Lavrentiy Beria selected the Semipalatinsk steppe in the Kazakh SSR as the Soviet Union’s primary nuclear weapons test site, initiating construction and test preparations that would underpin decades of Soviet nuclear development.
The USSR detonated RDS-1 (U.S. codename “Joe-1”) at the Semipalatinsk Test Site, becoming the world’s second nuclear-armed state and accelerating the early Cold War arms race.
The USSR tested RDS-6s (“Joe-4”), a “layer-cake” design that combined fission and fusion processes, marking the Soviet program’s first major thermonuclear milestone.
The Soviet Union successfully tested RDS-37 at Semipalatinsk, widely described as its first true two-stage thermonuclear (radiation-implosion) device—an important step toward compact, deliverable megaton-class weapons.
The USSR detonated Tsar Bomba (RDS-220/AN602) over Novaya Zemlya, producing the largest nuclear explosion ever recorded and demonstrating extreme-yield thermonuclear design (primarily as a political and strategic signal).
The Partial Nuclear Test Ban Treaty (banning nuclear tests in the atmosphere, outer space, and underwater) entered into force, pushing U.S. and Soviet testing predominantly underground and reshaping verification and test-site engineering.
The Treaty on the Non-Proliferation of Nuclear Weapons (NPT) opened for signature; the Soviet Union was among the original nuclear-weapon-state signatories, committing (with other nuclear powers) not to assist additional states in acquiring nuclear weapons.
The Seabed Arms Control Treaty was signed, prohibiting emplacement of nuclear weapons and other WMD on the seabed beyond a coastal zone—part of a broader arms-control environment alongside ongoing underground test programs.
The Anti-Ballistic Missile (ABM) Treaty was signed by the United States and the Soviet Union, constraining nationwide missile defenses and influencing strategic calculations that interacted with warhead design, numbers, and testing priorities.
The USSR and U.S. signed the Threshold Test Ban Treaty, setting a 150-kiloton yield cap for underground nuclear weapons tests (with later implementation), shaping high-yield test planning and verification debates.
Mikhail Gorbachev announced a unilateral moratorium on nuclear test explosions, aiming to spur reciprocal restraint and advance broader arms-control negotiations during a period of intensifying U.S.–Soviet diplomacy.
After declaring the moratorium ended (citing lack of U.S. participation), the Soviet Union resumed nuclear testing—illustrating limits of unilateral restraint without mutual verification and political alignment.
The Nevada–Semipalatinsk anti-nuclear movement was founded in Kazakhstan, becoming a major civil-society force against testing at “the Polygon” and helping drive political pressure for test-site shutdown.
The Soviet Union carried out its final nuclear weapons test at Novaya Zemlya, after which testing ceased—an important practical endpoint to Soviet-era explosive testing before the USSR’s dissolution.
Kazakhstan’s leadership issued a decree closing the Semipalatinsk Test Site, ending operations at the USSR’s primary test range and creating a major symbol of post–Cold War test cessation and nonproliferation policy.
Soviet Nuclear Weapons Development and Testing (1949–1991)
