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Patrick Springer, Published May 31 2011

Thunder at dawn: Area veteran witnessed largest US nuclear bomb test ever

The eerie silence that immediately followed the blinding burst of light surprised Roger Stenerson each time he saw an atomic bomb explode.

He would line up in the predawn darkness with his fellow soldiers from the Army Chemical Center outside an observation bunker at the Nevada Test Site, the firing range for A-bombs.

Their vantage point, on the rim of a vast bowl called Yucca Flat in the high desert scrubland, was four miles from the steel tower used to detonate atomic weapons.

In the days before each blast, Stenerson and the others in his unit were busy lining up smoke pots linked by wires so they could be activated by remote control at just the right moment.

This was during the early 1950s, a hot phase of the Cold War, when the United States and the Soviet Union were locked in a race to develop nuclear weapons.

Military and civilian officials viewed nuclear war as grim but likely, and they were desperate to learn how people and structures might survive the ravages of an atomic blast.

The question Stenerson, the fellow soldiers in his unit and their civilian colleagues sought to answer: Would a thick screen of smoke provide meaningful protection from the incendiary heat of the blast?

Their “guinea pigs” were combustible materials, including strips of plywood, laid out on the desert like offerings.

As dawn was ready to break, the banter of the men waiting for the bomb to explode was abruptly interrupted by an announcer’s voice, carried by loudspeaker.

“One minute to detonation,” the voice said. Get ready.

It was March 17, 1953, and a blast code-named Annie was about to burst from its pedestal 300 feet above the desert floor with the force of 16,000 tons of TNT.

Closer to the bomb tower, crews had built “Doom Town,” a few suburban wooden houses occupied by families of mannequins – inanimate guinea pigs.

With less than a minute before detonation, the men were instructed to don their goggles, with nearly opaque welding-mask lenses to protect their eyes.

Those with ear plugs were reminded to put them in. Stenerson, who was told the explosion would sound like a thunderclap from that distance, didn’t bother with ear protection.

What’s a little thunder to the son of Norwegian immigrant homesteaders who battled the harsh elements on the plains surrounding Van Hook, N.D.?

“Ten, nine, eight … ”

“Bingo, the sky lighted up,” Stenerson said. “It was very, very bright, even with the goggles on. The heat was twice as warm as the sun.”

Then came the odd silence and the sensation of suspended time for a few moments.

The flash of light reached the men in an instant, but sound plodded behind at 768 mph, taking almost 19 seconds to arrive.

Traveling toward them with the shock wave of sound was an invisible bulge of air, which caused the desert ground to erupt like popcorn as it was stirred up by the pressure.

As the bomb’s thunderclap reached the men, it came with a gust of air that rocked the men back on their feet. In the distance, where the tower once stood, a signature mushroom cloud sprouted over the desert.

It was the first of six atomic bomb blasts Stenerson would observe that spring, a series of atmospheric tests code-named Upshot-Knothole.

But the detonations – some twice as powerful as the blasts that devastated Hiroshima and Nagasaki – were merely the prelude for a weapon much, much more powerful.

And Stenerson, now retired after a career of teaching high school physics and living near Glyndon, would play an intriguing volunteer role in what would be the biggest nuclear explosion ever unleashed by the United States.


Months before he became a spectator of atomic weapons tests, Stenerson had been teaching high school physics in Hunter, N.D.

He had been drafted during World War II but never inducted. But now the army wanted him, presumably because of his physics degree from Concordia College, and assigned him to the Army Chemical Center, a research base near Baltimore.

It was during the Korean War, and the government was intensifying its atomic weapons program. Stenerson was to become a small cog in a secretive scientific machine.

The radiation team’s laboratory was housed in a Quonset hut. Its neighbors included some of the elites of academic science and industry, including MIT and Texas Instruments.

A short time later, Stenerson was transferred to the Nevada Test Site, a remote government installation in the desert 65 miles northwest of Las Vegas.

He had “Q” security clearance, enabling him to handle top-secret information, but his role strictly involved fieldwork evaluating bomb effects rather than the weapons themselves.

“Nothing secret about it,” he said. “I never saw the intricacies of a bomb. They never used the word ‘bomb.’ They used the word ‘device.’ ”

His task involved measuring heat and collecting fallout particles at certain distances from atomic blasts.

Before each detonation, at varying distances from ground zero, Stenerson and his fellow soldiers deposited trays to collect fallout particles, as well as combustible materials to test the heat.

The aftereffects were impressive.

“At one mile, the temperatures were way up,” Stenerson said. “It scorched everything. It set everything combustible on fire. All the yucca plants, the cactus within a half-mile were scorched.”

But at a distance of five seconds from the blast, more than a mile away, the heat already had noticeably faded. “Like blowing out a candle,” he said.

Actually witnessing the explosions, which usually happened around dawn on a Friday morning, was the workweek’s entertainment. The soldiers and civilian scientists would park their cars and jeeps and then gather in clusters to watch the ultimate fireworks display.

“We’d go out there, sort of like going out to a football game,” he said. “We were just college kids, in a sense.”

