A little over four years after the United States conducted its first nuclear test Trinity Site in New Mexico, the Soviet Union followed suit, successfully testing their RDS-1 device (also called First Lightning, and “Joe-1” by the Americans) at the Semipalatinsk Test Site. The bomb was similar in yield and design to the American “Fat Man” bomb, unsurprisingly, as it was later revealed that the Soviets had access to a ring of atomic spies, who passed along technical information sometimes directly from Los Alamos.
The first Soviet experiment was similar to to the American one, although the scientists had structures (bridges, buildings, towers) built and caged animals placed around point zero, in order to study the effects of radiation on both. The test was conducted by a program headed by Igor Kurchatov, called the “father of the Soviet atomic bomb”. In September of 1949, Harry Truman announced that the U.S. had reason to believe “that within recent weeks an atomic explosion occurred in the U.S.S.R.” Most American officials had anticipated that several more years would pass before the Soviets acquired an atomic bomb, but with Joe-1, American weapons supremacy was crushed with one blast. Once this fact was confirmed, pressure mounted in both countries to develop an even deadlier weapon - a hydrogen bomb.