Fat Man
In 1939, physicists Albert Einstein and Leo Szilard wrote a letter to President Franklin D. Roosevelt warning that Nazi Germany was working on an atomic bomb project. As it turned out, the Third Reich never came close to developing a nuclear weapon, but there was no way to know that at the time; Roosevelt duly commissioned the US military to begin a crash program to develop its own nuclear weapons. By 1942, this had evolved to become the Manhattan Project.
The Project's head scientists, including Szilard, Enrico Fermi, and J. Robert Oppenheimer, pursued three different bomb types, using either uranium (U-235) or plutonium (Pu-239). Each bomb was codenamed after movie characters--Thin Man (after a Dashiell Hammett character), and Fat Man and Little Boy (both characters from "The Maltese Falcon"). The Thin Man design proved a failure, so the Manhattan Project concentrated on Little Boy and Fat Man.
Little Boy, for all its destructive power at Hiroshima, was actually considered inefficient by the Manhattan Project: only two pounds of its uranium were used in the nuclear reaction. Plutonium was considered to be more effective, and Fat Man was designed to utilize Pu-239 as its fissible material. Moreover, the implosion-style detonation of Fat Man, in which a core of plutonium was bombarded by more plutonium to cause a nuclear reaction, did not need as much material. Because the implosion trigger was very much experimental, it was decided to test it in the Trinity test of 16 July 1945--the world's first nuclear explosion. At 10,300 pounds, Fat Man could barely be carried by the B-29 Superfortress.
Fat Man was dropped on the city of Nagasaki on 9 August 1945 by the crew of "Bockscar," again of the 509th Composite Group. (The initial target was Kokura, but smoke and clouds caused "Bockscar" to divert to the secondary target of Nagasaki.) Because the bomb was actually off-target, the fact that it detonated on contact with the ground rather than Little Boy's airburst, and the hilly terrain of Nagasaki, "only" 40,000 people were killed by blast and heat. Because ground nuclear detonations produce more fallout, long-term radiation deaths were higher in Nagasaki than Hiroshima. Fat Man's yield was about 21 kilotons.
For better or worse, the world now had to deal with the fact of nuclear energy and nuclear warfare. Fat Man's design was used in the Bikini bomb tests (Operation Crossroads); the design was stolen by Russian spies during the war and became the USSR's first nuclear weapon, RDS-1. The Fat Man design was the only nuclear weapon in service until 1950, when it was phased out in favor of even larger thermonuclear designs.
This mockup of Fat Man is on display at the EAA AirVenture Museum in Oshkosh, Wisconsin as part of their exhibit on the Manhattan Project. It is accurate: Fat Man was painted overall yellow so it could be tracked easier; the black "rings" on the real bomb was actually liquid asphalt applied as a sealant on the bomb's seams. Appropriately, it is placed in the museum's "Top Secret" section, with other wartime experiments (and the collection of nude nose art).
Fat Man
In 1939, physicists Albert Einstein and Leo Szilard wrote a letter to President Franklin D. Roosevelt warning that Nazi Germany was working on an atomic bomb project. As it turned out, the Third Reich never came close to developing a nuclear weapon, but there was no way to know that at the time; Roosevelt duly commissioned the US military to begin a crash program to develop its own nuclear weapons. By 1942, this had evolved to become the Manhattan Project.
The Project's head scientists, including Szilard, Enrico Fermi, and J. Robert Oppenheimer, pursued three different bomb types, using either uranium (U-235) or plutonium (Pu-239). Each bomb was codenamed after movie characters--Thin Man (after a Dashiell Hammett character), and Fat Man and Little Boy (both characters from "The Maltese Falcon"). The Thin Man design proved a failure, so the Manhattan Project concentrated on Little Boy and Fat Man.
Little Boy, for all its destructive power at Hiroshima, was actually considered inefficient by the Manhattan Project: only two pounds of its uranium were used in the nuclear reaction. Plutonium was considered to be more effective, and Fat Man was designed to utilize Pu-239 as its fissible material. Moreover, the implosion-style detonation of Fat Man, in which a core of plutonium was bombarded by more plutonium to cause a nuclear reaction, did not need as much material. Because the implosion trigger was very much experimental, it was decided to test it in the Trinity test of 16 July 1945--the world's first nuclear explosion. At 10,300 pounds, Fat Man could barely be carried by the B-29 Superfortress.
Fat Man was dropped on the city of Nagasaki on 9 August 1945 by the crew of "Bockscar," again of the 509th Composite Group. (The initial target was Kokura, but smoke and clouds caused "Bockscar" to divert to the secondary target of Nagasaki.) Because the bomb was actually off-target, the fact that it detonated on contact with the ground rather than Little Boy's airburst, and the hilly terrain of Nagasaki, "only" 40,000 people were killed by blast and heat. Because ground nuclear detonations produce more fallout, long-term radiation deaths were higher in Nagasaki than Hiroshima. Fat Man's yield was about 21 kilotons.
For better or worse, the world now had to deal with the fact of nuclear energy and nuclear warfare. Fat Man's design was used in the Bikini bomb tests (Operation Crossroads); the design was stolen by Russian spies during the war and became the USSR's first nuclear weapon, RDS-1. The Fat Man design was the only nuclear weapon in service until 1950, when it was phased out in favor of even larger thermonuclear designs.
This mockup of Fat Man is on display at the EAA AirVenture Museum in Oshkosh, Wisconsin as part of their exhibit on the Manhattan Project. It is accurate: Fat Man was painted overall yellow so it could be tracked easier; the black "rings" on the real bomb was actually liquid asphalt applied as a sealant on the bomb's seams. Appropriately, it is placed in the museum's "Top Secret" section, with other wartime experiments (and the collection of nude nose art).