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Ballistic Missile Defense:

A Potential Arms-Control Initiative

I
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V

LA-8632
UC-2
Issued: January 1981

Ballistic Missile Defense:

A Potential Arms-Control Initiative

G. E. Barasch
D. M. Kerr
R. H. Kupperman*
R. Pollock
H. A. Smith**

________________________________ DISCLAIMER -- ------------------------------------------------

This book was prepared as an account of work sponsored bv an agency of the United States Government.
Neither the United States Government nor any agency thereof, nor any of their employees, makes any
warranty, express or implied, or assumes any legal liability or responsibility for the accuracy,
completeness, or usefulness of any information, apparatus, product, or process disclosed, or
represents that its use would not infringe privately owned rights. Reference herein to any specific
commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does
not necessarily constitute or imply its endorsement, recommendation, or favoring by the United
States Government or any agency thereof. The views and opinions of authors expressed herein do not
necessarily state or reflect those of the United States Government or any agency thereof.

*Los Alamos Fellow. Executive Director, Center for Strategic and International
Studies, Georgetown University, 1800 K Street, N.W., Washington, DC 20006.
**Los Alamos Consultant. Chairman, Mathematics Department, Arizpna State
University, Tempe, AZ 85281.

ijiSTHIBilTiON OF THIS C0CIM;:T !S IT'L'

 BALLISTIC MISSILE DEFENSE:
A POTENTIAL ARMS CONTROL INITIATIVE

by
G. E. Barasch, D. M. Kerr, R. H. Kupperman,
R. Pollock, and H. A. Smith

SUMMARY

United States strategic forces must be restructured to meet national-security

objectives in a changing world. Growth and modernization of Soviet strategic missile
forces are causing our land-based strategic missiles to become increasingly vulnerable to
Soviet nuclear attack. American policy for deterring such an attack has evolved from
strict reliance on the threat of assured Soviet destruction to include nuclear war-fighting
concepts intended to deny Soviet hopes of winning the ensuing conflict. At the same
time, events in Iran and Afghanistan have underscored the need to expand and
modernize our conventional forces, requiring strict limitation of our strategic invest­
ments.
For some strategic force configurations, the goals of flexible nuclear deterrence and
strategic arms limitations appear mutually inconsistent With such forces, prospects for
arms limitations would degrade further if the current Soviet build-up were to continue,
or if the Soviets were to install unilaterally an anti-ballistic missile system capable of
wide-area, multicity defense, or both.
However, if the United States installs an anti-ballistic missile system along with
reduced but modernized offensive strategic forces, arms limitation appears compatible
with both assured destruction and war-fighting deterrence policies. This conclusion
appears equally valid for expanded Soviet forces even if the Soviets also install ballistic
missile defenses. In particular, we have analyzed an American strategic posture
including layered defense of MX missiles based deceptively in silos. The exoat-
mospheric-intercept component of this defense system could also defend some of our
cities and industrial and military installations. If the United States were to adopt this
strategic posture, we believe it would create incentives for the Soviet Union to restrain
strategic-arms expansion. Mutual arms-control initiatives could follow. In addition, this
defense system might offer stabilizing features: damage limitation for small attacks;
nonoffensive crisis response; and relative insensitivity to technological change. These
results do not seem to be available by deploying strategic offensive forces alone.
Test and installation of the needed defensive systems are now precluded by the
Anti-Ballistic-Missile Treaty adopted in 1972. An opportunity for Treaty reconsidera­
tion occurs in 1982. Substantiation of our results would suggest that consideration be
given to Treaty modifications or to replacing the Treaty with other agreements. Such
actions could lead to improved national security for the United States by enhancing our
deterrent posture and, at the same time, offer the potential for significant arms-control
initiatives.
I. INTRODUCTION retaliate if the other triad elements become vulnerable. If
the Soviets shelter or harden their strategic industry in an
Over the past two decades, significant changes have attempt to interfere with our assured-destruction deter­
occurred in the long-standing competition between the rent,2 ICBMs have the needed accuracy and yield to
•#
United States and the Soviet Union. Many of these counteract these actions. In a war-fighting role, ICBMs
changes have been adverse to American interests. A shift are the only strategic element capable of damage-limiting
in the global balance of power has taken place, as a attacks on time-urgent military targets.
result of a determined Soviet expansion of its military As offensive technology improves, deterrent strategic
power through growing defense expenditures. forces become more vulnerable to attack.
Critical strategic asymmetries between the two super­ Force-structure or doctrinal changes may therefore be
powers have thus emerged, including differing strategic needed. In particular, the ICBMs are becoming increas­
concepts of nuclear deterrence and warfare. For some ingly vulnerable to Soviet nuclear attack. Remedies
years American strategy rested on the premise that could include technology to reduce vulnerability, ex­
approximate equality of strategic forces would lead to pansion of the forces, or changes in strategic doctrine.
stable nuclear deterrence, which would be achieved Doctrinal changes might include launch under attack or
primarily through fear of mutual assured destruction. launch on warning, and might also necessitate pre­
Consequently, policies on weapons systems that might emptive attack upon time-urgent targets and disruption
threaten or undermine Soviet deterrent capabilities were of an expected attack. Although such changes in
eschewed by the United States as destabilizing. Although strategic doctrine could be an effective way to counter
the Soviet Union has expressed enthusiasm for the goal increased vulnerability, they impose imperatives for
of limiting American strategic forces, there is no clear action, which, in time of crisis, might increase the
evidence that they have embraced the restraint implicit in probability of nuclear war. To avoid this scenario, our
our policies. In contrast, the Soviets appear to have strategic forces must be survivable and our policy for
developed a strategy of seeking strategic superiority using them must be stable in a crisis: we must be able to
through balanced offensive and defensive forces, with gather information and deliberate before we have to act.
survival as the objective if nuclear war should occur. The Expansion of strategic forces to compensate for
Soviets have exploited these asymmetries to attempt to increased vulnerability is not attractive from either an
undermine American assurances to its allies and to call economic or an arms-control perspective. Thus, we are
into question the guarantee of America’s nuclear um­ left with the alternative of developing remedial technolo­
brella. gy to reduce strategic-force vulnerability. There is,
In recognition of the growing strategic imbalance, the however, another constraint on our selection of
United States recently announced a modification of its strategic-force structures.
nuclear targeting policy.1 In addition to a punitive In recent years, the Soviets have been able to exploit
assured-destruction strategy, our retaliation would at­ political, economic, and security instabilities in the
tempt to deny the Soviets any prospect of achieving Middle East, Asia, Africa, and Latin America, without
war-fighting objectives by destroying a range of needed effective opposition from the West. The invasion of
military installations. Elements of damage limitation in Afghanistan by the Soviet Union, coupled with the
this “countervailing” nuclear strategy are perceived both dilemma posed by the Iranian capture of the American
to enhance deterrence prospects and to provide needed hostages, underscores the inability of our strategic
options should deterrence fail. The adoption of the nuclear arsenal to deter attacks of a more limited or
countervailing strategy blurs somewhat the distinction conventional nature. These events also give evidence of
between United States and Soviet doctrines but cannot our failure to project an effective military presence
by itself compensate for existing force asymmetries. sufficient to achieve American interests in low-intensity
Restructuring of our strategic forces is also needed. To conflict.
allow the flexibility needed within the countervailing Without sufficient conventional forces, we face the
policy, American forces must be configured to serve both increasing risk that nuclear weapons would be used in
damage-limiting and assured-destruction roles. otherwise conventional conflicts. First use might be by
Invulnerable ICBMs can contribute to both deterrence the United States. National frustration, or a Soviet-
policies. In an assured-destruction role, they provide an inspired attack on our vital interests, or an initially
independent force within the strategic triad that could conventional war, might exceed our conventional-force

