Trinity: World's First Nuclear Test

The world's first nuclear explosion occurred on July 16, 1945, during the Trinity test. (Department of Energy)

The world's first nuclear explosion occurred on July 16, 1945, when a plutonium implosion device was tested at a site located 210 miles south of Los Alamos, New Mexico, on the plains of the Alamogordo Bombing Range, known as the Jornada del Muerto. The code name for the test was "Trinity."

Hoisted atop a 100-foot tower, a plutonium device, called "Gadget," detonated at precisely 5:30 am over the New Mexico desert, releasing 18.6 kilotons of power, instantly vaporizing the tower and turning the surrounding asphalt and sand into green glass, called "trinitite." Seconds after the explosion, an enormous blast sent searing heat across the desert, knocking observers to the ground.

Reports from witnesses came from as far as 200 miles away.  A forest ranger 150 miles west of the blast said he saw a flash of fire, an explosion and black smoke.  An individual 150 miles north said the explosion “lighted up the sky like the sun.” 

A U.S. Navy pilot flying at 10,000 feet near Albuquerque, New Mexico, said it lit up the cockpit of his plane and was like the sun rising in the south. When he radioed Albuquerque Air Traffic Control for an explanation, he was simply told, “Don’t fly south.”  After the test, the Alamogordo Air Base issued a press release that stated simply, “A remotely located ammunition magazine containing a considerable amount of high explosives and pyrotechnics exploded, but there was no loss of life or limb to anyone.”  The actual cause of the blast was not disclosed until after the U.S. bombing of Hiroshima, Japan, on Aug. 6. 

The success of the Trinity test meant an atomic bomb could be used by the U.S. military and it marked the start of the Atomic Age.

The Trinity Site is now part of the White Sands Missile Range and is owned by the Department of Defense. Ground zero is marked by an obelisk made of black lava rock, with an attached commemorative sign. A slightly depressed area several hundred yards across surrounds the monument, indicating where the blast scoured the ground. Only a few pieces of the green trinitite remain in a protected enclosure. 

Outside the fenced-in ground zero area lies Jumbo, the 214-ton steel container built to contain the plutonium, if the 5,300 pounds of high explosives in the bomb detonated but no nuclear explosion resulted. Ultimately, Jumbo was not used. 

The restored McDonald ranch house, where the device's plutonium core was assembled, is located about two miles to the south. The remnants of the base camp where some 200 scientists, soldiers, and technicians took up temporary residence during the summer of 1945 is about ten miles southwest of ground zero. 

Remnants of the observation points 10,000 yards out are also still visible.

The Trinity site is currently opened to the public by the National Park Service twice a year and tours are given by the Department of Defense on request:

A replica of the “Gadget,” the world’s first atomic bomb (courtesy photo).

Mushroom cloud from nuclear explosion 
On July 16, 1945, the world's first atomic bomb was detonated approximately 60 miles north of White Sands National Monument. (Army White Sands Missile Range photo)

Sources: US Air Force, US Army, Department of Energy and National Park Service