Editing Nuclear weapon design (section)

==Weapon design laboratories==

All the nuclear weapon design innovations discussed in this article originated from the following three labs in the manner described. Other nuclear weapon design labs in other countries duplicated those design innovations independently, reverse-engineered them from fallout analysis, or acquired them by espionage.<ref>William J. Broad, "The Hidden Travels of The Bomb: Atomic insiders say the weapon was invented only once, and its secrets were spread around the globe by spies, scientists and the covert acts of nuclear states", ''New York Times'', December 9, 2008, p. D1.</ref>

===Lawrence Berkeley===
{{Main|Lawrence Berkeley National Laboratory}}
The first systematic exploration of nuclear weapon design concepts took place in mid-1942 at the [[University of California, Berkeley]]. Important early discoveries had been made at the adjacent [[Lawrence Berkeley Laboratory]], such as the 1940 cyclotron-made production and isolation of plutonium. A Berkeley professor, [[J. Robert Oppenheimer]], had just been hired to run the nation's secret bomb design effort. His first act was to convene the 1942 summer conference.{{Citation needed|date=June 2021}}

By the time he moved his operation to the new secret town of Los Alamos, New Mexico, in the spring of 1943, the accumulated wisdom on nuclear weapon design consisted of five lectures by Berkeley professor [[Robert Serber]], transcribed and distributed as the (classified but now fully declassified and widely available online as a PDF) [[Los Alamos Primer]].<ref name="Primer">{{cite book |last1=Server |first1=Robert |title=The Los Alamos Primer |publisher=University of California Press |location=Berkeley |isbn=978-0520075764 |edition=1st |date=1992}}</ref> The Primer addressed fission energy, [[neutron]] production and [[neutron capture|capture]], [[nuclear chain reaction]]s, [[critical mass]], tampers, predetonation, and three methods of assembling a bomb: gun assembly, implosion, and "autocatalytic methods", the one approach that turned out to be a dead end.{{Citation needed|date=June 2021}}

===Los Alamos===
{{Main|Los Alamos National Laboratory}}
At Los Alamos, it was found in April 1944 by [[Emilio Segrè]] that the proposed [[Thin Man nuclear bomb|Thin Man]] Gun assembly type bomb would not work for plutonium because of predetonation problems caused by [[Pu-240]] impurities. So Fat Man, the implosion-type bomb, was given high priority as the only option for plutonium. The Berkeley discussions had generated theoretical estimates of critical mass, but nothing precise. The main wartime job at Los Alamos was the experimental determination of critical mass, which had to wait until sufficient amounts of fissile material arrived from the production plants: uranium from [[Oak Ridge, Tennessee]], and plutonium from the [[Hanford Site]] in Washington.{{Citation needed|date=June 2021}}

In 1945, using the results of critical mass experiments, Los Alamos technicians fabricated and assembled components for four bombs: the ''[[Trinity test|Trinity]]'' [[the gadget|Gadget]], Little Boy, Fat Man, and an unused spare Fat Man. After the war, those who could, including Oppenheimer, returned to university teaching positions. Those who remained worked on levitated and hollow pits and conducted weapon effects tests such as [[Operation Crossroads|Crossroads]] Able and Baker at [[Bikini Atoll]] in 1946.{{Citation needed|date=June 2021}}

All of the essential ideas for incorporating fusion into nuclear weapons originated at Los Alamos between 1946 and 1952. After the [[Teller-Ulam design|Teller-Ulam]] radiation implosion breakthrough of 1951, the technical implications and possibilities were fully explored, but ideas not directly relevant to making the largest possible bombs for long-range Air Force bombers were shelved.{{Citation needed|date=June 2021}}

Because of Oppenheimer's initial position in the H-bomb debate, in opposition to large thermonuclear weapons, and the assumption that he still had influence over Los Alamos despite his departure, political allies of [[Edward Teller]] decided he needed his own laboratory in order to pursue H-bombs. By the time it was opened in 1952, in [[Lawrence Livermore National Laboratory|Livermore]], California, Los Alamos had finished the job Livermore was designed to do.{{Citation needed|date=June 2021}}

===Lawrence Livermore===
{{Main|Lawrence Livermore National Laboratory}}
With its original mission no longer available, the Livermore lab tried radical new designs that failed. Its first three nuclear tests were [[fizzle (nuclear test)|fizzles]]: in 1953, two single-stage [[uranium hydride bomb|fission devices with uranium hydride pits]], and in 1954, a two-stage thermonuclear device in which the secondary heated up prematurely, too fast for radiation implosion to work properly.{{Citation needed|date=June 2021}}

Shifting gears, Livermore settled for taking ideas Los Alamos had shelved and developing them for the Army and Navy. This led Livermore to specialize in small-diameter tactical weapons, particularly ones using two-point implosion systems, such as the Swan. Small-diameter tactical weapons became primaries for small-diameter secondaries. Around 1960, when the superpower arms race became a ballistic missile race, Livermore warheads were more useful than the large, heavy Los Alamos warheads. Los Alamos warheads were used on the first [[intermediate-range ballistic missile]]s, IRBMs, but smaller Livermore warheads were used on the first [[intercontinental ballistic missile]]s, ICBMs, and [[submarine-launched ballistic missile]]s, SLBMs, as well as on the first [[multiple independently targetable reentry vehicle|multiple warhead]] systems on such missiles.<ref>Sybil Francis, ''Warhead Politics: Livermore and the Competitive System of Nuclear Warhead Design'', UCRL-LR-124754, June 1995, Ph.D. Dissertation, Massachusetts Institute of Technology, available from National Technical Information Service. This 233-page thesis was written by a weapons-lab outsider for public distribution. The author had access to all the classified information at Livermore that was relevant to her research on warhead design; consequently, she was required to use non-descriptive code words for certain innovations.</ref>

In 1957 and 1958, both labs built and tested as many designs as possible, in anticipation that a planned 1958 test ban might become permanent. By the time testing resumed in 1961 the two labs had become duplicates of each other, and design jobs were assigned more on workload considerations than lab specialty. Some designs were horse-traded. For example, the [[W38 (nuclear warhead)|W38 warhead]] for the [[Titan (rocket family)|Titan]] I missile started out as a Livermore project, was given to Los Alamos when it became the [[SM-65 Atlas|Atlas]] missile warhead, and in 1959 was given back to Livermore, in trade for the [[W54]] [[Davy Crockett (nuclear device)|Davy Crockett]] warhead, which went from Livermore to Los Alamos.{{Citation needed|date=June 2021}}

Warhead designs after 1960 took on the character of model changes, with every new missile getting a new warhead for marketing reasons. The chief substantive change involved packing more fissile uranium-235 into the secondary, as it became available with continued [[uranium enrichment]] and the dismantlement of the large high-yield bombs.{{Citation needed|date=June 2021}}

Starting with the [[Nova (laser)#Fusion in Nova|Nova]] facility at Livermore in the mid-1980s, nuclear design activity pertaining to radiation-driven implosion was informed by research with ''indirect drive'' laser fusion. This work was part of the effort to investigate [[Inertial confinement fusion#Nuclear weapons|Inertial Confinement Fusion]]. Similar work continues at the more powerful [[National Ignition Facility]]. The [[Stockpile stewardship#Stockpile Stewardship Management Program|Stockpile Stewardship and Management Program]] also benefited from research performed at [[National Ignition Facility#Stockpile experiments, 2013–2015|NIF]].{{Citation needed|date=June 2021}}