2
 response capacity. Depending on our distress, we might These goals, when coupled with strict force limita­
then use nuclear weapons under the assumption that a tions, appear from our analysis to be incompatible if we
nuclear exchange could remain limited. The Soviets seek strategies that use only offensive forces and exclude
could begin the exchange for similar or disparate rea­ defensive systems. This report, therefore, concentrates
sons. If then our deterrence forces were overly vulner­ on ballistic missile defense technology that could be
able, Soviet options would include an all-out coun­ introduced soon and might measurably foster the goals
terforce strike as an extremely effective way for them to of deterrence, arms control, and stability. Our analyses
limit damage to the Soviet Union. indicate that a properly configured force including a
Thus, we will need expanded and modernized conven­ ballistic missile defense system may permit deterrence at
tional forces to be able to avoid nuclear escalation from reduced force levels while resisting erosion of the deter­
limited conflicts. This need defines a constraint on our rent by technological advances. Moreover, the effective­
strategic-force procurements: we cannot divert effort or ness and structure of such a force do not appear to
funding away from the conventional forces that we need depend so crucially on treaty-specified actions as to be
to support measured diplomatic and military responses. critically vulnerable to violations of arms-control agree­
Our impotence in the Iranian crisis combined with the ments. Such a ballistic missile defense system would also
Soviet move into Afghanistan have effectively prepared add elements of crisis stability and damage limitation in
America for remedial action. Before these events, the case deterrence were to fail. Defensive systems could be
cold war was thought by liberal strategists to be a thing installed economically, together with or separately from
of the past; the Soviet Union and the United States the deceptive-basing modes now under development for
needed one another or, at least, were bent on coexistence. MX missile deployment.
The SALT II agreement, though hotly contested, might Previous consideration of ballistic missile defense has
well have been ratified by the Senate. Support for been seriously constrained by a long-standing and widely
strategic programs was limited. Subsequently, what had held concern: ballistic missile defenses would be
sometimes been seen as the professional paranoia of the destabilizing if capable of defending military, industrial,
conservative military strategists began to appear as and urban targets. Such area defenses would presumably
reality. America suddenly became aware that the Soviets interfere with the maintenance of assured-destruction
had built up mammoth arsenals of both conventional and retaliatory forces, thus tempting the nation possessing
nuclear weapons. We now seem ready to seek solutions defenses to launch a preemptive strike. Defense installa­
to the military imbalances. tions would presumably also lead to a defensive arms
Our objective in this report is to explore technologies race coupled with the ongoing offensive arms race. These
that will allow us to reduce forces and still meet both concerns are still current, as stated during 1980 by
assured-destruction and damage-limiting strategic objec­ Secretary of Defense Harold Brown (Ref. 1, p. 99):
tives. We attempt to find forces that will require min­
imum inventories and investments so as to maximize . . . attempting to construct a complete [ballistic
funds available for conventional forces. With limited missile] defense against massive nuclear attack
inventories, the effectiveness of the strategic forces must would be prohibitively costly, destabilizing, and in
be maintained in the face of maturing Soviet technology. the end, almost certain to fail;
Therefore it is essential that the force structure be and by President Carter’s Deputy Assistant for National
sufficiently diverse to withstand technological surprise. It Security Affairs, David Aaron:3
must also be relatively insensitive to “cheating” on
arms-control agreements; it becomes very difficult, in a I think we can be pleased that we’re not engaged in
political context, to acknowledge cheating or even inade­ both a defensive strategic arms race as well as an
quacy of verification once a treaty is accepted. The force offensive one.
structure must be able to respond economically to In this report we suggest how prospective ballistic missile
possible threat growth so that incentives for continued defense systems might overcome these concerns.
Soviet proliferation are reduced or denied. The force If both the Soviets and the United States are bent on
must be able to achieve arms-control, assured- strategic arms reductions, they can apparently retain
destruction, and damage-limiting objectives regardless of mutual deterrence by mutually assured destruction with
Soviet strategic policy. Finally, it should promote crisis moderate inventories of offensive and defensive strategic
stabilization.

