Policy Committee to help make decisions for the Manhattan Project.
October 3, 1942
E. I. du Pont de Nemours and Company agrees to build the chemical separation plant at Oak Ridge.
October 5, 1942
Compton recommends an intermediate pile at Argonne.
Fall 1942
J. Robert Oppenheimer and the luminaries report from Berkeley that more fissionable material may be needed than previously thought.
October 19, 1942
Groves decides to establish a separate scientific laboratory to design an atomic bomb.
October 26, 1942
Conant recommends dropping the centrifuge method.
November 22, 1942
On the recommendation of Groves and Conant, the Military Policy Committee decides to skip the pilot plant stage on the plutonium, electromagnetic, and gaseous diffusion projects and go directly from the research stage to industrial-scale production. The Committee also decides not to build a centrifuge plant.
November 14, 1942
The S-1 Executive Committee endorses the recommendations of the Military Policy committee.
November 1942
The Allies invade North Africa.
November 25, 1942
Groves selects Los Alamos, New Mexico as the bomb laboratory (codenamed Project Y). Oppenheimer is chosen laboratory director.
December 2, 1942
Scientists led by Enrico Fermi achieve the first self-sustained nuclear chain reaction in Chicago.
December 10, 1942
The Lewis committee compromises on the electromagnetic method. The Military policy Committee decides to build the plutonium production facilities at a site other than Oak Ridge.
December 28, 1942
Roosevelt approves detailed plans for building production facilities and producing atomic weapons.
January 13-14, 1943
Plans for the Y-12 electromagnetic plant are discussed. Groves insists that Y-12's first racetrack be finished by July 1.
January 14-24, 1943
At the Casablanca Conference, Roosevelt and British Prime Minister Churchill agree upon unconditional surrender for the h powers.
January 16, 1943
Groves selects Hanford, Washington as the site for the plutonium production facilities. Eventually three reactors, called B, D, and F, are built at Hanford.
January 1943
Bush encourages Philip Abelson's research on the thermal diffusion process.
February 18, 1943
Construction of Y-12 begins at Oak Ridge.
February 1943
Groundbreaking for the X-10 plutonium pilot plant takes place at Oak Ridge.
March 1943
Researchers begin arriving at Los Alamos.
April 1943
Bomb design work begins at Los Alamos.
June 1943
Site preparation for the K-25 gaseous diffusion plant commences at Oak Ridge.
Summer 1943
The Manhattan Engineer District moves its headquarters to Oak Ridge.
July 1943
Oppenheimer reports that three times as much fissionable material may be necessary than thought nine months earlier.
August 27, 1943
Groundbreaking for the 100-B plutonium production pile at Hanford takes place.
September 8, 1943
Italy surrenders to Allied forces.
September 9, 1943
Groves decides to double the size of Y-12.
September 27, 1943
Construction begins on K-25 at Oak Ridge.
November 4, 1943
The X-10 pile goes critical and produces plutonium by the end of the month.
Late 1943
John von Neumann visits Los Alamos to aid implosion research.
December 15, 1943
The first Alpha racetrack is shut down due to maintenance problems.
January 1944
The second Alpha racetrack is started and demonstrates maintenance problems similar to those that disabled the first.
January 1944
Construction begins on Abelson's thermal diffusion plant at the Philadelphia Naval Yard.
February 1944
Y-12 sends 200 grams of uranium-235 to Los Alamos.
March 1944
The Beta building at Y-12 is completed.
March 1944
Bomb models are tested at Los Alamos.
April 1944
Oppenheimer informs Groves about Abelson's thermal diffusion research in Philadelphia.
June 6, 1944
Allied forces launch the Normandy invasion.
June 21, 1944
Groves orders the construction of the S-50 thermal diffusion plant at Oak Ridge.
July 4, 1944
The decision is made to work on a calutron with a 30-beam source for use in Y-12.
July 17, 1944
The plutonium gun bomb (code named Thin Man) is abandoned.
July 1944
A major reorganization to maximize implosion research occurs at Los Alamos.
July 1944
Scientists at the Metallurgical Laboratory issue the "Prospectus on Nucleonics," concerning the international control of atomic energy.
August 7, 1944
Bush briefs General George C. Marshall, informing him that small implosion bombs might be ready by mid-1945 and that a uranium bomb will almost certainly be ready by August 1, 1945.
September 1944
Colonel Paul Tibbets' 393rd Bombardment Squadron begins test drops with dummy bombs called Pumpkins.
September 13, 1944
The first slug is placed in pile 100-B at Hanford.
September 1944
Roosevelt and Churchill meet in Hyde Park and sign an "aide memoire" pledging to continue bilateral research on atomic technology.
