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Ballistic Missile Defense:

A Potential Arms-Control Initiative

.qo%G. E. Barasch o

D. M. KerrR. H. Kupperman’

R. PollockH. A. Smith**

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*Los Alamos Fellow. Executive Director, Center for Strategic and InternationalStudies, Georgetown University, 1800 K Street, N.W., Washington, DC 20006.

● * Los Alamos Consultant. Chairman, Mathematics Department, Arizona State

University, Tempe, AZ 85281,

BALLISTIC MISSILE DEFENSE:A POTENTIAL ARMS-CONTROL INITIATIVE

byG. E. Barasch, D. M. Kerr, R. H. KuppermQ

R. Poilock, and H. A. Smith

SUMMARY

United States strategic forces must be restructured to meet national-securityobjectives in a changing world Growth and modernization of Soviet strategic missileforces are causing our land-based strategic missiles to become increasingly vulnerable toSoviet nuclear attack. American policy for deterring such an attack has evolved fromstrict reliance on the threat of assured Soviet destruction to include nuclear war-fightingconcepts intended to deny Soviet hopes of winning the ensuing conflict. At the sametime, events in Iran and Afghanistan have underscored the need to expand andmodernize our conventional forces, requiring strict limitation of our strategic invest-ments.

For some strategic force configurations, the goals of flexible nuclear deterrence andstrategic arms limitations appear mutually inconsistent. With such forces, prospects forarms limitations would degrade further if the current Soviet build-up were to continue,or if the Soviets were to install unilaterally an anti-ballistic missiIe system capable ofwide-are% multicity defense, or both.

‘ However, if the United States installs an anti-ballistic missile system along withreduced but modernized offensive strategic forces, arms limitation appears compatiblewith both assured destruction and war-fighting deterrence policies. This conclusionappears equally valid for expanded Soviet forces even if the Soviets also install ballisticmissile defenses. In particular, we have analyzed an American strategic postureincluding layered defense of MX missiles based deceptively in silos. The exoat-mospheric-intercept component of this defense system could also defend some of ourcities and industrial and military installations. If the United States were to adopt thisstrategic posture, we believe it would create incentives for the Soviet Union to restrainstrategic-arms expansion. Mutual arms-control initiatives could follow. In addition, thisdefense system might offer stabfliing features: damage lhnitation for small attacks;nonoffensive crisis response; and relative insensitivity to technological change. Theseresults do not seem to be available by deploying strategic offensive forces alone.

Test and installation of the needed defensive systems are now precluded by theAnti-Ballistic-Missile Treaty adopted in 1972. An opportunity for Treaty reconsidera-tion occurs in 1982. Substantiation of our results would suggest that consideration begiven to Treaty moditlcations or to replacing the Treaty with other agreements. Suchactions could lead to improved national security for the United States by enhancing ourdeterrent posture an~ at the same time, offer the potential for significant arm=ontrolinitiatives.

I. INTRODUCTION

Over the past two decades, significant changes haveoccurred in the long-standing competition between theUnited States and the Soviet Union. Many of thesechanges have been adverse to American interests. A shiflin the global balance of power has taken place, as aresult of a determined Soviet expansion of its militarypower through growing defense expenditures.

Critical strategic asymmetries between the two super-powers have thus emerged, including ditYering strategicconcepts of nuclear deterrence and warfare. For someyears American strategy rested on the premise thatapproximate equality of strategic forces would lead tostable nuclear deterrence, which would be achievedprimarily through fear of mutual assured destruction.Consequently, policies on weapons systems that mightthreaten or undermine Soviet deterrent capabilities wereeschewed by the United States as destabilizing. Althoughthe Soviet Union has expressed enthusiasm for the goalof limiting American strategic forces, there is no clearevidence that they have embraced the restraint implicit inour policies. In contrast, the Soviets appear to havedeveloped a strategy of seeking strategic superioritythrough balanced offensive and defensive forces, withsurvival as the objective if nuclear war should occur. TheSoviets have exploited these asymmetries to attempt toundermine American assurances to its allies and to callinto question the guarantee of America’s nuclear um-brella.

In recognition of the growing strategic imbalance, theUnited States recently announced a modification of itsnuclear targeting policy.* In addition to a punitiveassured-destruction strategy, our retaliation would at-tempt to deny the Soviets any prospect of achievingwar-fighting objectives by destroying a range of neededmilitary installations. Elements of damage limitation inthis “countervailing” nuclear strategy are perceived bothto enhance deterrence prospects and to provide neededoptions should deterrence fail. The adoption of thecountervailing strategy blurs somewhat the distinctionbetween United States and Soviet doctrines but cannotby itself compensate for existing force asymmetries.Restructuring of our strategic forces is also needed. Toallow the flexibility needed within the countervailingpolicy, American forces must be configured to serve bothdamage-limiting and assured-destruction roles.

Invulnerable ICBMS can contribute to both deterrencepolicies. In an assured-destruction role, they provide anindependent force within the strategic triad that could

retaliate if the other triad elements become vulnerable. Ifthe Soviets shelter or harden their strategic industry in anattempt to interfere with our assured-destruction deter-rent,z IC BMs have the needed accuracy and yield tocounteract these actions. In a war-fighting role, ICBMSare the only strategic element capable of damage-limitingattacks on time-urgent military targets.

As offensive technology improves, deterrent strategicforces become more vulnerable to attack,Force-structure or doctrinal changes may therefore beneeded. In particular, the ICBMS are becoming increas-ingly vulnerable to Soviet nuclear attack, Remediescould include technology to reduce vulnerability, ex-pansion of the forces, or changes in strategic doctrine,Doctrinal changes might include launch under attack orlaunch on warning, and might also necessitate pre-emptive attack upon time-urgent targets imd disruptionof an expected attack. Although such changes instrategic doctrine could be an effective way to counterincreased vulnerability, they impose imperatives foraction, which, in time of crisis, might increase theprobability of nuclear war. To avoid this scenario, ourstrategic forces must be survivable and our policy forusing them must be stable in a crisis: we must be able togather information and deliberate txfore we have to act.

Expansion of strategic forces to compensate forincreased vulnerability is not attractive from either aneconomic or an arms-control perspective. Thus, we areleft with the alternative of developing remedial technolo-gy to reduce strategic-force vulnerability. There is,however, another constraint on our “selection ofstrategic-force structures.

In recent years, the Soviets have been able to exploitpolitical, economic, and security instabilities in theMiddle East, Asia, Africa, and Latin America, withouteffective opposition from the West. The invasion ofAfghanistan by the Soviet Union, coupled with thedilemma posed by the Iranian capture of the Americanhostages, underscores the inability of our strategicnuclear arsenal to deter attacks of a more limited orconventional nature. These events also give evidence ofour failure to project an effective military presencesufficient to achieve American interests in low-intensityconflict.

Whhout sufficient conventional forces, we face theincreasing risk that nuclear weapons would be used inotherwise conventional contlicts, First use might be bythe United States. National frustration, or a Soviet-inspired attack on our vital interests, or an initiallyconventional war, might exceed our conventional-force

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response capacity. Depending on our distress, we mightthen use nuclear weapons under the assumption that anuclear exchange could remain limited. The Sovietscould begin the exchange for similar or disparate rea-sons. If then our deterrence forces were overly vulner-able, Soviet options would include an all-out coun-terforce strike as an extremely effective way for them tolimit damage to the Soviet Union.

Thus, we will need expanded and modernized conven-tional forces to be able to avoid nuclear escalation fromlimited conflicts. This need defines a constraint on ourstrategic-force procurements: we cannot divert effort orfunding away from the conventional forces that we needto support measured diplomatic and military responses.

Our impotence in the Iranian crisis combined with theSoviet move into Afghanistan have effectively preparedAmerica for remedial action. Before these events, thecold war was thought by liberal strategists to be a thingof the past; the Soviet Union and the United Statesneeded one another or, at leas~ were bent on coexistence.The SALT II agreement, though hotly contested, mightwell have been ratitied by the Senate. Support forstrategic programs was limited. Subsequently, what hadsometimes been seen as the professional paranoia of theconservative military strategists began to appear asreality. America suddenly became aware that the Sovietshad built up mammoth arsenals of both conventional andnuclear weapons. We now seem ready to seek solutionsto the military imbalances.

Our objective in this report is to explore technologiesthat will allow us to reduce forces and still meet bothassured-destruction and damage-limiting strategic objec-tives. We attempt to find forces that will require min-imum inventories and investments so as to maximizefunds available for conventional forces. With limitedinventories, the effectiveness of the strategic forces mustbe maintained in the face of maturing Soviet technology.Therefore it is essential that the force structure besufficiently diverse to withstand technological surprise. Itmust also be relatively insensitive to “cheating” onarms-control agreements; it becomes very ditlcult, in apolitical context, to acknowledge cheating or even inade-quacy of verification once a treaty is accepted. The forcestructure must be able to respond economically topossible threat growth so that incentives for continuedSoviet proliferation are reduced or denied. The forcemust be able to achieve arms-control, assured-destruction, and damage-limiting objectives regardless ofSoviet strategic policy. Finally, it should promote crisisstabilization.