3
components. The systems need not be costly nor lead to sents less mature technology. However, . . .
instabilities. If, on the other hand, the Soviets continue advances [in exoatmospheric ballistic missile de­
their strategic arms build-ups at the current pace, then fense technology] make it feasible to develop
American force structures that include ballistic missile autonomous long-range interceptors . . . [This
defense might provide the most economical and flexible system] is being validated ... and promises to give
options for deterring Soviet attack by the countervailing defense the cost advantage for the first time . . .
deterrence strategy. Continued offensive missile pro­
Based on a brief review of ballistic missile defense
liferation by the Soviets would not need to be mirrored
technology conducted by Los Alamos during 1980, we
by the United States. Our results suggest that we could
concur with General Tate’s optimism. We believe
instead maintain stable deterrence by moderate increases
ballistic missile defense soon could be ready to assume
in hardware, mainly defense components. In this case,
the postulated strategic roles.
the Soviets would not be likely to perceive our response
In the next section of this report, we describe some
as a threat to which they would have to respond.
elements of the current technology and summarize our
Reciprocal pressures for an arms race could ease. Of
technical assessment, comparing it with the Department
course, the Soviets could continue their arms build-up
of Defense assessment. We then continue our analysis of
anyway, and we would have to respond; but our results
assured-destruction deterrence postures by describing
indicate significant economic advantages for the United
simple mathematical models and applying them to a set
States in this scenario.
of strategic options available to the United States. We
The perceived Soviet/American balance of power rests
use the results to amplify our suggestions that timing and
on military capacities well beyond the maintenance of a
cost advantages may accrue to strategic options includ­
reliable assured-destruction (punitive) nuclear deterrent.
ing ballistic missile defense.
Thus our derivation of assured-destruction strategic
forces represents but a first step in the needed
force-structure analysis. We continue the analysis by II. TECHNOLOGY OF BALLISTIC MISSILE
suggesting some ways in which the countervailing DEFENSE
strategy might be enhanced by the capacity for limited
defense of military, industrial, and urban targets. The ballistic missile defense systems considered in this
The force structures postulated in this study would report can be categorized according to where an of­
require defense components whose development and fensive weapon is intercepted along its trajectory. System
testing are now precluded by the Anti-Ballistic-Missile concepts include early-trajectory or boost-phase in­
Treaty, which was adopted in 1972 and is scheduled for tercepts, midcourse or exoatmospheric intercepts, and
review in 1982. At that time either party can withdraw or terminal or endoatmospheric intercepts. Systems that
propose modifications without prejudice to future treaty specify two groups of intercepts, one after the other, are
activities. Strategic defense concepts discussed in this referred to as layered defense systems.
report suggest that serious consideration should be given Boost-phase or early-trajectory intercepts by
to modifying the Treaty or replacing it with an agree­ “directed-energy weapons” (intense laser beams or parti­
ment that would allow the benefits of the new defensive cle beams) hold the potential for an extraordinarily
technologies to accrue in support of both na­ effective defense of all national assets. Directed-
tional-security and arms-limitation goals. energy-weapon development in the United States is at so
Consideration of possible treaty actions rests partly on limited a stage at present that it is extremely unlikely that
the readiness of ballistic missile defense technology. The such systems could improve our strategic position in the
Ballistic Missile Defense Program Manager, Major Gen­ coming decade. Well-funded 5- to 10-year research
eral Grayson D. Tate, Jr., in testimony presented to the programs will be required to establish the needed tech­
Senate Appropriations Committee in March 1980, was nology bases in these areas before we can begin to realize
subdued but positive in his overall assessment of the their potential. These systems are not part of the present
technology.4 analysis.
Our analysis is based on conventional exoatmospheric
[Low-altitude defense] technology is low risk and and endoatmospheric defense systems that intercept
ready for preprototype demonstration now. The between the midpoint of the ballistic trajectory and 1-2
exoatmospheric element of layered defense repre­ kilometers before impact. These systems operate by

4
guiding rocket-powered vehicles to intercept incoming These functions are depicted in Fig. 1; the subsequent
warheads. They require system descriptions and assessments are discussed in
• early warning that a threat has been launched; terms of these system functions and the technologies
• detection and assessment of the approaching threat; supporting them.
• derivation of trajectories and prediction of impact Current ballistic missile defense technologies are sub­
points; stantially different from predecessor technologies used
• discrimination between warheads and decoys; by the Safeguard ballistic missile defense system of the
• commitment, launch, and guidance of interceptors; early 1970s. Safeguard was widely perceived as in­
and capable of fulfilling the missions it faced. It is ap­
• destruction of the warheads. propriate, therefore, to contrast Safeguard with current

EXOATMOSPHERIC / X THREAT
/X TRAJECTORY
INTERCEPTOR
RVs
ATTACKING
MISSILE

f RVs /
ATTACKING
INTERCEPTOR
SILO /

EARLY WARNING
MESSAGE

loads
r' INTERCEPTOR
3. RADAR _ _ / COMMAND
MISSILE AND
. FIELD CONTROL"

INTERCEPTOR SILO' SILO WITH MX MISSILE

(NOW EMPTY)

Layered batUstic missile defense of MX missiles deceptively based in silos. In this depiction three warheads are on a
trajectory aimed at an MX missile in one silo, and three more are aimed at an exoatmospheric interceptor in an adjacent
silo. The exoatmospheric interceptor is launched and destroys two of the warheads attacking the missile. Warheads
attacking the now-empty interceptor silo are ignored. The surviving warhead aimed at the missile is intercepted by the
terminal defense.’ Not shown explicidy are the separate threat detecdon and assessment functions.

5
systems and show how the deficiencies of Safeguard can for multiple nonnuclear intercepts instead of sin­
be overcome by the new technology. gle-vehicle nuclear interceptors.
In the current designs, early-warning messages either
from satellites or radars trigger the threat detection and
A. Safeguard assessment functions carried out by infrared sensors.
These sensors can be emplaced on satellites or carried
Safeguard was a layered defense that used aloft on rocket-borne probes launched from the continen­
ground-based radars for detection, assessment, tracking, tal United States. Each payload consists of a sensitive
discrimination, and interceptor guidance for both mid­ infrared telescope, a data-processing computer, and
course and terminal defenses. Long-range perimeter down-link communications equipment. The sensors scan
acquisition radars provided early warning and de­ the threat corridor specified by the early-warning
termined the size of the attack and its targets. As message and detect, at ranges of several-thousand kilo­
attackers neared the intercept range, battle management meters, the attacking reentry vehicles, accompanying
and engagement were taken over by smaller missile site objects, and penetration aids.
radars, coupled to central computers, with one Typical threats could have approximately 5000 reen­
radar-computer assembly for each wing of the Minute- try vehicles and upwards of 20 000 other objects in the
man force. For the exoatmospheric layer, multistage field of view; the computer must process information for
Spartan interceptors, guided by the radars, operated out all of them. The sensor tracks all these objects for
to several-hundred kilometers. The Spartan carried a minutes, measuring angular information and infrared
single high-yield nuclear warhead. Those warheads leak­ spectral intensities in several bands as a function of time.
ing past the Spartan’s defense layer would be intercepted The on-board computer stores this information, com­
by fast-reacting Sprint low-yield nuclear interceptors at putes approximate trajectories and launch and impact
altitudes of 3-30 kilometers also guided to intercept by points, and uses infrared discrimination algorithms to
radar. Each interceptor would engage one warhead. differentiate the reentry vehicles from the other objects in
The large ground-based radars were Safeguard’s the threat. This information is then relayed to a
weakest point. It was soon recognized that the first ground-based battle-management computer in real time
Spartan nuclear explosions would render large regions of via multiple-path communications links. Based on the
the atmosphere opaque to radar propagation, thereby attack breadth, predicted impact points, and relative
blinding the radars and making them vulnerable to strength of the defense, the batde-management computer
attack. Other problems existed as well: assigns targets to interceptors and launches them.
• the computers needed were beyond the state of the Impact-point prediction, if accurate enough, permits
art; the battle-management computer to defend targets pref­
• discrimination by radar signatures was only erentially, that is, to defend some targets and to ignore
marginally effective; and warheads attacking others. Such a capability is impor­
• the system was easily defeatable by a cost-effective tant if the attack size is larger than the defense can
increase in the threat size. intercept fully, or if deceptive techniques are being used
by the attacked party to thin the effective attack on each
real target.
B. Exoatmospheric Defense for the 1980s Following launch, the exoatmospheric interceptor
rockets operate autonomously, reacquiring their assigned
Current designs for exoatmospheric ballistic missile portions of the threat via infrared sensors, repeating the
defense depend on two major innovations: (1) small, discrimination procedures, and finally deploying multi­
high-resolution, sensitive, long-wavelength infrared de­ ple-kill vehicles to engage the attack while still several
tectors, installed with computers in space-borne minutes from impact. Using still another infrared sensor,
threat-assessment sensors and in interceptors, which each kill vehicle homes on a separate warhead, getting
replace large ground-based radars and central computers close enough to destroy it by direct impact or by firing a
for long-range threat acquisition, assessment, tracking conventional explosive warhead.
and discrimination; and (2) homing infrared guidance A fraction of the attack can survive this engagement.
that enables each interceptor to disperse many vehicles Some objectives are deliberately ignored (penetration

