The first nuclear bomb to be used in warfare was the “Little Boy” bomb, which was dropped by the United States on the Japanese city of Hiroshima on August 6, 1945, during World War II. The bomb was designed and built by a team of scientists led by physicist J. Robert Oppenheimer as part of the Manhattan Project, a top-secret research program to develop atomic weapons.
The Little Boy bomb was an uranium gun-type bomb, which means it relied on the impact of two subcritical masses of uranium to achieve a critical mass and initiate a nuclear chain reaction. It was dropped by the B-29 bomber Enola Gay, piloted by Colonel Paul Tibbets.
The Little Boy bomb was dropped at around 8:15 a.m. local time and exploded at an altitude of around 1,900 feet (580 meters) above the city. The explosion produced a yield of around 15 kilotons of TNT, equivalent to 15,000 tons of dynamite. The explosion generated a bright flash, a powerful shockwave, and a mushroom cloud that reached heights of around 30,000 feet (9,000 meters).
The bombing of Hiroshima resulted in the deaths of around 70,000 people, most of them civilians, and injured another 70,000. Three days later, a second nuclear bomb, the “Fat Man” was dropped on Nagasaki, killing an estimated 35,000-40,000 people. These bombings, along with the Soviet Union’s entry into the Pacific War, caused Japan to surrender on August 15, 1945, bringing an end to World War II.