These goals, when coupled with strict force limita-tions, appear from our analysis to be incompatible if weseek strategies that use only offensive forces and excludedefensive systems. This report, therefore, concentrateson ballistic missile defense technology that could beintroduced soon and might measurably foster the goalsof deterrence, arms control, and stability. Our analysesindicate that a properly coqflgured force including aballistic missile defense system may permit deterrence atreduced force levels while resisting erosion of the deter-rent by technological advances. Moreover, the effective-ness and structure of such a force do not appear todepend so crucially on treaty-specified actions as to becritically vulnerable to violations of arms-control agree-ments. Such a ballistic missile defense system would alsoadd elements of crisis stability and damage limitation incase f@errence were to fail. Defensive systems could beinstalled economically, together with or separately fromthe deceptive-basing modes now under development forMX missile deployment. ~

Previous consideration of ballistic missile defense hasbeen seriously constrained by a long-standing and widelyheld concern: ballistic missile defenses would bedestabilizing if capable of defending military, industrial,and urban targets. Such area defenses would presumablyinterfere with the ihaintenance of assured-destructionretaliatory forces, thus tempting the nation possessingdefenses to launch a preemptive strike. Defense installa-tions would presumably also lead to a defensive armsrace coupled with the ongoing offensive arms race. Theseconcerns are still current, as stated during 1980 bySecretary of Defense Harold Brown (Ref. 1, p. 99):

. . . attempting to construct a complete [ballisticmissile] defense against massive nuclear attackwould be prohibhively costly, destabilizing, and inthe end, almost certain to fail;

and by President Carter’s Deputy Assistant for NationalSecurity Affairs, David Aaron:3

I think we can be pleased that we’re not engaged inboth a defensive strategic arms race as well as anoffensive one.

In this report we suggest how prospective ballistic missiledefense systems might overcome these concerns.

If both the Soviets and the United States are bent onstrategic arms reductions, they can apparently retainmutual deterrence by mutually assured destruction withmoderate inventories of offensive and defensive strategic

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components. The systems need not be costly nor lead toinstabilities. If, on the other hand, the Soviets continuetheir strategic arms build-ups at the current pace, thenAmerican force structures that include ballistic missiledefense might provide the most economical and flexibleoptions for deterring Soviet attack by the countervailingdeterrence strategy. Continued offensive missile pro-liferation by the Soviets would not need to be mirroredby the United States. Our results suggest that we couldinstead maintain stable deterrence by moderate increasesin hardware, mainly defense components. In this case,the Soviets would not be likely to perceive our responseas a threat to which they would have to respond.Reciprocal pressures for an arms race could ease. Ofcourse, the Soviets could continue their arms build-upanyway, and we would have to respond; but our resultsindicate significant economic advantages for the UnitedStates in this scenario.

The perceived Soviet/American balance of power restson military capacities well beyond the maintenance of areliable assureddestruction (punitive) nuclear deterrent.Thus our derivation of assured-destruction strategicforces represents but a first step in the neededforce-structure analysis. We continue the analysis bysuggesting some ways in which the countervailingstrategy might be enhanced by the capacity for limiteddefense of military, industrial, and urban targets.

The force structures postulated in this study wouldrequire defense components whose development andtesting are now precluded by the Anti-Ballistic-MissileTreaty, which was adopted in 1972 and is scheduled forreview in 1982. At that time either party can withdraw orpropose modifications without prejudice to future treatyactivities. Strategic defense concepts discussed in thisreport suggest that serious consideration should be givento modifying the Treaty or replacing it with an agree-ment that would allow the benefits of the new defensivetechnologies to accrue in support of both na-tional-security and arms-limitation goals.

Consideration of possible treaty actions rests partly onthe readiness of ballistic missile defense technology. TheBallistic Missile Defense Program Manager, Major Gen-eral Grayson D. Tate, Jr., in testimony presented to theSenate Appropriations Committee in March 1980, wassubdued but positive in his overall assessment of thetechnology.’

[Low-altitude defense] technology is low risk andready for preprototype demonstration now. Theexoatmospheric element of layered defense repre-

sents less mature technology. However, . . .advances [in exoatmospheric ballistic missile de-fense technology] make it feasible to developautonomous long-range interceptors . . . [Thissystem] is being validated. . . and promises to givedefense the cost advantage for the fwst time . . .

Based on a brief review of ballistic missile defensetechnology conducted by Los Alamos during 1980, weconcur with General Tate’s optimism. We believeballistic missile defense soon could be ready to assumethe postulated strategic roles.

In the next section of this report, we describe someelements of the current technology and summarize ourtechnical assessment, comparing it with the Departmentof Defense assessment. We then continue our analysis ofassured-destruction deterrence postures by describingsimple mathematical models and applying them to a setof strategic options available to the United States. Weuse the results to amplify our suggestions that timing andcost advantages may accrue to strategic options includ-ing ballistic missile defense.

II. TECHNOLOGY OF BALLISTIC MISSILEDEFENSE

The ballistic missile defense systems considered in thisreport can be categorized according to where an of-fensive weapon is intercepted along its trajectory. Systemconcepts include early-trajectory or boost-phase in-tercepts, midcourse or exoatmospheric intercepts, andterminal or endoatmospheric intercepts. Systems thatspecify two groups of intercepts, one after the other, arereferred to as layered defense systems.

Boost-phase or early-trajectory intercepts by“directed-energy weapons” (intense laser beams or parti-cle beams) hold the potential for an extraordinarilyeffective defense of all national assets. Directed-energy-weapon development in the United States is at solimited a stage at present that it is extremely unlikely thatsuch systems could improve our strategic position in thecoming decade. Well-funded 5- to 10-year researchprograms wiU be required to establish the needed tech-nology bases in these areas before we can begin to realizetheir potential. These systems are not part of the presentanalysis.

Our analysis is based on conventional exoatmosphericand endoatmospheric defense systems that interceptbetween the midpoint of the ballistic trajectory and 1-2kilometers before impact. These systems operate by

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guiding rocket-powered vehicles to intercept incomingwarheads. They require

● early warning that a threat has been launched;● detection and assessment of the approaching threat;● derivation of trajectories and prediction of impact

points;● discrimination between warheads and decoys;● commitment, launch, and guidance of interceptors;

and● destruction of the warheads.

These functions are depicted in Fig. 1; the subsequentsystem descriptions and assessments are discussed interms of these system functions and the technologiessupporting them.

Current ballistic missile defense technologies are sub-stantially different from predecessor technologies usedby the Safeguard balbstic missile defense system of theearly 1970s. Safeguard was widely perceived as in-capable of fulfilling the missions it faced. It is ap-propriate, therefore, to contrast Safeguard with current

EXOATINTE

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Layered ballistic missile defense of MX missiles deceptively based in silos. In this depicdon three warheads are on a

trajectory aimed at an MX missile in one silo, and three more are airned at an exoatmospheric interceptor in an adjacentsilo. The exoatmospheric interceptor is launched and destroys two of the warheads attacking tbe missile. Warheadsattacking the now-empty interceptor silo are ignored. The surviving warhead aimed at the missile is intercepted by theterminal defense: Not shown explicitly are the separate threat detection and assessment functions.

systems and show how the deficiencies of Safeguard canbe overcome by the new technology.

A. Safeguard

Safeguard was a layered defense that usedground-based radars for detection, assessment, tracking,discrimination, and interceptor guidance for both mid-course and terminal defenses. Long-range perimeteracquisition radars provided early warning and de-termined the size of the attack and its targets. Asattackers neared the intercept range, battle managementand engagement were taken over by smaller missile siteradars, coupled to central computers, with oneradar-computer assembly for each wing of the Minute-man force. For the exoatmosphenc layer, multistageSpartan interceptors, guided by the radars, operated outto several-hundred kilometers. The Spartan carried asingle high-yield nuclear warhead. Those warheads leak-ing past the Spartan’s defense layer would be interceptedby fast-reacting Sprint low-yield nuclear interceptors ataltitudes of 3-30 kilometers also guided to intercept byradar. Each interceptor would engage one warhead.

The large ground-based radars were Safeguard’sweakest point. It was soon recognized that the firstSpartan nuclear explosions would render large regions ofthe atmosphere opaque to radar propagation, therebyblinding the radars and making them vulnerable toattack. Other problems existed as well:

● the computers needed were beyond the state of theart;

. discrimination by radar signatures was onlymarginally effective; and

● the system was easily defeatable by a cost-effective

increase in the threat size.

B. Exoatmospheric Defense for the 1980s

Current designs for exoatmospheric ballistic missiledefense depend on two major innovations: (1) small,high-resolution, sensitive, long-wavelength infrared de-tectors, installed with computers in space-bornethreat-assessment sensors and in interceptors, whichreplace large ground-based radars and central computersfor long-range threat acquisition, assessmen~ trackingand discrimination; and (2) homing infrared guidancethat enables each interceptor to disperse many vehicles

for multiple nonnuclear intercepts instead of sin-gle-vehicle nuclear interceptors.

In the current designs, early-warning messages eitherfrom satellites or radars trigger the threat detection andassessment functions carried out by infrared sensors.These sensors can be emplaced on satellites or carriedalofi on rocket-borne probes launched from the continen-tal United States. Each payload consists of a sensitiveinfrared telescope, a data-processing computer, anddown-link communications equipment. The sensors scanthe threat corridor specified by the early-warningmessage and detect, at ranges of several-thousand kilom-eters, the attacking reentry vehicles, accompanyingobjects, and penetration aids.

Typical threats could have approximately 5000 reen-try vehicles and upwards of 20000 other objects in thefield of view; the computer must process information forall of them. The sensor tracks all these objects forminutes, measuring angular information and infraredspectral intensities in several bands as a function of time.The on-board computer stores this information, com-putes approximate trajectories and launch and impactpoints, and uses infrared discrimination algorithms todifferentiate the reentry vehicles from the other objects inthe threat. This information is then relayed to aground-based battle-management computer in real timevia multiple-path communications links. Based on theattack breadth, predicted impact points, and relativestrength of the defense, the battle-management computerassigns targets to interceptors and launches them.