6
aids, accompanying objects, warheads allowed through held in several years. Guidance simulations in­
by a preferential defense). Some engaged objects pene­ dicate a warhead can be brought close enough to
trate the defense (leakage). The surviving warheads either achieve a kill. Impact kill is a back-up approach
reach their targets or are further depleted by subsequent that was demonstrated in laboratory tests several
defense layers. years ago.
Assessment. The Ballistic Missile Defense Program
Based on our review of exoatmospheric technology,
Office is guardedly optimistic about the potential for
Los Alamos supports the optimism expressed by the
exoatmospheric technology. General Tate reported that4
Program Office. The technology base for the exoat­
The [exoatmospheric component of the] Layered mospheric system appears to be either in hand or on the
Defense Concept is feasible because [of] advances immediate horizon. We also are able to add detail to the
made in the extensive research and develop­ Program Office assessment. Integrated circuit technolo­
ment . . . [The] first two flights [of an experiment] gy is progressing so rapidly that adequate computer
. . . confirmed that optical sensors can be used to capability appears assured. Laboratory models, experi­
perform [ballistic missile defense] functions. ments, and calculations of nonnuclear kill give high
confidence in performance capabilities. Infrared detec­
His Deputy Program Manager, William A. Davis, tion and discrimination have been studied carefully, and
supplied a more conservative and detailed treatment:3 useful techniques and knowledge of their limitations
Midcourse technologies are relatively immature, appear in hand, pending proof test within a few years.
pose a higher technical risk than terminal technolo­ Impact-point prediction is expected to be capable of
gies, and enjoy only a meager data base. There are permitting preferential exoatmospheric defense of silos,*
a host of technical issues to be addressed in [our] but it is not expected to be able to resolve impacts among
research and development program over the next closely spaced shelters of any of the multi­
several years, two of which are examined here: ple-protective-structure emplacement schemes under
optical discrimination and nonnuclear kill. consideration.
We identified several outstanding technical issues
Technical evidence exists that optical discrimina­ needing further study. These issues are dominated by
tion is sufficiently developed to make midcourse concern over extreme system complexity. Some analysts
operation feasible. Some optical flight data is have considerable reservations about system operability;
available on both reentry vehicles and exoat­ others are optimistic. Large-scale simulations in progress
mospheric penetration aids, and there is extensive lend credence to system operability. Other issues include
laboratory data that correlates well with the flight operability of sensors, computers, communications, and
data. Moreover, the essential finding from sim­ interceptors in a nuclear environment, potential for
ulation exercises carried out jointly with the Air means of overcoming infrared discrimination, and inte­
Force’s Advanced Ballistic Reentry Systems gration of active defense with an already strained
(ABRES) shows that all but the most sophisticated national command-communications-control system. The
penetration aids can be readily discriminated. special problems of attacks launched by nuclear sub­
However, more data and more functional demon­ marines lying close to American shores are particularly
strations are necessary, and there are plans to meet stressing to exoatmospheric defense, owing to the short
these needs. flight times. Intercepting such attacks would require
The evidence is that nonnuclear kill can be previous placement of threat assessment sensors or—at
achieved in one of two ways—with a warhead or reduced efficiency—operation without them. In addition,
by direct impact. In both cases, passive homing a number of actions could be taken by the Soviets in
rather than the conventional radar command gui­ response to our installation of an exoatmospheric defense
dance will be used. The primary approach is to use
*For impact resolution within 5 km, silo-to-silo preferential
a warhead, and actual flight tests (Homing Overlay defense would be effective. For poorer resolution, preferential
Experiment) to demonstrate this approach will be defense of groups of silos would be used.

