Editing Fat Man (section)

==Early decisions==
[[Robert Oppenheimer]] held conferences in Chicago in June 1942,  and in [[Berkeley, California]], in July, at which various engineers and physicists discussed nuclear bomb design issues. They chose a [[Gun-type fission weapon|gun-type]] design in which two sub-critical masses would be brought together by firing a "bullet" into a "target".{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=42–44}} [[Richard C. Tolman]] suggested an [[implosion-type nuclear weapon]], but the proposal attracted little interest.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=55}}

The feasibility of a [[plutonium]] bomb was questioned in 1942. [[Wallace Akers]], the director of the British "[[Tube Alloys]]" project, told [[James Bryant Conant]] on 14 November that [[James Chadwick]] had "concluded that plutonium might not be a practical [[Fissile material|fissionable material]] for weapons because of impurities".{{sfn|Nichols|1987|p=64}} Conant consulted [[Ernest Lawrence]] and [[Arthur Compton]], who acknowledged that their scientists at Berkeley and Chicago, respectively, knew about the problem, but they could offer no ready solution. Conant informed [[Manhattan Project]] director [[Brigadier General (United States)|Brigadier General]] [[Leslie R. Groves Jr.]], who in turn assembled a special committee consisting of Lawrence, Compton, Oppenheimer, and McMillan to examine the issue. The committee concluded that any problems could be overcome simply by requiring higher purity.{{sfn|Nichols|1987|pp=64–65}}

Oppenheimer reviewed his options in early 1943 and gave priority to the gun-type weapon,{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=55}} but he created the E-5 Group at the [[Los Alamos Laboratory]] under [[Seth Neddermeyer]] to investigate implosion as a hedge against the threat of pre-[[detonation]]. Implosion-type bombs were determined to be significantly more efficient in terms of explosive yield per unit mass of fissile material in the bomb, because compressed fissile materials react more rapidly and therefore more completely. Nonetheless, it was decided that the plutonium gun would receive the bulk of the research effort, since it was the project with the least uncertainty involved. It was assumed that the [[uranium]] gun-type bomb could be easily adapted from it.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=87}}