- On July 16, 1945, at 5:29 a.m., the first nuclear weapon test in history was conducted near Socorro, New Mexico.
- For years a team of some of the world's greatest scientists had labored in secret to make the weapon in a New Mexico base. It was codenamed the Manhattan Project.
- Years later in interviews with the Atomic Heritage Foundation and publications, those who witnessed the first nuclear explosion described their awe and terror.
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Before the world's first nuclear weapons test, the scientists who created the atom bomb debated whether the explosion might be so powerful that it would ignite the atmosphere and destroy life on Earth.
The physicist J. Robert Oppenheimer — who would later be appointed the leader of the team making the bomb — was so concerned that he even took his concerns to Arthur Compton, a fellow Nobel laureate and one of the key members of the team.
"It would be the ultimate catastrophe," Compton recalled years later, according to Scientific American. "Better to accept the slavery of the Nazis than to run the chance of drawing the final curtain on mankind!"
But after Compton calculated the chance of the explosion destroying the world was about one in 3 million, the top-secret project, which came to be known as the Manhattan Project, went ahead.
US Department of Energy
When top scientists and military chiefs assembled in the desert near Socorro, New Mexico, to watch the first nuclear explosion on July 16, 1945, many were nervous. No one, after all, knew for sure what would happen.
Elsie McMillan recalled the thought processes of her husband, the physicist Edwin McMillan, before the test.
"We know that there are three possibilities," she said in an interview with the nonprofit Atomic Heritage Foundation, which has collected many eyewitness accounts of the day. "One, that we will all be blown to bits, if it is more powerful than we expect. If this happens, you and the world will be immediately told. Two, it may be a complete dud. If this happens, you will also be told. Third, it may as we hope be a success. We pray without loss of any lives.
"In this case, there will be a broadcast to the world with a plausible explanation for the noise and the tremendous flash of light which will appear in the sky."
Nicknamed Gadget, the bomb had been three years in the making. At 10 p.m. local time on July 15 it was winched to the top of a metal tower 800 meters from the ground zero site Oppenheimer had named Trinity, after a poem by the 17th-century English writer John Donne.
The team originally planned to detonate the bomb at 4 a.m., but a passing storm caused delays, and it wasn't until just before 5:29 a.m. that the countdown began.
AP Photo/Eddie Adams
"There was a countdown by Sam Allison, the first time in my life I ever heard anyone count backwards," recalled the physicist Marvin Wilkening, who watched the explosion from a shelter about 20 miles away with top scientists and military chiefs.
"We used welder's glass in front of our eyes, and covered all our skin. When the countdown ended, it was like being close to an old-fashioned photo flashbulb."
Brig. Gen. Thomas F. Farrell was astonished by how "the whole country was lighted by a searing light with the intensity many times that of the midday sun."
He continued: "It was golden, purple, violet, gray, and blue. It lighted every peak, crevasse, and ridge of the nearby mountain range with a clarity and beauty that cannot be described but must be seen to be imagined. It was that beauty the great poets dream about but describe most poorly and inadequately."
While some witnesses were stunned by the terrible beauty of the explosion, others were terrified by its raw power.
"It was the most shocking, enormous explosion that I had ever seen. I was about 20 miles away from the site. We were supposed to keep our eyes closed for the first 10 seconds because of ultraviolet radiations," recalled William Spindel, a member of the Special Engineer Detachment.
"I estimated that at 20 miles away, the explosion traveling at the speed of sound would take about a minute to reach me. It was the most intimidating minute I have ever spent.
"Seeing the terrible ball, growing and growing, enormous colors. What kind of blast could it be when it finally got to me? Fortunately, it wasn't that great because I'm still here."
Roger Rasmussen, another member of the Special Engineer Detachment, remembered in his interview with the Atomic Heritage Foundation: "The brightest light came that I had ever observed with my eyes closed. That was the detonation, but there was no noise and no sound and nothing to see until our troop master said we could look up.
"We stood up and looked into this black abyss ahead of us. There was this beautiful color of the bomb, gorgeous. The colors were roving in and out of our visual range of course. The neutrons and gamma rays and all that went by with the first flash while we were down. There we stood, gawking at this."
It was not just the spectacle of the mushroom cloud as it rose before them that struck the spectators that day, but the terrifying realization that they had created a weapon more powerful and more deadly than any other in history.
Asked to describe his reaction to seeing the explosion, Oppenheimer quoted a verse from the Bhagavad Gita, a Hindu devotional text.
"Now I am become Death, the destroyer of worlds."