7
system that could degrade its capabilities. They include small component size, the system can be deceptively
maneuvering reentry vehicles, defense suppression at­ based in any of the basing modes proposed so far for
tacks, and new decoy techniques. MX. In modified configuration it could also be used to
Although exoatmospheric defense capabilities are not defend silos.
yet fully perfected or demonstrated, we feel development
is advanced enough to warrant beginning studies of Assessment. In his Senate testimony regarding termi­
potential applications. nal defense. General Tate reported:
[Low Altitude Defense System] is considered a
low-risk development because of the extensive
C. Endoatmospheric Defense for the 1980s
validation testing accomplished ... on the Termi­
nal Defense (Site Defense) concept. This testing ...
Endoatmospheric defense uses radars for all sensing
has proven beyond reasonable doubt that we have
functions. Small radars can be specified because the
the technology to build an effective terminal de­
radars need not have ranges necessary for exoat­
fense system that can detect, discriminate, and
mospheric defense (a departure from Safeguard). Dis­
intercept ICBM warheads even in the extreme
crimination against decoys is based on different radar
environment caused by massive ICBM attacks . ..
signatures, as objects penetrate the atmosphere, depend­
and penetration aids.4
ing on weight, shape, and surface characteristics. Such
* * * *
atmospheric effects begin to be apparent on radar
signatures at altitudes below 90 km. Based on time The basic technology for Low Altitude De­
delays associated with discrimination and interceptor fense—LoAD—has been demonstrated with the
flight, a practical upper altitude for intercepts is 20-30 exception of nuclear hardness for the radar and the
kilometers. interceptor. Nuclear hardness will be tested and
The limiting lower altitude for intercept is determined demonstrated . . . prior to MX IOC* and the
by the capacity of the defended target to withstand LoAD preprototype demonstration flight tests.6
defensive weapon bursts and, possibly, nuclear detona­
As was the case for exoatmospheric defense, we
tion of the intercepted warhead. By this criterion a
concurred with the Program Office assessment of termi­
shelter or silo could be defended successfully with
nal defense technology. We felt that the use of smaller
intercepts spaced as closely as 2 kilometers.
United States endoatmospheric defense research and and less complex components make low-altitude defense
development effort is concentrated in two programs: a relatively low-technical-risk system with less costly
Baseline Terminal Defense and Low-Altitude Defense components than exoatmospheric systems. However, the
System. stressful nuclear environment envisioned requires in­
terceptor and radar hardness values exceeding those of
(1) Baseline Terminal Defense is a direct descendant
predecessor systems. Ability to defeat an intense attack
of Safeguard. It uses improved Sprint interceptors, a
against any single target will be limited because, with the
commercial computer, and phased-array radars con­
very short time available for acquisition, track, and
siderably smaller than Safeguard’s missile site radar.
intercept, multiple sequential intercepts will be difficult.
This system, based on established technology, would be
The limited space available for interception would also
less vulnerable than Safeguard because it would use
reduce the ability of the system to cope with repeated
multiple radars in dispersed sites. Since intercepts would
attack, due to nuclear-fireball interference with radar
occur in the altitude range of 10-20 kilometers, this
propagation and to interceptor-interceptor fratricide. In
system would be useful for soft targets.
such a dense attack, fratricide between attacking war­
(2) Low-Altitude Defense System, the major ongoing
heads could also be a problem for the attacker.
low-endoatmospheric intercept program, is shown
Interceptor technology for endoatmospheric defense is
schematically in Fig. 2. A derivative of the Baseline
well in hand, provided that nuclear warheads are carried.
Terminal Defense System designed mainly for defense of
(Nonnuclear kill may become feasible, particularly for
MX-MPS, it uses single-stage nuclear-warhead intercep­
engagements at higher altitudes, but will require further
tors with a range of only a few kilometers. The
Low-Altitude Defense System uses phased-array radars *That is, the date currently scheduled for initial operational
of modest power, coupled to minicomputers. Because of capability of MX in multiple protective structures.

8
 RADAR

INTERCEPTORS

SHELTER DEFENSE

RADAR

• SMALL-LOW COST
• INERTIAL GUIDANCE
• PHASED-ARRAY
• SINGLE STAGE

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

development in sensor, guidance, warhead, and missile At the end of the trajectory, as an alternative to
technology.) Distributed data processing and the use of conventional hard-target endoatmospheric defense, sev­
multiple small, hard radars would ensure that the system eral last-ditch methods for destroying warheads by
performance would degrade gracefully against even nonguided missiles have been proposed. We considered a
moderately heavy attack. For low-altitude defense of number of techniques using nonpowered missiles
hard targets, an endoatmospheric system of the Low (projectiles, dust clouds) and felt that none was feasible.
Altitude Defense System design could be ready for However, a concept specifying dense barrages of pow­
deployment by the mid-1980s, as reported by General ered but unguided missiles, which recently came to our
Tate :6 attention, may offer near-term potential for endoat­
mospheric defense of hard targets.
[With $25M additional funds starting in Fiscal
Year 1981 it would be feasible] to enter engineering
development in Fiscal Year 1982 to support a
[low-altitude missile defense] deployment concur­ D. Layered Defense
rent with MX deployment in 1986.*
*The Ballistic Missile Defense Program received an additional
Combination of exoatmospheric, infrared, non-
$15M in Fiscal Year 1981 funding following General Tate’s nuclear-intercept technology and endoatmospheric,
testimony. small-radar, nuclear-intercept technology into a layered

9
defense system offers a number of synergistic advantages The needed strategic inventories for deterrence depend
over either system operated alone: on the offensive and defensive systems used. We treat
• leakage factors can be multiplicative, so that two four options:
relatively leaky components can combine into a (1) new ICBMs (MX) based nondeceptively in silos,
system with very low leakage; no defenses (extension of current status);
• two different discrimination phenomenologies place (2) new ICBMs (MX) in multiple protective structures
severe demands upon decoy designs; (MPS), no defenses (current DoD planning);
• the low leakage produces lower costs per intercept; (3) MX-MPS, defended by terminal missile defenses
• reduced inventories and complexities accrue to both (extended DoD planning); and
layers, relative to single-layered defenses; (4) MXs based deceptively in silos, defended by
• the upper layer avoids saturation of the endoat­ layered defenses.
mospheric defense component; and We assume that when the United States implements a
• exoatmospheric-system threat assessment improves particular technology, such as exoatmospheric defense,
engagement planning for the endoatmospheric de­ the Soviets can simultaneously implement an equivalent
fense components. Soviet technology if they choose to do so. We do not
An equivalent set of factors was reported by General attempt in this analysis to account for differences in
Tate (Ref. 4, p. 2872). emplacement dates for American and Soviet inventories.
The forces required for the United States to achieve
the specified deterrence criterion also depend on the
HI. FORCE-STRUCTURE ANALYSIS forces maintained by the Soviet Union. The result
achieved by any change in American force structures
On the premise that current ballistic missile defense thus depends strongly on the Soviet response, or lack of
systems will mature as anticipated, it becomes necessary response, to the United States initiative. Expectations
to consider how such systems would affect the strategic concerning Soviet responses depend on Soviet motiva­
situation. We begin this consideration by exploring, with tions and policies. We consider two cases:
simple models, the arms-control implications of ballistic • a responsive Soviet behavior in which the Soviet
missile defense and other strategic options. Alternately, aim is also to maintain a minimal expected deterrent
we explore how well these options could do in a world in the face of possible United States counterforce
devoid of arms-limiting agreements. attack, and
We perform the analysis by estimating United States • an independent Soviet behavior in which the Soviet
strategic inventories needed to ensure the expected forces are determined by internal considerations not
survival of a predetermined deliverable retaliatory strike dependent on American force structures.
by the United States after a Soviet first strike. For The initial forces needed to achieve the deterrent
assured destruction, the retaliatory strike is taken to criterion can be estimated, based on known, inferred, or
consist of a fixed number of warheads that can be assumed capabilities of the opposing force structures and
delivered against Soviet targets of value—cities, in­ policies for their employment. Such computations must
dustry, transportation, etc. The number of deliverable be quite detailed to account properly for design vari­
warheads is taken arbitrarily as 1000 (that is, 100 ations within and between Soviet and American forces.
MX-equivalent payloads). Other numbers can be postu­ Consideration must be given to many aspects and details
lated, but our qualitative conclusions do not change if beyond the capability of the simple sorts of analyses we
this assumption is varied. can attempt here. For example, to model correctly the
Deterrence could be based alternatively on developing missile-force exchange we study here, one must consider
a war-fighting posture, in which forces are so structured variations of such parameters as warheads launched on
as to permit their flexible use throughout a nuclear each missile, their accuracies, and their delivery-vehicle
exchange. In this case the needed analysis is much more performance.
complex and is less amenable to simple modeling. However, an estimate of the required force sizes can
Consequently, we are limited to discussing at the end of be obtained from simple models that average over these
this section some elements of war-fighting deterrence in variables. Such models are much too limited to define
qualitative terms, and deferring quantitative treatment. actual strategic forces needed, but they are valuable in

