The third member of the Minuteman family, it is the product of over 40 years of continual innovation and improvement. It was and remains the crux of the American nuclear deterrent. When it entered service in 1970, it brought the size of the total Minuteman force to over a thousand missiles. It is an effective response system with an extremely fast launch time, a nearly 100 percent reliability, and backup airborne launch controllers to ensure a counterstrike.
The Minuteman III missile has a maximum range of 13,000 km (8078 miles) and carries a payload of three Reentry Vehicles (RVs). The missile originally used the 170 kT yield Mark 12 RV and later, the slightly heavier 335-350 kT Mark 12A RV. However, it is reported that increasing numbers of the LGM-30G missiles are equipped with the larger and likely more accurate single 300-475 kT Mark 21 RV. The original inertial navigation system provided it with an accuracy of about 200 m CEP, but an updated inertial guidance system gives it 120 m CEP. The missile is 18.2 m long with a diameter of 1.85 m and a launch weight of 34,468 kg. The missile technically has a three-stage solid propellant design, though it has a quasi-powered fourth stage. Its Multiple Independent Reentry Vehicles (MIRV) platform was designed in such a way that it is arguably a fourth stage, but as this is restricted by the second Strategic Arms Limitation Treaty (SALT II), it is not referred to as such.
The Minuteman III entered development in 1966 as an improvement program for the earlier Minuteman missile systems. The system first entered operational service in 1970 and reached a total of 550 missiles for many years, until the LGM-118 Peacemaker program began in 1986. In 1993, 529 Minuteman III missiles remained in service, with 45 reportedly non-operational. In 2007, the U.S. airforce reduced the numbers to 450 with about 50 to 75 in reserve. These 450 Minuteman III are having their service lives extended until 2030.
The LGM-30G Minuteman III missiles are in the process of being downgraded to single RV designs and are undergoing a series of improvement programs to maintain combat effectiveness. The reduction in the number of warheads is occurring in order to decrease the threat from our missile systems, based on the theory that it will decrease the probability of a counterforce strike from rival nuclear nations. This effectively eliminates two-thirds of our strike capacity and has the side effect of significantly decreasing the probability of a successful counterstrike. With the removal of the LGM-118 Peacemaker missile in 2005, the Minuteman III has become the only US land-based ICBM in service. [Source: wikipedia]