The Case for Mobile ICBMs

Feb. 1, 1988

The year 1988 shapes up as a fateful time for the nation’s plan to modernize its land-based missile force. Major decisions now are pending on two key elements-.–the deployment of multiwarhead Peacekeep­er ICBMs on rail cars and the development of single-warhead “Midgetman” missiles aboard transporter ve­hicles. Both are controversial. Missile mobility appears to enjoy overall support. But tight defense budgets, arms-control considerations, strategic arguments, and politics raise concerns that the two-missile scheme could unravel.

ICBMs are at the heart of US deterrence strategy. They perform the prompt, hard-target retaliatory role that no other US strategic forces are capable of perform­ing. For several years now, the US plan for ICBMs has pointed increasingly toward mobile systems, specifical­ly the Peacekeeper (MX) deployed in a rail-mobile mode and the Small ICBM (also called Midgetman) carried on hardened mobile launchers.

Mobility would improve the prelaunch survivability of the US triad force in general and the ICBM force in particular in the face of the Soviet fourth- and fifth-generation missile threat. The combination of Peace­keeper missiles deployed on trains and Small ICBMs deployed on rugged wheeled vehicles capable of on-road and off-road mobility would enhance the overall survivability and effectiveness of each force and of US ICBMs overall.

Mobile ICBMs are difficult to track, target, and de­stroy. Mobiles, once dispersed, are more likely to sur­vive a Soviet first-strike attack than are such fixed tar­gets as silo-based ICBMs. Even superhard silos, twenty-five times more blast-resistant than present US ICBM silos, could not protect US ICBMs if Soviet missile accuracy continues to improve to current US accuracy levels. Mobile US ICBMs can be an effective means of ensuring that the Soviet Union could not shift the balance of military power decisively against us in the first hour of a conflict.

At present, the Soviet Union has three times as many SS-18 warheads as the United States has ICBM silos. Fratricide effects might limit the Soviet forces to two­-on-one targeting, but even so, the currently deployed SS-18 Mod 4 force theoretically has the capability to destroy sixty-five percent to eighty percent of the US ICBM silos in an attack.

US mobile missiles would trump the Soviet ace by confronting them with moving targets traveling in unpre­dictable directions over a very large area. Even if the Soviet force had real-time intelligence of the locations of the US mobile missile force at the time of the launch of their own ICBMs, they would have no guarantee that the

US mobiles would be at the point of impact thirty to forty minutes later.

Closing the Window of Vulnerability

US mobile missiles would help close the US ICBM “window of vulnerability,” which has been of such con­cern to US officials, by neutralizing much of the strength of the Soviet ICBM force. US rail-garrison Peacekeep­ers and mobile Small ICBMs would alleviate the “use or lose” dilemma faced by US decision-makers now reliant on fixed silo-based ICBMs. Soviet warplanners faced with US mobiles would confront the daunting prospect of expending as many as nineteen warheads to knock out just one Small ICBM warhead.

Analysis done by Rep. Les Aspin (D-Wis.), the Chair­man of the House Armed Services Committee, and his staff indicates that “to destroy ninety percent of a 500-Midgetman deployment (the damage level that it is be­lieved the Soviets seek) would require 112 SS-18s if Midgetman were dispersed more than 4,000 square miles (a likely peacetime dispersal on government lands) or 787 SS-18s if Midgetman were dispersed more than 28,000 square miles (a likely dispersal with warning of an attack).” The Soviet inventory does not contain that many SS-18s (the current estimate is 308). Clearly, Sovi­et employment of their ICBMs in this manner would force them to leave scores of other critical US targets untouched.

Peacekeeper ICBMs mounted on railway cars can also disperse beyond the limits of the Soviet ICBM threat if given any kind of warning time. Within three hours after dispersal has begun, the attack price to the USSR for destroying the Peacekeeper rail-mobile force would exceed the entire projected SS-18 warhead in­ventory. Trying to target US mobile ICBM forces as they dispersed—along with other triad elements and fixed US targets—would be a targeting nightmare for Soviet warplanners. Nor is a bolt-from-the-blue scenario con­sidered likely. A Soviet first strike from ungenerated forces would not be capable of disarming US forces. Moreover, the process of generating their forces would give strategic warning to the US and time to disperse US forces.