10
estimating how extensive those forces must be to achieve Option (1) Missiles based nondeceptively in silos, no
specified deterrence levels. They are thus also useful in defense. All silos are assumed to have
comparing force inventories and costs, both between first missiles in them (H = M).
striker and retaliator, and among the various strategic
options considered by the retaliator. Our approach uses S = M (1 - p') '‘'MVM ;
such a simple model.
and
A. Force-Structure Model
W = pS .
To estimate the required deterrent forces, we assume
the following scenario: the Soviets strike first, using their
Option (2) Missiles based deceptively in multiple pro­
entire missile inventory to attack our ICBM fields; we
tective structures (H > M); no defense.
ride out the attack, using any active defenses we have to
defend our missiles; our subsequent retaliatory attack is
S = M (1 - p') '‘'MVH ;
aimed at Soviet value targets; and any Soviet active
defenses attempt to intercept the fraction of the re­
and
taliatory strike within range of the Soviet defense system.
Attack on our land-based ICBMs by the entire Soviet W = pS .
missile force is only one of many possible scenarios,
although it is the one often considered in arms-control
Option (3) Missiles based deceptively in silos or multi­
analyses. This scenario is not realistic, but for our
ple protective structures (H > M); with
purpose it is conservative in that any lesser attack
low-altitude missile-only defenses.
against the ICBMs either destroys fewer of our missiles
or engages fewer of our defenders. The additional
survivors would then be usable in damage-limiting roles. S = M(1 — p'Ln)'‘'M'/H ,
Although implications of Soviet reserve forces are neg­
lected in this preliminary study, they are critical and
where
must be treated subsequently in the broader context of
countervailing deterrence. Ln = (1 - r) yH/2'‘'M'
To determine force structures, we derived formulas
relating survivable, deliverable warheads to initial inven­ for MPS,* or
tories, based on the above exchange scenario. In the
Ln = (1 - r) 5,H/'‘'M'
responsive case, both Soviet and American inventories
were assumed coupled. Inventories were increased to­ for silos*; and
gether until the calculations showed each side achieved
the specified deterrence criterion. This approach pro­ W = pS .
duced minimum inventories and costs for both sides. In
the independent case, Soviet missile inventories were Option (4) Missiles based deceptively in silos, with
postulated at fixed levels, and the remaining Soviet and partially ambiguous exoatmospheric defenses
American inventories were varied until the United States coupled with low-altitude missile-only de­
achieved the specified deterrence criterion. United States fenses.
inventories were structured for minimum cost at each
threat level. For this model, we assumed that there are no
With the notation given in Table I, and using primed empty silos; each silo contains either a
quantities for Soviet hardware, the needed formulas are* missile or an exoatmospheric interceptor (H
= M + X). We assumed that two rockets
*The expression (1 — p')“ is rigorously correct in these
formulas only for integral values of a. For nonintegral values, *The rationale for this difference is that for MPS the defense
the correct expression would be (1 — p')[o1 (1 — <a> p'), where unit is assumed to be in a shelter adjacent to the missile’s
[a] is the integer part of a and <a> the fractional part. For shelter, far enough away to require defending it explicitly,
conciseness, we continue to show the simpler form; however, whereas for silos, the defense unit is assumed close enough to
we used the cored form in all our inventory estimates. the silo to be defended implicitly as the silo is defended.

11
 TABLE I

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

Inventories M Missiles
H Silos/Shelters
X Exoatmospheric interceptors
N Endoatmospheric interceptors
y Endoatmospheric interceptors per defense cluster
(defense unit)
Outcomes S Missiles surviving missile-field attack
W Warheads delivered on target
Parameters p Warheads/missile [10]a
X Kill vehicles/exoatmospheric interceptor [10]
f Ambiguity factorb
Kill Probabilities p Warhead on silo or shelter0 [0.80]
q Exoatmospheric kill vehicle on warheadd [0.80]
r Endoatmospheric interceptor on warheadd [0.70]'
Leakage Factors Lx Exoatmospheric defense of missiles
Ax Exoatmospheric defense of value targets
Ln Endoatmospheric defense (missiles only)

aAs specified in SALT II for new missiles.

