Trinity Site, New Mexico

Content Cover Image

Trinity Site explosion, 0.016 second after explosion, July 16, 1945. Note that the viewed hemisphere's highest point in this image is about 200 meters high. (By Berlyn Brixner [Public domain], via Wikimedia Commons)


caption Trinity Site obelisk. The black plaque on top reads: Trinity Site Where The World's First Nuclear Device Was Exploded On July 16, 1945 Erected 1965 White Sands Missile Range J. Frederick Thorlin Major General U.S. Army Commanding The gold plaque below it declares the site a National Historic Landmark, and reads: Trinity Site has been designated a National Historical Landmark This Site Possesses National Significance In Commemorating The History of the United States of America 1975 National Park Service United States Department of the Interior (Source: By Samat Jain [CC-BY-SA-2.0 (], via Wikimedia Commons) Trinity Site, Alamogordo Bombing Range, New Mexico ( 33°40'30.00"N, 106°28'30.00"W) was the site of the first atmospheric atomic bomb test which took place on July 16, 1945. The test was part of the federal government’s top-secret program, the Manhattan Project—the United States’ war-time effort to create the first atomic bomb—and was conducted and overseen by the Manhattan Engineer District (MED). The test took place less than three years after the first demonstration of a controlled fission chain reaction by Enrico Fermi at the University of Chicago, Illinois on December 2, 1942.

The Los Alamos Scientific Laboratory (LASL), under contract to the MED, was in charge of much of the planning and testing that led up to the test at the Trinity Site. The Scientific Director of the Manhattan Project, Julius Robert Oppenheimer, along with a team made up of the day’s leading physicists including Fermi, designed two atomic bombs—one fueled by plutonium, and the other by uranium. However, before the atomic bomb could be used as a weapon of war, a test was needed outside of the laboratory. It was decided that the plutonium-fueled design would be tested at the Trinity Site.

The location of the Trinity Site was settled upon after careful evaluation by Oppenheimer and other Manhattan Project scientists. The site, located in the Alamogordo Bombing Range in the south-central New Mexico desert Jornada del Muerto (Journey of Death), measures 29 by 39 kilometers. The location, owned by the federal government, was chosen because of its good weather and distance from major population centers. The site still exists today in what is now named the White Sands Missile Range which is overseen by the United States Army.

The Testing of the First Atomic Bomb

At the time of the testing, much of the personnel were sheltered in three underground bunkers constructed of reinforced concrete. The bunkers were located to the north, south, and west, approximately 10,000 yards from ground zero. Each shelter was equipped with a radiological monitor for atmospheric testing during and after the detonation of the plutonium-fueled bomb. In addition to radiological testing, scientists were interested in the symmetry of the explosion as well as the amount of energy released from the device. Also, despite favorable weather conditions, which led the team to believe that any radiation released would be transported to the upper atmosphere, the U.S. Army was prepared to evacuate surrounding populations if necessary.

caption The Trinity Site blast. On July 15, 1945, final assembly of the atomic bomb, nicknamed “Gadget”, was complete. The device was placed atop a 100-foot tall firing tower. On the morning of July 16, 1945, the device was armed and set to detonate at 5:30 a.m. While the personnel waited in their assigned locations, many were nervous not only about what would happen when the bomb exploded but whether the bomb would explode at all. Yet at 5:30 a.m. sharp, the atomic bomb exploded as scheduled. The explosion vaporized the tower, sent waves of heat across the desert site, and created an orange and yellow fireball which settled into the well-know mushroom shape associated with the atomic bomb. Shockwaves from the explosion were felt as far from the site as 160 miles, and although the project was still being kept top-secret, it was clear to the public that something had happened that day. However, the event would not be disclosed until after the U.S. bombings of Japan which began only three weeks after the Trinity Site test.

The Bombings of Japan

Although the uranium-fueled atomic bomb had not yet been tested, the U.S. detonated this design of the bomb over the city of Hiroshima, Japan on August 6, 1945. Three days later, on August 9, the U.S. detonated another atomic bomb over Nagasaki, Japan. This time it was a plutonium-fueled device, identical to the one tested at the Trinity Site. Only days after the bombings of Hiroshima and Nagasaki, the Japanese stated their intentions to end the war. It was not until September 2, 1945 that the Japanese government officially surrendered and World War II came to a close. While the events at the Trinity Site on July 16, 1945 were truly momentous and ground-breaking, the nuclear events that followed would leave an even greater mark on the history of humankind.

Further Reading



Angelo, L. (2014). Trinity Site, New Mexico. Retrieved from


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