The Berlin Airlift began in June 1948, when the U.S.S.R. imposed a blockade on the sectors of Berlin occupied by the Western powers, and ended in May 1949 when the blockade was lifted. America and her capitalist allies flew supplies into the city daily, effectively foiling the blockade.
According to Paval Sudoplatov, Director of Red Army counterintelligence unit called SMERSH (acronym for 'Smertzy Shpyionam', or 'Death to Spies'), Stalin provoked the Berlin crisis deliberately to divert attention from the crucial struggle for power in China. Atomic espionage had proven as valuable to in the political and diplomatic spheres as it was in the military. Klaus Fuchs had provided key data on the production of uranium 235. Fuchs revealed that American production was one hundred kilograms of U-235 a month and twenty kilos of plutonium per month. From this information Soviet intelligence could calculate the number of atomic bombs possessed by the Americans. The Soviet Intelligence was able to determine that the United States was not prepared for a nuclear war with the Soviet Union at the end of the 1940s or even in the early 1950s.
That information helped to assure a Communist victory in China's civil war in 1947-1948. The Soviet Union was aware that President Harry Truman was seriously considering the use of nuclear weapons to prevent a Chinese Communist victory. Stalin initiated the Berlin crisis, blockading the Western-controlled sectors of the city in 1948. Western press reports indicated that Truman and Clement Attlee, the British prime minister, were prepared to use nuclear weapons to prevent Berlin's fall to communism, but the Soviet Union we knew that the Americans did not have enough nuclear weapons to deal with both Berlin and China. The American government overestimated our threat in Berlin and lost the opportunity to use the nuclear threat to support the Chinese nationalists.
In 1951, Soviet Foreign Minister Vyacheslav Molotov told Sudoplatov that the Soviet position in Berlin helped the Chinese Communists. Stalin pursued a tough policy of confrontation against the United States when the Cold War started; he knew he did not have to be afraid of the American nuclear threat, at least until the end of the 1940s. The Chinese Communist victory supported his policy of confrontation with America. Only by 1955 did we estimate the stockpile of American and British nuclear weapons to be sufficient to destroy the Soviet Union. 
- Pavel Sudoplatov and Anatoli Sudoplatov, Special Tasks: The Memoirs of an Unwanted Witness - A Soviet Spymaster, with Jerrold L. and Leona P. Schecter, Little Brown and Co., London 1994.