Deployment of mobiles by the United States should sharply alter, in favor of the United States, the likely exchange rate of a Soviet attack. Soviet awareness of that fact should improve stability and US security in future crises and confrontations. Soviet decision-makers would be unlikely to enter a conflict in which they perceived at the outset that their forces would be depleted and exhausted before those of the United States. That would be a path to their own ruin and defeat.

The Soviet Move to Mobiles

Clearly, the Soviet leadership has seen the value of mobile ICBMs. The USSR has tested the SS-X-24 ICBM, a ten-warhead, rail-mobile missile that will be deployed along the Soviet rail network. In August 1987, Viktor Karpov, head of the Disarmament Agency of the Foreign Ministry of the USSR, announced that the first SS-X-24s had been deployed, a claim initially confirmed by the White House but later disputed by the Defense Department and US intelligence agencies, which, never­theless, had been predicting such a deployment for the past three years. All US sources agree that such SS-X-24 deployments are imminent if they have not yet happened. Since 1986, the USSR has deployed another mobile ICBM, the SS-25, a smaller, one-warhead ICBM that is about the size of a US Minuteman missile and can be mounted on a truck-launcher. Later models of the SS-25 could be developed in a three-warhead MIRVed version.

It is highly likely that the Soviet interest in mobility is a response to growing US counterforce capabilities and the corresponding vulnerability of their own silo-based intercontinental ballistic missile forces. Soviet leaders obviously believe that mobile land-based missiles en­hance their prelaunch survivability.

This has led some to conclude that the world will be a safer place once both sides have secure second-strike ICBM forces since neither side would need to adopt a launch-on-warning, hair-trigger posture in an acute crisis. Soviet trigger fingers may be much less itchy when their own premier strategic force is mobile, hence survivable, against surprise attack.

Deployment of Soviet mobiles should not necessarily make US decision-makers sleep easier at night. If the Soviet Union keeps its large, silo-based ICBM force intact while adding mobile missiles as well, then they would possess both a missile force that can be used effectively in a first salvo (their silo-based SS-11s, SS-13s, SS-17s, SS-18s, and SS-19s) as well as a secure reserve force (their mobile SS-X-24s and SS-25s) useful for later stages of a conflict. It is for this reason that US arms-control negotiators must seek to limit the Soviet silo-based ICBM inventory as more Soviet mobile mis­siles are deployed. Their overall force structure affects strategic and crisis stability in a more fundamental way than any one component of it.

Given the very heavy Soviet investments in the SS­X-24s and SS-25s, it was always unlikely that they would agree at the Strategic Arms Reduction Talks (START) to ban mobile ICBMs even if the United States began to build its own mobile force. Nor was it in the US interest to ban mobiles.

If the United States and Soviet governments were to reach a deep-cuts START agreement along the lines of what was discussed at the Reykjavik summit and at the Geneva negotiations, then the United States would need to field its most survivable, highest quality deterrent. Older systems should be scrapped first, as should sys­tems that are incompatible with the countervailing strat­egy of deterrence. Forces that do not have good pros­pects for prelaunch survivability would need to give way to make room for those that do. Deployment of far fewer warheads and launchers would require that the remaining retaliatory capability be the most effective that the United States can field.

Mobile ICBMs also are likely to be valuable tools for crisis signaling and warning. During a tense period of US-Soviet confrontation characterized by great danger, significant opportunity, surprise, and a short time for decision, the dispersal of mobile US missiles could send a “don’t tread on me” signal to the enemy while simulta­neously making the US ICBM retaliatory capability more secure. If war broke out, the greater survivability of US mobile ICBMs could make that force available for intrawar deterrence, for midconflict use, or for war ter­mination leverage. Mobile ICBMs that can disappear from enemy view or reach, together with bombers and SLBM forces, could form part of the US strategic re­serve force.

