Fat Man

Fat Man was the codename for the type of nuclear bomb that was detonated over the Japanese city of Nagasaki by the United States on August 9, 1945. It was the second of the only two nuclear weapons ever used in warfare, the first being Little Boy, which was dropped on Hiroshima on August 6, 1945.

Design and Development

Fat Man was an implosion-type nuclear weapon with a plutonium core. The design was more complex than the gun-type design used in Little Boy. The development of Fat Man was part of the Manhattan Project, the United States' research and development project during World War II that produced the first nuclear weapons.

The bomb's design was based on the "Trinity" test, which was the first detonation of a nuclear device, conducted on July 16, 1945, in the New Mexico desert. The successful test of the Trinity device confirmed the viability of the implosion method for a plutonium bomb.

Implosion Mechanism

The implosion mechanism of Fat Man involved a spherical assembly of high-explosive lenses surrounding a plutonium core. When detonated, the explosives compressed the core to a supercritical state, initiating a nuclear chain reaction. This method was necessary for plutonium bombs because of the higher rate of spontaneous fission in plutonium-239 compared to uranium-235, which made a gun-type design impractical.

Plutonium Core

The core of Fat Man was made of plutonium-239, a fissile isotope produced in nuclear reactors. The core was surrounded by a tamper, which reflected neutrons back into the core to increase the efficiency of the reaction.

Deployment and Impact

Fat Man was dropped by the B-29 bomber Bockscar, piloted by Major Charles Sweeney. The bomb exploded at an altitude of about 1,650 feet (500 meters) above Nagasaki, with a yield equivalent to 21 kilotons of TNT. The explosion resulted in the immediate deaths of an estimated 40,000 people, with total casualties reaching 70,000 by the end of 1945 due to injuries and radiation sickness.

The use of Fat Man, along with Little Boy, played a significant role in Japan's decision to surrender, leading to the end of World War II.

Legacy

The deployment of Fat Man and Little Boy marked the beginning of the nuclear age, raising ethical and strategic questions about the use of nuclear weapons. The bombings of Hiroshima and Nagasaki remain the only instances of nuclear weapons being used in armed conflict.

Also see

• Little Boy
• Manhattan Project
• Trinity (nuclear test)
• Nuclear weapon
• Hiroshima
• Nagasaki