Little Boy was the atomic bomb dropped on Hiroshima on August 6, 1945.
The United States Army Air Forces used the Boeing B-29 bomber Enola Gay for the mission. Little Boy detonated over Hiroshima at about 8:15 a.m. local time. It was a uranium-235 gun-type weapon and was the first nuclear weapon used in warfare.
The bombing occurred during the final stage of the Pacific War, when Japan had not accepted the Allied demand for surrender. President Harry S. Truman announced the attack publicly and warned Japan that further destruction would follow if it did not surrender.
Little Boy is often confused with Fat Man, the plutonium implosion bomb dropped on Nagasaki three days later, on August 9. Trinity was the code name for the first nuclear test, held in New Mexico on July 16, 1945; it was not a bomb used against a Japanese city.