The Logic of Two Mobile Missiles

The US deployment of two types of mobile ICBMs makes good strategic sense, as the Soviet leaders them­selves have decided with their rail-based SS-25s and road-mobile SS-X-24s. Enemy warplanners considering a surprise attack could not be certain whether or not the train-based Peacekeepers would be launched while in garrison when given confirmed warning of an attack-in-­progress. The Small ICBM can also be based on a hard­ened mobile launcher (HML) capable of on-road and off-road travel. Small ICBMs on military reservations will be dispersed at all times, and the entire force would be able to spread very wide and far with only tactical warning of the impending attack.

The first fifty Peacekeeper ICBMs and their 500 war­heads are now being deployed in silos at F E. Warren AFB in Wyoming. Fifty more mobile Peacekeeper ICBMs, combined with 500 mobile Small ICBMs, would contribute another 1,000 warheads that could hold at prompt risk a total of 1,500 high-value, time-urgent, time-sensitive targets in the Soviet Union.

The combination of the two types of US mobile ICBMs would create a synergism resulting in enhanced survivability for each force when faced with an attack. Each mobile force would increase the problems facing a Soviet warplanner contemplating an attack on the United States and its strategic forces. Therefore, the Soviets would be forced into treating mobile ICBMs as relocatable targets requiring multiple warheads for mul­tiple aimpoints. Each of the two US mobile ICBM forces, if deployed, would stretch and deplete the Soviet warhead inventory. Together, they would add consider­able uncertainty to the thinking of Soviet warplanners as to the outcome of a simultaneous strike against them both. Soviet warheads assigned to cover the rail-gar­rison Peacekeeper force could not be used to target the mobile Small ICBM force, and vice versa.

The single-warhead Small ICBM would offer US mili­tary planners considerable targeting flexibility. A mis­sile with multiple warheads must be painstakingly matched against a collection of targets equal in number and value to the warheads carried by that missile. More­over, a MIRVed missile can only attack targets located within a certain geographic area, an area determined by the “footprint” of the missile.

A single-warhead ICBM, in contrast, could be fired against a target located virtually anywhere in enemy territory. Only one target would need to be allocated to each Small ICBM. This means isolated and widely dis­persed targets could be assigned to the Small ICBM force. In addition, the single-warhead payload of the Small ICBM, combined with its high accuracy, makes it a useful weapon for selective strikes at the outset of any conflict begun by the adversary. During conflict, the highly survivable HML-mounted Small ICBMs could be readily reassigned to targets that escaped initial US retaliatory attacks or to newly discovered targets.

SLBMs vs. Mobile ICBMs

Some participants in the US strategic debate have suggested that the United States already has a surviv­able mobile ballistic missile in the works, the Trident II (D5) submarine-launched ballistic missile. Therefore, they argue, there is no need to deploy the Peacekeeper ICBMs on trains or Small ICBMs on hardened mobile launchers. They believe the D5 SLBM, when it is de­ployed, will be able to handle the entire deterrence and military missions currently assigned to ICBMs.

Unfortunately, life is not that simple. The D5 will not be capable of performing all the functions assigned to our ICBMs. The ICBM is the only US weapon capable of performing the prompt retaliatory role against Soviet high-value, hardened, and time-urgent or time-sensitive targets in the event of war. Only the ICBM force is capable of disorganizing a Soviet missile attack-in-prog­ress and of preventing a massive shift in the military balance of power in favor of the-Soviet Union in the first minutes of a nuclear exchange. This is important be­cause Soviet military doctrine states that victory is pos­sible only when such a shift in the correlation of forces takes place at the inception of conflict. US bombers and SLBM forces are too slow to interrupt the adversary’s attack-in-progress.

Today, US ICBMs alone have the needed combination of assured penetration to target, great accuracy, speed of delivery, force-wide alert status, rapid retargeting, and reliable and speedy command control and communica­tions between the US leadership and the retaliatory forces. US submarine forces have their own advantages, but, today, their overall force reaction time may be too slow and their communications with the US National Command Authority are too uncertain to provide a high-confidence prompt-retaliation deterrent force.

Furthermore, even if command and control at sea were as fast and secure as that for ICBMs, the D5 SLBM will still lack some of the accuracy and hard-target capa­bility being designed into the Peacekeeper and Midget­man ICBMs. Using D5 warheads to attack the hardest targets would lead to an inefficient allocation of the total US warhead inventory and would pose a less credible deterrent threat.

