Editing Trinity (nuclear test) (section)

==Preparation==
===Decision===
[[File:Trinity Test Site.jpg|thumb|upright=1.6|right|Map of the Trinity Site]]
The idea of testing the implosion device was brought up in discussions at Los Alamos in January 1944 and attracted enough support for Oppenheimer to approach Groves. Groves gave approval, but he had concerns. The Manhattan Project had spent a great deal of money and effort to produce the plutonium, and he wanted to know whether there would be a way to recover it. The Laboratory's Governing Board then directed [[Norman Ramsey]] to investigate how this could be done. In February 1944, Ramsey proposed a small-scale test in which the explosion was limited in size by reducing the number of generations of chain reactions, and that it take place inside a sealed containment vessel from which the plutonium could be recovered.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=174–175}}

The means of generating such a controlled reaction were uncertain, and the data obtained would not be as useful as that from a full-scale explosion.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=174–175}} Oppenheimer argued that the bomb "<!--implosion gadget -->must be tested in a range where the energy release is comparable with that contemplated for final use."{{sfn|Norris|2002|p=395}} In March 1944, he obtained Groves's tentative approval for testing a full-scale explosion inside a containment vessel, although Groves was still worried about how he would explain the loss of "a billion dollars worth" of plutonium in the event the test failed.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=174–175}}

===Code name===
The origin of the code name "Trinity" for the test is unknown, but it is often attributed to Oppenheimer as a reference to the poetry of [[John Donne]], which in turn references the Christian belief of the [[Trinity]]. In 1962, Groves wrote to Oppenheimer about the origin of the name, asking if he had chosen it because it was a name common to rivers and peaks in the West and would not attract attention, and elicited this reply:
{{blockquote|I did suggest it, but not on that ground&nbsp;... Why I chose the name is not clear, but I know what thoughts were in my mind. There is a poem of John Donne, written just before his death, which I know and love. From it a quotation: "As West and East / In all flatt Maps{{snd}}and I am one{{snd}}are one, / So death doth touch the Resurrection."{{sfn|Donne|1896|pp=211–212}}{{efn|From the poem "[https://www.poetryfoundation.org/poems/44114/hymn-to-god-my-god-in-my-sickness Hymn to God, My God, in My Sickness]"}} That still does not make a Trinity, but in another, better known devotional poem Donne opens: "[[Batter my heart, three person'd God]]."{{efn|''[[Holy Sonnets]]'', [[s:Holy Sonnets/Holy Sonnet 14|Holy Sonnet 14]]}}{{sfn|Donne|1896|p=165}}{{sfn|Rhodes|1986|pp=571–572}}}}

===Organization===
In March 1944, planning for the test was assigned to [[Kenneth Bainbridge]], a professor of physics at [[Harvard University]], working under explosives expert [[George Kistiakowsky]]. Bainbridge's group was known as the E-9 (Explosives Development) Group.{{sfn|Hawkins|Truslow|Smith|1961|p=266}} Stanley Kershaw, formerly from the [[National Safety Council]], was made responsible for safety.{{sfn|Hawkins|Truslow|Smith|1961|p=266}} [[Captain (United States O-3)|Captain]] Samuel P. Davalos, the assistant post engineer at Los Alamos, was placed in charge of construction.{{sfn|Jones|1985|p=478}} [[First Lieutenant]] Harold C. Bush became commander of the Base Camp at Trinity.{{sfn|Bainbridge|1976|p=4}} Scientists [[William Penney]], [[Victor Weisskopf]] and [[Philip Burton Moon|Philip Moon]] were consultants. Eventually seven subgroups were formed:{{sfn|Hawkins|Truslow|Smith|1961|pp=269–270}}
* TR-1 (Services) under [[John Harry Williams|John H. Williams]]
* TR-2 (Shock and Blast) under [[John Henry Manley|John H. Manley]]
* TR-3 (Measurements) under [[Robert R. Wilson]]
* TR-4 (Meteorology) under J. M. Hubbard
* TR-5 (Spectrographic and Photographic) under Julian E. Mack
* TR-6 (Airborne Measurements) under [[Bernard Waldman]]
* TR-7 (Medical) under [[Louis Hempelmann|Louis H. Hempelmann]]

The E-9 group was renamed the X-2 (Development, Engineering and Tests) Group in the August 1944 reorganization.{{sfn|Hawkins|Truslow|Smith|1961|p=266}}

===Test site===
[[File:TrinitySiteISS008-E-5604.jpg|thumb|right|Trinity Site (red arrow) near [[Carrizozo Malpais]]]]
Safety and security required a remote, isolated and unpopulated area. The scientists also wanted a flat area to minimize secondary effects of the blast, and with little wind to spread [[Nuclear fallout|radioactive fallout]]. Eight candidate sites were considered: the [[Tularosa Basin|Tularosa Valley]]; the [[Jornada del Muerto Valley]]; the area southwest of [[Cuba, New Mexico]], and north of [[Thoreau, New Mexico|Thoreau]]; and the lava flats of the [[El Malpais National Monument]], all in New Mexico; the [[San Luis Valley]] near the [[Great Sand Dunes National Monument]] in Colorado; the [[Desert Training Center|Desert Training Area]] and [[San Nicolas Island]] in Southern California; and the sand bars of [[Padre Island]], Texas.{{sfn|Bainbridge|1976|p=3}}

