The first nuclear test was supposed to be a fizzle. The Los Alamos scientists had calculated the most likely yield of the plutonium implosion device at 5 to 10 kilotons, with the outer edge of any realistic prediction around 20. The “Gadget,” detonated at 5:29 a.m. Mountain War Time on July 16, 1945 at the Trinity Site on the Alamogordo Bombing Range in central New Mexico, produced a yield of about 21 kilotons — right at the top of the most optimistic estimate — the largest man-made explosion ever recorded up to that point.
The site was the Jornada del Muerto — the “dead man’s journey” stretch of Chihuahuan Desert — selected by Oppenheimer in late 1944. It met the requirements: flat, dry, remote, and accessible to Los Alamos. A 100-foot steel tower was erected on the desert floor, with base camps, instrumentation bunkers, and a 10,000-yard control bunker built into the sand. For context, see the Manhattan Project and the atomic bomb.
The Gadget was assembled on site. The plutonium core — 6.2 kg of nearly pure Pu-239 produced at Hanford — was installed on July 13. Rain delayed the test; the originally planned date of July 16 held. At 5:10 a.m. the countdown began, final safety check was completed at 5:29 a.m.
The blast vaporized the steel tower and fused the desert sand into a green glass — trinitite — found in fragments for decades. The fireball was visible 250 miles away. The blast wave was recorded at 100 miles. Oppenheimer later recalled a line from the Bhagavad Gita: “Now I am become Death, the destroyer of worlds.” Test director Kenneth Bainbridge told him, “Now we are all sons of bitches.”
Trinity validated the implosion design used in “Fat Man.” The gun-type design of “Little Boy” was untested when dropped on Hiroshima; the U.S. command accepted that risk because the design was judged too simple to fail. The Trinity Site, on what is now the White Sands Missile Range, is open to the public twice a year.