Roger Rasmussen stood at the base of the Oscura Mountains staring at a boiling cloud of ash and smoke rising up in southern New Mexico’s Jornada del Muerto desert. It was 5:30 a.m. on July 16, 1945.

Not a minute before, Rasmussen had been face down on the ground, arms over his head and eyes shut, waiting for the blast that would soon lead to the end of World War II and hearken the dawn of the nuclear era.

“I was buried, eyes shut tight, and it was bright like daylight,” he said during an April interview at the Los Alamos Historical Museum in New Mexico. “It all boiled up and I could see all the colors.”

He added, “They told us and I knew it was over, so I got up and pretty soon the ground shock, this big arc, came over across the flat plain and that fascinated me.

“I was looking off in the distance and couldn’t see anything until the blast showed up, that boiling cloud,” he said. “It was easily visible out there.”

Rasmussen, 94, witnessed the world’s first nuclear bomb detonation just seven months after his arrival at the Los Alamos Laboratory in January 1945. He was in Los Alamos as part of the United States Army’s special engineering detachment to the Manhattan Project.

This year marks the 70th anniversary of the Trinity test of the plutonium bomb designed and built as part of the United States’ secret Manhattan Project.

The Trinity Site is located at the U.S. Army’s White Sands Missile Range and is generally open to the public twice a year. This year, thousands visited the site on April 4, and more will have an opportunity to visit the site on Oct. 3.

Visitors to the site walk around the blast’s ground zero, marked by a black lava obelisk and remnants of one of the footings from the steel tower the bomb was mounted on. The rest of the tower was vaporized by the blast.

Two miles away, visitors can walk through the McDonald ranch house where the bomb’s plutonium core was assembled.

The test ultimately led to the bombings of Hiroshima on Aug. 6 and Nagasaki on Aug. 9.

Rasmussen said he learned of the United States’ use of the atomic bombs on Hiroshima and Nagasaki when Japan’s surrender was announced on Aug. 14.

“All I could think of was thank God it’s over,” he said.

“I was so grateful that it was a surrender and not a (U.S.) invasion,” he continued. “I was just afraid we would have to do the same thing we did in Europe. That was gruesome.”

Rasmussen had enlisted in the U.S. Army at 21 after Japan’s attack on Pearl Harbor. He was originally trained for combat, most likely to be deployed to Europe, he said, but then sent to learn electrical engineering instead. Prior to enlisting, Rasmussen had studied physics in college.

After he finished the program in December 1944, he was put on a train heading west out of Morgantown, West Virginia, but didn’t know where he was being sent or what he would be doing.

“I had no idea, really, where I was,” Rasmussen said. “The secret orders were in the hands of the sergeant in charge, who was one of us that came out. I didn’t know anything about this place (Los Alamos) or what was going on.”

Once in Los Alamos, Rasmussen said he was assigned to build electronic equipment, working from diagrams he described as “crude by today’s standards.”

Aside from the work he did, he knew little else about the project. Workers on different parts of the project tended not to mingle and were discouraged from discussing their work with others, he said.

However, rumors and suspicions circulated and Rasmussen said he was pretty sure he knew what the project was before the July 16 test.

“You can’t really keep a secret when everybody is jammed in,” he said.

Late at night on July 14, Rasmussen said he and seven other soldiers were transported from Los Alamos down to a spot at the foot of the Oscura Mountains, tasked with evacuating residents from the area. He estimates they were roughly 6 to 8 miles east of the Trinity test site.

It rained hard the following night, but the weather cleared early in the morning on July 16 while it was still dark. The group was told to lie on the ground and wait for instructions to talk or stand.

And then came the blast.

“Thinking back all those years, I know I was more excited at the time,” Rasmussen said. “I’m more laid-back now, after all these years, but it was an experience.”

Rasmussen continued working in Los Alamos on nuclear-related projects for more than 35 years, and stayed involved even after retiring in 1982.

But despite devoting his life working in the field, Rasmussen acknowledges that one of the biggest threats to the world now is nuclear.

“The genie’s out of the bottle and look what’s happening right now,” he said. “Here we are 70 years later and the world’s in an uproar.”

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