By the end of World War II, Stalin’s spies had delivered the secrets of the atomic bomb to the Kremlin. This accelerated Moscow’s bomb project. When the Soviets detonated their first atomic ...

So it's an indication of the importance Stalin gave to the Soviet atomic bomb program that he appointed Beria to head it on August 7, 1945, the day after the U.S. dropped an atomic bomb on Hiroshima.

The chair of the Special Committee on the atomic bomb, Lavrentii Beria, arrived in the middle of August. He observed the assembly work and reported back to Soviet leader Joseph Stalin.