Just as the Second World War was wrapping up, the United States made a huge technological breakthrough: the atomic bomb. Through the Manhattan Project, the US had researched a weapon that changed the geopolitical landscape with its destructive capability, and they created an atomic bomb arms race cold war. While WWII saw Russia and the United States as allies, by the time the war was over, the world was already shifting to them becoming rivals. Unfortunately, that meant the Soviet Union had a lot of ground to catch up. If they wanted to compete with the United States, they were going to have to develop their own nuclear arsenal.
How they achieved that goal, however, is a story full of hard work, intrigue, and espionage. Just like any Cold War race, the Soviet Manhattan Project – the Soviet Union's quest to obtain a nuclear weapon better than the Americans' – was filled with drama. And the results were truly frightening, culminating in the largest nuclear detonation in the history of the human race.
Four years after the end of World War II, in 1949, the Soviet Union exploded its own atomic bomb. The test was code named "First Lightning." While the Russians were certainly on their way to developing an atomic bomb, a physicist by the name of Klaus Fuchs passed the American's atomic secrets to the Soviets, which sped up the process. In fact, the plans were so detailed that that first bomb the Russians detonated was a copy of the first American A-Bomb. There are also rumors that spies stole other documents and supplied them to Russian scientists. By 1951, the Soviets were detonating their own versions of the atomic bomb.
Even though the Soviets had managed to create an atomic bomb quickly, such haste was not without its drawbacks. The production system to create the first bomb was not streamlined at all and was actually quite hazardous. Realizing that they were working off a shaky foundation, the scientists spent time reexamining the fundamentals of their program so they could safely recreate their results. The culmination of that effort was the detonation of "Joe-2" in 1951, which was even more powerful than their first attempt.
When Russian spy Klaus Fuchs confessed to his crimes in January 1950, his revelations ousted another spy who was located in New Mexico: Harry Gold. The FBI tracked Gold down and arrested him, resulting in him being sentenced to 30 years in prison. When Gold confessed to his crimes, that put the FBI on the trail of two infamous Russian spies: Julius and Ethel Rosenberg. Their colleague David Greengrass had given them detailed documents and drawings he had made by hand. The Rosenbergs were eventually arrested, and they denied everything. They were executed in 1953. Greengrass, however, cooperated with the authorities and was only sentenced to 15 years in prison.
The first atom bombs utilized fission to create their explosions, which essentially boils down to one piece of material shooting into another to split an atom inside the bomb. The Soviets, however, developed a new method with their fourth weapons test in 1953. "Joe-4," as it would be known in the West, had a core of Uranium-235 surrounded by alternating layers of fusion fuel and fusion tamper inside a highly explosive implosion system.