Many Germans in what would become East Germany were forced by the Communist authorities to work in German uranium mines producing the majority of the raw material of the Soviet atomic bomb project.[16] Beginning in the summer of 1946 the Soviets began explorations in the Erzgebirge, and sealing off the old radium hot springs by September of the same year. An initial workforce of four to five thousand was established, with another 20,000 called for by the end of the year. The work was dangerous and stressful and the Soviets made no effort to improve it; as a result the mines became filled with forced labor conscripts and has been compared to a death march and the Gulags of Kolyma.