Editing Edwin McMillan (section)

==World War II==
[[File:Mcmillan-edwin m.jpg|thumb|Edwin McMillan Los Alamos badge]]
McMillan's abrupt departure was caused by the outbreak of [[World War II]] in Europe. In November 1940, he began working at the [[MIT Radiation Laboratory]] in [[Cambridge, Massachusetts]], where he participated in the development and testing of airborne [[microwave radar]] during [[World War II]].{{sfn|Lofgren|Abelson|Helmolz|1992|pp=118–119}} He conducted tests in April 1941 with the radar operating from an old [[Douglas B-18 Bolo]] [[medium bomber]]. Flying over the [[Naval Submarine Base New London]] with [[Luis Walter Alvarez]] and [[Air Chief Marshal]] [[Hugh Dowding]], they showed that the radar was able to detect the [[conning tower]] of a partly submerged submarine.<ref name="Oral3" /> McMillan married Elsie Walford Blumer in [[New Haven, Connecticut]], on June 7, 1941.{{sfn|Seaborg|1993|p=291}}<ref name="Oral3">{{cite web |url=https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4773-3 |title=Edwin McMillan – Session IIII |date=March 19, 2015 |publisher = [[American Institute of Physics]]  | access-date = July 16, 2015 }}</ref> Her father was George Blumer, Dean Emeritus of the [[Yale Medical School]].<ref name="Nobel bio" /> Her sister Mary was Lawrence's wife.{{sfn|Jackson|Panofsky|1996|p=216}} The McMillans had three children: Ann Bradford, David Mattison and Stephen Walker.<ref name="Nobel bio" /><ref name="Obit" />

McMillan joined the [[Navy Electronics Laboratory|Navy Radio and Sound Laboratory]]  near [[San Diego]] in August 1941. There he worked on a device called a polyscope. The idea, which came from Lawrence, was to use [[sonar]] to build up a visual image of the surrounding water. This proved to be far more difficult than doing so with radar, because of objects in the water and variations in water temperature that caused variations in the speed of sound. The polyscope proved to be impractical, and was abandoned. He also, however, developed a sonar training device for submariners, for which he received a patent.<ref name="Oral3" /><ref>{{US patent|2,694,868}}</ref>{{sfn|Seaborg|1993|p=289}}

Oppenheimer recruited McMillan to join the [[Manhattan Project]], the wartime effort to create [[atomic bomb]]s, in September 1942. Initially, he commuted back and forth between San Diego, where his family was, and Berkeley.<ref name="Oral3" /> In November he accompanied Oppenheimer on a trip to [[New Mexico]] on which the [[Los Alamos Ranch School]] was selected as the site of the project's weapons research laboratory, which became the [[Los Alamos Laboratory]].{{sfn|Rhodes|1986|pp=449–451}} With Oppenheimer and [[John H. Manley]], he drew up the specifications for the new laboratory's technical buildings.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=62}} He recruited personnel for the laboratory, including [[Richard Feynman]] and [[Robert R. Wilson]], established the test area known as the Anchor Ranch, and scoured the country for technical equipment from machine tools to a cyclotron.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=84}}

As the laboratory took shape, McMillan became deputy head of the [[gun-type nuclear weapon]] effort under Navy [[Captain (United States O-6)|Captain]] [[William S. Parsons]], an ordnance expert.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=84}} The plutonium gun, codenamed [[Thin Man nuclear bomb|Thin Man]],{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=114}} needed a [[muzzle velocity]] of at least {{convert|3000|ft}} per second, which they hoped to achieve with a modified Navy [[3"/50 caliber gun|3-inch antiaircraft gun]]. The alternative was to build an [[implosion-type nuclear weapon]]. McMillan took an early interest in this, watching tests of this concept conducted by [[Seth Neddermeyer]]. The results were not encouraging. Simple explosions resulted in distorted shapes.{{sfn|Rhodes|1986|pp=477–479, 541}} [[John von Neumann]] looked at the implosion program in September 1943, and proposed a radical solution involving [[explosive lens]]es. This would require expertise in explosives, and McMillan urged Oppenheimer to bring in [[George Kistiakowsky]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=130–133}} Kistiakowsky joined the laboratory on February 16, 1944, and Parsons's E (Explosives) Division was divided in two, with McMillan as deputy for the gun and Kistiakowsky as deputy for implosion.
{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=139}}

McMillan heard disturbing news in April 1944, and drove out to Pajarito Canyon to confer with Segrè. Segrè's group had tested samples of plutonium bred in the Manhattan Project's nuclear reactors and found that it contained  quantities of [[plutonium-240]], an isotope that caused spontaneous fission, making Thin Man impractical.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=238–239}} In July 1944, Oppenheimer reorganised the laboratory to make an all-out effort on implosion. McMillan remained in charge of the gun-type weapon,{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=245}} which would now be used only with [[uranium-235]]. This being the case, Thin Man was replaced by a new, scaled-back design called [[Little Boy]].{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=256–257}} McMillan was also involved with the implosion as the head of the G-3 Group within the G (Gadget) Division, which was responsible for obtaining measurements and timings on implosion,{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=272–273}} and served as the laboratory's liaison with [[Project Camel]], the aerial test program being carried out by Caltech. On July 16, 1945, he was present at the [[Trinity (nuclear test)|Trinity nuclear test]], when the first implosion bomb was successfully detonated.{{sfn|Jackson|Panofsky|1996|p=225}}