• 1930: Ernest Lawrence builds the first cyclotron in Berkeley, Calif.
• 1934: Enrico Fermi produces fission.
• Aug. 2, 1939: Albert Einstein writes President Franklin Roosevelt about how research on chain reactions might create powerful bombs.
• Oct. 9, 1941: Roosevelt instructs officials to find out if a bomb can be built and at what cost.
• Dec. 7, 1941: The Japanese attack Pearl Harbor.
• Jan. 19, 1942: Roosevelt approves production of the atomic bomb.
• Aug. 13, 1942: The Manhattan Engineer District is established in New York City.
• Sept. 19, 1942: Manhattan Engineer District head Gen. Leslie Groves selects the Oak Ridge, Tenn., site for the pilot plant.
• Nov. 25, 1942: Groves selects Los Alamos, N.M., as the bomb laboratory.
• Dec. 2, 1942: Scientists led by Fermi achieve the first self-sustained nuclear chain reaction in Chicago.
• Jan. 16, 1943: Groves selects Hanford as the site for the plutonium production facilities.
• July 16, 1945: Los Alamos scientists successfully test a plutonium implosion bomb at Alamogordo, N.M.
• Aug. 6, 1945: The uranium bomb, called Little Boy, is dropped on Hiroshima.
• Aug. 9, 1945: The plutonium bomb, called Fat Man, is dropped on Nagasaki.
• Aug. 14, 1945: Japan surrenders.
Source: atomicarchive.com