Impact-point prediction, if accurate enough, permitsthe battle-management computer to defend targets pref-erentially, that is, to defend some targets and to ignorewarheads attacking others. Such a capability is impor-tant if the attack size is larger than the defense canintercept fully, or if deceptive techniques are being usedby the attacked party to thin the effective attack on eachreal target.

Following launch, the exoatmospheric interceptorrockets operate autonomously, reacquiring their assignedportions of the threat via infrared sensors, repeating thediscrimination procedures, and finally deploying muM-ple-kill vehicles to engage the attack while still severalminutes from impact. Using still anotlm infrared sensor,each kill vehicle homes on a separate warhead, gettingclose enough to destroy it by direct impact or by tiring aconventional explosive warhead.

A fraction of the attack can survive this engagement.Some objectives are deliberately ignored (penetration

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aids, accompanying objects, warheads allowed throughby a preferential defense). Some engaged objects pene-trate the defense (leakage). The surviving warheads eitherreach their targets or are further depleted by subsequentdefense layers.

Assessment. The Ballistic Missile Defense ProgramOflice is guardedly optimistic about the potential forexoatmospheric technology. General Tate reported that’

The [exoatmospheric component of the] LayeredDefense Concept is feasible because [of] advancesmade in the extensive research and develop-ment . . . [The] first two flights [of an experiment].,. confiied that optical sensors can be used toperform [ballistic missile defense] functions,

His Deputy Program Manager, William A. Davis,supplied a more conservative and detailed treatment :s

Midcourse technologies are relatively immature,pose a higher technical risk than terminal technolo-gies, and enjoy only a meager data base. There area host of technical issues to be addressed in [our]research and development program over the nextseveral years, two of which are examined here:optical discrimination and nonnuclear kill.

Technical evidence exists that optical discrimina-tion is sufficiently developed to make midcourseoperation feasible. Somk optical flight data isavailable on both reentry vehicles and exoat-mospheric penetration aids, and there is extensivelaboratory data that correlates well with the flightdata. Moreover, the essential finding from sim-ulation exercises carried out jointly with the AirForce’s Advanced Ballistic Reentry Systems(ABRES) shows that all but the most sophisticatedpenetration aids can be readily discriminated.However, more data and more functional demon-strations are necessary, and there are plans to meetthese needs.

The evidence is that nonnuclear kill can beachieved in”one of two ways—with a warhead orby direct impact. In both cases, passive homingrather than the conventional radar command gui-dance will be used, The primary approach is to usea warhead, and actual flight tests (Homing OverlayExperiment) to demonstrate this approach will be

held in several years. Guidance simulations in-dicate a warhead can be brought close enough toachieve a kill. Impact kill is a back-up approachthat was demonstrated in laboratory tests severalyears ago.

Based on our review of exoatmospheric technology,Los Alamos supports the optimism expressed by theProgram Office. The technology base for the exoat-mospheric systcrn appears to be either in hand or on theimmediate horizon. We also are able to add detail to theProgram Oflice assessment, Integrated circuit technolo-gy is progressing so rapidly that adequate computercapability appears assured. Laboratory models, experi-ments, and calculations of nonnuclear kill give highconfidence in performance capabilities, Infrared detec-tion and discrimination have been studied carefully, anduseful techniques and knowledge of their limitationsappear in hand, pending proof test within a few years.Impact-point prediction is expected to be capable ofpermitting preferential exoatmospheric defense of silos,*but it is not expected to be able to resolve impacts amongclosely spaced shelters of any of the multi-ple-protective-structure emplacement schemes underconsideration.

We identified several outstanding technical issuesneeding further study. These issues are dominated byconcern over extreme system complexity. Some analystshave considerable reservations about system operability;others are optimistic. Large-scale simulations in progresslend credence to system operability. Other issues includeoperability of sensors, computers, communications, andinterceptors in a nuclear environment, potential formeans of overcoming infrared discrimination, and inte-gration of active defense with an already strainednational command-communications-control system. Thespecial problems of attacks launched by nuclear sub-marines lying close to American shores are particularlystressing to exoatmospheric defense, owing to the shortflight times. Intercepting such attacks would requireprevious placement of threat assessment sensors or—atreduced etliciency-operation without them, In addition,a number of actions could be taken by the Soviets inresponse to our installation of an exoatmospheric defense——— —*For impact resolution within 5 km, silo-to-silopreferentialdefense wouId be effective.For poorer resolution, preferentialdefenseof groups of silos would be used.

7

system that could degrade its capabilities. They inclu<demaneuvering reentry vehicles, defense suppression at-tacks, and new decoy techniques.

Although exoatmospheric defense capabilities are notyet fully perfected or demonstrated, we feel developmentis advanced enough to warrant beginning studies ofpotential applications,

C. Endoatmospheric Defense for the 1980s

Endoatmospheric defense uses radars for all sensingfunctions. Small radars can be specified because theradars need not have ranges necessary for exoat-mospheric defense (a departure from Safeguard). Dis-crimination against decoys is based on different radarsignatures, as objects penetrate the atmosphere, depend-ing on weight, shape, and surface characteristics. Suchatmospheric effects begin to be apparent on radarsignatures at altitudes below 90 km. Based on timedelays associated with discrimination and interceptorflight, a practical upper altitude for intercepts is 20-30kilometers.

The limiting lower altitude for intercept is determinedby the capacity of the defended target to withstanddefensive weapon bursts and, possibly, nuclear detona-

2

tion of the intercepted warhead. By this criterion ashelter or silo could be defended successfully with

(, intercepts spaced as closel~meters.Unid States endoatmospheric defense research and

development effort is concentrated in two programs:Baseline Terminal Defense and Low-Altitude DefenseSystem.

(1) Baseline Termbud Defense is a direct descendantof Safeguard. It uses improved Sprint interceptors, acommercial computer, and phased-array radars con-siderably smaller than Safeguard’s missile site radar,This system, based on established technology, would beless vulnerable than Safeguard because it would usemultiple radars in dispersed sites. Since intercepts wouldoccur in the altitude range of 10-20 kilometers, thissystem would be useful for soft targets.

(2) Low-Altitude Defense System, the major ongoingIow-endoatmospheric intercept program, is shownschematically in Fig. 2. A derivative of the BaselineTerminal Defense System designed mainly for defense ofMX-MPS, it uses single-stage nuclear-warhead intercep-tors with a range of only a few kilometers. TheI.mw-Altitu& Defense System uses phased-array radarsof modest power, coupled to minicomputers. Because of

small component size, the system can be deceptivelybased in any of the basing modes proposed so far forMX. In modified configuration it could also be used todefend silos.

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Assessment. In his Senate testimony regarding termi-nal defense, General Tate reported: . .

[Low Altitude Defense System] is considered alow-risk development because of the extensivevalidation testing accomplished . . . on the Termi-nal Defense (Site Defense) concept, This testing . . .has proven beyond reasonable doubt that we havethe technology to build an effective terminal de-fense system that can detect, discriminate, andintercept ICBM warheads even in the extremeenvironment caused by massive ICBM attacks. . .and penetration aids.’

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The basic technology for Low Altitude De-fense—LoAD-has been demonstrated with theexception of nuclear hardness for the radar and theinterceptor. Nuclear hardness will be tested anddemonstrated . . . prior to MX IOC* and theLoAD preprototype demonstration flight tests.6

As was the case for exoatmospheric defense, weconcurred with the Program OffIce assessment of termin-al defense technology. We felt that the use of smallerand less complex components make low-altitude defensea relatively low-technical-risk system with less costlycomponents than exoatmospheric systems. However, thestressful nuclear environment envisioned requires in-terceptor and radar hardness values exceeding those ofpredecessor systems. Ability to defeat an intense attackagainst any single target will be limited because, with thevery short time available for acquisition, track, andintercept, multiple sequential intercepts witl be ditXcult.The limited space available for interception would alsoreduce the ability of the system to cope with repeatedattack, due to nuclear-fireball interference with radarpropagation and to interceptor-interceptor fratricide. Insuch a dense attack, fratricide between attacking war-heads could also be a problem for the attacker.

Interceptor technology for endoatmospheric defense iswell in hand, provided that nuclear warheads are carried.(Nonnuclear kill may become feasible, particularly forengagements at higher altitudes, but will require further———— —●That is, the date currently scheduled for initial operationalcapability of MX in multipleprotectivestructures.

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SILO DEFENSE

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RADAR

EPTORS

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SHELTER DEFENSEl!!!!

INTERCEPTOR

● SMALL.LOW COST

● PHASED-ARRAY

Fig. 2.Low-altitude endoatmospheric ballistic missile defense.

development in sensor, guidance, warhead, and missiletechnology.) Distributed data processing and the use ofmultiple small, hard radars would ensure that the systemperformance would degrade gracefully against evenmoderately heavy attack. For low-altitude defense ofhard targets, an endoatmospheric system of the LawAltitude Defense System design could be ready fordeployment by the mid- 1980s, as reported by GeneralTate:6

[With $25M additional funds starting in Fiscal.Year 1981 it would be feasible] to enter engineeringdevelopment in Fiscal Year 1982 to support a[low-altitude missile defense] deployment concur-rent with MX deployment in 1986.*

.—— ——— ——●The BallisticMissileDefense Program receivedan additional$ 15M in Fiscal Year 198~ funding foUowingGeneral Tate’stestimony.

