Fat Man (Nagasaki Bomb) Blast Radius

Fat Man was dropped on Nagasaki at 11:02 a.m. local time on 9 August 1945, three days after the Hiroshima bombing. The primary target had been Kokura, but the crew diverted to the secondary target, Nagasaki, after the primary was obscured.^{[5, 6]}

Fat Man was released by the B-29 Superfortress Bockscar, commanded by Major Charles W. Sweeney, who was 25 at the time. It took off from the island of Tinian in the Mariana Islands.^{[6, 7, 5]}

Fat Man was about 10 feet 8 inches long and 60 inches in diameter (Sublette gives 128 by 60.25 inches). Reported weights range from about 10,000 lb (US Air Force museum) to 10,300 lb (Sublette) and 10,800 lb (National Museum of Nuclear Science & History).^{[10, 11, 12]}

Published figures differ: about 10,000 lb per the National Museum of the US Air Force, 10,300 lb per Carey Sublette's specification table, and 10,800 lb per the National Museum of Nuclear Science & History. The spread reflects different source documents rather than different bombs.^{[12, 11, 10]}

Fat Man had a yield of 21 kilotons, or 21,000 tons of TNT equivalent, according to DOE/NV-209. That is about 40% more than the 15-kiloton Hiroshima bomb, although Nagasaki's hilly terrain limited the area actually destroyed.^[1]

Fat Man was an implosion-type plutonium weapon: a plutonium core compressed by surrounding high explosives. That is the one-phrase description given by the National Museum of the US Air Force; this page carries no internal design detail.^[12]

In an air burst at optimum height, the Fat Man produces a fireball roughly 0.21 km in radius and a 5 psi moderate-blast zone of about 1.73 km — the area in which most residential buildings would collapse. The 1 psi light-damage radius extends to roughly 4.78 km, where windows shatter.

In an air burst at optimum height, thermal radiation from the Fat Man can cause 3rd-degree burns out to roughly 2.55 km, 2nd-degree burns to 3.26 km, and 1st-degree burns to 4.28 km.