Preamble to the nuclear age: How did the USSR steal the US nuclear secret?

**Prelude to the Nuclear Age: How the USSR Stole America's Nuclear Secret**

On August 2, 1945, in the German city of Potsdam, leaders of three nations that determined the fate of World War II — the former Soviet Union, the US, and Great Britain — gathered around a single table. Although the war had not yet officially ended, the victors were already busy deciding the fate of the postwar world.

It was during this time that US President Harry Truman, in a conversation with Soviet leader Joseph Stalin, whispered to him that America possessed a "weapon of unusual destructive force." Stalin immediately understood what Truman meant. However, neither surprise nor concern appeared on his face. He merely smiled faintly...

But what did Stalin know? Why did he not panic upon hearing Truman's secret message? The reason was that while the US was trying to keep its history's most secret and largest scientific project — the Manhattan Project — strictly confidential, Soviet intelligence had already managed to penetrate inside it.

### The "Manhattan Project": Beginning of a Great Secret

On August 13, 1942, a new entity called the "Manhattan Engineer District" appeared in US military documents. In reality, this was not just an ordinary military-administrative unit, but the official beginning of a top-secret nuclear weapon development program that fundamentally changed human history and later became famous under the name "Manhattan Project".

In fact, the project did not start from scratch. Its roots trace back to the research of the "Uranium Committee" formed in 1939 under the leadership of Lyman Briggs. In August 1939, concerned that Nazi Germany was close to unlocking the secrets of uranium fission, physicists Leó Szilárd and Eugene Wigner sent a letter to US President Franklin Roosevelt on behalf of the famous Albert Einstein. This appeal, which entered history under the name "Einstein–Szilárd letter", conveyed the scale of the threat to Washington and served as an impetus for giving attention to atomic research at the state level.

### Scientists Who Worked on the "Manhattan Project"

The project was managed in two directions. It was led by Robert Oppenheimer on the scientific side and General Leslie Groves on the military side. As a result of the project, three atomic bombs were created. They were: "The Gadget", "Little Boy", and "Fat Man".

Through this project, the US leadership aimed not only to bring World War II to an end, but also to achieve absolute military and political hegemony in the postwar world. However, those in Washington were still unaware that this "great secret" was already in the crosshairs of the intelligence of the USSR — an ally, but a potential future rival...

### Checkmate After Potsdam: The Kremlin's Nuclear Response

In the summer of 1945, the political map of the world changed fundamentally. On July 16, the first nuclear explosion in history was carried out at the Trinity test site located in the Jornada del Muerto desert in New Mexico. This event was not only the result of scientific research, but also a "trump card" in Washington's hand ahead of the approaching Potsdam Conference.

At Potsdam, when the new US President Harry Truman hinted to Soviet leader Joseph Stalin about a "new weapon of unprecedented destructive force", Stalin seemed to accept it calmly. But behind this composure lay deep concern. Because the Kremlin understood America's striving for sole dominance very well.

Just one day after the Potsdam meeting, more precisely on August 6 and 9, 1945, the "Little Boy" and "Fat Man" nuclear bombs dropped on the Japanese cities of Hiroshima and Nagasaki not only brought World War II to an end, but also became the prelude to the approaching "Cold War".

For Moscow, these explosions were seen not merely as a means to force Japan to surrender, but as a direct warning and demonstration of force aimed at the USSR. The strategic balance was disrupted.

The very next day after the attack on Hiroshima, by order of Stalin, a "Special Committee" with full powers to control the nuclear project was formed under the State Defense Committee of the USSR. Lavrentiy Beria, head of the NKVD who directed the entire intelligence and espionage network, was appointed to lead it. The scientific and technical research was led by the prominent physicist Igor Kurchatov.

Realizing that the USSR lagged several years behind the US through traditional research methods, Beria focused his main attention not only on his own scientists, but on intelligence. As part of the secret operation "Enormoz", a network of agents that penetrated deep into the "Manhattan Project" across the ocean was created by the NKVD and the Main Intelligence Directorate (GRU).

### Operation "Enormoz": Eyes Behind the Wall

Soviet intelligence had begun targeting the American atomic program back in 1942. The NKVD and GRU gradually formed complex espionage networks that penetrated the project's most important centers. They reached strategically significant sites such as Los Alamos, Oak Ridge, and the Metallurgical Laboratory at the University of Chicago.

To achieve this, they primarily used scientists and technical personnel who were politically sympathetic to communism or to the Soviet Union's war effort.

Many agents were motivated by ideological views, the desire to help the Soviet Union defeat Germany, and the goal of preventing America's sole dominance over nuclear weapons. Others were recruited under the influence of money or blackmail.

"The information coming from our agents in the United States is extremely valuable. They are allowing us not to waste years of labor and millions of rubles on useless research," Lavrentiy Beria stated.

Klaus Fuchs was one of the most important Soviet spies in the Manhattan Project, perhaps the most important. Electrical engineer Julius Rosenberg led a group of spies. This network included his wife Ethel, her relative David Greenglass, and the courier Harry Gold, who passed information.

Greenglass worked as a machinist at Los Alamos and supplied sketches and descriptions of the specialized explosive lens mold required for the atomic bomb's implosion mechanism.

This information allowed Soviet scientists to avoid the necessity of conducting research through years of trial and error.

"When we received intelligence about the Americans' work, it became clear that we were on the right track. This information helped us avoid many mistakes," Igor Kurchatov stated.

### The Soviet Union's First Nuclear Test

The information delivered by Soviet spies and scientists shortened the USSR's timeframe for creating atomic weapons by decades. On August 29, 1949, the testing of the first Soviet nuclear bomb, which resounded at the Semipalatinsk test site in Kazakhstan, shifted the balance of power in the world.

Washington enjoyed the "great secret" it had created and its absolute monopoly for only a short time. By creating a nuclear weapon, the Soviet Union led the world into a new and extremely dangerous era of the "Cold War"...