● INERTIAL GUIDANCE

● SINGLE S,TAGE

At the end of the trajectory, as an alternative toconventional hard-target endoatmospheric defense, sev-eral last-ditch methods for destroying warheads bynonguided missiles have been proposed. We considered anumber of techniques using nonpowered missiles(projectiles, dust clouds) and felt that none was feasible.However, a concept specifying dense barrages of pow-ered but unguided missiles, which recently came to ourattention, may offer near-term potential for endoat-mospheric defense of hard targets.

D. Layered Defense /

Combination of exoatmospheric, infrared, non-nuclear-intercept technology and endoatmospheric,small-radar, nuclear-intercept technology into a layered

9

defense system offers a number of synergistic advantagesover either system operated alone:

● leakage factors can be multiplicative, so that two

relatively leaky components can combine into asystem with very low leakage;

● two different discrimination phenomenologies place

severe demands upon decoy designs;● the low leakage produces lower costs per intercept;● reduced inventories and complexities accrue to both

layers, relative to single-layered defenses;● the upper layer avoids saturation of the endoat-

mospheric defense component; and● exoatmospheric-sy stem threat assessment improves

engagement planning for the endoatmospheric de-fense components.

An equivalent set of factors was reported by GeneralTate (Ref. 4, p. 2872).

III. FORCE-STRUCTURE ANALYSIS

On the premise that current ballistic missile defensesystems will mature as anticipated, it becomes necessaryto consider how such systems would affect the strategicsituation. We begin this consideration by exploring, withsimple models, the arms-control implications of ballisticmissile defense and other strategic options. Alternately,we explore how well these options could do in a worlddevoid of arms-limiting agreements.

We perform the analysis by estimating United Statesstrategic inventories needed to ensure the expectedsurvival of a predetermined deliverable retaliatory strikeby the United States after a Soviet first strike. Forassured destruction, the retaliatory strike is taken toconsist of a fixed number of warheads that can bedelivered against Soviet targets of value—cities, in-dustry, transportation, etc. The number of deliverablewarheads is taken arbitrarily as 1000 (that is, 100MX-equivalent payloads). Other numbers can be postu-lated, but our qualitative conclusions do not change ifthis assumption is varied.

Deterrence could be based alternatively on developinga war-fighting posture, in which forces are so structuredas to permit their flexible use throughout a nuclearexchange. In this case the needed analysis is much morecomplex and is less amenable to simple modeling.Consequently, we are limited to discussing at the end ofthis section some elements of war-fighting deterrence inqualitative terms, and deferring quantitative treatment.

The needed strategic inventories for deterrence dependon the offensive and defensive systems used. We treatfour options:

(1)

(2)

(3)

(4)

new ICBMS (MX) based nondeceptively in silos,no defenses (extension of current status);new ICBMS (MX) in multiple protective structures “:(MPS), no defenses (current DoD planning);- ,MX-MPS, defended by terminal missile defenses(extended DoD planning); andMXS based deceptively in silos, defended bylayered defenses.

We assume that when the United States implements aparticular technology, such as exoatmospheric defense,the Soviets can simultaneously implement an equivalentSoviet technology if they choose to do so. We do notattempt in this analysis to account for differences inemplacement dates for American and Soviet inventories.

The forces required for the United S@tes to achievethe specified deterrence criterion also depend on theforces maintained by the Soviet Union. The resultachieved by any change in American force structuresthus depends strongly on the Soviet response, or lack ofresponse, to the United States initiative. Expectationsconcerning Soviet responses depend on Soviet motiva-tions and policies. We consider two cases:

● a responsive Soviet behavior in which the Sovietaim is also to maintain a minimal expected deterrentin the face of’ possible United States counterforceattack, and

● an independent Soviet behavior in which the Soviet

forces are determined by internal considerations notdependent on American force structures.

The initial forces needed to achieve the deterrentcriterion can be estimated, based on known, inferred, orassumed capabilities of the opposing force structures andpolicies for their employment. Such computations mustbe quite detailed to account properly for design vari-ations within and betsveen Soviet and American forces.Consideration must be given to many aspects and detailsbeyond the capability of the simple sorts of analyses wecan attempt here. For example, to model correctly themissile-force exchange we study here, one must considervariations of such parameters as warheads launched oneach missile, their accuracies, and their delivery-vehicleperformance.

However, an estimate of the required force sizes canbe obtained from simple models that average over thesevariables. Such models are much too limited to defineactual strategic forces needed, but they are valuable in

A

.

10

estimating how extensive those forces must be to achievespecified deterrence levels. They are thus also useful incomparing force inventories and costs, both between firststriker and retaliator, and among the various strategicoptions considered by the retaliator. Our approach usessuch a simple model.

A. Force-Structure Model

To estimate the required deterrent forces, we assumethe following scenario: the Soviets strike fwst, using theirentire missile inventory to attack our ICBM fields; weride out the attack, using any active defenses we have todefend our missiles; our subsequent retaliatory attack isaimed at Soviet value targets; and any Soviet activedefenses attempt to intercept the fraction of the re-taliatory strike within range of the Soviet defense system.

Attack on our land-based ICBMS by the entire Sovietmissile force is only one of many possible scenarios,although it is the one often considered in arms-controlanalyses. This scenario is not realistic, but for ourpurpose it is conservative in that any lesser attackagainst the ICBMS either destroys fewer of our missilesor engages fewer of our defenders. The additionalsurvivors would then be usable in damage-limiting roles.Although implications of Soviet reserve forces are neg-lected in this preliminary study, they are critical andmust be treated subsequently in the broader context ofcountervailing deterrence.

To determine force structures, we derived formulasrelating survivable, deliverable warheads to initial inven-tories, based on the above exchange scenario. In theresponsive case, both Soviet and American inventorieswere assumed coupled, Inventories were increased to-gether until the calculations showed each side achievedthe specified deterrence criterion, This approach pro-duced minimum inventories and costs for both sides. Inthe independent case, Soviet missile inventories werepostulated at freed levels, and the remaining Soviet andAmerican inventories were varied until the United Statesachieved the specified deterrence criterion. United Statesinventories were structured for minimum cost at eachthreat level.

With the notation given in Table I, and using primedquantities for Soviet hardware, the needed formulas are*

*The expression (1 — p’)mis rigorously correct in theseformulas only for integral values of a For nonintegral values,the correct expressionwouldbe (1 – p’)rul(1 – <a> p’),where[a] is the integer part of a and <a> the fractional part, Forconciseness, we continue to show the simpler form; however,we used the corect form in all our inventory estimates.

Option (1)

Option (2)

Option (3)

Missiles based nondeceptively indefense. All silos are assumedmissiles in them (H = M).

S= M(l–p’)@’m ;

and

W=ps .

silos, noto have

Missiles based deceptively in multiple pro-tective structures (H > M); no defense.

S = M (1 – p’) ~w”x ;

and

W=ps .

Missiles based deceptively in silos or muki-ple protective structures (H > M); withlow-altitude missile-only defenses.

S = M (1 – p’ L~ ~’”’/* ,

where

Ln = (1 – r) YHW~’

for MPS,* or

L“ = (1 – r) ‘WIIW’

for silos*; and

W=ps .

Option (4) Missiles based deceptively in silos, withpartially ambiguous exoatmospheric defensescoupled with low-altitude missile-ordy de-fenses.

For this model, we assumed that there are noempty silos; each silo contains either amissile or an exoatmospheric interceptor (H= M + X). We assumed that two rockets

●The rationale for this difference is that for MPS the defenseunit is assumed to be in a shelter adjacent to the missile’sshelter, far enough away to require defending it explicitly,whereas for silos,the defenseunit is assumed close enough tothe silo to be defendedimplicitlyas the silo is defended.

11

TABLE I

NOTATION(Values used in this analysis are given in [ ])

Inventories MHx

N

Y

Outcomes s

w

Parameters Pxf

Kill Probabilities Pqr

Leakage Factors LXAXLn

MissilesSilos/SheltersExoatmospheric interceptorsEndoatmospheric interceptorsEndoatmospheric interceptors per defense cluster(defense unit)

Missiles surviving missile-field attackWarheads delivered on target

Warheads/missile [10]’Kill vehicles/exoatmospheric interceptor [10]Ambiguity factorb

Warhead on silo or shelter’ [0.80]Exoatmospheric kill vehicle on warheadd [0.80]Endoatmospheric interceptor on warheadd [0.70]’

Exoatmospheric defense of missilesExoatmospheric defense of value targetsEndoatmospheric defense (missiles only)

‘As specified in SALT II for new missiles.‘The “ambiguity factor” represents the degree to which the exoatmospheric defense can be used todefend value (area) targets. f is defined as the fraction of value targets, attacked by the retaliatorystrike, that are within range of the exoatmospheric defense. Reasonable values are 0.5 to 0.8. Wetreated f as a parameter, using f = 0.6 for comparative results.Tncludes an estimate of operational reliability.‘Approximates in one constant both interceptor-related factors (reliability, warhead lethality) andsystem-related factors (detection, discrimination, radar availability).“For first intercept; degrades by 20% for each subsequent intercept.