The sites were surveyed by car and by air by Bainbridge, R. W. Henderson, Major W. A. Stevens and Major [[Peer de Silva]]. The site finally chosen, after consulting with [[Major General (United States)|Major General]] [[Uzal Ent]], the commander of the [[Second Air Force]] on September 7, 1944,{{sfn|Bainbridge|1976|p=3}} lay at the northern end of the [[Alamogordo Bombing Range]], in [[Socorro County, New Mexico|Socorro County]] near the towns of [[Carrizozo, New Mexico|Carrizozo]] and [[San Antonio, New Mexico|San Antonio]] ({{Coord|33|40.636|N|106|28.525|W|region:US-NM_type:landmark_scale:60000|display=inline}}).<ref name="wsmr">{{cite web |title=Trinity Site |publisher=White Sands Missile Range |url=http://www.wsmr.army.mil/pao/TrinitySite/trinst.htm |archive-url=https://web.archive.org/web/20070806045224/http://www.wsmr.army.mil/pao/TrinitySite/Trinst.htm |archive-date=August 6, 2007 |access-date=July 16, 2007 |quote=GPS Coordinates for obelisk (exact GZ) =&nbsp;N33.40.636 W106.28.525 }}</ref> The Alamogordo Bombing Range was renamed the White Sands Proving Ground on July 9, 1945, one week before the test.<ref>{{cite web |title=White Sands Missile Range Fact Sheet |publisher=NASA |url=https://www.nasa.gov/pdf/449089main_White_Sands_Missile_Range_Fact_Sheet.pdf |access-date=July 29, 2023 |archive-date=February 24, 2017 |archive-url=https://web.archive.org/web/20170224060917/https://www.nasa.gov/pdf/449089main_White_Sands_Missile_Range_Fact_Sheet.pdf |url-status=live }}</ref> Despite the criterion that the site be isolated, nearly half a million people lived within {{convert|150|mi}} of the test site; soon after the Trinity test, the Manhattan Project's chief medical officer, Colonel [[Stafford L. Warren]], recommended that future tests be conducted at least 150 miles from populated areas.<ref name="NG">{{Cite news |date=September 21, 2021 |title=U.S. lawmakers move urgently to recognize survivors of the first atomic bomb test |publisher=National Geographic |url=https://www.nationalgeographic.com/history/article/lawmakers-move-urgently-to-recognize-survivors-of-the-first-atomic-bomb-test |access-date=August 2, 2023 |archive-date=July 21, 2023 |archive-url=https://web.archive.org/web/20230721020808/https://www.nationalgeographic.com/history/article/lawmakers-move-urgently-to-recognize-survivors-of-the-first-atomic-bomb-test |url-status=dead }}</ref>

The only structures in the vicinity were the [[McDonald Ranch House]] and its ancillary buildings, about {{convert|2|mi}} to the southeast.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=311}} Like the rest of the Alamogordo Bombing Range, it had been acquired by the government in 1942. The [[patented land]] had been [[eminent domain|condemned]] and [[grazing rights]] suspended.<ref>{{cite web |url=http://www.wsmr.army.mil/PAO/Trinity/Pages/TrinitySiteHistoryAcopyofthebrochuregiventositevisitors.aspx |title=Trinity Site History: A copy of the brochure given to site visitors |publisher=[[White Sands Missile Range]], [[United States Army]] |access-date=September 11, 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140831125557/http://www.wsmr.army.mil/PAO/Trinity/Pages/TrinitySiteHistoryAcopyofthebrochuregiventositevisitors.aspx |archive-date=August 31, 2014 }}</ref><ref name="McDonald">{{cite web |url=http://www.nmfarmandranchmuseum.org/oralhistory/detail.php?interview=207 |publisher=New Mexico Farm & Ranch Heritage Museum |title=McDonald, David G |access-date=September 11, 2014 |archive-date=September 11, 2014 |archive-url=https://web.archive.org/web/20140911005509/http://www.nmfarmandranchmuseum.org/oralhistory/detail.php?interview=207 |url-status=live }}</ref> Scientists used this as a laboratory for testing bomb components.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=311}} Bainbridge and Davalos drew up plans for a base camp with accommodation and facilities for 160 personnel, along with the technical infrastructure to support the test. A construction firm from [[Lubbock, Texas]], built the barracks, officers' quarters, mess hall and other basic facilities.{{sfn|Jones|1985|p=478}} The requirements expanded and by July 1945 250 people worked at the Trinity test site. On the weekend of the test, there were 425 present.{{sfn|Bainbridge|1975|p=40}}
[[File:Trinity basecamp.jpg|thumb|left|The Trinity test base camp]]

