A ballistic missile is a type of missile that is propelled by a rocket engine and follows a ballistic trajectory. The term 'ballistic missile' is derived from the Greek word for 'throwing.' The term THOR is an acronym for 'Tactical High-speed Offensive Rocket, ' which is a type of ballistic missile developed by the United States in the 1950s. It was designed to be used as a short-range nuclear weapon and was capable of carrying a nuclear warhead.