Fat Man

Plutonium is easier to Produce

Explosive Power

21 kt

Hiroshima Equivalent Factor

1.4x

Dimensions

19 feet, 8 inches x 60 inches

Weight

10,800 lbs

Year(s)

1945

Purpose

Force Japanese Surrender

About Fat Man

The Fat Man implodes before it explodes, its shell of shaped explosives, fast explosives and slow explosives, compressing the little ball of plutonium within, a mere three and a half inches across, squeezing it down to a density that allows the nuclear chain reaction to take place at the proper intensity for a bomb. The mathematical equations to calculate that compression wave, the result of thirty-two high-explosive lenses each hexagonal in shape, smaller on one side, all fitted together with their ends pointing at the plutonium, were so complicated and laborious to perform that human computers—local women and members of the Women’s Army Corps running IBM punch-card accounting machines—were kept busy for months searching for that perfectly spherical compression.

It’s the forgotten bomb, a bomb without a best-selling book or blockbuster movie, a bomb that bombed its second-choice city (if that), a bomb that missed even then.

The bombing of Nagasaki wasn’t a surprise to the Japanese who saw Hiroshima destroyed three days earlier but it was a surprise to Truman who hadn’t realized that he should have direct control over the use of the atomic bombs, that he should authorize the target selections, the atomic bomb then not quite understood as something fundamentally different than anything before, something more than a bigger bomb.

Fat Man straddles the new and the old. Its design is the grown-up version of the Hiroshima bomb, its technical ideas carrying over into the post-war period (even the Soviet’s first bomb four years later looked like a blueprint for the Los Alamos bomb). Its development enabled by the vast increase in humans’ ability to count things with machines, to add and subtract very quickly, mechanically.

Fat Man straddles the old and the new. Before Fat Man the Japanese fanatically embraced national suicide, now tricked into war, the dead sacrificed for peace. Before Fat Man the Manhattan Project, a patriotic project, a bomb to end the war early, saving lives. Yet, after Nagasaki, with Japan occupied, bomb development went on.

Gallery
Nukemap

NUKEMAP is a web-based mapping program that attempts to give the user a sense of the destructive power of nuclear weapons. It was created by Alex Wellerstein, a historian specializing in nuclear weapons (see his book on nuclear secrecy and his blog on nuclear weapons). The screenshot below shows the NUKEMAP output for this particular weapon. Click on the map to customize settings.

Videos

Click on the Play button and then the Full screen button on the lower right (the brackets on a mobile device) to view each video. Click on the Exit full screen button (the “X” on a mobile device) to return.

Further Reading
  • Wikipedia, Atomic Archive, and the Atomic Heritage Foundation.
  • Richard Rhodes’ The Making of the Atomic Bomb, first published in 1987, is still the first book someone should read if they are interested in the development of Fat Man and Little Boy.
  • Hard to find but worth reading are two first-hand accounts–one by Leslie Groves (the head of the Manhattan Project) who wrote And Now It Can be Told, and Kenneth Nichols (who worked under Groves to produce the uranium and plutonium for the bombs) who wrote The Road to Trinity. See also an interview with Nichols at OpenVault.
  • I’ve not read Reed’s book, The History and Science of the Manhattan Project, but it is said to be a more technical but still accessible history. It is also expensive.
  • It is always worthwhile to mention John Coster-Mullen’s book. He was a photographer turned truck driver turned model builder turned nuclear archeologist and made several interesting discoveries and built a full-scale models of Little Boy. He wrote a book of his findings, Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man, still sold (via Amazon) by his estate. I received a copy for Christmas.
  • The full-scale model of Fat Man at the Historic Wendell Airfield, in Utah, was commissioned by the museum and built by NewRuleFX, a movie prop company based in Van Nuys, California.
  • Just over four years from the detonation of Fat Man over Nagasaki, the Soviets denoted their first nuclear bomb, the RDS-1 (referred to as Joe-1 by the United States). The RDS-1 (seen in the uncaptioned photo on this page from the Nuclear Museum) looks strikingly similar to Fat Man.
  • Nuclear historian Alex Wellerstein has several articles worth noting here. First is his New Yorker article, “Nagasaki, the Last Bomb” (paywall) an excellent short account of the bombing. The second is a post from his blog, Restricted Data, “Hiroshima and Nagasaki at 70,” written for the anniversary in 2015. Note the picture of the bomb damage map of Nagasaki and the links in the picture’s caption to a view of the full map and the legend.
  • Although his name seems largely unknown outside of scientific circles, George Kistiakowsky was a key player in the development of Fat Man, designing the high-explosive layer that would compress the plutonium. Here is an interview with Richard Rhodes at the Atomic Heritage Foundation and a panel discussion much later in his life.
  • Counting the Dead at Hiroshima and Nagasaki” summarizes the efforts to determine the number of casualties of the bombs–a much more complex question than it might at first seem. (Wellerstein–who I link to above and elsewhere–is a busy guy. I had read and picked out this article for including here before I realized he was the author. )
  • Life Magazine has a worthwhile compilation of images, “Hiroshima and Nagasaki: Photos from the Ruins,” made in the weeks after Little Boy and Fat Man, coupled with excerpts of letters from their photographer Bernard Hoffman and from various articles published in Life after the war.
  • This report, Japan’s Struggle to End the War, was published in 1946 by The United States Strategic Bombing Survey, describes efforts within Japan’s political system to formulate a surrender policy in the months leading up to the atomic bombings.
  • Perhaps surprisingly, the Manhattan Project released a report to the public on as much as they felt they could share about the atomic bombs, how they worked and how they were made. The shared a lot. The report was published three days after the Nagasaki bombing and was part of a publicity campaign to shape public opinion about the weapons and to preserve some level of secrecy.
  • The Nagasaki atomic bombing wasn’t the first time a Fat Man-style bomb had been dropped on Japan during the war, It was the 50th. Starting in July of 1945 and ending two weeks before the atomic strike, the Enola Gay, Bockscar, and other planes dropped high-explosive versions of Fat Man as rehearsals for the atomic bomb attack.