Lieutenant Bush's twelve-man [[Military Police Corps (United States)|MP]] unit arrived at the site from Los Alamos on December 30, 1944. This unit established initial security checkpoints and horse patrols. The distances around the site proved too great for the horses, so they were repurposed for [[polo]] playing, and the MPs resorted to using jeeps and trucks for transportation.{{sfn|Bainbridge|1976|p=3}}<ref name="Building a test site">{{cite web |url=http://www.atomicarchive.com/History/trinity/building.shtml |title=Building a test site |publisher=atomicarchive.com |access-date=August 23, 2014 |archive-date=July 2, 2014 |archive-url=https://web.archive.org/web/20140702220339/http://www.atomicarchive.com/History/trinity/building.shtml |url-status=live }}</ref> Maintenance of morale among men working long hours under harsh conditions along with dangerous reptiles and insects was a challenge. Bush strove to improve the food and accommodation and to provide organized games and nightly movies.{{sfn|Jones|1985|p=481}}

Throughout 1945, other personnel arrived at the Trinity Site to help prepare for the bomb test. They tried to use water out of the ranch wells, but found the water so [[alkaline]], it was not drinkable. They were forced to use [[U.S. Navy]] [[saltwater soap]] and hauled drinking water in from the firehouse in Socorro. Gasoline and diesel were purchased from the [[Standard Oil]] plant there.<ref name="Building a test site"/> Freshwater was trucked in, {{convert|700|gal}} per load, from {{convert|40|mi}} away.<ref name="wellerstein20150716">{{Cite magazine |last=Wellerstein |first=Alex |date=2015-07-16 |title=The Light of Trinity, the World's First Nuclear Bomb |url=https://www.newyorker.com/tech/annals-of-technology/the-first-light-of-the-trinity-atomic-test |access-date=2024-11-22 |magazine=The New Yorker |language=en-US |issn=0028-792X}}</ref> Military and civilian construction personnel built warehouses, workshops, a magazine and commissary. The [[siding (rail)|railroad siding]] at Pope, New Mexico, was upgraded by adding an unloading platform. Roads were built, and {{convert|200|mi}} of telephone wire were strung. Electricity was supplied by portable generators.{{sfn|Jones|1985|p=480}}{{sfn|Bainbridge|1975|p=41}} [[Bomb shelter]]s to protect test observers were the most expensive to construct.{{r|wellerstein20150716}}

Due to its proximity to the bombing range, the base camp was accidentally bombed twice in May. When the lead plane on a practice night raid accidentally knocked out the generator or otherwise doused the lights illuminating their target, they went in search of the lights, and since they had not been informed of the presence of the Trinity base camp, and it was lit, they bombed it instead. The accidental bombing damaged the stables and the carpentry shop, and a small fire resulted.{{sfn|Bainbridge|1975|p=42}}

===Jumbo===
[[File:Trinity - Jumbo brought to site.jpg|thumb|right|Jumbo arrives at the site]]
Responsibility for the design of a containment vessel for an unsuccessful explosion, known as "Jumbo", was assigned to Robert W. Henderson and Roy W. Carlson of the Los Alamos Laboratory's X-2A Section. The bomb would be placed into the heart of Jumbo, and if the bomb's detonation was unsuccessful the walls of Jumbo would not be breached, making it possible to recover the bomb's plutonium. [[Hans Bethe]], Victor Weisskopf, and [[Joseph O. Hirschfelder]] made the initial calculations, followed by a more detailed analysis by Henderson and Carlson.{{sfn|Bainbridge|1976|p=4}} They drew up specifications for a steel sphere {{convert|13|to|15|feet|2}} in diameter, weighing {{convert|150|ST|t}} and capable of handling a pressure of {{convert|50000|psi}}. After consulting with the steel companies and the railroads, Carlson produced a scaled-back cylindrical design that would be much easier to manufacture. Carlson identified a company that normally made boilers for the Navy, [[Babcock & Wilcox]]; they had made something similar and were willing to attempt its manufacture.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=366–367}}

As delivered in May 1945,{{sfn|Bainbridge|1975|p=43}} Jumbo was {{convert|10|feet|2}} in diameter and {{convert|25|feet|2}} long with walls {{convert|14|in|0}} thick, and weighed {{convert|214|ST|LT t}}.<ref name="Jumbo">{{cite web |url=http://www.atomicarchive.com/History/trinity/jumbo.shtml |title=Jumbo |publisher=atomicarchive.com |access-date=August 23, 2014 |archive-date=October 10, 2014 |archive-url=https://web.archive.org/web/20141010230118/http://www.atomicarchive.com/History/trinity/jumbo.shtml |url-status=live }}</ref><ref name="Moving Jumbo"/> A special train brought it from the Babcock & Wilcox plant in [[Barberton, Ohio]], to the siding at Pope, where it was loaded on a large trailer and towed {{convert|25|miles}} across the desert by [[crawler tractor]]s.{{sfn|Jones|1985|p=512}} At the time, it was the heaviest item ever shipped by rail.<ref name="Moving Jumbo">{{cite web |title=Moving "Jumbo" at the Trinity Test Site |publisher=Brookings Institution Press |url=http://www.brookings.edu/about/projects/archive/nucweapons/jumbo |access-date=February 7, 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130530124159/http://www.brookings.edu/about/projects/archive/nucweapons/jumbo |archive-date=May 30, 2013 }}</ref>
[[File:Trinity - Jumbo after test.jpg|thumb|left|Jumbo was not used for its originally intended purpose in the Trinity test but was in a tower some distance from the bomb when it went off]]

