Trinity (nuclear test)

On July 16, 1945, at 5:29 a.m. Mountain War Time (11:29:21 GMT), the United States Army detonated the world’s first nuclear weapon in the New Mexico desert. This test, code-named “Trinity” by Los Alamos Laboratory director J. Robert Oppenheimer—possibly referencing John Donne’s poetry—was part of the Manhattan Project. The device, called the “gadget,” used an implosion design with a plutonium core, similar to the Fat Man bomb later dropped on Nagasaki, Japan, on August 9, 1945, though the two devices had some differences in design and casing. The test was deemed necessary because scientists worried the complex Fat Man design might fail.

Planned and overseen by Kenneth Bainbridge, the test took place on the Alamogordo Bombing and Gunnery Range, about 35 miles (56 km) southeast of Socorro, New Mexico, in the Jornada del Muerto desert. Just before the test, the area was renamed the White Sands Proving Ground. The only nearby structures were the McDonald Ranch House and its outbuildings, which served as a laboratory for bomb-component testing.

Concerns about a possible fizzle led to the construction of “Jumbo,” a steel container meant to contain the plutonium for recovery, but it was never used. On May 7, 1945, a rehearsal detonated 108 short tons (98 t) of high explosive with a small amount of radioactive material placed nearby. The Trinity bomb released energy equivalent to approximately 21 kilotons of TNT (88 TJ), and produced a large radioactive fallout cloud. Nearby residents were not evacuated; postwar radiation safety standards, informed partly by Trinity data, would have required evacuation at that distance.

A total of 425 people attended the test that weekend. Observers included Bainbridge, Oppenheimer, Vannevar Bush, James Chadwick, James B. Conant, Thomas Farrell, Enrico Fermi, Hans Bethe, Richard Feynman, Isidor Isaac Rabi, Leslie Groves, Philip Morrison, Frank Oppenheimer, Geoffrey Taylor, Richard Tolman, Edward Teller, and John von Neumann. The site was declared a National Historic Landmark district in 1965 and added to the National Register of Historic Places in 1966.

**Background**

Nuclear weapons emerged from scientific and political developments in the 1930s, a decade that saw discoveries about atomic structure and nuclear fission.