The SS-20, also known as the Pioneer, was a Soviet intermediate-range ballistic missile developed in the 1970s. It was designed to carry nuclear warheads and had a range of approximately 5,000 kilometers, allowing it to target various locations in Europe and Asia. The missile was mobile, making it harder to detect and destroy. The deployment of the SS-20 raised concerns during the Cold War, leading to tensions between the Soviet Union and NATO countries. In response, NATO initiated the Double-Track Decision in 1979, which involved both arms control negotiations and the deployment of new missiles in Europe to counter the SS-20 threat.