Nuclear — fission · United States · 1945
Fat Man
Fat Man (Mk III)
The second and last nuclear weapon used in war. More powerful than Little Boy, it relied on the implosion of a plutonium core.
See Fat Man in the 3D simulator- Yield
- 21 ktPublic estimate
- Energy
- 87.9 TJ
- Mass
- 4.7 tDocumented
- Dimensions
- 3.25 m · Ø 1.52 mDocumented
- Type
- Fission atomic bomb (plutonium, implosion)
- Period
- World War II
- Status
- Historical
Fat Man releases about 1.4 times the energy of Little Boy (Hiroshima, 1945).
Key points
- Same principle as the device tested at Trinity three weeks earlier.
- Nagasaki’s hilly terrain partly limited the extent of the destruction.
History
Dropped on Nagasaki by the B-29 “Bockscar”, three days after Hiroshima. Japan announced its surrender on 15 August 1945.
- 16 July 1945 The principle is validated by the Trinity test.
- 9 August 1945 Dropped on Nagasaki.
- 1946–1950 The design becomes the basis of the first mass-produced weapons (Mk 3, then Mk 4).
How does it work?
A fission weapon releases energy by splitting heavy nuclei (uranium-235 or plutonium-239). Each fission releases about 200 MeV and a few neutrons.
If these neutrons cause further fissions, a chain reaction runs away in less than a millionth of a second.
The energy heats matter to tens of millions of degrees: fireball, thermal radiation and shock wave.
General principle of implosion: conventional explosives strongly compress the fissile material, which becomes “supercritical” and sustains the chain reaction.
Deliberately general explanations: the application provides no design or manufacturing information.
Frequently asked questions
How powerful is Fat Man?
Fat Man has an estimated yield of 21 kt of TNT equivalent, about 87.9 TJ of energy.
What is the history of Fat Man?
Used once, on 9 August 1945 over Nagasaki. Dropped on Nagasaki by the B-29 “Bockscar”, three days after Hiroshima. Japan announced its surrender on 15 August 1945.
What does the Fat Man explosion look like?
The Bomb Simulator shows the fireball, shock wave and cloud of Fat Man at real scale, over Paris, London or New York, with the sources and reliability of each value.
Sources
- Little Boy and Fat Man — Atomic Heritage Foundation / National Museum of Nuclear Science & History
- Fat Man — Wikipedia (overview, to be cross-checked)
- The Effects of Nuclear Weapons, 3rd ed. (Glasstone & Dolan, 1977) — U.S. DoD / DOE (OSTI)
Other weapons
- Trinity — 25 kt
- Little Boy — 15 kt
- RDS-1 — 22 kt
- Hurricane — 25 kt
- RDS-6s — 400 kt
- Gerboise Bleue — 70 kt
- 596 — 22 kt
- Davy Crockett — 20 t
- Ivy Mike — 10.4 Mt
- Castle Bravo — 15 Mt
- RDS-37 — 1.6 Mt
- Mk 17 — 15 Mt
This application is an educational tool. The animations and effect zones are simplified representations meant to illustrate orders of magnitude. They are neither a prediction of the effects of a real weapon nor a military planning tool.