Courtesy of the Mississippi Department of Archives and History

In 1963 and 1964, at the height of the Cold War, tensions were high between the United States and the Soviet Union, as both nations stockpiled tens of thousands of nuclear devices.

Both countries had signed a treaty to stop testing nuclear devices on the surface or underwater, but the treaty did not cover underground tests.

Scientists didn't know if underground tests could reliably be detected by seismographs, so they did the only thing they could to find out: they detonated two nuclear devices deep underground in Mississippi.

In the photo, Henry G. Vermillion, office of information director for U.S. Atomic Energy Commission, details the area of the test site.

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Courtesy of the Mississippi Department of Archives and History

The plan was to detonate a 5.3 kiloton nuclear device inside a rock formation called the Tatum Salt Dome, about 2,700 feet underground.

It was believed that the first blast would create a cavity where a second, smaller nuclear device could be detonated without detection on the surface.

Here reporters and officials with the U.S. Atomic Energy Commission and Department of Defense gather to record the first blast.

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Courtesy of the Mississippi Department of Archives and History

Seismographs like this were used to detect underground nuclear tests, but this one may not have been needed to detect the first blast. It reportedly created a series of three shock waves rolling through the countryside that damaged property and injured cattle and other wildlife.

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Courtesy of the Mississippi Department of Archives and History

Horace Burge, who lived about two miles away from the test site, came home to a kitchen that looked as if it had been "ransacked," according to a report in the Hattiesburg American newspaper.

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U.S. Department of Energy

The tests took place in a lightly populated area of Lamar County, Miss., about 21 miles southwest of Hattiesburg. The location of the tests, near the town of Baxterville, became known as the Salmon Site. The project to detonate the first bomb was called Project Salmon, though the overall effort was called Project Dribble.

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Courtesy of the Mississippi Department of Archives and History

There were still people living in the area, though. About 400 people were paid $10 for adults and $5 for children to evacuate the area around the test site, and the shock waves from the first blast damaged a number of homes.

This photograph, originally printed in the Hattiesburg American newspaper, shows damage in the kitchen of Horace Burge, who lived approximately two miles from the test site.

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Courtesy of the Mississippi Department of Archives and History

The first test was scheduled for Oct. 9, 1964, but was pushed back several times to wait for favorable wind conditions, causing a lot of waiting around at the test site.

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Courtesy of the Mississippi Department of Archives and History

That created a lot of down time for the many people gathered at the site, including this Atomic Energy Commission worker who used one of the delays to catch a nap.

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Courtesy of the Mississippi Department of Archives and History

Finally, at 10 a.m. on Oct. 22, 1964, the first device was detonated inside the Tatum Salt Dome.

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Courtesy of the Mississippi Department of Archives and History.

A crowd of more than 50 reporters, politicians and observers gathered to watch the event from a command post about two and a half miles away from the blast site.

Reporters at the scene said the earth rolled and shook three or four times after the blast.

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This documentary film, called "Atomic Journeys: Mississippi," shows archive footage from the actual tests. According to the film, when a camera was lowered into the cavity created by the blast three and a half months later, the temperature inside the salt dome was still around 400 degrees Fahrenheit.

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Courtesy of the Mississippi Department of Archives and History.

The seismograph shows one of the shock waves from the Salmon blast.

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Courtesy of the Mississippi Department of Archives and History

Residents living near the blast site were allowed back into their homes some time after 1 p.m. Some did not like what they found.

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Courtesy of the Mississippi Department of Archives and History

Several photographs of Burge's kitchen survive in the online archives of the Mississippi Departmant of Archives and History, but he wasn't the only homeowner impacted.

The Atomic Energy Commission received more than 400 complaints of structural damage to homes the week following the first test. Local papers reported at least one home was determined to be uninhabitable after the blast.

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Courtesy of the Mississippi Department of Archives and History

Many residents at the time were not overly concerned about the testing. According to an Oct. 1, 1964 article in the Hattiesburg American, Claudette Ezell (pictured) was concerned that the tests would damage the "thousands of plaster of paris plaques she made as a hobby."

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Courtesy of the Mississippi Department of Archives and History

After the Oct. 22 blast, many residents complained to local newspapers later that the shocks from the explosion were larger than they had been led to believe. In this archived photo, an unnamed resident stacks pecans before the first detonation.

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Courtesy of the Mississippi Department of Archives and History

Several homeowners braced their chimneys and other vulnerable structures prior to the tests, as shown in this photo taken before the blast.

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Student Printz

"You could see trees moving up in the air," Purvis, Miss. native Tom Breshears said in a video interview with The University of Southern Mississippi's campus newspaper Student Printz.

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Courtesy of the Mississippi Department of Archives and History

On Dec. 3, 1966, two years after the Salmon blast, the Atomic Energy Commission detonated a smaller nuclear device in the cavity left behind inside the salt dome.

The blast, named Sterling, registered on seismographs "about 100 times weaker than would have been expected with the same sized bomb placed in solid rock or salt," according to the Mississippi historians.

The project had been a success and proved that it was possible to conceal underground nuclear tests by conducting them inside a large cave or cavity created by a prior explosion.

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Courtesy of the Mississippi Department of Archives and History

The AEC said that the radiation from the blasts was contained underground and did not pose a health risk to nearby residents.

The Department of Labor did, however, pay a total of $16.8 million to resolve health claims of people who worked near the test site, according to a 2015 story in the Sun Herald newspaper in Gulfport, Miss.

In the photo, Baxterville postmaster C. E. Bond comforts his dog, "Old Blu," after the first test blast.

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Courtesy UAB School of Public Health

The Department of Energy shut down the Salmon test site in 1971, fencing the property off from the public and installing groundwater wells for long-term monitoring.

The Department transferred the property to the state of Mississippi in 2010.

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Courtesy UAB School of Public Health

Students from the UAB School of Public Health visited the site in May 2018, as part of a two-week road trip through prominent public health-related sites in Alabama, Mississippi, Louisiana and Georgia.

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Courtesy UAB School of Public Health

This stone marker, installed by the Department of Energy, warns future generations not to drill at the site due to potential contamination deep underground.

For more information: UAB students visit nuke test site, TB sanitarium, other historic public health spots