Summer 1944-Spring 1945
The Manhattan Project's chances for success advance from doubtful to probable as Oak Ridge and Hanford produce increasing amounts of fissionable material, and Los Alamos makes progress in chemistry, metallurgy, and weapon design.
September 27, 1944
The 1OO-B reactor goes critical and begins operation.
September 30, 1944
Bush and Conant advocate international agreements on atomic research to prevent an arms race.
December 1944
The chemical separation plants (Queen Marys) are finished at Hanford.
February 2, 1945
Los Alamos receives its first plutonium.
February 4-11, 1945
Roosevelt, Churchill, and Soviet Premier Joseph Stalin meet at Yalta.
March 1945
S-50 begins operation at Oak Ridge.
March 1945
Tokyo is firebombed, resulting in 100,000 casualties.
March 12, 1945
K-25 begins production at Oak Ridge.
April 12, 1945
President Roosevelt dies.
April 25, 1945
Stimson and Groves brief President Truman on the Manhattan Project.
May 1945
Stalin tells Harry Hopkins that he is willing to meet with Truman and proposes Berlin as the location.
May 7, 1945
The German armed forces in Europe surrender to the Allies.
May 23, 3945
Tokyo is firebombed again, this time resulting in 83,000 deaths.
May 31 - June 1, 1945
The Interim Committee meets to make recommendations on wartime use of atomic weapons, international regulation of atomic information, and legislation regarding domestic control of the atomic enterprise (the Committee's draft legislation becomes the basis for the May- Johnson bill).
June 6, 1945
Stimson informs President Truman that the Interim Committee recommends keeping the atomic bomb a secret and using it as soon as possible without Warning.
June 1945
Scientists at the Metallurgical Laboratory issue the Franck Report, advocating international control of atomic research and proposing a demonstration of the atomic bomb prior to its combat use.
June 14, 1945
Groves submits the target selection group's recommendation to Marshall.
June 21, 1945
The Interim Committee, Supporting its Scientific Panel, rejects the Franck Report recommendation that the bomb be demonstrated prior to combat.
July 2-3, 1945
Stimson briefs Truman on the Interim Committee's deliberations and outlines the peace terms for Japan.
July 16, 1945
Los Alamos scientists successfully test a plutonium implosion bomb in the Trinity shot at Alamogordo, New Mexico.
July 17 - August 2, 1945
Truman, Churchill, and Stalin meet in Potsdam.
July 21, 1945
Groves sends Stimson a report on the Trinity test.
July 24, 1945
Stimson again briefs Truman on the Manhattan Project and peace terms for Japan. In an evening session, Truman informs Stalin that the United States has tested a powerful new weapon.
July 25, 1945
The 509th Composite Group is ordered to attack Japan with an atomic bomb "after about" August 3.
July 26, 1945
Truman, Chinese President Chiang Kai-Shek, and new British Prime Minister Clement Atlee issue the Potsdam Proclamation, calling for Japan to surrender unconditionally.
July 29, 1945
The Japanese reject the Potsdam Proclamation.
August 6, 1945
The gun model uranium bomb, called Little Boy, is dropped on Hiroshima. Truman announces the raid to the American public.
August 8, 1945
Russia declares war on Japan and invades Manchuria.
August 9, 1945
The implosion model plutonium bomb, called Fat Man, is dropped on Nagasaki.
August 12, 1945
The Smyth Report, containing unclassified technical information on the bomb project, is released.
August 14, 1945
Japan surrenders.
September 2, 1945
The Japanese sign articles of surrender aboard the U.S.S. Missouri
September 9, 1945
S-50 shuts down.
September 1945
Y-12 shutdown begins.
October 3, 1945
Truman advocates passage of the May-Johnson bill
December 20, 1945
Senator Brien McMahon introduces a substitute to the May-Johnson bill, which had been losing support, including Truman's.
January 1946
Hearings on the McMahon bill begin.
June 14, 1946
Bernard Baruch presents the American plan for international control of atomic research.
July 1, 1946
Operation Crossroads begins with Shot Able, a plutonium bomb dropped from a B-29, at Bikini Atoll.
July 15, 1946
Operation Crossroads continues with Shot Baker, a plutonium bomb detonated underwater, at Bikini Atoll.
August 1, 1946
President Truman signs the Atomic Energy Act of 1946, a slightly amended version of the McMahon bill.
December 1946 - January 1947
The Soviet Union opposes the Baruch Plan, rendering it useless.
January 1, 1947
In accordance with the Atomic Energy Act of 1946, all atomic energy activities are transferred from the Manhattan Engineer District to the newly created United States Atomic Energy Commission. The Top Policy Group and the Military Policy Committee had already disbanded.
August 15, 1947
The Manhattan Engineer District is abolished.
December 31, 1947
The National Defense Research Committee and the Office of Scientific Research and Development are abolished. Their functions are transferred to the Department of Defense.