The Soviet Union tested its first atomic bomb in 1949. The device, known as RDS-1 or First Lightning, was detonated on 29 August 1949 at the Semipalatinsk Test Site in the Kazakh Soviet Socialist Republic, producing an estimated yield of 22 kilotons of TNT.
The test ended the United States’ exclusive possession of nuclear weapons, which had begun with the American Trinity test in July 1945. U.S. intelligence had expected the Soviet program to take several more years, so the explosion came as a strategic and political shock in Washington. American aircraft detected radioactive evidence from the test in early September.
RDS-1 was an implosion-type plutonium device influenced by information obtained through Soviet espionage and by the study of the American Fat Man bomb. Soviet scientists, including Igor Kurchatov and Yulii Khariton, led major parts of the weapons effort, while Lavrentiy Beria oversaw the secret program.
The test accelerated the nuclear arms race and increased pressure on the United States to develop a hydrogen bomb. It is sometimes confused with the first U.S. atomic test, Trinity, which took place in 1945.