The Atomic Bomb research began in the U.K. (United Kingdom) in 1940 but was transferred to the U.S. after the entry to World War II the following year. The atomic bomb project was known as the Manhattan Project the the work was carried out by Robert Oppenheimer at Los Alamos, New Mexico. In the U.S. the first atomic bomb was successfully tested in Alamogordo, New Mexico. No one knew what it would do to a city. After being tested two more bombs were made and dropped. One was dropped on Hiroshima , Japan Aug. 6, 1945. The other was dropped on Nagasaki , Japan on Aug. 9, 1945. The bomb dropped on Hiroshima was as powerful as 12,700 metric tons of TNT. The one dropped on Nagasaki was as powerful as 22,000 metric tons of TNT. The atomic bomb is the most powerful weapon on earth.