The plutonium bomb, known in the West as "Joe-1", yielded about 22 kilotons and was closely modelled on the American Fat Man design, details of which had reached Moscow through spies including Klaus Fuchs. The physicist Igor Kurchatov led the scientific work; the secret-police chief Lavrentiy Beria ran the project. An American reconnaissance plane detected radioactive fallout days later, and on September 23 President Harry Truman announced the test, years earlier than many American officials had expected.
Stalin ordered an all-out effort to build a bomb after Hiroshima in August 1945. The project mobilised huge resources, including prisoner labour to mine uranium and build reactors. Beria, head of the NKVD, supervised it, and scientists understood that failure could be fatal. Intelligence from the Manhattan Project allowed the Soviets to copy a proven design rather than risk a new one.
The test tower stood on the steppe about 150 kilometers from the town of Semipalatinsk. Around it the engineers placed buildings, bridges, tanks, and animals to measure the effects. At 7:00 a.m. local time on August 29, 1949, the bomb exploded with a yield of about 22 kilotons.
The Soviet government made no announcement. A US Air Force WB-29 flying from Japan collected radioactive debris over the North Pacific on September 3, and analysts concluded that a bomb had been tested. Truman's announcement shocked the American public and helped push him to approve development of the far more powerful hydrogen bomb in January 1950.
Key people: Igor Kurchatov, Lavrentiy Beria, Joseph Stalin