There are two authoritative books on the Soviet atomic project in English, which came out at about the same time; I have already read Richard Rhodes's Dark Sun, which also has the American hydrogen bomb as the main subject, and this is the other one. There is a dramatic story about young Soviet nuclear physicist Georgy Flyorov, who was a lieutenant in the Red Army during World War II, coming upon the abandoned science library of a university evacuated to the rear, reading American scientific journals and discovering that all the American nuclear physicists have suddenly stopped publishing. He concluded from this dog that didn't bark that the United States was working on an atomic bomb, and wrote a letter to Stalin proposing that the Soviet Union do the same. This story is actually true, but his letter was not why the Soviet Union launched an atomic project. The real reason was that an intelligence source, most likely John Cairncross, one of the Cambridge Five spy ring, indicated that the United Kingdom was doing it. Holloway says that in Stalin's Soviet Union, priority was only given to high-technology projects if it was known that capitalist Western countries were working on the same; in addition to the atomic project, Holloway cites examples from rocketry, jet engines and radar. If scientists set their own goals, they were potential spies or wreckers; Georgy Langemak, the rocket engineer who designed the Katyusha rocket launcher used with great success during World War II, was executed during the Great Purge on a trumped-up charge of "wrecking the adoption of new weaponry." This was the Communist version of the Confucian dictum, "a gentleman is not an implement."
It took about the same time for the Soviet atomic project headed by Igor Kurchatov to build the atomic bomb that it did for the American project headed by J. Robert Oppenheimer. Unlike the American project, the Soviet one took place in a country devastated by war, where around 27 million citizens had been killed; also unlike it, the Soviet atomic project could rely on as much prisoner (effectively, slave) labor as it needed, in particular for construction and for mining uranium. It also utilized the intelligence provided by atomic spies such as Klaus Fuchs and Alan Nunn May, although Holloway cites estimates that this only shaved a year or two off the schedule. The American project made use of scientists who fled Nazi-dominated Europe; the Soviet one employed German prisoners of war, but Holloway says that with one exception, they were not important for building the first Soviet atomic bomb. The first Soviet nuclear test, of a clone of the Nagasaki bomb, took place on August 29, 1949 at the Semipalatinsk Test Site in Kazakhstan. There is an urban legend that those who would have been shot had the test failed became Heroes of Socialist Labor, receiving the Soviet Union's highest civilian award, those who would have received maximum prison terms got Order of Lenin instead, and so on. Thus was the American nuclear monopoly broken. In September 1951 a bomb of indigenous Soviet design was tested; in August 1953 a bomb that may or may not be called the world's first hydrogen bomb, since the thermonuclear device exploded by the United States a year earlier was not a bomb; in November 1955 the first indubitably true hydrogen bomb, using a version of the Teller-Ulam design independently invented by Andrei Sakharov. The calculations for these were made on the Soviet Union's first electronic digital computers.
We now think of nuclear weapons as horrible things capable of destroying civilization. This only became true with the invention of the hydrogen bomb. Many American scientists opposed its development on these grounds; Holloway thinks that if the United States had abstained from developing it, the Soviet Union would have done so anyway, but the Americans would have quickly caught up. Many people in the Soviet leadership did not think of the atomic war as a no-no; Anastas Mikoyan declared in a speech at the 20th CPSU Congress that "a hydrogen and atomic war could lead to great destruction, but it could not lead to the annihilation of humankind or its civilization. It will annihilate an obsolete and pernicious system - capitalism in its imperialist stage." The world is so lucky it didn't come to that.