The 70 years during which Russia was known as the Soviet Union were frightening—not just for so many Russian citizens, but throughout the world. Many Americans in particular were afraid that the Soviet’s development of nuclear weapons meant the imminent destruction of the country.

Luckily, the Cold War as we knew it is over, and Russia itself is a much different place. Yet when you consider what the Soviet government was doing in secret, it becomes clear that we had every reason to be nervous!

The long-running arms race between the Soviet Union and the United States throughout the Cold War has been well-documented. For many frightening years in the 20th century, two of the world’s greatest “superpowers” competed for nuclear superiority.

U.S. National Archives and Records Administration / Wikimedia Commons

Yet what many people don’t know is that Soviet development of nuclear weapons began as early as 1942—while World War II was still ongoing and before the infamous bombings in Japan. Even fewer likely know how how far the Soviet Union actually went…

Hohum / Wikimedia Commons

It wasn’t until two weeks after August 6, 1945—when the atomic bombs that were dropped on Hiroshima and Nagasaki, Japan, effectively ended the war—that the Soviet government decided to ramp up its efforts to match the United States in terms of atomic weaponry.

509th Operations Group / Wikimedia Commons

A team of experts, lead by the People’s Commissar of Internal Affairs, Lavrentiy Beria (pictured), was established. With a massive budget, they were tasked with quickly developing nuclear weapons that would rival the United States. On August 29, 1949, they performed their first successful test of an atomic bomb.

Poeticbent / Wikimedia Commons

Soviet nuclear research hardly ended there, though; with that came an increased need for plutonium, so two special plants were constructed. Yet there was still one problem: both of these were above-ground. What would happen if they were attacked?

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In 1950, Beria wrote a letter to Joseph Stalin himself, describing the need for a facility in the mountainous region of Krasnoyarsk Krai. It would be located deep underground to protect the plutonium and other dangerous materials. The dictator obliged, and soon Combine No. 815 began construction.

The Soviet government relied on cheap miners and other laborers—even prisoners—from around the taiga to complete the project in the mountains bordering the Yenisei River. Just a year into the construction of the facility, close to 30,000 people had already worked on it.

For 24 hours each day, seven days per week, workers tirelessly pushed deeper and deeper into the mountain’s surface. Their goal? To eventually reach a depth of 200 to 230 meters, or roughly 656 to 754 feet.

In the middle of the mountain, a massive, 72-meter (236-foot) camera was built to monitor the project. Even with this constant oversight, though, the construction continued for several years. It wasn’t until 1956 that tunnels for transportation were created.

Finally, by August 28, 1958—almost exactly eight years after the project was started—Combine No. 815 was operational, although it was renamed the Mining and Chemical Combine. Located deep in a Siberian mountain, its sole purpose was to produce plutonium.

For many years, while shrouded in secrecy, weapons-grade plutonium was shaped into nuclear warheads capable of mass destruction. But for many around the world, especially the Soviet Union’s rival, the United States, it would have seemed like a nightmare.

Even without the weapons being built inside, the facility itself was quite an impressive feat of engineering. The mountain was protected by a 200-meter layer of granite that could have withstood a nuclear blast!

The Mining and Chemical Combine even featured a real railway that worked similarly to a New York City subway, except it was used more for transporting materials throughout the plant than people.

The Mining and Chemical Combine was located near Zheleznogorsk, a “closed city” in Krasnoyarsk Krai that was forbidden for ordinary Soviet citizens. It was actually surrounded by barbed wire to keep strangers out.

This region, known as “Krasnoyarsk-26,” was largely kept secret from the Soviet people until the start of the “Glasnost” era in the late-1980s, when the government made a greater effort towards transparency. Before, it wasn’t even shown on official maps!

Somewhat strangely, while Zheleznogorsk was “closed,” it was reportedly not an uncomfortable place to live. The entire project was well-financed, and the living quarters offered homes that were typical of other Soviet houses of the day.

As a matter of fact, those living in Zheleznogorsk may have had it even better than their fellow citizens in the rest of the Soviet Union! They had plenty of food, department stores to buy just about anything they needed, and even a lower crime rate.

Of course, it was difficult for non-residents to move freely through the region’s borders. Plus, Zheleznogorsk couldn’t remain a secret forever. The CIA even published reports about a secret plutonium facility somewhere in Krasnoyarsk as far back as 1962.

MaxBioHazard / Wikimedia Commons

While American intelligence regarding such a facility was certainly correct, the exact location of the Mining and Chemical Combine remained a mystery. In April 2010, with the Cold War effectively over, the project was finally—permanently—shuttered.

Now that the dust has settled, we can look at the Mining and Chemical Combine as the extraordinary feat of human ingenuity as it was. It may have been intended for unsavory purposes, but that doesn’t change the inventiveness involved!

It’s amazing that this project went on for so long that, by the time it was revealed, it was no longer a viable threat. What a relief!

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