High Quality Content by WIKIPEDIA articles! The following is a timeline of the Manhattan Project, the effort by the United States, United Kingdom, and Canada to develop the first nuclear weapons for use during World War II. The following includes a number of events prior to the official formation of the Manhattan Project as the Manhattan Engineering District (MED) in August 1942 and a number of events after the atomic bombings of Hiroshima and Nagasaki, until the MED was formally replaced by the United States Atomic Energy Commission in 1947.