Timeline of The Manhattan Project - 1944

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 "Thin Man" is abandoned. Designing a workable implosion design becomes the top priority of the laboratory.
• July 20: The Los Alamos organizational structure is completely changed to reflect the new priority.
• September 2: chemists Peter N. Bragg, Jr., and Douglas P. Meigs are killed, and Arnold Kramish almost killed, while attempting to unclog a uranium enrichment device which is part of the pilot thermal diffusion plant at the Philadelphia Navy Yard. Two soldiers also receive extensive injuries. An explosion of liquid uranium hexafluoride burst nearby steam pipes, and steam combined with the uranium hexafluoride to spray them with highly corrosive hydrofluoric acid.
• September 22: First RaLa test with a radioactive source performed at Los Alamos.
• September 26: The largest nuclear reactor, the B reactor, goes critical at the Hanford Site.
• 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.