I visited the Genbaku (A-bomb) Dome in Hiroshima in March 2014.
On August 6, 1945, an atomic bomb was used in war for the first time in history. At 8:16 in the morning, the uranium-type bomb ‘Little Boy’ exploded over the city of Hiroshima, Japan. The destruction was massive.
Little Boy had its uranium divided in two, and used an explosion of gun powder to make the two parts crash into each other and reach critical mass for a nuclear chain reaction. This chain reaction in only one kilogram of uranium caused a nuclear explosion equal to 16 kilotons of TNT.