——. ——— —— ____ ————

share booster hardware and differ only in the heads, not wasting interceptors on warheadspayloads; they thereby look enough alike targeted on (now empty) interceptor silos.that the opponent cannot tell which siloshave missiles, To maintain long-term decep-tion, covert missile-to-interceptor in-terchanges would be required periodically.These interchanges could be made by smallvehicles transporting only the payloads, thuseliminating transport of entire missiles, as isrequired in the MX-MPS concepts.

To select the optimum mix of interceptorsand missiles, we chose the inventories thatwould minimize the expression (M + X +0.2N), representing a factor approximatelyproportional to cost. This expression as-sumes that exoatmospheric interceptors andmissiles cost the same, and that endoat-mospheric interceptors cost 1/5 as much. We

To strike first, the opponent must target all constrained N to be an integer y times H,silos. We assumed that we can determine by that is, we assumed deployment of y endoat-infrared trackingat missiles. We

which warheads are aimed mospheric interceptors per silo.intercept only those war-

.

.

.

.

12 /-’(./’

.

S= M(l–p’Ln L~~M”H ,

where

LX= (1 – q) ‘XWI’’M’M,,

Ln = (1 – r) ‘H’~’M’~ ;

and

W = @ [f’A’X+ (1 – f’)] ,

where

A’, = (1 – q’) “x’’@f’ .

1. Responsive Soviet Behavior. The underlying as-sumption of a responsive relationship based on minimalmutual deterrence capabilities is not justified by Sovietwritings or behavior. Nevertheless, the responsive as-sumption results in estimates of minimum force levels forboth sides, and so provides a means of determining lowerlimits for the strategic inventories needed to assuredeterrence. Those options that require unreasonablylarge inventories in this environment would fare evenworse under less constraining assumptions and can beeliminated from further consideration.

For each option, we derived minimum inventoriesneeded on both sides to achieve the specified deterrencecriteria. Such criteria, and the resulting inventories, neednot be symmetric. For example, the Soviets could specifythat their deterrent be twice what we choose. Differingparameters, such as warheads per missile, would alsoresult in asymmetric inventories.

We have solved here only the fully symmetric case inwhich all inventories, parameters, and kill probabilitiesare equal for the two sides. This case retains many of thecharacteristics of the general solution, but the equationsare much easier to solve.

Inventones needed to assure a 100@warhead re-taliatory force were computed using the formulas givenearlier and the parameters listed in Table I. The assump-tions of cooperation and symmetry were treated bysetting all primed quantities in the formulas equal to theirnonprimed counterparts. The results are summarized inTable II.

Three of the four strategic options considered canproduce satisfactory results in this symmetric, responsivecase. The exception is offensive missiles based nondecep-tively in silos; in this case assured destruction and crisis

stability are mutually unattainable. MX-MPS, defendedor undefended, requires only 115 to 150 MX-typemissiles, emplaced deceptively among a few-thousandshelters, to achieve deterrence. Use of missile defenseswith MX-MPS halves shelter and land requirements.Such basing options are vulnerable if the deceptivebasing is not fully effective. This vulnerability would notbe prevented by expanded terminal defense.

What may be surprising in this analysis are the -moderate inventories associated with layered defense ofsilos. Although many believe that mutual deterrencewould be overly costly if systems included ballisticmissile defenses capable of wide-area defense, our modelsuggests that this belief may not be entirely correct. Evenin the case of a totally ambiguous exoatmosphericdefense component capable of defending all valuesattacked by a retaliatory force, stable assured-destruction deterrence could be achieved with as few as300 silo-based MX missiles and 200 silo-based exoat-mosphenc interceptors.

Whereas MX-MPS is catastrophically sensitive to

failures of deception, failure modes for layered defense ofsilos are apparently more gradual and therefore for-giving, A number of examples support this assertion.

First, the required degree of deception for this layereddefense concept is much less demanding than thatneeded for MX-MPS; deception, therefore, is much lesslikely to fail. But suppose deception were to fail for asymmetric layered defense posture with the inventoriesgiven in Table 11 for f = 0.6~ In this case, failure ofdeception would reduce the deliverable retaliato~y deter-rent from 1000 to 400 warheads, a serious but notcatastrophic degradation. On the other hand, if we learnthat deception is no longer reliable, we can increaseinventories to reestablish the full deterrent. Withoutdeception, symmetric inventories would be 260 missiles,760 silos, 500 exoatmospheric interceptors, and 260endoatmospheric interceptors; although sign~lcantlygreater than those needed with reliable deception, thesequantities are still reasonable.

Another calculation shows the resilience of layereddefense in the face of treaty verification problems.Optimal cost-effectiveness for both sides would beachieved with a 220:200 ratio of siloed missiles to siloedexoatmospheric interceptors. It is easy to verify howmany silos are in use but ditlicult to verify the mixbetween missiles and interceptors. What if the Sovietscheat on some future treaty by replacing interceptors bymissiles, or vice versa, within the ver~lable f~ed numberof silos? Our model indicates that departures by the

13

TABLE H

APPROXIMATE INVENTORIES TO ACHIEVE MUTUALLY ASSURED DESTRUCTION(W= 1000) IN THE RESPONSIVE, SYMMETRIC CASE

Inventories

silos,Option Basing Defense Shelters Missiles Exos Endos Notes

(1) Silos None 109 109 ‘ --- --- Passive posture’ (ride outattack, crisis stable).

5000 5000 --- --- Dueling posture’ (launch underattack, crisis unstable).

(2) MPS None 3500 150 --- --- Assuming 23 shelters per missileas in DoD plans for MX-MPS.

(3) MPS Endos 1600 115 --- 230 Optimized by using 14 sheltersper missile.

(4) Silos Layeredb 500 300 200 1000 f = 1.0 (worst case).420 220 200 420 f = 0.6 (nominal case).

‘Following terminology and treatment developedby R. H. Kupperman and H. A. Smith, Ref. 7.‘Inventoriesdepend on missile-to. exoatmospheric interceptor ratio. This ratio was chosen to minimize the expression (M + X + 0.2N), representing afactor approximately proportional to system cost.

Soviets from this optimum mix could indeed degrade ourretaliatory capability in the face of a Soviet first strike.The Soviets, however, would at the same time incurmuch greater degradation of their ability to retaliateagainst an American first strike.

Figure 3 relates the number of retaliatory warheadsthat could be delivered following a first strike to thenumber of missiles deployed by the Soviets in their 420silos. United States retaliation following a Soviet firststrike is plotted as the solid curve; Soviet retaliationcapacity atter an American first strike is plotted as thebroken curve. The symmetric solution, resulting in 1000warheads deliverable after either side strikes first, isshown as a dot.

As an example of the situation if the Soviets cheat,consider what happens if the Soviets convert 80 of theirexoatmospheric interceptors to missiles, giving a total of300 missiles. If the Soviets strike first, the United Statesretaliation produces approximately 850 warheads ontarget, not a significant degradation. But if the_UnitedStatgs w~lQstrike first, the weakened Soviet defensewould leave them with less than 200 retaliatory war-heads, a highly significant concern to Soviet planners.The same disparity exists across the range of Sovietmissile counts producing substantial degradations of the

u)n<

3

1000

800

600

400

200

t)

I i I

. . . . . . . . . . . . . . . . . . . . . .

❑

....“

..”A

$“

●A..&”

X’

.&””

.8” 1

a“”‘,,

a Q.I

o 100 200 300 400

SOVIET MISSILES

● SYMMETRIC SOLUT ION

~ SOVIET FIRST STRIKE - US RETALIATION

.... . . . . US FIRST STRIKE - SOVIET RETALIATION&

Fig. 3.Deerease of retaliatory warheads due to assumed departuresby the Soviets from solutions of the symmetrk equations forlayered defense. The total number of Soviet silos is ●ssumedconstant.

.

.

.

.

United States deterrent,

14

This disparity may prove to be a strong incentive foreach side to keep close to the optimum mis-sile-interceptor mix, even in the absence of any verifiableor unverifiable treaty agreements.

As a third example of gradual response by layereddefense to failure modes, clandestine increase in thenumber of warheads carried by each Soviet missile is apotentially serious threat. Such fractionation is inevitablyaccompanied by reduced warhead yield, but this de-crease can be more than overcome by the increasednumbers of warheads in the threatened attack, Figure 4shows how Soviet fractionation might affect our deter-rent. For W’ s 20, we estimate serious but notcatastrophic deterrent degradation. For even greaterSoviet fractionation, ICBM survival could become prob-lematical. Of course, if the fractionation were overt, or ifwe became aware of it by intelligence means, we couldcounter its effect by modest increases of our inventories.

For most of the potential failure modes of layereddefense, degradation of the retaliatory force wouldbecome more severe and abrupt if the Soviets were ableto defend a larger fraction of their assets. Evaluation ofthis effect awaits more detailed computations.

2. Independent Soviet Behavior. In this case, weassumed the United States faces a freed Soviet threat thatis not responsive to American arms-reduction initiatives.

600

400

200

1o~

10 12 14 16 18 20

SOVIET WARHEADS PER MISSILE

Fig. 4.Degradation of United States nuclear deterrent (establishedwith layered defense of silos) when the Soviets clandestinelyadd more warheads.

This appears to many observers to describe recent Soviet ‘~behavior more accurately than does the “responsive” ‘‘,assumption. Consistent with this assumption, the Sovietshave publicly repudiated the mutual deterrencephilosophy that has formed the basis of much recentAmerican thinking in the field of arms control.