For many of the Los Alamos scientists, Jumbo was "the physical manifestation of the lowest point in the Laboratory's hopes for the success of an implosion bomb."{{sfn|Bainbridge|1975|p=43}} By the time it arrived, the reactors at the [[Hanford Engineer Works]] produced plutonium in quantity, and Oppenheimer was confident that there would be enough for a second test.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=366–367}} The use of Jumbo would interfere with the gathering of data on the explosion, the primary objective of the test.{{sfn|Jones|1985|p=512}} An explosion of more than {{convert|500|tonTNT}} would vaporize the steel and make it difficult to measure the thermal effects. Even {{convert|100|tonTNT}} would send fragments flying, presenting a hazard to personnel and measuring equipment.{{sfn|Bainbridge|1976|p=5}} It was therefore decided not to use it.{{sfn|Jones|1985|p=512}} Instead, it was hoisted up a steel tower {{convert|800|yards|0}} from the explosion, where it could be used for a subsequent test.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=366–367}} In the end, Jumbo survived the explosion, although its tower did not.<ref name="Jumbo"/>

Jumbo was destroyed on April 16, 1946, when an Army ordnance team detonated eight 500 lb bombs in the bottom of the steel container. Jumbo, with its steel banding around the middle, had been designed to contain the 5,000 lbs of high explosive in the atomic bomb while it was suspended in the center of the vessel. With the conventional bombs placed in the bottom of Jumbo, the resulting blast sent fragments flying in all directions as far as three quarters of a mile.{{sfn|Fraikor|2021|p=100}} Who authorized the destruction of Jumbo remains controversial.{{sfn|Fraikor|2021|pp=102–106}} The rusting skeleton of Jumbo sits in the parking lot at the Trinity site on the White Sands Missile Range, where it was moved in 1979.<ref>{{cite web |title=Trinity History |publisher=White Sands Missile Range |url=https://www.wsmr.army.mil/Trinity/Pages/TrinityHistory.aspx |access-date=September 26, 2021 |url-status=dead |archive-url=https://web.archive.org/web/20220316003531/https://www.wsmr.army.mil/Trinity/Pages/TrinityHistory.aspx |archive-date=March 16, 2022 }}</ref>

The development team also considered other methods of recovering active material in the event of a dud explosion. One idea was to cover it with a cone of sand. Another was to suspend the bomb in a tank of water. As with Jumbo, it was decided not to proceed with these means of containment. The {{nowrap|CM-10}} (Chemistry and Metallurgy) group at Los Alamos also studied how the active material could be chemically recovered after a contained or failed explosion.{{sfn|Bainbridge|1976|p=5}}

===100-ton test===
[[File:Trinity 100 ton.jpg|thumb|right|0.1 kiloton conventional explosives rehearsal test, Trinity]]
Because there would be only one chance to carry out the test correctly, Bainbridge decided that a rehearsal should be carried out to allow the plans and procedures to be verified, and the instrumentation to be tested and calibrated. Oppenheimer was initially skeptical but gave permission, and he later agreed that it contributed to the success of the Trinity test.{{sfn|Bainbridge|1975|p=41}}

A {{convert|20|ft|m|adj=mid|-high|0}} wooden platform was constructed {{convert|800|yd|-1}} to the southeast of Trinity [[ground zero]]. The high explosive was piled in its wooden shipping boxes in the shape of a pseudo-octagonal prism on it. The charge consisted of {{convert|89.75|ST|t}} tons of [[TNT]] and {{convert|14.91|ST|t}} tons of [[Composition B]] (with the total explosive power of approximately {{convert|108|tonTNT}}), actually a few tons more than the stated "100-tons".<ref>{{cite book |last=Walker |first=Raymond L. |date=1950 |title=100-ton Test: Piezo Gauge Measurements |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015086443556&seq=3 |publisher=U.S. Atomic Energy Commission, Technical Information Division |page=1}}</ref><ref>{{cite book |last=Loring |first=William S. |date=2019 |title=Birthplace of the Atomic Bomb: A Complete History of the Trinity Test Site |url=https://books.google.com/books?id=h0CIDwAAQBAJ&pg=PT141 |location=Jefferson, North Carolina |publisher=McFarland & Company, Inc., Publishers |page=133 |isbn=978-1-4766-3381-7}}</ref> Kistiakowsky assured Bainbridge that the explosives used were not susceptible to shock. This was proven correct when some boxes fell off the elevator lifting them up to the platform. Flexible tubing was threaded through the pile of boxes of explosives. A radioactive slug from Hanford with {{convert|1000|Ci|TBq|lk=on}} of [[beta ray]] activity and {{convert|400|Ci|TBq}} of [[gamma ray]] activity was dissolved, and Hempelmann poured the solution into the tubing.{{sfn|Bainbridge|1975|pp=41, 58}}{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=360–362}}{{sfn|Bainbridge|1976|p=11}}

