29 August 1949 - First Soviet nuclear test

29 August 1949 - First Soviet nuclear test

On 29 August 1949, the Soviet Union conducted its first nuclear test, code-named 'RDS-1', at the Semipalatinsk test site in modern-day Kazakhstan. The device had a yield of 22 kilotons.

The bombings of Hiroshima and Nagasaki in 1945 had prompted Joseph Stalin to order the development of nuclear weapons within five years. The young nuclear physicist Igor Kurchatov was charged with leading this project.

It was no coincidence that the RDS-1-device bore a close resemblance to the U.S. ‘Fat Man’ bomb dropped on Nagasaki, as Soviet espionage had managed to obtain details about the U.S. Manhattan Project and the ‘Trinity’ test on 16 July 1945. The Soviet device was therefore also a plutonium-based implosion device.

The fallout from the nuclear test drifted to the northeast, reaching the region of Altai Krai. Traces from it were also detected by the United States, altering it to the fact that its monopoly on nuclear weapons had been broken, which was public confirmed by U.S. President Truman on 23 September 1949 and a day later by the Soviet Union itself.

Within a few years, the Cold War nuclear arms race was at full steam. In 1951, the United States exploded the first thermonuclear device in the ‘George’ test, to be followed two more years later by the Soviet Union with the RDS-6 test. Until the end of the Cold War, the United States would conduct 1,032 nuclear tests, the Soviet Union 715.

The Soviet Union conducted 456 of its tests at the Semipalatinsk test site, with severe consequences for the local population, including high cancer rates, genetic defects and deformations in babies. Read more on the effects of Soviet nuclear testing.

After its independence from the Soviet Union, Kazakhstan closed the test site on 29 August 1991, exactly 42 years after RDS-1. On the initiative of Kazakhstan, the United Nations proclaimed 29 August as the International Day against Nuclear Tests in 2009.


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23 September - Last U.S. nuclear test