Following each test, the men drove by jeep to the mess hall for breakfast. Then they would go out to pick up their radioactive test materials, wearing only canvas overalls and standard-issue boots.

After a few blasts, Stenerson and the others grew more nonchalant. They didn’t always wear their goggles for the blasts but held them in front of their eyes.

Before one detonation, Stenerson wrote his name in block letters on a strip of plywood, using aluminum tape. The exposed wood was scorched black, but the letters, covered by tape, retained its lighter shade.

At Hiroshima and Nagasaki, the intense heat from the atomic bombs triggered huge conflagrations. Many of the victims died from burns.

Many of those toiling at the Nevada Test Site thought it was unlikely such horrible weapons would ever be used again, Stenerson said. But the mood during the detonations always turned somber.

“I can’t remember anybody saying anything humorous or dramatic at all,” he said.

One of the bombs, Encore, was dropped from a B-50 bomber and detonated at an altitude much higher than the tower shots. The bomb glistened in the sunlight as it plunged toward earth, looking strangely beautiful.

The last shot Stenerson observed at the Nevada Test Site, Grable, was fired from a 280-millimeter canon, the first artillery atomic weapon.

The heavily publicized demonstration of firepower is credited by some historians with helping to achieve the ceasefire, struck two months later, to end the Korean War.

But the smokescreen tests Stenerson participated in had disappointing results. It was deemed impractical.

So smoke would offer no shield against Armageddon. And a bomb that would dwarf anything that erupted in the Nevada desert soon would be born.


A ring of tiny islands in the South Pacific called the Bikini Atoll would be the stage for a new era of nuclear weapons, the hydrogen bomb.

Stenerson found himself floating on a naval ship 20 miles south of the atoll, waiting for the H-bomb’s inaugural blast.

His job in what was dubbed Operation Castle was to assist with placing trays to collect radioactive fallout particles on the corral beaches of the tiny islands.

On the day of the detonation, March 1, 1954, he was aboard a small aircraft carrier used to launch helicopters flying missions associated with the test, code-named Bravo.

He stood on an enclosed upper deck and looked north toward the watery proving ground. Once again a voice on a loudspeaker provided narration.

The sky lit up with the familiar intense white light but lasted what seemed like a minute, compared to a few seconds, the flash duration of the A-bomb tests.

Stenerson’s ship remained south of the ring of islands, waiting for the radiation to dissipate. Unexpectedly, those onboard discovered the fallout cloud from Bravo had drifted overhead.

The men were told to go below deck to the mess to have coffee while crews doused the deck and other surfaces to wash away radioactive particles, and the ship immediately sailed away.

Unknown at the time, Bravo exploded with more than twice its predicted force, yielding a 15-megaton blast, the most powerful ever detonated by the U.S.

Before going to retrieve fallout collectors that had been prepositioned on some of the islands, the task forces of Castle-Bravo waited at least 48 hours for the radiation levels to subside.

The night before the retrievals, Stenerson volunteered to be one of the men to be dropped by helicopter on an island to collect the traps.

As his helicopter approached his designated island, eight miles east of ground zero, Stenerson and his partner saw thousands of dead fish and birds.

They hovered over the island, dropping a line with a sensor for a radiation reading, which they radioed back to their commander.

“You have two minutes to go and collect what you can; then get off,” the colonel said. If the pair remained 10 minutes, they were told, they would receive a lethal dose and would be dead within six months.

Luckily, a backup helicopter hovered nearby. Wearing shorts and short-sleeve shirts with thong sandals on their feet, Stenerson and his fellow soldier dashed over the corral sand, grabbing metal traps and stuffing them into belly sacks.

The tiny island was a wasteland, with palm trees stripped of their leaves, as if denuded by a hurricane. Dead fish washed up on the shoreline, and thousands of birds, all dead or dying of radiation poisoning, littered the island.

The dying birds’ heads drooped, blood dripping from their beaks. Stenerson and his partner sprinted to the collection racks, grabbed their trays, and scrambled back onto the waiting helicopter.

Estimated time on the ground: 90 seconds. Neither of the two soldiers spoke a word while they carried out their mission for nuclear science.

Back aboard the aircraft carrier, Stenerson was immediately taken to a shower, where he discarded his clothes and rinsed away any radioactive particles.

The radiation he was briefly exposed to on the Pacific island was estimated to be almost seven times what he was exposed to in the six shots he observed in the Nevada desert.


After his tour of duty, Stenerson settled near Glyndon, where he taught high school physics. He was originally drawn there to help a friend build the nearby Ponderosa Golf Course.

Now 85 and long retired, Stenerson and his wife, Joan, have three grown children. He is healthy and doesn’t believe he suffered any ill effects from his exposure to radiation.

As keepsakes of his service in Operation Upshot-Knothole and Operation Castle, he still has the canvas overalls and protective goggles he wore, along with a few other mementos, including the plywood with his name written by scorching atomic heat.

Over the years, he has told his stories of the blinding light and the rumble of thunder at dawn to science classes and community groups in the area.

“My wife probably wonders,” he jokes, “how she stayed married so long to someone radioactive.”


Readers can reach Forum reporter Patrick Springer at (701) 241-5522