The test was scheduled for May 5 but was postponed for two days to allow for more equipment to be installed. Requests for further postponements had to be refused because they would have affected the schedule for the main test. The detonation time was set for 04:00 [[history of time in the United States#War Time 1918 and 1942|Mountain War Time]] (MWT), on May 7, but there was a 37-minute delay to allow the observation plane,{{sfn|Bainbridge|1976|p=9}} a [[Boeing B-29 Superfortress]] from the [[216th Army Air Forces Base Unit]] flown by Major Clyde "Stan" Shields,{{sfn|Dvorak|2013|pp=9–10}} to get into position.{{sfn|Bainbridge|1976|p=9}}
[[File:Trinity 100ton Test.gif|thumb|left|Men stack crates of high explosives for the 100-ton test]]

The fireball of the conventional explosion was visible from [[Alamogordo Army Air Field]] {{convert|60|mi|-1}} away, but there was little shock at the base camp {{convert|10|miles}} away.{{sfn|Bainbridge|1976|p=9}} Shields thought that the explosion looked "beautiful", but it was hardly felt at {{convert|15000|feet}}.{{sfn|Dvorak|2013|pp=9–10}} [[Herbert L. Anderson]] practiced using a converted [[M4 Sherman]] tank lined with lead to approach the {{convert|5|ft|m|adj=mid|-deep}} and {{convert|30|ft|m|adj=mid|-wide|0}} blast crater and take a soil sample, although the radioactivity was low enough to allow several hours of unprotected exposure. An electrical signal of unknown origin caused the explosion to go off 0.25 seconds early, ruining experiments that required split-second timing. The [[piezoelectric]] gauges developed by Anderson's team correctly indicated an explosion of 108 tons of TNT, but [[Luis Walter Alvarez|Luis Alvarez]] and Waldman's airborne condenser gauges were far less accurate.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=360–362}}{{sfn|Bainbridge|1976|p=12}}

In addition to uncovering scientific and technological issues, the rehearsal test revealed practical concerns as well. Over 100 vehicles were used for the rehearsal test, but it was realized more would be required for the main test, and they would need better roads and repair facilities. More radios and more telephone lines were required. Lines needed to be buried to prevent damage by vehicles. A [[Teleprinter|teletype]] was installed to allow better communication with Los Alamos. A town hall was built to allow for large conferences and briefings, and the mess hall had to be upgraded. Because dust thrown up by vehicles interfered with some of the instrumentation, {{convert|20|miles}} of road was sealed.{{sfn|Bainbridge|1976|p=12}}{{sfn|Bainbridge|1975|p=41}}

===The bomb===
{{See also|Nuclear weapon design#Implosion-type weapon}}
[[File:Trinity tower.jpg|thumb|right|upright=1|The {{convert|30|m|adj=on|-2}} "shot tower" constructed for the test]]
The term "[[gadget]]"—a laboratory euphemism for a bomb<ref>{{cite web |url=https://www.atomicheritage.org/profile/robert-f-christy |title=Robert F. Christy |publisher=Atomic Heritage Foundation |access-date=November 8, 2014 |archive-date=October 13, 2014 |archive-url=https://web.archive.org/web/20141013203837/http://www.atomicheritage.org/profile/robert-f-christy |url-status=live }}</ref>—gave the laboratory's weapon physics division, "G Division", its name in August 1944.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=307–308}} At that time it did not refer specifically to the Trinity Test device as that had yet to be developed,{{sfn|Hawkins|Truslow|Smith|1961|p=228}} but once it was, it became the laboratory code name.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=307–308}} The Trinity bomb was officially a Y-1561 device, as was the Fat Man used later in the bombing of Nagasaki. The two were very similar, though the Trinity bomb lacked fuzing and external ballistic casing. The bombs were still under development, and small changes continued to be made to the Fat Man design.{{sfn|Coster-Mullen|2012|pp=47–53}}

