Seventy-two years ago Sunday, a group of scientists working for the United States government during World War II changed the world and how we think about warfare. They worked on a device that, just before dawn on July 16, 1945, in New Mexico, set off a nuclear chain reaction lasting a fraction of a second and altering the course of human history.
My grandfather, Edgar Tatum, was part of that effort.
As part of the boilermakers' union, he was sent from neighboring Kentucky to work on one of the two nuclear bombs that ended the war in the Pacific, traveling to Oak Ridge, Tennessee, along with 75,000 others who uprooted their lives to contribute -- without knowing what the ultimate objective of the project was -- to the US war effort. The city in eastern Tennessee was the headquarters for the Manhattan Project, a top-secret military venture aimed at developing the world's most devastating weapons.
The job needed experts in all crafts, and Granddaddy, as we called him, was a boilermakers' union steward for the effort to build the Hiroshima bomb, called "Little Boy," a small and simple uranium device.
Its counterpart, a complex, more powerful plutonium device and a precursor to the bomb dropped on Nagasaki called "Fat Man," was being developed and tested simultaneously in Los Alamos, about 1,400 miles away.
That early bomb, nicknamed "Gadget," was hidden among sand dunes in the vast New Mexico desert at the Trinity Site in what is now White Sands Missile Range. When tested on that July morning in New Mexico, it became the world's first nuclear bomb detonation.
"It was actually 5:29 and some seconds," Jim Eckles, a historian who started working in the White Sands Missile Range public affairs office in 1977, told CNN.
The plutonium device required a precise detonation of lens-shaped conventional explosives surrounding the plutonium core that would compress the plutonium into a critical mass and set off a chain reaction.
"Every neutron splits an atom, two neutrons come out they each split atoms, they split four more and it's a chain reaction, and it cascades and it all happens in a billionth of a second. Boom, you've got a nuclear explosion," Eckles said.
All that remains at ground zero of the explosion is a piece of metal protruding from the base of the tower that cradled the bomb over Trinity Site.
Because scientists were confident the simpler uranium device built at Oak Ridge would work, it was decided a detonation test was not necessary according to Eckles.
Grandaddy and his brothers went to enlist in the US Navy the day following the attack on Pearl Harbor, but a bout of scarlet fever as a child had left him with a heart murmur and prevented him from being able pass the military physical, so instead he went back to what he had been doing -- working as a boilermaker. In just a short period of time he was sent to Oak Ridge, my father, Mike Tatum, told me.
I grew up hearing stories about World War II from my father who would talk about Granddaddy's stories from working at Oak Ridge and his uncles who fought in Europe under General George Patton and in the Pacific -- including one uncle who was on the same battleship as Johnny Carson.
"Like all families, sons and fathers went all over the world in all branches of the military," my father recalled. "It was an all-out effort."
Oak Ridge remains a national laboratory in addition to a national historical park, and visitors can tour the industrial complex where they produced plutonium and developed uranium enrichment technology, among other things, according to the National Parks Services. Oak Ridge is nestled inside a valley, a short distance from the Clinch River between the rolling, tree-lined ridges of Tennessee.
The landscape around Trinity, however, is straight out of a Cormac McCarthy novel -- desolate, windswept and slightly radioactive. Project leader Robert Oppenheimer and his team of scientists assembled the core of the bomb in the master bedroom of a ramshackle house a couple of miles from ground zero.
Ranchers abandoned the land around the test site in 1942, when the US government took over the area for use as a training range for bomber crews.
The McDonald Ranch House, built in 1913, is still intact and is currently used as a museum during the site's twice a year open house.
The surrounding area remains an active military base. But on two days each year, visitors can tour the area, including the monument at ground zero and the ranch house.
Despite the powerful nuclear blast 72 years ago, background radiation on the site today is about the same as flying on a cross-country commercial flight, Eckles said.
"Where else can you walk on a nuclear test bed and an atomic bomb crater site?" Eckles said.
And where else can you walk on the site that marked the beginning of the end of the second World War and the start of a forever changed geopolitical landscape?