Soviet nuclear weapons
In the early parts of World War II, the Soviet Union conducted effective espionage, and, by late 1945, Joseph Stalin had ordered Operation Bododino, a committed attempt to build Soviet nuclear weapons.  Minister of State Security Lavrenti Beria, an effective manager if a brutal secret policeman, became the Party head of the program. The earliest study program had begun in 1939, under Igor Kurchatov. Kurchatov had become aware American and German physicists were disappearing from sight.
World War II
The United States intelligence community estimated 1950 as the first plausible bomb test date, the uncooperative Soviets prepared for the first static test at Semipalitinsk in late August 1949, with a 20 KT yield from an implosion fission device, the RDS-1, called "Joe-1" in the West.
They exploded RDS-2, also known in the U.S. as Joe-2, a device with a yield of 38 KT, in September 1951. RDS-3, a 42 KT airdrop, succeeded in October, and the Avangard Electromechanical Plant, opened in 1951 at the secret city of Arzamas-16, went into production in 1951, with a quota of 24 airdroppable variants of the RDS-1.
Movement toward thermonuclear
Soviet enhanced efforts went much further into what they called the Layer Cake design, called Alarm Clock in the U.S. and tamper boosting in the U.K. This was distinct from the Teller-Ulam design and the original Teller "super", being a series of concentric spheres of alternating fission, fusion, and tamper around a fission core.
Eventually, they also moved to the Teller-Ulam design, with the RDS-37 on at the 22 November 1955 test. Its 1.6 MT yield reduced from the design yield by decreasing the amount of fuel.
On October 30, 1961, the Soviets detonated the largest fusion device in history, RDS-202 or Tsar Bomba, with an actual yield estimated between 50 and 58 megatons, which again was reduced from the design yield of 100 MT. This was seen as psychological; there was little military need for such a weapon, given multiple bursts are generally more effective. There was, however, a period before accurate missile delivery was practical, and bombers had limited survivability, where both sides worked on large bombs; the U.S. did deploy the 25 MT Mark 41 (nuclear weapon) between 1960 and 1976.
Cold War balance
Russia was estimated, in 2009, to have 2080 tactical nuclear weapons, which is more than any other country. This has been a substantial reduction since 5390 in 1991. Eliminated completely were tactical weapons for the Army. The Navy’s tactical nuclear weapons are not deployed at sea under normal circumstances but stored on land; Russia does continue to keep nuclear torpedoes and depth charges in its inventory.
700 are dedicated to air and missile defense, missions for which other countries exclusively use conventional weapons. The remaining 650 are air-delivered bombs and air-to-surface missiles.
- Jeffrey Richelson (2006), Spying on the Bomb: American Nuclear Intelligence from Nazi Germany to Iran and North Korea, W.W. Norton, ISBN 8769393053838, pp. 62-67
- Richard Rhodes (1985), The Making of the Atom Bomb, Touchstone, ISBN 0686813785,p. 500-502
- Hans Kristensen (25 March 2009), Strategic Security Blog, Federation of American Scientists