To keep the design as simple as possible, a nearly solid spherical core was chosen rather than a hollow one, although calculations showed that a hollow core would be more efficient in its use of plutonium.<ref name="Christy">{{cite web |url=http://www.webofstories.com/play/robert.christy/8 |last=Christy |first=Robert |author-link=Robert Christy |title=Constructing the Nagasaki Atomic Bomb |publisher=Web of Stories |access-date=October 12, 2014 |url-status=dead |archive-url=https://web.archive.org/web/20141010073928/http://www.webofstories.com/play/robert.christy/8 |archive-date=October 10, 2014 }}</ref>{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=293}} The core was compressed to [[prompt critical|prompt super-criticality]] by the implosion generated by the high explosive lens. This design became known as a "Christy Core"{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=270–271, 293–294}} or "[[Pit (nuclear weapon)#Christy pits|Christy pit]]" after physicist [[Robert F. Christy]], who made the solid pit design a reality after it was initially proposed by [[Edward Teller]].<ref name="Christy"/><ref>{{cite web |publisher=Restricted Data: The Nuclear Secrecy Blog |last=Wellerstein |first=Alex |title=Christy's Gadget: Reflections on a death |url=http://blog.nuclearsecrecy.com/2012/10/05/christys-gadget/ |access-date=October 7, 2014 |archive-date=October 11, 2014 |archive-url=https://web.archive.org/web/20141011050606/http://blog.nuclearsecrecy.com/2012/10/05/christys-gadget/ |url-status=live }}</ref><ref>{{cite web |url=https://www.webofstories.com/play/hans.bethe/94 |title=Hans Bethe 94 – Help from the British, and the 'Christy Gadget' |publisher=Web of Stories |access-date=October 12, 2014 |archive-date=April 4, 2020 |archive-url=https://web.archive.org/web/20200404220148/http://www.webofstories.com/play/hans.bethe/94 |url-status=live }}</ref>

Of the several [[allotropes of plutonium]], the metallurgists preferred the malleable δ ([[Delta (letter)|delta]]) [[Phase (matter)|phase]]. This was stabilized at room temperature by alloying it with 5% [[gallium]].<ref name="neim">{{cite web |year=2005 |title=The drama of plutonium |url=http://www.neimagazine.com/story.asp?storyCode=2029280 |url-status=dead |archive-url=https://web.archive.org/web/20100915115554/http://www.neimagazine.com/story.asp?storyCode=2029280 |archive-date=2010-09-15 |access-date=2010-01-25 |publisher=Nuclear Engineering International}}</ref> Two equal hemispheres of plutonium-gallium alloy were plated with silver,{{sfn|Coster-Mullen|2012|pp=47–53}}{{sfn|Hawkins|Truslow|Smith|1961|pp=256–257}} and designated by serial numbers HS-1 and HS-2.<ref>{{cite web |publisher=Restricted Data: The Nuclear Secrecy Blog |last=Wellerstein |first=Alex |title=The third core's revenge |url=http://blog.nuclearsecrecy.com/2013/08/16/the-third-cores-revenge/ |access-date=April 4, 2014 |archive-date=April 7, 2014 |archive-url=https://web.archive.org/web/20140407081649/http://blog.nuclearsecrecy.com/2013/08/16/the-third-cores-revenge/ |url-status=live }}</ref> The {{convert|6.19|kg|adj=on}} radioactive core generated 15 W of heat, which warmed it up to about {{convert|100|to|110|F|C}},{{sfn|Coster-Mullen|2012|pp=47–53}} and the silver plating developed blisters that had to be filed down and covered with gold foil; later cores were plated with [[nickel]] instead.<ref>{{cite web |title=Cyril S. Smith's Interview |url=https://www.manhattanprojectvoices.org/oral-histories/cyril-s-smiths-interview |last1=Smith |first1=Cyril S. |last2=Sanger |first2=S.L. |publisher=The Voices of the Manhattan Project and National Museum of Nuclear Science and History |year=1986 |access-date=March 29, 2020 |archive-date=March 29, 2020 |archive-url=https://web.archive.org/web/20200329120705/https://www.manhattanprojectvoices.org/oral-histories/cyril-s-smiths-interview |url-status=live }}</ref>
[[File:Fat Man design model.png|thumb|left|Basic nuclear components of the bomb. The uranium slug containing the plutonium sphere was inserted late in the assembly process.]]
A trial assembly of the bomb, without active components or explosive lenses, was carried out by the bomb assembly team headed by [[Norris Bradbury]] at Los Alamos on July 3. It was driven to Trinity and back. A set of explosive lenses arrived on July 7, followed by a second set on July 10. Each was examined by Bradbury and Kistiakowsky, and the best ones were selected for use.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=365}} The remainder were handed over to [[Edward Creutz]], who conducted a test detonation at Pajarito Canyon near Los Alamos without nuclear material.{{sfn|Rhodes|1986|p=657}} Magnetic measurements from this test suggested that the implosion might be insufficiently simultaneous and the bomb would fail. Bethe worked through the night to assess the results and reported that they were consistent with a perfect explosion.{{sfn|Rhodes|1986|pp=661–663}}

Assembly of the nuclear capsule began on July 13 at the McDonald Ranch House, where the master bedroom had been turned into a [[clean room]]. The polonium-beryllium [[Urchin (detonator)|"Urchin" initiator]] was assembled, and [[Louis Slotin]] placed it inside the two hemispheres of the plutonium core. [[Cyril Stanley Smith|Cyril Smith]] then placed the core in the natural uranium [[tamper (nuclear weapon)|tamper]] plug, or "slug". Air gaps were filled with {{convert|0.5|mil|adj=on}} gold foil, and the two halves of the plug were held together with uranium washers and screws which fit smoothly into the domed ends of the plug.{{sfn|Coster-Mullen|2012|pp=56–57}}
[[File:Trinity device readied.jpg|thumb|right|The bomb being unloaded at the base of the tower for the final assembly]]