bThe “ambiguity factor” represents the degree to which the exoatmospheric defense can be used to
defend value (area) targets, f is defined as the fraction of value targets, attacked by the retaliatory
strike, that are within range of the exoatmospheric defense. Reasonable values are 0.5 to 0.8. We
treated f as a parameter, using f = 0.6 for comparative results.
'Includes an estimate of operational reliability.
dApproximates in one constant both interceptor-related factors (reliability, warhead lethality) and
system-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 warheads
payloads; they thereby look enough alike targeted on (now empty) interceptor silos.
that the opponent cannot tell which silos
To select the optimum mix of interceptors
have missiles. To maintain long-term decep­
and missiles, we chose the inventories that
tion, covert missile-to-interceptor in­
would minimize the expression (M + X -I-
terchanges would be required periodically.
0.2N), representing a factor approximately
These interchanges could be made by small
proportional to cost. This expression as­
vehicles transporting only the payloads, thus
sumes that exoatmospheric interceptors and
eliminating transport of entire missiles, as is
missiles cost the same, and that endoat­
required in the MX-MPS concepts.
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 tracking which warheads are aimed mospheric interceptors per silo.
at missiles. We intercept only those war­
 S = M (1 - p'Ln LJ ^'MVH , stability are mutually unattainable. MX-MPS, defended
or undefended, requires only 115 to 150 MX-type
where missiles, emplaced deceptively among a few-thousand
shelters, to achieve deterrence. Use of missile defenses
Lx = (l — q)*XHVM'M , with MX-MPS halves shelter and land requirements.
Such basing options are vulnerable if the deceptive
Ln = (1 — r) ynV'M'Lx ; basing is not fully effective. This vulnerability would not
be prevented by expanded terminal defense.
and What may be surprising in this analysis are the
moderate inventories associated with layered defense of
W = pS [f'A'x + (1 - f)] , silos. Although many believe that mutual deterrence
would be overly costly if systems included ballistic
where missile defenses capable of wide-area defense, our model
suggests that this belief may not be entirely correct. Even
A'x = (1 — q') •*:'X'/Msf' . in the case of a totally ambiguous exoatmospheric
defense component capable of defending all values
1. Responsive Soviet Behavior. The underlying as­ attacked by a retaliatory force, stable assured-
sumption of a responsive relationship based on minimal destruction deterrence could be achieved with as few as
mutual deterrence capabilities is not justified by Soviet 300 silo-based MX missiles and 200 silo-based exoat­
writings or behavior. Nevertheless, the responsive as­ mospheric interceptors.
sumption results in estimates of minimum force levels for Whereas MX-MPS is catastrophically sensitive to
both sides, and so provides a means of determining lower failures of deception, failure modes for layered defense of
limits for the strategic inventories needed to assure silos are apparently more gradual and therefore for­
deterrence. Those options that require unreasonably giving. A number of examples support this assertion.
large inventories in this environment would fare even First, the required degree of deception for this layered
worse under less constraining assumptions and can be defense concept is much less demanding than that
eliminated from further consideration. needed for MX-MPS; deception, therefore, is much less
For each option, we derived minimum inventories likely to fail. But suppose deception were to fail for a
needed on both sides to achieve the specified deterrence symmetric layered defense posture with the inventories
criteria. Such criteria, and the resulting inventories, need given in Table II for f = 0.6. In this case, failure of
not be symmetric. For example, the Soviets could specify deception would reduce the deliverable retaliatory deter­
that their deterrent be twice what we choose. Differing rent from 1000 to 400 warheads, a serious but not
parameters, such as warheads per missile, would also catastrophic degradation. On the other hand, if we learn
result in asymmetric inventories. that deception is no longer reliable, we can increase
We have solved here only the fully symmetric case in inventories to reestablish the full deterrent. Without
which all inventories, parameters, and kill probabilities deception, symmetric inventories would be 260 missiles,
are equal for the two sides. This case retains many of the 760 silos, 500 exoatmospheric interceptors, and 260
characteristics of the general solution, but the equations endoatmospheric interceptors; although significantly
are much easier to solve. greater than those needed with reliable deception, these
Inventories needed to assure a 1000-warhead re­ quantities are still reasonable.
taliatory force were computed using the formulas given Another calculation shows the resilience of layered
earlier and the parameters listed in Table I. The assump­ defense in the face of treaty verification problems.
tions of cooperation and symmetry were treated by Optimal cost-effectiveness for both sides would be
setting all primed quantities in the formulas equal to their achieved with a 220:200 ratio of siloed missiles to siloed
nonprimed counterparts. The results are summarized in exoatmospheric interceptors. It is easy to verify how
Table II. many silos are in use but difficult to verify the mix
Three of the four strategic options considered can between missiles and interceptors. What if the Soviets
produce satisfactory results in this symmetric, responsive cheat on some future treaty by replacing interceptors by
case. The exception is offensive missiles based nondecep­ missiles, or vice versa, within the verifiable fixed number
tively in silos; in this case assured destruction and crisis of silos? Our model indicates that departures by the

13
 TABLE II

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 lO9 109 Passive posture* (ride out

attack, crisis stable).
5000 5000 — ... Dueling posture* (launch under
attack, crisis unstable).
(2) MPS None 3500 150 — ... Assuming 23 shelters per missile
as in DoD plans for MX-MPS.
(3) MPS Endos 1600 115 — 230 Optimized by using 14 shelters
per 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 developed by R. H. Kupperman and H. A. Smith, Ref. 7.

hInventories depend on missile-to-exoatmospheric interceptor ratio. This ratio was chosen to minimize the expression (M + X + 0.2N), representing a
factor approximately proportional to system cost.

Soviets from this optimum mix could indeed degrade our

retaliatory capability in the face of a Soviet first strike.
The Soviets, however, would at the same time incur
much greater degradation of their ability to retaliate
against an American first strike.
Figure 3 relates the number of retaliatory warheads
that could be delivered following a first strike to the
number of missiles deployed by the Soviets in their 420
silos. United States retaliation following a Soviet first
strike is plotted as the solid curve; Soviet retaliation
capacity after an American first strike is plotted as the
broken curve. The symmetric solution, resulting in 1000
warheads deliverable after either side strikes first, is
shown as a dot.
As an example of the situation if the Soviets cheat,
consider what happens if the Soviets convert 80 of their SOVIET MISSILES
exoatmospheric interceptors to missiles, giving a total of • SYMMETRIC SOLUTION
300 missiles. If the Soviets strike first, the United States □ SOVIET FIRST STRIKE - US RETALIATION
retaliation produces approximately 850 warheads on
US FIRST STRIKE - SOVIET RETALIATION
target, not a significant degradation. But if the United
States were to strike first, the weakened Soviet defense
would leave them with less than 200 retaliatory war­ Fig. 3.
Decrease of retaliatory warheads due to assumed departures
heads, a highly significant concern to Soviet planners.
by the Soviets from solutions of the symmetric equations for
The same disparity exists across the range of Soviet layered defense. The total number of Soviet silos is assumed
missile counts producing substantial degradations of the constant
United States deterrent.

