First detonation of a nuclear weapon
Trinity was the code name of the first detonation of a nuclear weapon, conducted by the United States Army at 5:29 a.m. MWT (11:29:21 GMT) on July 16, 1945, as part of the Manhattan Project. The test was of an implosion-design plutonium bomb, nicknamed "The Gadget", of the same design as the Fat Man bomb later detonated over Nagasaki, Japan, on August 9, 1945. Concerns about whether the complex Fat Man design would work led to a decision to conduct the first nuclear test. The code name "Trinity" was assigned by J. Robert Oppenheimer, the director of the Los Alamos Laboratory, possibly inspired by the poetry of John Donne.
The test, both planned and directed by Kenneth Bainbridge, was conducted in the Jornada del Muerto desert about southeast of Socorro, New Mexico, on what was the Alamogordo Bombing and Gunnery Range (renamed the White Sands Proving Ground just before the test). The only structures originally in the immediate vicinity were the McDonald Ranch House and its ancillary buildings, which scientists used as a laboratory for testing bomb components. Fears of a fizzle prompted construction of "Jumbo", a steel containment vessel that could contain the plutonium, allowing it to be recovered; but ultimately Jumbo was not used in the test. On May 7, 1945, a rehearsal was conducted, during which of high explosive spiked with radioactive isotopes was detonated.
Some 425 people were present on the weekend of the Trinity test. In addition to Bainbridge and Oppenheimer, observers included Vannevar Bush, James Chadwick, James B. Conant, Thomas Farrell, Enrico Fermi, Hans Bethe, Richard Feynman, Isidor Isaac Rabi, Leslie Groves, Frank Oppenheimer, Geoffrey Taylor, Richard Tolman, Edward Teller, and John von Neumann. The Trinity bomb released the explosive energy of ± , and a large cloud of fallout. Thousands of people lived closer to the test than would have been allowed under guidelines adopted for subsequent tests, but no one living near the test was evacuated before or afterward.
The test site was declared a National Historic Landmark district in 1965 and listed on the National Register of Historic Places the following year.
Background.
The creation of nuclear weapons arose from the scientific and political developments of the 1930s. The decade saw many new discoveries about the nature of atoms, including the existence of nuclear fission. The concurrent rise of fascist governments in Europe led to a fear of a German nuclear weapon project, especially among scientists who were refugees from Nazi Germany and other fascist countries. When their calculations showed that nuclear weapons were theoretically feasible, the British and United States governments supported an all-out effort to build them.
These efforts were transferred to the authority of the U.S. Army in June 1942 and became the Manhattan Project. Brigadier General Leslie R. Groves, Jr. was appointed its director in September. The weapons development portion of this project was located at the Los Alamos Laboratory in northern New Mexico, under the directorship of physicist J. Robert Oppenheimer. The University of Chicago, Columbia University and the Radiation Laboratory at the University of California, Berkeley conducted other development work.
Manhattan Project scientists had identified two fissile isotopes for potential use in bombs: uranium-235 and plutonium-239. Uranium-235 became the basis of the Little Boy bomb design, first used (without prior testing) in the bombing of Hiroshima; the design used in the Trinity test, and eventually used in the bombing of Nagasaki (Fat Man), was based on plutonium. The original design considered for a weapon based on plutonium-239 was Thin Man, in which (as in the Little Boy uranium bomb) two subcritical masses of fissile material would be brought rapidly together to form a single critical mass.
Plutonium is a synthetic element with complicated properties about which little was known at first, as until 1944 it had been produced only in cyclotrons in very pure microgram amounts, whereas a weapon would require kilogram quantities bred in a reactor. In April 1944, Los Alamos physicist Emilio Segrè discovered that plutonium produced by the X-10 Graphite Reactor at Clinton Engineer Works contained plutonium-240 as an impurity. Plutonium-240 undergoes spontaneous fission at thousands of times the rate of plutonium-239, and the extra neutrons thereby released made it likely that plutonium in a gun-type fission weapon would detonate too soon after a critical mass was formed, producing a "fizzle"—a nuclear explosion many times smaller than a full explosion. The Thin Man design would therefore not work.
Project scientists then turned to a more technically difficult implosion design. In September 1943, mathematician John von Neumann had proposed surrounding a fissile "core" by two different high explosives which produced shock waves of different speeds. Alternating the faster- and slower-burning explosives in a carefully calculated configuration would produce a compressive wave upon their simultaneous detonation. This so-called "explosive lens" focused the shock waves inward with sufficient force to rapidly compress the solid plutonium core to several times its original density. The increase in density caused the core – previously subcritical – to become supercritical. At the same time, the shock wave activated a small neutron source at the center of the core, thereby assuring that the chain reaction would begin in earnest immediately at the moment of compression. Such a complicated design required substantial research and experimentation in engineering and hydrodynamics, and in August 1944 the entire Los Alamos Laboratory was reorganized to focus on this work.
Preparation.
Decision.
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.
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. Oppenheimer argued that the bomb "must be tested in a range where the energy release is comparable with that contemplated for final use." 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.
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:
 ;templatestyles src="Template:Blockquote/styles.css" / ;I did suggest it, but not on that ground ... 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 – and I am one – are one, / So death doth touch the Resurrection." That still does not make a Trinity, but in another, better known devotional poem Donne opens: "Batter my heart, three person'd God."
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. Stanley Kershaw, formerly from the National Safety Council, was made responsible for safety. Captain Samuel P. Davalos, the assistant post engineer at Los Alamos, was placed in charge of construction. First Lieutenant Harold C. Bush became commander of the Base Camp at Trinity. Scientists William Penney, Victor Weisskopf and Philip Moon were consultants. Eventually seven subgroups were formed:
The E-9 group was renamed the X-2 (Development, Engineering and Tests) Group in the August 1944 reorganization.
Test site.
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 radioactive fallout. Eight candidate sites were considered: the Tularosa Valley; the Jornada del Muerto Valley; the area southwest of Cuba, New Mexico, and north of 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 Area and San Nicolas Island in Southern California; and the sand bars of Padre Island, Texas.
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 Uzal Ent, the commander of the Second Air Force on September 7, 1944, lay at the northern end of the Alamogordo Bombing Range, in Socorro County near the towns of Carrizozo and San Antonio (). The Alamogordo Bombing Range was renamed the White Sands Proving Ground on July 9, 1945, one week before the test. Despite the criterion that the site be isolated, nearly half a million people lived within 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.
The only structures in the vicinity were the McDonald Ranch House and its ancillary buildings, about to the southeast. Like the rest of the Alamogordo Bombing Range, it had been acquired by the government in 1942. The patented land had been condemned and grazing rights suspended. Scientists used this as a laboratory for testing bomb components. 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. 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.
Lieutenant Bush's twelve-man 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. 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.
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. Freshwater was trucked in, per load, from away. Military and civilian construction personnel built warehouses, workshops, a magazine and commissary. The railroad siding at Pope, New Mexico, was upgraded by adding an unloading platform. Roads were built, and of telephone wire were strung. Electricity was supplied by portable generators. Bomb shelters to protect test observers were the most expensive to construct.
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.
Jumbo.
Responsibility for the design of a containment vessel for an unsuccessful explosion, known as "Jumbo", was assigned