To better understand the likely effect of a bomb dropped from a plane and detonated in air, and generate less nuclear fallout, the bomb was to be detonated atop a {{convert|100|ft|adj=on}} steel tower.{{sfn|Rhodes|1986|p=654}} The bomb was driven to the base of the tower, where a temporary [[eye bolt]] was screwed into the {{convert|105|lb|adj=on}} capsule and a [[Hoist (device)|chain hoist]] was used to lower the capsule into the bomb. As the capsule entered the hole in the uranium tamper, it stuck. [[Robert Bacher]] realized that the heat from the plutonium core had caused the capsule to expand, while the explosives assembly with the tamper had cooled during the night in the desert. By leaving the capsule in contact with the tamper, the temperatures equalized and, in a few minutes, the capsule had slipped completely into the tamper.{{sfn|Coster-Mullen|2012|pp=49–50}} The eye bolt was then removed from the capsule and replaced with a threaded uranium plug, a boron disk was placed on top of the capsule (to complete the thin spherical shell of plastic boron around the tamper), an aluminum plug was screwed into the hole in the pusher (aluminum shell surrounding the tamper), and the two remaining high explosive lenses were installed. Finally, the upper [[Duralumin|Dural]] polar cap was bolted into place.{{sfn|Coster-Mullen|2012|p=58}} The assembly of active material and high explosives was finished at 17:45 hours on 13 July.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=370}}

The gadget was hoisted to the top of the tower. The tower stood on four legs extending {{convert|20|ft}} into the ground, with concrete footings. Atop it was an oak platform and a [[corrugated iron]] shack open to the west. The gadget was hauled up with an electric winch.{{sfn|Rhodes|1986|p=654}} A truckload of mattresses was placed underneath in case the cable broke and the gadget fell.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=368–370}}{{efn|The mattresses would not have protected the gadget, but they helped the men to feel better.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|p=483}}}} A crew then attached each of the 32 Model 1773 [[Exploding-bridgewire detonator|EBW]] detonators. Full assembly of the bomb was completed by 17:00 on July 14.{{sfn|Coster-Mullen|2012|p=314}} The seven-man arming party, consisting of Bainbridge, Kistiakowsky, [[Joseph McKibben]] and four soldiers including Lieutenant Bush, drove out to the tower to perform the final arming shortly after 22:00 on July 15.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=368–370}}

===Personnel===
[[File:Louis Slotin and the Gadget Bomb.jpg|thumb|right|[[Louis Slotin]] and Herbert Lehr prior to insertion of the bomb's tamper plug (visible in front of Lehr's left knee)<ref name="AHF Herbert Lehr">{{cite web |title=Herbert Lehr |url=https://www.atomicheritage.org/profile/herbert-lehr |publisher=Atomic Heritage Foundation |access-date=September 8, 2020 |archive-date=January 16, 2021 |archive-url=https://web.archive.org/web/20210116134534/https://www.atomicheritage.org/profile/herbert-lehr |url-status=live }}</ref>]]
In the final two weeks before the test, some 250 personnel from Los Alamos were at work at the Trinity Site,{{sfn|Bainbridge|1976|p=15}} and Lieutenant Bush's command had ballooned to 125 men guarding and maintaining the base camp. Another 160 men under Major T.O. Palmer were stationed outside the area with vehicles to evacuate the civilian population in the surrounding region should that prove necessary.{{sfn|Bainbridge|1976|p=25}}{{r|wellerstein20150716}} They had enough vehicles to move 450 people to safety and had food and supplies to last them for two days. Arrangements were made for Alamogordo Army Air Field to provide accommodation.{{sfn|Hacker|1987|p=90}} Groves warned [[Governor of New Mexico]] [[John J. Dempsey]] that [[martial law]] might have to be declared in the southwestern part of the state.{{sfn|Norris|2002|p=402}}{{r|wellerstein20150716}}

Shelters were established {{convert|10000|yd}} due north, west, and south of the tower, each with its own chief: Robert Wilson at N-10,000, John Manley at W-10,000 and [[Frank Oppenheimer]] at S-10,000.{{sfn|Bainbridge|1976|pp=29–30}} Many other observers were around {{convert|20|mi}} away, and some others were scattered at different distances, some in more informal situations. [[Richard Feynman]] claimed to be the only person to see the explosion without the goggles provided, relying on a truck windshield to screen out harmful [[ultraviolet]] wavelengths.{{sfn|Feynman|1985|p=134}} Bainbridge asked Groves to keep his VIP list down to ten. He chose himself, Oppenheimer, [[Richard Tolman]], [[Vannevar Bush]], [[James Bryant Conant|James Conant]], Brigadier General [[Thomas F. Farrell]], [[Charles Lauritsen]], [[Isidor Isaac Rabi]], Sir [[G. I. Taylor|Geoffrey Taylor]], and Sir [[James Chadwick]].{{sfn|Bainbridge|1976|p=25}} The VIPs viewed the test from Compania Hill (also called Compaña Hill or Cerro de la Colorado), about {{convert|20|mi}} northwest of the tower.<ref name="ABQ"/><ref>{{cite web |url=https://brendafleming.com/blog/2022/1/19/photo-essay-trinity-site |title=PHOTO ESSAY: TRINITY SITE |last=Fleming |first=Brenda |date=January 19, 2022 |access-date=2024-07-22}}</ref>
[[File:HD.4G.053 (10540204545).jpg|thumb|left|[[Norris Bradbury]] with the assembled bomb atop the test tower. He later succeeded Oppenheimer as director of Los Alamos.]]

