any of several nuclear warheads carried on the front end, or “bus,” of a ballistic missile. Each MIRV allows separately targeted nuclear warheads to be sent on their independent ways after the main propulsion stages of the missile launch have shut down. The warheads can be released from the bus at different speeds and on different trajectories. MIRV technology was first developed by the United States. By the late 20th century both the United States and the Soviet Union had many intercontinental and submarine-launched ballistic missiles equipped with MIRVs.