In March 1976, the Soviet Union first deployed the RSD-10 Pioneer (called SS-20 Saber in the West) in its European territories, a mobile, concealable intermediate-range ballistic missile (IRBM) with a multiple independently targetable reentry vehicle (MIRV) containing three nuclear 150-kiloton warheads. The SS-20's range of 4,700–5,000 kilometers (2,900–3,100 mi) was great enough to reach Western Europe from well within Soviet territory; the range was just below the SALT II minimum range for an intercontinental ballistic missile, 5,500 km (3,400 mi). The SS-20 replaced aging Soviet systems of the SS-4 Sandal and SS-5 Skean, which were seen to pose a limited threat to Western Europe due to their poor accuracy, limited payload (one warhead), lengthy preparation time, difficulty in being concealed, and immobility (thus exposing them to pre-emptive NATO strikes ahead of a planned attack). Whereas the SS-4 and SS-5 were seen as defensive weapons, the SS-20 was seen as a potential offensive system.
The US, then under President Jimmy Carter, initially considered its strategic nuclear weapons and nuclear-capable aircraft to be adequate counters to the SS-20 and a sufficient deterrent against possible Soviet aggression. In 1977, however, Chancellor Helmut Schmidt of West Germany argued in a speech that a Western response to the SS-20 deployment should be explored, a call which was echoed by NATO, given a perceived Western disadvantage in European nuclear forces. Leslie H. Gelb, the US Assistant Secretary of State, later recounted that Schmidt's speech pressured the US into developing a response.
On 12 December 1979, following European pressure for a response to the SS-20, Western foreign and defense ministers meeting in Brussels made the NATO Double-Track Decision. The ministers argued that the Warsaw Pact had "developed a large and growing capability in nuclear systems that directly threaten Western Europe": "theater" nuclear systems (i.e., tactical nuclear weapons). In describing this "aggravated" situation, the ministers made direct reference to the SS-20 featuring "significant improvements over previous systems in providing greater accuracy, more mobility, and greater range, as well as having multiple warheads". The ministers also attributed the altered situation to the deployment of the Soviet Tupolev Tu-22M strategic bomber, which they believed to display "much greater performance" than its predecessors. Furthermore, the ministers expressed concern that the Soviet Union had gained an advantage over NATO in "Long-Range Theater Nuclear Forces" (LRTNF), and also significantly increased short-range theater nuclear capacity.
To address these developments, the ministers adopted two policy "tracks".
One thousand theater nuclear warheads, out of 7,400 such warheads, would be removed from Europe and the US would pursue bilateral negotiations with the Soviet Union intended to limit theater nuclear forces. Should these negotiations fail, NATO would modernize its own LRTNF, or intermediate-range nuclear forces (INF), by replacing US Pershing 1a missiles with 108 Pershing II launchers in West Germany and deploying 464 BGM-109G Ground Launched Cruise Missiles (GLCMs) to Belgium, Italy, the Netherlands, and the United Kingdom beginning in December 1983.