[[Photographic film]] was placed in nearby towns to detect radioactive contamination, and [[seismograph]]s were placed in [[Tucson]], [[Denver]], and [[Chihuahua City|Chihuahua, Mexico]] to determine how far the explosion could be sensed. Calculations stated that even if the mechanical and electrical systems did not fail, the likelihood of a non-optimal test was greater than 10%.{{r|wellerstein20150716}} The observers set up a [[betting pool]] on the results of the test. Teller was the most optimistic, predicting {{convert|45|ktonTNT}}.{{sfn|Rhodes|1986|p=656}} He wore gloves to protect his hands and sunglasses underneath the [[welding goggles]] that the government had supplied everyone with.<ref name="ABQ"/> He was one of the few scientists to watch the test (with eye protection), instead of following orders to lie on the ground with his back turned.<ref>{{cite journal |title=Edward Teller, RIP |url=https://www.thenewatlantis.com/publications/edward-teller-rip |journal=The New Atlantis |issue=3 |pages=105–107 |date=Fall 2003 |access-date=January 7, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20160303233937/http://www.thenewatlantis.com/publications/edward-teller-rip |archive-date=March 3, 2016 }}</ref> He also brought suntan lotion, which he shared with the others.{{sfn|Rhodes|1986|p=668}} Ramsey chose zero (a complete [[dud]]), Robert Oppenheimer chose {{convert|0.3|ktonTNT}}, Kistiakowsky {{convert|1.4|ktonTNT}}, and Bethe chose {{convert|8|ktonTNT}}.{{sfn|Rhodes|1986|p=656}} Rabi, the last to arrive, took the only remaining choice{{snd}}{{convert|18|ktonTNT}}, which turned out to be the winner.{{sfn|Rhodes|1986|p=677}} Bethe later stated that his choice of 8 kt was exactly the value calculated by Segrè, and he was swayed by Segrè's authority over that of a more junior [but unnamed] member of Segrè's group who had calculated 20 kt.<ref>{{cite web |url=https://www.webofstories.com/play/hans.bethe/95 |title=The atomic bomb test for 'Fat Man' – Hans Bethe |publisher=Web of stories |access-date=October 19, 2016 |archive-date=April 4, 2020 |archive-url=https://web.archive.org/web/20200404220157/http://www.webofstories.com/play/hans.bethe/95 |url-status=live }}</ref>

[[Enrico Fermi]] offered to take wagers among the top physicists and military present on whether the atmosphere would ignite, and if so whether it would destroy just the state or incinerate the entire planet.{{sfn|Rhodes|1986|p=664}}<ref name="WP-20220722">{{cite news |last=Johnson |first=Mark |title=How Oppenheimer weighed the odds of an atomic bomb test ending Earth |url=https://www.washingtonpost.com/science/2023/07/22/oppenheimer-manhattan-project-history-atomic-bomb-test/ |date=July 22, 2023 |newspaper=[[The Washington Post]] |url-status=live |archive-url=https://archive.today/20230722123414/https://www.washingtonpost.com/science/2023/07/22/oppenheimer-manhattan-project-history-atomic-bomb-test/ |archive-date=July 22, 2023 |access-date=July 22, 2023 }}</ref> This last result had been previously calculated by Bethe to be almost impossible,{{sfn|Hamming|1998|pp=640–650}}<ref name="LA602">{{cite web |url=https://fas.org/sgp/othergov/doe/lanl/docs1/00329010.pdf |title=Report LA-602, Ignition of the Atmosphere With Nuclear Bombs |publisher=[[Los Alamos National Laboratory]] |access-date=December 29, 2013 |archive-date=March 31, 2020 |archive-url=https://web.archive.org/web/20200331041344/https://fas.org/sgp/othergov/doe/lanl/docs1/00329010.pdf |url-status=live }}</ref>{{efn|The reaction Teller was most concerned with was: {{nuclide|nitrogen|14}} + {{nuclide|nitrogen|14}} → {{nuclide|magnesium|24}} + {{nuclide|helium|4}} (alpha particle) + 17.7 MeV.<ref>{{harvnb|Bethe|1991|p=30}}.</ref>}} although for a while it had caused some of the scientists some anxiety. Bainbridge was furious with Fermi for frightening the guards, some of whom asked to be relieved;{{sfn|Lamont|1966|p=197}} his own biggest fear was that nothing at all would happen, in which case he would have to return to the tower to investigate.{{sfn|Bainbridge|1975|p=44}}