LGM-30G Minuteman III
As early as 1965, planning was underway for a MIRVed, longer-range version of the Minuteman II, using a wider third stage to accommodate the additional warheads. There was some dissent within the USAF over the development of a third Minuteman model, with some factions arguing for the procurement a new baseline missile, variants of which would include a two-stage medium missile for deployment in Western Europe and a three-stage silo-based ICBM. Such a design could take advantage of advances in solid motor design, and there was interest in the possibility of using refitted Minuteman facilities to base missiles of up to ten feet in diameter.
By 1966, the Minuteman II follow-on had been designated as the Minuteman III; the principal improvement cited for the weapon was a new guidance system and a correspondingly greater capability against hardened targets. But MIRV capability was also a strong factor in developing the LGM-30G; besides providing a counter to possible widespread Soviet ABM development, MIRV also allowed the targeting of an ever-growing list of Soviet targets without adding additional missiles and support infrastructure. The basic technological background for MIRV had been demonstrated with the first launch of multiple satellites from a single booster, but the concept was really introduced to the American public at large in 1967, when the DoD spoke of a “space bus” system that could strike at individual targets. This was MIRV in a nutshell, although targets had to fall within the bus’ “footprint”.
MIRV was widely seen, in the popular press at least, as a response to the Soviet development of the Fractional Orbital Bombardment System, wherein a bomb-carrying vehicle would be launched into a low orbit rather than typical ballistic trajectory. Although accuracy would suffer, FOBS opened up the possibility of an ICBM attack on the United States, from the south, thus going unnoticed by sensors looking toward the north polar region. A FOBS strike could be used to knock out critical C3 installations prior to the arrival of standard warheads, especially by being detonated at altitude to produce EMP effects. As it would turn out, the Soviet FOBS deployment would be limited to a few SS-9 derivatives; of course, given the nature of the system, a few such weapons still posed a threat. The development of an American FOBS was considered but not carried out.
Minuteman III was based on the LGM-30F, but incorporated an entirely new third stage. Powered by a Thiokol-built motor, this stage was the same diameter as the second, permitting a wider nose cone (to house the MIRVs) without the need for a “hammerhead” fairing. Fitting MIRVs actually made the Minuteman III a four-stage missile, as a Post-Boost Control system was placed atop the third stage to carry and dispense the RVs, and this had its own liquid-fueled motors for pitch and roll control.
As late as 1970, the idea of procuring a mobile Minuteman (or making existing missiles mobile) was still alive, but attention would soon turn to mobility studies for the next generation ICBM, the MX. Putting Minuteman III on surface vessels was another alternative, but given traditional inter-service rivalries and the prospect of such a system potentially taking funding away from the Navy’s nascent ULMS/Trident program, it is no wonder that such employment never took place.
In March 1970, the USAF announced that Minot would be the first base to be reequipped with Minuteman III, starting in June. Given the politically touchy subject of deploying MIRVs, the announcement did not state that the new missiles would be equipped with multiple warheads. Indeed, the Minuteman III system had been referred to in some press reports of the time as not being a true MIRV at all. The projected buy of the Minuteman III weapons system was 500 missiles, to be deployed by 1975, allowing retirement of the Minuteman I system.
The USAF fought hard to keep the Minuteman line open even after deployment had ended, hoping to maintain a “warm” ICBM production line while MX was being developed, while also allowing for replacement of additional LGM-30Fs with the newer model. Some extra examples did end up being built, but Minuteman production finally ended on November 30, 1978 after just over 2,400 missiles of all subtypes had been built. The final LGM-30 R&D flight took place in 1980.
Faced with a burgeoning Soviet ICBM threat and restricted by SALT from increasing Minuteman deployment, the USAF looked at several ways of maximizing the LGM-30’s capabilities. One such option was to increase the missile’s MIRV yield by using smaller RVs; this was tested under the Pave Pepper program, with a launch taking place in May 1975. On the other side of the warhead size spectrum, the Large Advanced Ballistic Reentry Vehicle (LABRV) was a proposed carrier for a single high-yield warhead for use on Minuteman IIIs and advanced missiles that were tasked with taking out difficult targets.
There was also interest in RVs equipped with terminal homing guidance, allowing point targets such as missile silos and C3 facilities to be more precisely attacked, and in May 1975, GE and McDonnell Douglas were awarded contracts to study PGRV designs. Putting the Navy Mk.500 MARV on part of the LGM-30F/G force was yet another option looked at. As it turned out, the only new RV/warhead to be fitted to the Minuteman III force was the Mk.12A, carrying the more powerful W78 warhead. The RV design was no larger than its predecessor, but smaller internal systems opened up volume, allowing the new warhead to be fitted.
Complicating the W78’s creation was the fact that in 1976 the US announced that it would follow the tenets of the Threshold Test Ban Treaty, which outlawed nuclear tests over 150 kilotons in yield. W78 tests were conducted before this went into force, but were not wholly successful. Fielding the new heavier-yield warhead also meant that there would be an increased demand for nuclear fuel, and this would came at a bad time, as new warheads for Trident and MX would also need their share of the scarce Oralloy.
These problems notwithstanding, the Mk.12A program progressed, and 300 missiles were refitted to the new standard, heightening their counterforce capability, although the corresponding increase in RV weight reduced the MIRV footprint and missile range. The warhead refit was complete by 1983, with proposals to rearm the remaining LGM-30Gs not having been taken up.
Although the ERCS remained a Minuteman II mission, the LGM-30G was considered for use in a similar role, namely launching communications and other satellites to augment existing constellations in times of crisis, or to replace “birds” lost to the Soviet ASAT system; Minuteman boosters would have been employed from silos to allow rapid launchings from hardened sites in wartime conditions. Minuteman space boosters had been first proposed back in the early 1960s, with some concepts calling for the fitting of a fourth stage.
By the early 1980s, much of the Minuteman system infrastructure was two decades old, and many subsystems needed replacement. To thoroughly rehabilitate the aging silos and launch control centers, the Rivet MILE program was underway by 1985. This was not the first silo retrofit program, as during the 1970s efforts had been made to make the installations more survivable as Soviet missile accuracy increased. Almost a foot of additional concrete was added to the silo doors over for radiation protection, while improved suspension systems for the missiles and equipment were fitted to counter the seismic waves from nearby detonations. The missiles themselves also had to be hardened, as it had to be assumed that surviving Minutemen would have to launched into an environment polluted with nuclear effects.
The Command Data Buffer system introduced to the LGM-30G force in the 1970s was also a major upgrade to the missile’s capabilities. Prior to the installation of CDB, loading new target sets was something of a laborious affair, as it was necessary to go to individual silos to swap out tapes. CDB allowed for remote and comparatively swift retargeting; this was a major benefit for SIOP planners, as it allowed them to rapidly shift target sets to compensate for missiles that were off-line.