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[a] (11:29:21 GMT) on July 16, 1945, as part of the Manhattan Project.

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.

[9] 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.

[10] In April 1944, Los Alamos physicist Emilio Segrè[11] discovered that plutonium produced by the X-10 Graphite Reactor at Clinton Engineer Works contained plutonium-240 as an impurity.

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.

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,[14] and in August 1944 the entire Los Alamos Laboratory was reorganized to focus on this work.

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.

"[c][19][20]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.

The site finally chosen, after consulting with Major General Uzal Ent, the commander of the Second Air Force on September 7, 1944,[25] lay at the northern end of the Alamogordo Bombing Range, in Socorro County near the towns of Carrizozo and San Antonio (33°40.636′N 106°28.525′W / 33.677267°N 106.475417°W / 33.677267; -106.475417).

[38] 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.

[23] They drew up specifications for a steel sphere 13 to 15 feet (3.96 to 4.57 m) in diameter, weighing 150 short tons (140 t) and capable of handling a pressure of 50,000 pounds per square inch (340,000 kPa).

[41][42] 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 25 miles (40 km) across the desert by crawler tractors.

[54] Herbert L. Anderson practiced using a converted M4 Sherman tank lined with lead to approach the 5-foot-deep (1.5 m) and 30-foot-wide (9 m) blast crater and take a soil sample, although the radioactivity was low enough to allow several hours of unprotected exposure.

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.

[76] In the final two weeks before the test, some 250 personnel from Los Alamos were at work at the Trinity Site,[80] and Lieutenant Bush's command had ballooned to 125 men guarding and maintaining the base camp.

[83][35] Shelters were established 10,000 yards (9,100 m) 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.

[92] 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.

It was feared that the danger from radiation and fallout would be increased by rain, and lightning had the scientists concerned about a premature detonation,[101] as had happened with a model of the electrical system.

These included Captain Deak Parsons, the associate director of the Los Alamos Laboratory and the head of Project Alberta; Luis Alvarez, Harold Agnew, Bernard Waldman, Wolfgang Panofsky, and William Penney.

It lighted every peak, crevasse and ridge of the nearby mountain range with a clarity and beauty that cannot be described but must be seen to be imagined ...[112]William L. Laurence of The New York Times had been transferred temporarily to the Manhattan Project at Groves's request in early 1945.

I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, 'Now I am become Death, the destroyer of worlds.'

[35] The Second Air Force issued a press release with a cover story that Groves had prepared weeks before, which described the explosion as the accidental destruction of a magazine on the base.

Weather conditions affecting the content of gas shells exploded by the blast may make it desirable for the Army to evacuate temporarily a few civilians from their homes.

[142] A newspaper article published the same day stated that "the blast was seen and felt throughout an area extending from El Paso to Silver City, Gallup, Socorro, and Albuquerque.

[146] The results of the test were conveyed to Secretary of War Henry L. Stimson at the Potsdam Conference in Germany in a coded message from his assistant George L. Harrison: Operated on this morning.

It stated: At 0530, 16 July 1945, in a remote section of the Alamogordo Air Base, New Mexico, the first full scale test was made of the implosion type atomic fission bomb.

The fallout there was reported to have settled in a white mist onto some of the livestock in the area, resulting in local beta burns and a temporary loss of dorsal or back hair.

[155][156][157][158] Dose reconstruction published in 2020 under the auspices of the National Cancer Institute[159] documented that five counties in New Mexico experienced the greatest radioactive contamination: Guadalupe, Lincoln, San Miguel, Socorro, and Torrance.

It featured many people involved with the project, including J. Robert Oppenheimer and Ernest Lawrence, as actors in re-creations of real discussions and events that led up to the Trinity test.