The United States forces required for deterrence wereestimated as a function of the Soviet force by using thesame formulas and parameters used previously, withoutthe assumptions of complete United States/Soviet forcesymmetry. The results were applied in two eras:

● Near term. Some analysts project a continuedgrowth of the Soviet threat consistent with recenthistory. We evaluated how each strategic optionwould respond throughout the next decade underthe assumption that Soviet missile forces grow at arate of 10?40per year. This assumption imposes atime scale with which to compare the options, ratherthan suggesting a realistic estimate of Soviet inten-tions, a matter well beyond the scope of our effort.

● Long term. We estimated how well and at what(approximate) cost each of the strategic optionscould respond to continued growth of the Sovietthreat, past the next decade. Without regard to aspecific time scale, this analysis permits com-

parisons of long-range costs among the strategic

options and cost-exchange comparisons between

threat and response.

a. Near Term. The postulated Soviet threat growth isplotted in Fig. 5. We used this threat as an inputcondition and estimated the year-by-year capability ofeach strategic option to respond to it. To make theseestimates, we needed to project availability of thetechnology for each option. Such projections have a highdegree of uncertainty. Estimates are best for systemsalready planned and whose technologies are in hand.Estimates are worst for systems with untested, immaturetechnologies.

Ballistic missile defense suffers from a larger degree ofpredictive uncertainty than the other strategic options. Insome areas its technology is new. In other areas, wherethe technology is mature, budget constraints have pre-cluded prototype construction. Not only defense suffersfrom such uncertainty, however. Schedules for MX-MPScould be delayed by social and political issues beingraised at present. Technology problems associated withmaintaining deception and yet permitting verificationhave yet to be fully resolved. Nevertheless, MX-MPS is

15

10000

8000

6000

4000

3000

2000

,000 ~

84 85 86 87 88 89 90 91

CALENDAR YEAR

Fig. 5.Postulated Soviet threat growth.

much farther along the chain of approvals than any ofthe ballistic missile defense programs.

Setting these qualifications aside, it is appropriate toestimate how soon the various technologies could beeffective if they were driven by technical constraintsalone. We used the technology schedules given in TableIII. Actual availability could approach these schedules iftechnological preparation continues while the politicaldebate about American implementation of the variousstrategic options goes on.

Using our model, we estimated how the AmericanICBM retaliatory deterrent could recover as the newlyavailable strategic forces become available in the nextdecade and beyond. We assumed that installation of newoffensive and defensive hardware occurs at the technolo-gy-limited schedules given in Table III. Until the newsystems are emplaced in quantity, the existing silo-basedMinuteman missiles represent a significant element in ourdeterrent posture. Consequently, we assumed thatMinuteman missiles (with an average of 2.5 warheadseach) are permitted to remain active in existing silos notrequired for MX missiles or interceptors. We assumed aSoviet attack given by the postulated threat projection ofFig. 5 and apportioned between MX missiles andMinuteman missiles so as to destroy the maximumpossible number of United States warheads.

We also considered the effect a Soviet area-defensivesystem could have on recovery of our retaliatory deter-

rent. Currently, the Soviets have a limited ballistic missiledefense system installed around Moscow (as reported bySecretary Brown, Ref. 1, p. 57), but its areadefensecapabilities appear too limited to afTect our retaliatorydeterrent appreciably. However, if the Soviets were toinstall an eflectfve area defense, as for example one withcapabilities equivalent to those projected for Americantechnologies, then recovery of our retaliatory deterrentcould be delayed further. The additional delay wouldarise from the Soviet capacity to intercept United Stateswarheads that survive the Soviet first strike and are thenlaunched in retaliation. The assumption that the Sovietswould add an area defense cannot be ignored if theUnited States were to install one. On the other hand, theSoviets may-overtly or clandestinely-install an effec-tive area defense whether or not we do.

To quantify this effect, we computed retaliatory-forcerecovery for two cases, one without Soviet area defenses,and one in which we assumed Soviet area-defensecapabilities and schedules similar to those available inthe United States. Although arbitrary, this assumptioneither represents Soviet responsiveness if both sidesinstaU ballistic missile defense systems or it is a realisticschedule if we do not but they do.

For both cases, we computed expected surviving anddeliverable United States retaliatory warheads, for eachof the four strategic options considered, on ayear-to-year basis. In the fwst option, MX and Minute-man missiles based nondeceptively in undefended silos,none would survive the postulated Soviet threat through-out the near-term period. For the remaining threeoptions, we have plotted in Fig. 6 the estimates ofAmerican retaliatory warheads that could be deliveredtier a Soviet first strike. The horizontal line marks theassumed deterrence criterion of 1000 deliverable war-heads. We take recovery of adequate ICBM-force sur-vivability to occur for each option at the date when thedeterrent reaches that line.

In the absence of Soviet defenses (Fig. 6a), MXmissiles in MPS, without defense, would achieve thespecified deterrent criterion by about 1991. That is laterthan the current fully operational MX-MPS date of 1989because the currently planned MX-MPS deployment(200 MX, 4600 shelters) is not adequate for the threatwe have assumed. Two years later, the modeledMX-MPS deployment would have grown to 340 MX,7820 shelters, attaining the expectation of 1000-warheadsurvival.

With defense by a Iow-altitude terminal-defense sys-tem, our model predicts that MX-MPS would reach

.

16

TABLE III

TECHNOLOGY-LIMITED PROJECTIONSOF HARDWARE AVAILABILITY

Technology Permits

Current Hardware SubsequentSchedule Availability Construction

Technology Ioc/Foc’ During Rate

MX missileMPSEndoatmospheric

defenseb

986/1989 1985 70/yr986/1989 1985 610/yr99 1/? 1985 000/yr

Exoatmospheric Not scheduled 1987&fense

100/yr

‘IOC = initisI operational capability; FOC = fully operational capability.bLOW AltitU& Defense system”

Note: MX and MPS schedules taken from Ref. 8. Baltistic missile defenseprojections assume an accelerated, aggressive, but not crash ap-proach to technology preparation. Endoatmospheric defense sched-ules are based on the Congressional testimony by Major GeneralGrayson D. Tate, Jr., Ballistic Missile Defense Program Manager,cited on page 8. Exoatmospheric defense schedules are our ownprojection and appear realistic to us, but they have been criticized asunduly optimistic by others.

deterrence by 1988. This would be accomplished with adeployment of 130 missiles, 3000 shelters, and far fewerthan the scheduled inventory of interceptors.

Our model suggests that layered defense of MXmissiles in silos could not be effective much before1988-1989, due to the expected availabilityy dates ofexoatmospheric defense components. Operating by itselfin defense of silos, the endoatmosphenc component oflayered defense could be enhanced to protect silos beforethe availability of the exoatmospheric technology(dashed curve of Fig. 6a). This must be considered atbest an interim solution because terminal defense byitself is easily overwhelmed as the threat grows.

If the Soviets were to add area defenses, the date whenthe American ICBM force could deliver the desiredretaliato~ force on Soviet targets would be fufiherdelayed by 3 to 5 years (or more) as shown in Fig. 6b.We again project deterrent recovery to be most delayedwith undefended MX-MPS and to occur soonest withdefended MX-MPS. But even in this best case, deterrentrecovery is delayed until about 1990. The contrastbetween Figs. 6a and 6b quantities concerns aboutSoviet ballistic missile defense breakouts, p~cularly if

the United States cannot respond promptly with defensesystems of its own.

According to our model, low-altitude defense ofMX-MPS, or layered defense of MX missiles in silos, orboth, offers the earliest recovery of ICBM survivabilityin the near term. Obviously, we have not accounted forother elements of our triad. Thus, in the near term,degradation of our deterrent capacity should not be asgreat as that suggested here.

b. Long term. To counter possible continued Sovietthreat growth, continued growth of American strategicinventories is also necessary. The extent of that growthrelative to Soviet investments in strategic inventories, in asense, influences Soviet incentives to proliferate weaponssystems. If our costs are much higher than theirs,continued Soviet proliferation may exceed our will orcapability to respond. This might be a powerful incentivefor the Soviets to continue proliferating. If, on the otherhand, our costs can be much smalIer than theira, anequally powerful incentive may exist for them to limitproliferation.

17

3000

2000

1000

0

WITHOUT SOVIET AREA DEFENSE

I I I I [ [ [0 MX–MPS + LoADS

O LAYERED DEFENSEOF SILOS

A MX–MPS

3000

2000

1000

0

WITH SOVIET AREA DEFENSE

I I I I I I I

❑ MX-MPS + LoADS

O LAYERED DEFENSE OF SILOS

A MX-MPS UNOEFENDEO

85 87 89 91 85 87 89 91

CALENDAR YEAR

Fig. 6.Modeled recovery of United States ICBM retaliatory deterrent if variousAmerican strategicforces are emplacedaccordingto technology-iimitedschedules (Table III): (a) delays in ICBM recovery if the Sovietsinstall no new area defenses, and (b)further delays incurred if the Soviets install a new area-defense system with technology and schedules similar to those●vailable in the United States.

To evaluate this situation, we used our model toestimate American inventories needed to counteractthreats much larger than those achieved in the short-termprojection. Our short-term threat projection ended in1992 with arriving threats of fewer than 10000 war-heads. For the long term we considered threats of up to40000 warheads (that is, the payloads of 4000 missileswith 10 warheads each). We then added an approximatecost model for comparisons among the strategic options.

hwentorfes. Estimated American inventories re-quired to establish assured-destruction deterrence againstpotential long-term threats were computed with ourmodel. We do not present results for missiles basednondeceptively in silos because the estimated inventoriesare too large to be considered achievable, In Fig. 7, weplot inventories for the other three options, and contrastthem with Soviet missile inventories needed to launch thethreat. We also show (as dots) inventories for thecooperative-symmetric case given earlier.

