Thin Man (nuclear bomb) Thin Man (nuclear bomb) "Thin Man" was the code name for a proposed plutonium gun-type nuclear bomb using plutonium-239 which the United States was developing during the Manhattan Project. They aborted its development when they discovered that the spontaneous fission rate of their nuclear reactor-bred plutonium was too high for use in a gun-type design, due to the high concentration of the isotope plutonium-240. In 1942, prior to the Army taking over wartime atomic research, Robert Oppenheimer held conferences in Chicago in June and Berkeley, California, in July at which various engineers and physicists discussed nuclear bomb design issues. A
B61 nuclear bomb Mod 12. With reductions planned of nuclear weapons in Europe, which may retire the older Mod 3 and 4 and the Mod 10 already slated for retirement, and the possibility that European nations may not build or procure new aircraft to carry the Mod 12 would eliminate the need for consolidation into a new type. While the B83 nuclear bomb is not as old as the B61, the Pentagon sees it as a "relic of the Cold War," believing that deploying a megaton-yield gravity bomb, the highest level nuclear weapon left in the U.S. inventory, to Europe is "inconceivable" at