Nor is cost an argument for opting for SLBM or bomber weapons over ICBMs. If costs were computed on a realistic US capability to put a given type of nuclear warhead on an adversary target in a window of time and in the midst of a conflict started by the other side, then the projected cost per delivered warhead on destroyed targets for the Peacekeeper and Midgetman ICBMs is in the same general range as the projected cost per deliv­ered warhead for those deployed by bombers or by SLBMs. Warheads on future mobile ICBMs will be just as cheap because of their very high alert rates, high survivability and penetration capability, and their ex­treme accuracy when compared to the projected cost and performance of future bombers or SLBMs in these categories.

The 500/Fifty Mix

The pursuit of a single-RV ICBM is important to US interests. This is dictated by strategic logic and by the political need to maintain a bipartisan congressional consensus in support of US strategic goals and moderni­zation programs.

In time of completely unconstrained defense budgets and in the absence of any new START agreement, the United States might wish to deploy 1,000 additional Small ICBMs and forgo the deployment of additional MIRVed ICBMs. There is obviously some benefit to be gained from dispersing US warheads in such a fashion that a single Soviet warhead can destroy no more than one US warhead in an attack. Preferably, many enemy warheads would be needed to cancel a single US war­head.

A very large Small ICBM force, however, makes no fiscal or arms-control sense from the US perspective. The Midgetman force would be too expensive for full deployment of 1,000 missiles, and 1,000 additional Small ICBM launchers would run in the opposite direction from our stated START goal of deep cuts in numbers of launchers.

For these reasons, it will also be necessary to deploy additional Peacekeeper ICBMs on a mobile launch plat­form rather than deploy an excess of Small ICBMs in order to give the United States the number of survivable yet accurate and prompt warheads it needs to deter the Soviet Union effectively while staying within economic and START constraints.

Most analysts believe it would be a mistake to put large numbers of additional warheads on ICBMs based in silos. Those warheads need to be placed on mobile platforms in order to frustrate any Soviet first-strike planning or execution. If the United States and the Soviet Union were to agree to a deep-cut START Treaty limiting each side to 1,600 launchers and 6,000 war­heads, it would be unwise in the extreme to place most of those warheads on the Small ICBMs because the Small ICBM program would crowd out most of the rest of the US strategic triad. For example, a thousand Small ICBMs, combined with the fifty Peacekeeper ICBMs deployed in silos, would leave precious little room for either the strategic bomber component of the triad or for the fleet ballistic missile force.

The cost per warhead of the Midgetman program com­pared to the rail-garrison Peacekeeper also argues that the United States government ought to deploy a more cost-effective mix of Peacekeepers and Small ICBMs rather than opting solely for a Midgetman force. In an era of massive federal deficits, the United States ought to purchase the most efficient mix of ICBMs that can still do the deterrent job, perhaps something like a mix of 500 Small ICBMs on HMLs and fifty additional Peace­keepers on trains. This combination would fit more reasonably with any future START limits on launchers and warheads, would permit the deployment of a bal­anced US deterrent triad, and would be more affordable while still being able to threaten the Soviet target set in such an effective and timely way that it will maximize US war deterrence.

Such a mixed program of rail-mobile Peacekeepers and road-mobile Small ICBMs also makes more politi­cal sense than proposed alternatives, such as relying exclusively on Trident II D5s for counterforce capabili­ty. If any bipartisan consensus exists in the country and on Capitol Hill in support of US strategic policy, it includes support for both the Peacekeeper and the Small ICBM programs in the context of a strategic arms-con­trol agreement reducing arms. This was the consensus reached by the President’s Commission on Strategic Forces chaired by Lt. Gen. Brent Scowcroft, USAF (Ret.), and it remains the force mix and strategic mod­ernization package that probably stands the best chance of meeting the tests of military utility and economic viability needed to carry out US strategic policy in a coherent manner.

Barry R. Schneider is a Senior Defense Analyst with National Security Research, Inc., in Fairfax, Va. He speaks and writes frequently on US defense and arms-control policy issues. He has taught at six universities, served both in the executive branch and on Capitol Hill, and has worked on national security issues for several Washington, D. C. think tanks.