Figure 7a shows inventories for undefendedMX-MPS. In this case, the United States would need toinstall roughly one-third as many missiles as the Soviets,but would have to emplace them among a huge number

of shelters. For example, against a threat of 2000 Sovietmissiles, we would need about 700 missiles and about19000 shelters.

With terminal defense installed with MX-MPS (Fig,7b), estimated inventories would be significantly re-duced; for the same example as above, the United Statescould maintain deterrence with 300-350 missiles,8000-9000 shelters, and approximately 1500 termi-nal-defense interceptors.

With layered defense of MX missiles based deceptive-ly in silos, the estimated inventories depend on whetherthe Soviets also install an area defense. If they do not(Fig. 7c), the United States can maintain its ICBMdeterrent with the minimum inventories of any of theoptions considered. For the 2000-missile threat, wewould need 115 missiles, 660 exoatmospheric intercep-tors, and 775 silos and endoatmospheric interceptors.

If the Soviets choose to instaU an area defense, theUnited Statea layered defense inventories needed tomaintain our ICBM deterrent (Fig. 7d) would be largerthan without such Soviet defenses. To assess Americaninventory growth, we assumed (as before) that the Sovietdefense inventories mirror our own. For the 2000-rnissi.le

,

18

I

MX-MPS-UNDEFENDED MX-MPS-LOADS

t

.

100000

I.Ll

E 10000

01-ZLu> 1000z—

100o 2000 4000

LAYERED DEFENSEWITHOUT SOVIET DEFENSE

100000 ~ I I I

10000

SOVIET MISSILES

1000

-$= ;EXO INTERCEPTORS

US MISSILES

100 ~ 1

0 2000 4000

t I I I I 4

US SHELTERS

SOVIET MISSILES

,

,; ●

● I I I

o 2000 4000

LAYERED DEFENSEWITH SOVIET DEFENSE

~

SOVIET MISSILES

;4= -EXO INTERCEPTORS

‘.US MISSILES

I I I 1

0 2000 4000

SOVIET MISSILES USED IN STRIKE

Fig.7.Inventories needed to achieve deterrence criterion (W = 1000) against possible long-term Soviet threats. (a) MX-MPSundefended; (b) MX-MPS with low-altitude defense; and layered defense of MX based deceptively m silos, without

equivalent Soviet defenses (c), and with them (d). Dots show inventories given earlier for the cooperative-symmetricsolutions.

19

threat, the American inventories would be: 270 missiles,930 exoatmospheric interceptors, and 1200 silos andendoatmospheric interceptors. The Soviet force wouldalso have 930 exoatmospheric interceptors, and wouldspecify 2930 silos and endoatmospheric interceptors.This option also has the stabilizing feature that the bestAmerican response to increased Soviet threat growth isto add dominantly exoatmospheric interceptors, with buta few additionrd missiles.

Costs. The economic comparisons among strategicoptions were based on two functions: the initial installa-tion costs, and the way costs would grow as the threatgrows. A system whose initial cost exceeds that of thethreat, and whose cost continues to grow faster than thatof the threat, is less effective by this definition than asystem that consistently costs much less than the threatit faces.

Costs were based on dollar estimates of developmentand inventory expenses of the various components. Thesame estimates were used for equivalent Soviet andUnited States systems—for example, Soviet missiles andMX missiles-as a basis for comparing Soviet andAmerican costs. The cost data from which estimateswere derived are given in Table IV.

There are additional costs associated with nuclearwarheads that cannot be quoted in an unclassifiedforrhat. Including warhead costs would make all respon-ses appear more cost-effective relative to the threat, and

would favor the nonnuclear ballistic missile defenseresponses relative to the other responses.

Cost curves are presented for the modeled strategicoptions, giving the emplacement costs as a function ofthreat, in Fig. 8. All three American options we con-sidered cost about the same at the low end of the Sovietthreat spectrum. However, the costs of the three optionsbecome very different as the threat grows.

MX-MPS, undefended, consistently costs twice asmuch as the Soviet threat because of the large number ofshelters needed. This cost behavior suggests that ex-panded Soviet arms build-ups might eventually cause theUnited States to reach limits of national resolve orcapacity to respond. This certainly violates the spirit ofany arms-control climate ever proposed. By addingterminal defenses to MX-MPS, United States costsdecrease to approximate Soviet costs; this offers neitherside marginal incentive for or against arms limitations.

Layered defense of MX missiles based deceptively insilos appears to offer stabilizing economic advantagesthat tend to deny incentives for continued Soviet armsbuild-up. The lower curves of Fig. 8b represent cost vsthreat estimates if the Soviets do not install an areadefense but the United States does. Here, our estimatedcosts exceed the Soviets’ at the low end of the threatspectrum; costs are equal at moderate threats; andAmerican costs remain significantly below Soviet coststhereafter. The economics of introducing layered defense

TABLE IV

ASSUMED COSTS AND SCALING FACTORS OF OFFENSIVE ANDDEFENSIVE SYSTEMS AND COMPONENTS

Development Quantity Cost(a)Component Sytnbol ($M) ($M)

Missile M 8ooo@1

Exo interceptor x 7000 \

60 (M+X).7S@)[c)

Endo interceptor N 5000 16 No78Silo H o 6 H(d)

Shelter (MX-MPS) H 50000) 3 H(b)

(Wle scaling function N“’s for the cost of N units, as applied to missile and interceptor hardware, wassuggested by McDonnell Douglas Aircraft Corporation.‘b)Based on MX development costs obtained from Congressional Budget Ofllce Budget Issue Paper, Ref. 8.(cWiiuringthe exoatmospheric interceptor to use nissile hardware.(d)si10 cost assumed to be twice that of shelter cost due to added complexity.

.

.

.

20

MX-MPS LAYERED DEFENSE

140

120

nm 100

u80

m+ 60~ do

20

0

MX-SILOS

I I I I I 140 ~

UNDEFENDED

●●$) ,.”

. .. .

I I I I I

o 2000 4000

20

00

80

60

40

20

0

— US COSTS

. . . . . SOVIET COSTS . . -●.

.*

.“O

/

,.. . .

..-. .;.,&=-,..#.-.....,. WITHOUT SOVIET..” DEFENSES -

I I 1 I

o 2000 4000

SOVIET MISSILES USED IN STRIKE

Fig. 8.Estimated costs of strategic options contlgured to ensure deterrence (W = 1000) against long-term Soviet threats. Dots

show costs associated with symmetric solutions.

using deceptive basing of MX missiles in silos thusinhibits Soviet expansion of its ICBM force by placingthe Soviet forces at a substantial cost disadvantage.

However, what if the Soviets were to implement acomparable area-defense concept, one that we assumewould force them to incur development and inventorycosts mirroring our own? The results are shown as theupper curves, of Fig. 8b. In this case, an especially

favorable arms control setting would ensue. As theSoviet threat level increases, American costs to maintainits deterrent posture would increase as well; but theincremental costs needed to offset Soviet investmentsand reestablish the strategic balance would stronglyfavor the United States. In this setting, Soviet armslimitations would be driven strongly by the economics; atreaty might well be superfluous.

B. Additional Considerations: Countervailing Strategy

By concentrating on ICBM survival and as-sured-destruction deterrence, our analysis has so farignored much of the real-world complexity of deterrence.

As Secretary Brown noted in his 1981 Posture State-ment:’

For deterrence to operate successfully, ouc poten-

tial adversaries must be convinced that we possess

sufficient military force so that if they were to start

a course of action which could lead to war, theywould be frustrated in their effort to achieve theirobjective or suffer so much damage that theywould gain nothing by their action. Put differently,we must have forces and plans for the use of ourstrategic nuclear forces such that in consideringaggression against our interests, our adversarywould recognize that no plausible outcome wouldrepresent a success-or any rational definition ofsuccess. The prospect of such a failure would thendeter an adversary’s attack on the United States orour vital interests. The preparation of forces andplans to create such a prospect has come to bereferred to as a “countervaihg strategy.”

To achieve this objective we need, fwst of all, asurvivable and enduring retaliatory capability todevastate the industry and cities of the Soviet

21

Union. We must have such a capability even if theSoviets wae to attack tirs~ without warning, in amanner optimized to reduce that capability asmuch as possible. What has come to be known asassured destruction is the bedrock of nucleardeterrence, and we will retain such a capacity inthe future. It is not, however, sufficient in itself as astrategic doctrine, Under many circumstanceslarge-scale countervalue attacks may not be ap-propriate—nor will their prospect always be suffi-ciently credible—to deter the full range of actionswe seek to prevent.

Secretary Brown went on to discuss the role of damagelimitation in the countervailing strategy:l

Our goal is to make a Soviet victory as improbable(seen through Soviet eyes) as we can make it, overthe broadest plausible range of scenarios. We musttherefore have plans for attacks which pose a morecredible threat than an ail-out attack on Sovietindustry and cities , , . We could . . . attack, in aselective and measured way, a range of military,industrial, and political control targets, while re-taining an assured destruction capacity in reserve,

But Secretary Brown did not emphasize defense in hisstrategy. The Department of Defense was constrained byconcerns about instabilities associated with ballisticmissile defense (see quote cited in Sec. I) and by theAnti-Ballistic-Missile Treaty of 1972. Secretary Brownnoted (Ref. 1, p. 99):

Our current programs of active defense reflectthese constraints and the emphasis we place ono~ensive forces for deterrence.

