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But right after the Nazis were stopped at Stalingrad (Jan. 31, 1943) and the tide of battle turned, the Russians resumed atomic studies. They continued on a laboratory (but not an industrial) scale for the rest of the war. They may have heard about Enrico Fermi's achievement in Chicago (Dec. 2, 1942) of the world's first nuclear chain reaction. Espionage may have helped them. At any rate, they seem to have been convinced, long before the U.S. exploded its first atom bomb (July 16, 1945), that atomic weapons were well worth trying for.
"Far from starting ... at scratch in 1945," says the Rand report, "the Russians should not have been, by that time, too far behind the knowledge and skill that had been achieved in the United States . . . Instead of being surprised that the Russians got the atomic bomb as early as they did, we should perhaps have been surprised that it took them so long."