White Sands Missile Range Museum Archives.
Minor Scale test at the White Sands Missile Range utilized 4880 tons of ANFO to simulate an equivalent airblast of a tactical nuclear weapon. Photograph from the blast sequence of the Minor Scale test taken by US Army on 27 June 1985 at the White Sands Missile Range, NM.
In 1931, the Carey Salt Company opened an underground mine just outside Winnfield, Louisiana, that became one of the nation’s most important sources of salt. It came to employ about one hundred people and was a popular destination for local students on field days.
When the mine suddenly flooded in 1965, rumors spread that the flooding was the result of damage inflicted on the mine when the Atomic Energy Commission (A.E.C.) conducted nuclear tests there a few years earlier.
As it turned out, the A.E.C. did, in fact, detonate explosives in the Carey mine in 1959-1960 as part of a national defense study.
After WWII, the United States’ nuclear arsenal gave it a military edge over the Soviet Union, but the Soviets shocked the world in 1949 by detonating their own atomic bomb. The U.S. only detected it by discovering elevated radiation levels in the atmosphere. The world suddenly became a much more dangerous place as the two adversaries rapidly built up their nuclear arsenals.
Each side regularly conducted open air tests with their nuclear weapons, but such tests were easy to detect because radiation fallout was spread out over a large area. Testing soon moved underground to hide them from prying eyes.
There were concerns that the Soviets might be able to detect America’s underground tests by using seismic equipment to measure the shock waves sent through the Earth’s crust. But the RAND Corporation, a national security think tank, predicted that underground tests could possibly be hidden from our adversaries if they were conducted in an underground cavity (called a decoupled shot) rather than being tamped down in the Nevada desert (known as a coupled shot).
RAND’s theory was that a decoupled shot in an underground cavity would send less energy through the earth that could be detected seismically than a coupled shot where dirt and rock were tightly packed against the explosive device.
The A.E.C. chose to test the theory in Winnfield’s Carey Salt Mine. Between December 1959 and March 1960, at least fifteen explosive charges ranging from 20 to 2,000 lbs. of TNT were set off in an abandoned part of the mine. Some were coupled, or tamped, and set off in close contact with the salt dome, and some were decoupled in cavities ranging from 12 to 30 feet in diameter. To record the shock waves, seismic instruments were placed from close proximity to the explosions to many miles away.
In February 1960, one tamped, or coupled, shot of 1,000 lbs. of TNT was detonated at the bottom of a 727 ft. shaft. The explosion created fractures in the salt dome up to 45 feet long.
In comparison, an uncoupled charge of similar size was detonated in a 12-foot-diameter chamber, but it left fractures less than 2 feet long.
Such tests proved that a decoupled explosion in a hollowed out underground chamber was less likely to be detected seismically than a coupled one because the shock wave through the earth’s crust was smaller. In fact, a coupled, or tamped, shot produced a seismic signal 120 times larger than the same sized shot detonated in a cavity.
Project Cowboy proved that underground nuclear tests could be hidden by detonating them within a cavity, and RAND concluded that an underground explosion up to 20 KT (about the size of the Nagasaki bomb) could be held in existing underground cavities in Nevada without the Soviets detecting it. Theoretically, enlarged cavities could be made that would conceal a 100 KT test.
The U.S. and Soviet Union continued both open air and underground nuclear tests but turned more and more to underground blasts because they were more secretive, produced far less radioactivity contamination and actually provided better scientific information. In 1963, the nuclear powers (which also included Great Britain) signed the Limited Test Ban Treaty banning nuclear tests except for those underground. Later in 1996, all nuclear bomb tests were banned by the Comprehensive Nuclear-Test Ban Treaty.
The A.E.C. followed up Project Cowboy with Project Plowboy, which was to investigate the salt dome fractures caused by Cowboy’s underground explosions. Carey Salt Mine workers helped set up some of the instruments needed for the project and were told that the fractures were a result of a previous “atomic testing program.”
Apparently, some of the workers interpreted this to mean that actual atomic bombs had been detonated within the salt dome. We now know that is not true; in fact, no nuclear weapon has ever been detonated in Louisiana.
Dr. Terry L. Jones is a professor emeritus of history at the University of Louisiana at Monroe. An autographed copy of “Louisiana Pastimes,” a collection of the author’s stories, costs $25. Contact him at tljones505@gmail.com
