The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. The purpose of the Manhattan Project was to develop an Atomic Bomb. The “Little Boy” atomic bomb dropped on Hiroshima and the “Fat Man” atomic bomb was dropped on Nagasaki. It was called the Manhattan Project because the program began under the Manhattan Engineering District of the War Department and its scientists worked in Columbia University in Manhattan, NY. The Manhattan Project started on May 12, 1942 when President Roosevelt signed an order creating a top secret project to develop the nuclear weapon. US physicist Robert Oppenheimer and General Leslie R. Groves served as directors of the Manhattan Project.