It was developed as a counter to the mobile medium- and intermediate- range ballistic nuclear missiles deployed by the Soviet Union in Eastern Bloc European countries. The GLCM and the U.S. Army's Pershing II were the incentives that fostered Soviet willingness to sign the Intermediate-Range Nuclear Forces Treaty (INF treaty), and thus eventually reduced both the number and the threat of nuclear warheads in Europe. GLCM is also a generic term for any ground-launched cruise missile. Since the US deployed only one modern cruise missile in the tactical role, the GLCM name stuck. The GLCM was built by General Dynamics.
A conventionally-configured cruise missile, the BGM-109 was essentially a small, pilotless flying machine, powered by a turbofan engine. Unlike ballistic missiles, whose aimpoint is usually determined by gravitic trajectories, a cruise missile is capable of complicated aerial manoeuvres, and can fly a range of predetermined flight plans. Also, it flies at much lower altitudes than a ballistic missile, typically with a terrain-hugging flight plan. The trade-off for this low-observability flight is strike time; cruise missiles travel far more slowly than a ballistic weapon, and the GLCM was typical in this regard.
GLCM was developed as a ground-launched variant of the Tomahawk missile in use by the U.S. Navy (along with an undeveloped air-launched version, the Medium Range Air to Surface Missile [MRASM]). Unlike other variants of the Tomahawk, the GLCM carried only a nuclear warhead; no conventional capability was provided. The W84 warhead was a variable-yield kiloton-range weapon. Some estimates put the yield at between 10 and 50 kT. This tactical warhead contrasts with the W80 warhead found on other versions of the Tomahawk, and on the ALCM, which had a yield of 200 kT.2 The Pentagon credited the GLCM with a range of 2000-2500 kilometers. Like other US cruise missiles of this period, accuracy after more than 2000km of flight was within half the width of a football field or 100 ft (approximately 30 meters). The missile was entirely subsonic, powered by a turbofan engine with a rocket booster assisting at launch.3
Militarily, the GLCM was targeted against fixed targets -- at the outer edge of its range, the missile's flight time with its subsonic turbofan was more than 2 1/2 hours. This contrasted sharply with Pershing II, which had a flight time of 10-15 minutes. However, the range of the GLCM gave it the ability to strike deep within then-Soviet territory, and the weapon's low-altitude flight profile, TERCOM guidance, and low RCS would have made it far more difficult to intercept a GLCM even if the launch were detected in time.
Designed to be road-mobile, BGM-109 was carried in a four-pack on a wheeled MAN AG transporter erector launcher (TEL), and could travel in convoy. Normal basing was in shelters at military installations, with deployment to other sites, on- or off-road, to be carried out in an alert situation. GLCMs were deployed in the United Kingdom (at RAF Greenham Common and RAF Molesworth), Belgium, Netherlands, Germany, and Italy. Initial operating capability (or IOC) occurred in 1983. The launchers (sans warheads) were sent out on a number of simulated scrambles. Four TELs and their missiles (including reloads) made up each flight of GLCMs.4
Although deployed in the face of a range of Soviet IRBMs, including the brand-new and extremely capable SS-20 Saber, the GLCM (sometimes referred to by its phonetic nickname, Glick-em) faced widespread public protest in Europe. Many anti-nuclear Europeans felt that the United States was deploying weapons meant to win a tactical nuclear war, without adequate consideration of the effects that even a 'victory' would bring. Critics also argued that the Reagan Administration was unduly escalating tensions in Central Europe. Between them, GLCM and Pershing II made a lethal combination. GLCM missiles could be launched, undetected, followed 2 hours later by a Pershing strike, which would fly so quickly that it was possible no response could be made before the Pershings struck. Aside from presenting an attractive course of action to NATO commanders in the event of Soviet aggression, it put the Kremlin leaders (in range of the GLCM and possibly the Pershing, even in Moscow) in a position of fearing a decapitating NATO first strike, which could have moved them toward a launch on warning policy as the only way to maintain deterrence.5
Ironically, and despite the protesters' fears to the contrary, the deployment of GLCM actually brought greater stability to Central Europe, and lessened the incentive/need for a tactical nuclear exchange, through the mechanism of the INF treaty. The recognition by Soviet leaders of the threat posed by the GLCM and Pershing II missiles made them far more inclined to agree to negotiate their own intermediate-range weapons, especially the SS-20, out of service, in exchange for the elimination of the threat posed by the GLCM and the Pershing II.6
Unlike SALT II or START I, which set limits to maximum nuclear arsenals, the INF Treaty banned whole categories of intermediate-range tactical nuclear weapons outright. All ground-launched cruise missiles and ballistic missiles with ranges greater than 500 but less than 5500 kilometers were barred to the U.S. and USSR under this treaty. This meant the withdrawal of GLCM and Pershing II on the American side; the Soviets withdrew the SS-4 Sandal, SS-5 Skean, SS-12 Scaleboard, SS-20 Saber, SS-22 Scaleboard B, and SS-23 Spider MRBM/IRBM/LRBM ballistic missiles, in addition to the GLCM's most direct counterpart: the SSC-4 (dubbed the Tomahawksi in the Western press) and its supersonic follow-on, the SSC-X-5 cruise missiles.7
GLCM was removed from Europe beginning in 1988, and all units were removed from service by 1991, being either destroyed or converted into displays. Eight missiles survive for static display only. No follow-on design has been authorized.8