Timeline of the Manhattan Project


The Manhattan Project was a research and development project that produced the first atomic bombs during World War II. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project was under the direction of General (United States)|Major General] Leslie Groves of the US Army Corps of Engineers. The Army component of the project was designated the Manhattan District; "Manhattan" gradually became the codename for the entire project. Along the way, the project absorbed its earlier British counterpart, Tube Alloys. The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 people and cost nearly US$2 billion. Over 90% of the cost was for building factories and producing the fissionable materials, with less than 10% for development and production of the weapons.
Two types of atomic bombs were developed during the war. A relatively simple gun-type fission weapon was made using uranium-235, an isotope that makes up only 0.7 percent of natural uranium. Since it is chemically identical to the most common isotope, uranium-238, and has almost the same mass, it proved difficult to separate. Three methods were employed for uranium enrichment: electromagnetic, gaseous and thermal. Most of this work was performed at Oak Ridge, Tennessee. In parallel with the work on uranium was an effort to produce plutonium. Reactors were constructed at Oak Ridge and Hanford, Washington, in which uranium was irradiated and transmuted into plutonium. The plutonium was then chemically separated from the uranium. The gun-type design proved impractical to use with plutonium so a more complex implosion-type nuclear weapon was developed in a concerted design and construction effort at the project's principal research and design laboratory in Los Alamos, New Mexico.
The following is a timeline of the Manhattan Project. It includes a number of events prior to the official formation of the Manhattan Project, and a number of events after the atomic bombings of [Hiroshima and Nagasaki], until the Manhattan Project was formally replaced by the Atomic Energy Commission in 1947.

1939

1940

1941

1942

1943

1944

  • January 11: A special group of the Theoretical Division is created at Los Alamos under Edward Teller to study implosion.
  • March 11: Beta calutrons commence operation at Oak Ridge.
  • April 5: At Los Alamos, Emilio Segrè receives the first sample of reactor-bred plutonium from Oak Ridge, and within ten days discovers that the spontaneous fission rate is too high for use in a gun-type fission weapon.
  • May 9: The world's third reactor, LOPO, the first aqueous homogeneous reactor, and the first fueled by enriched uranium, goes critical at Los Alamos.
  • July 4: Oppenheimer reveals Segrè's final measurements to the Los Alamos staff, and the development of the gun-type plutonium weapon
  • July 17: "Thin Man" is abandoned. Designing a workable implosion design becomes the top priority of the laboratory, and design of the uranium gun-type weapon continued.
  • July 20: The Los Alamos organizational structure is completely changed to reflect the new priority.
  • September 2: Two chemists are killed, and Arnold Kramish almost killed, after being sprayed with highly corrosive hydrofluoric acid while attempting to unclog a uranium enrichment device which is part of the pilot thermal diffusion plant at the Philadelphia Navy Yard.
  • September 22: First RaLa Experiment with a radioactive source performed at Los Alamos.
  • September 26: The largest nuclear reactor, the B reactor, goes critical at the Hanford Site.
  • Late November: Samuel Goudsmit, scientific head of the Alsos Mission, concludes, based on papers recovered in Strasbourg, that the Germans did not make substantial progress towards an atomic bomb or nuclear reactor, and that the programs were not even considered high priority.
  • December 14: Definite evidence of achievable compression obtained in a RaLa test.
  • December 17: 509th Composite Group formed under Colonel Paul W. Tibbets to deliver the bomb.
  • December:General Groves met Franklin Delano Roosevelt once; in December 1944 during the Battle of the Bulge. Worried by American losses, FDR asked if an atomic bomb could be dropped on Germany and Groves told him that the first workable bomb was months away.

1945

1946

  • February: News of the Russian spy ring in Canada exposed by defector Igor Gouzenko is made public, creating a mild "atomic spy" hysteria, pushing American Congressional discussions about postwar atomic regulation in a more conservative direction.
  • May 21: Physicist Louis Slotin receives a fatal dose of radiation when the screwdriver he was using to keep two beryllium hemispheres apart slips.
  • July 1: Able test at Bikini Atoll as part of Operation Crossroads.
  • July 25: Underwater Baker test at Bikini.
  • August 1: Truman signs the Atomic Energy Act of 1946 into law, ending almost a year of uncertainty about the control of atomic research in the postwar United States.

1947