If the concerns felt by the Department of Defensecould be alleviated, what then would be some of thepotential roles for ballistic missile defense in support ofthe countervailing strategy?

We have already shown how ballistic missile defensesmight economically ensure the survival of enoughland-based missiles to achieve assured-destruction deter-rence. More of our land-based missiles would be neededfor damage-limiting roles in support of the countemailingstrategy; the optimal way to ensure their survival wouldvery likely also include missile defenses. This remains tobe confirmed.

Missile and area defenses structured to limit damagefrom a massive nuclear attack would probably be evenmore highly capable against limited nuclear attacks.

Small attacking forces tight be expected in a number ofscenarios, for example,

● attack by a superpower in the early nuclear phases

of the escalation ladder;. attack by a superpower on selected, critical compo-

nents of the national command authority and forcestructure;

● attack by an enemy with limited nuclear resources,

including attack by a third party in an attempt toinitiate a superpower exchange (“catalytic launch”);and

. accidental launch.Against such limited attacks, interceptor inventories

would be so large compared to the threat that they couldbe flown redundantly to reduce leakage. Against verylimited attacks there might be a high probability oftotally successful defense. The availability of a non-nuclear defensive response thus adds elements of crisisstability not available without defensive systems.

However, even against massive attacks, area-defensesystems would provide additional means to limit damageto targets of a Soviet attack. Warheads attacking targetsof value could be intercepted directly. Such defensewould not be perfect, but it would offer much improvedchances for military, industrial, and urban survival. Asignificant fraction of the defended targets would beavailable to deny Soviet objectives in any subsequentconflict. This capability of ballistic missile defense seemsto meet in an optimal way a criterion specified for thecountervailing strategy by Secretary Brown:’

. . . leave open the possibility of ending anexchange before the worst escalation and damagehad occurred, even if avoiding escalation to mutualdestruction is not likely.

Such a prospect seems, at best, much less likely to bepossible for strategic systems without ballistic missiledefenses.

Enhanced capability against limited attack, seen as anasset by the United States, may be perceived differentlyby our allies. They have limited nuclear missile arsenalswhose effectiveness might be seriously degraded in thepresence of an extensive Soviet area defense. Thisconcern is one of many such political/strategic questionsregarding the assets and liabilities of ballistic missiledefenses in our strategic posture. They must all beconsidered in the coming debate on ballistic missiledefense. Our quantitative results, and this brief quali-tative discussion of some elements of damage limitation

22

and crisis stability potentially available through activedefense, suggest that such analysis not be delayed.

IV. CONCLUSIONS

Strategic arms control is a national priority. Recent

Soviet and third-world aggression has underscored the

requirement to limit United States strategic investments

so as to free effort and funds for needed conventional

forces.

Paradoxically, the goal of significant arms reduction

has appeared inconsistent with the deterrence objectives

on which our military planning is based, Although often

termed “unthinkable,” we must face the possibility that

deterrence by threat of assured retaliation may fail. Somemeans of damage limitation would then be America’s

only recourse: preparation of such means is also seen bymany to strongly enhance deterrence.

Our purpose has been to investigate alternative tech-nological and force-structure opportunities that couldsimultaneously achieve mutual assured destruction andcontribute to damage limitation. We feel that ballisticmissile defense, when deceptively based along withmissiles in ICBM silos, may offer the opportunisty for

. reducing armaments substantially;● ftiing the gap between competing security and

arms-control goals;. thwarting limited ICBM attacks including acciden-

tal or catalytic launches against missile fields orurban targets;

● supplementing an inadequate theater nuclear forceby maintaining a strategic force structure andbalance, which would be relatively insensitive to thelimited use of our strategic forces against theatertargets; and

. offeringadditionalcrisismanagement ~d stabiliza-

tion tools to the United States and the Soviet Union.We emphasize the preliminary nature of our results,

but they do suggest profound effects that should not beignored. Credibility of the concept-even at the expenseof reopening the anti-ballistic missile controversy-hasbeen demonstrated. But much more analysis and veryinvolved simulations are mandatory if the present’resultsare to withstand scrutiny.

Specifically, the models provide these suggestions.. Layered defense of ICBMS based deceptively in

silos may provide an exceptional opportunity forstrategic arms reduction.

● The resultant mix between ballistic missile defense

and offensive weapons is stabilizing in that theeffects of Soviet cheating, were a new SALTagreement in force, would be comparatively small.

● Arms-control objectives are satisfied; the systemalso provides a limited capacity to reduce damageto urban/industrial targets, Exoatmospheric in-terceptors can be used to defend both value andcounterforce targets without denying the secondstriker his ability to retaliate.

. Similar economic and stabtlity advantages are ex-hibited in non-arms-control settings.

. In contrast with other proposed measures for reduc-ing ICBM vulnerability, ballistic missile defensedoes not depend on maintaining deception in basing.

● Crisis stabilizing measures are introduced by allow-ing for nonnuclear interceptor launch under real orapparent attack.

o Environmental problems posed by alternative MXschemes are avoided.

● Availability of exoatmospheric technology is thecritical path constraining the implementation ofsuch a system.

. In the search for near-term solutions, survival of the

United States ICBM force could be significantlyenhanced, with reduced environmental impact, iflow-altitude terminal defense were installed concur-rently with MX-MPS.

This preliminary analysis has given many indicationsof the potential value of a hybrid ballistic missiledefense/deceptive MX-basing system. The subject clear-ly warrants further analysis. We will need detailedmodels, in@iing large-scale computer simulations oftargeting, time-phased attacks, defense-suppression at-tacks, and game theory.

Our analysis was based on assured-destruction deter-rence, modeled by a 1000-warhead retaliatory force.Deterrence by this definition can be achieved even ifthere are large departures from missile parity, asevidenced by Soviet/United States inventory dfierencesfor layered defense of silo-based MX. However, ourcapability to achieve elements of war-fighting deterrencewould be degraded if our forces were much smaller thanthe Soviets’. The actual American strategic forces neededagainst very large Soviet threats would be structured bystriking a compromise between the large forces needed toachieve war-fighting goals and the smaller forces sufX-cient for assured-destruction deterrence. Ballistic missile

23

defense appears to give the greatest latitude for such acompromise.

Arms control will continue to be a basic national goal,now emphasized by the need to modernize both strategicand conventional forces with limited funds. The prospectof using exoatmospheric defense to achieve this goal willsurprise many arms-control advocates who will needtime to rethink the ballistic missile defense issue. Theextensive analyses needed to corroborate and extend thepresent results will take many months. The 1982 reviewof the present Anti-Ballistic-Missile Treaty is imminent.Prompt, vigorous action on these issues is needed.

Even if the analytic results hold, and even if ourlayered defense concept proves politically viable, we mayfind ourselves without the needed technology to imple-ment the concept. It would seem prudent, therefore, toengage in accelerated research and prototype develop-ment of ballistic missile defense systems so that technolo-gy limitations do not constrain future decisions.

ACKNOWLEDGMENTS

A Los Alamos National Laboratory team assembledby E. O. Chapin was responsible for the brief assessmentof ballistic missile defense technology upon which thisanalysis is based. R. G. Shrefller was the source of theidea that MX-missile/exoatmospheric interceptor similar-ities could offer advantages for deceptive basing. Wethank D. R. Westervelt, T. W. Dowler, and S. A.Maaranen for critical review, Rongriego for preparingthe figures, and J. W. McDonald and H. Frauenglass foreditorial comments. We thank K. K, Fenner for process-ing the multiple dratls of this document.

REFERENCES

1. Secretary of Defense Harold Brown, 1981 PostureStatemen4 Congressional Record, Comrnittce on Ap-

2.

3.

4.

5.

6.

7.

8.

propriations, United States Senate, March 12, 1980,pp. 49-51.

Some analysts report this action is already underway. See, for example, J. K. Davis, R. L. Pfaltzgraff,Jr., U. Ra’anan, M. J. Deane, and J. M. Collins, “TheSoviet Union and Ballistic Missile Defense: Institutefor Foreign Policy Analysis, Inc., Special Report(March 1980), pp. 6-7.

“The MX Missile Debate;’ Bill Meyers’ Journalbroadcast by the Public Broadcasting System, April24, 1980.

Major General Grayson D. Tate, Jr., Ballistic MissileDefense Program Manager, “Status of the BallisticMissile Defense Research and Development Pro-gram:’ (Prepared Statement) Congressional Record,Committee on Armed Services, United States Senate,testimony of March 12, 1980, p. 2869.

W. Schneider, Jr., D. G. Brennan, W. A. Davis, Jr.,and H. Ruble, “U. S. Strategic Nuclear Policy andBallistic Missile Defense: The 1980s and BeyondflInstitute for Foreign Policy Analysis, Inc., SpecialReport (April 1980), p. 42.

Major General Grayson D, Tate, Jr., testimony inresponse to questions by Senator John W. Warner,Ref. 4, p. 2923.

R. H. Kupperman and H. A. Smith, “DeterrentStability and Strategic Warfare,” in MathematicalSystems in International Relations Research, J.Gillespie and D. Zuines, Eds. ‘(Praeger Publishers,Inc., New York, 1977).

“The MX Missile and Multiple Protective StructureBasing: Long-Term Budgetary Implications~’ Con-gressional Budget Otllce, Budget Issue Paper forFiscal Year 1980 (June 1979).

.

●

24

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