1940 
                                 June 3-German scientists fail to observe neutron multiplication in the reactor in Hamburg. 

                          1941 
                                 January-Based on experiments with a natural uranium reactor, the Germans reject graphite as a
                                 moderator.
                                 July-British 'Maud' Committee reports that a weapon could be made with 10 kg of U-235; U.S.
                                 Academy of Sciences endorses bomb program. 

                          1942 
                                 May-Heisenberg and Dopel observe the first multiplication of neutrons.
                                 December 2-First nuclear chain reaction at Chicago's Stagg Field by Fermi. 

                          1943 
                                 March 15-Oppenheimer moves the bomb development to Los Alamos. 

                          1944 
                                 August 26-Bohr presents his memorandum on intentional control of nuclear weapons to
                                 Roosevelt.
                                 November-First batch of spent fuel obtained from Hanford reactors.
                                 November-Goudsmit's ALSOS mission obtains documents which imply that the German's rate
                                 of progress toward a bomb had diminished. 

                          1945 
                                 January- First Pu reprocessing production run at Hanford
                                 January 20- First U-235 separated at Oak Ridge.
                                 June 11- The Franck Report was sent to the Secretary of War.
                                 July 16-U.S. explodes first atomic bomb, the Trinity test, at Alamogordo.
                                 August 6,9-Atomic bombs dropped on Hiroshima and Nagasaki. 

                          1946 
                                 June 14-Baruch presents the Acheson-Lilienthal plan to internationalize the atom to the U.N.
                                 June 30- First subsurface detonation by U.S. at Bikini atoll.
                                 July- Demonstrations in Times Square, New York, against nuclear testing.
                                 December 31-AEC takes over nuclear weapons program from the Army. 

                          1948 
                                 April, May-U.S. atomic tests, Eniwetok Atoll. 

                          1949 
                                 April 4- NATO established.
                                 August 29- First Soviet detonation, in the Ustyurt desert.
                                 October 30-General Advisory Committee of the AEC recommends that the more powerful atomic
                                 bombs should be built rather than hydrogen bombs.