14
 This disparity may prove to be a strong incentive for This appears to many observers to describe recent Soviet
each side to keep close to the optimum mis­ behavior more accurately than does the “responsive”
sile-interceptor mix, even in the absence of any verifiable assumption. Consistent with this assumption, the Soviets
or unverifiable treaty agreements. have publicly repudiated the mutual deterrence
As a third example of gradual response by layered philosophy that has formed the basis of much recent
defense to failure modes, clandestine increase in the American thinking in the field of arms control.
number of warheads carried by each Soviet missile is a The United States forces required for deterrence were
potentially serious threat. Such fractionation is inevitably estimated as a function of the Soviet force by using the
accompanied by reduced warhead yield, but this de­ same formulas and parameters used previously, without
crease can be more than overcome by the increased the assumptions of complete United States/Soviet force
numbers of warheads in the threatened attack. Figure 4 symmetry. The results were applied in two eras:
shows how Soviet fractionation might affect our deter­ • Near term. Some analysts project a continued
rent. For p' < 20, we estimate serious but not growth of the Soviet threat consistent with recent
catastrophic deterrent degradation. For even greater history. We evaluated how each strategic option
Soviet fractionation, ICBM survival could become prob­ would respond throughout the next decade under
lematical. Of course, if the fractionation were overt, or if the assumption that Soviet missile forces grow at a
we became aware of it by intelligence means, we could rate of 10% per year. This assumption imposes a
counter its effect by modest increases of our inventories. time scale with which to compare the options, rather
For most of the potential failure modes of layered than suggesting a realistic estimate of Soviet inten­
defense, degradation of the retaliatory force would tions, a matter well beyond the scope of our effort.
become more severe and abrupt if the Soviets were able • Long term. We estimated how well and at what
to defend a larger fraction of their assets. Evaluation of (approximate) cost each of the strategic options
this effect awaits more detailed computations. could respond to continued growth of the Soviet
threat, past the next decade. Without regard to a
2. Independent Soviet Behavior. In this case, we specific time scale, this analysis permits com­
assumed the United States faces a fixed Soviet threat that parisons of long-range costs among the strategic
is not responsive to American arms-reduction initiatives. options and cost-exchange comparisons between
threat and response.

a. Near Term. The postulated Soviet threat growth is

plotted in Fig. 5. We used this threat as an input
condition and estimated the year-by-year capability of
each strategic option to respond to it. To make these
estimates, we needed to project availability of the
technology for each option. Such projections have a high
degree of uncertainty. Estimates are best for systems
already planned and whose technologies are in hand.
Estimates are worst for systems with untested, immature
technologies.
Ballistic missile defense suffers from a larger degree of
predictive uncertainty than the other strategic options. In
some areas its technology is new. In other areas, where
the technology is mature, budget constraints have pre­
cluded prototype construction. Not only defense suffers
SOVIET WARHEADS PER MISSILE from such uncertainty, however. Schedules for MX-MPS
could be delayed by social and political issues being
Fig. 4.
raised at present. Technology problems associated with
Degradation of United States nuclear deterrent (established
with layered defense of silos) when the Soviets clandestinely maintaining deception and yet permitting verification
add more warheads. have yet to be fully resolved. Nevertheless, MX-MPS is

15
 10000 rent. Currently, the Soviets have a limited ballistic missile
defense system installed around Moscow (as reported by
8000 Secretary Brown, Ref. 1, p. 57), but its area-defense
capabilities appear too limited to affect our retaliatory
6000
deterrent appreciably. However, if the Soviets were to
install an effective area defense, as for example one with
4000 capabilities equivalent to those projected for American
technologies, then recovery of our retaliatory deterrent
3000 could be delayed further. The additional delay would
arise from the Soviet capacity to intercept United States
2000 warheads that survive the Soviet first strike and are then
launched in retaliation. The assumption that the Soviets
Q- < would add an area defense cannot be ignored if the
United States were to install one. On the other hand, the
Soviets may—overtly or clandestinely—install an effec­
tive area defense whether or not we do.
84 85 86 87 88 89 90 91
To quantify this effect, we computed retaliatory-force
CALENDAR YEAR recovery for two cases, one without Soviet area defenses,
Fig. 5.
and one in which we assumed Soviet area-defense
Postulated Soviet threat growth. capabilities and schedules similar to those available in
the United States. Although arbitrary, this assumption
either represents Soviet responsiveness if both sides
much farther along the chain of approvals than any of install ballistic missile defense systems or it is a realistic
the ballistic missile defense programs. schedule if we do not but they do.
Setting these qualifications aside, it is appropriate to For both cases, we computed expected surviving and
estimate how soon the various technologies could be deliverable United States retaliatory warheads, for each
effective if they were driven by technical constraints of the four strategic options considered, on a
alone. We used the technology schedules given in Table year-to-year basis. In the first option, MX and Minute-
III. Actual availability could approach these schedules if man missiles based nondeceptively in undefended silos,
technological preparation continues while the political none would survive the postulated Soviet threat through­
debate about American implementation of the various out the near-term period. For the remaining three
strategic options goes on. options, we have plotted in Fig. 6 the estimates of
Using our model, we estimated how the American American retaliatory warheads that could be delivered
ICBM retaliatory deterrent could recover as the newly after a Soviet first strike. The horizontal line marks the
available strategic forces become available in the next assumed deterrence criterion of 1000 deliverable war­
decade and beyond. We assumed that installation of new heads. We take recovery of adequate ICBM-force sur­
offensive and defensive hardware occurs at the technolo­ vivability to occur for each option at the date when the
gy-limited schedules given in Table III. Until the new deterrent reaches that line.
systems are emplaced in quantity, the existing silo-based In the absence of Soviet defenses (Fig. 6a), MX
Minuteman missiles represent a significant element in our missiles in MPS, without defense, would achieve the
deterrent posture. Consequently, we assumed that specified deterrent criterion by about 1991. That is later
Minuteman missiles (with an average of 2.5 warheads than the current fully operational MX-MPS date of 1989
each) are permitted to remain active in existing silos not because the currently planned MX-MPS deployment
required for MX missiles or interceptors. We assumed a (200 MX, 4600 shelters) is not adequate for the threat
Soviet attack given by the postulated threat projection of we have assumed. Two years later, the modeled
Fig. 5 and apportioned between MX missiles and MX-MPS deployment would have grown to 340 MX,
Minuteman missiles so as to destroy the maximum 7820 shelters, attaining the expectation of 1000-warhead
possible number of United States warheads. survival.
We also considered the effect a Soviet area-defensive With defense by a low-altitude terminal-defense sys­
system could have on recovery of our retaliatory deter­ tem, our model predicts that MX-MPS would reach

16
 TABLE III

TECHNOLOGY-LIMITED PROJECTIONS
OF HARDWARE AVAILABILITY

Technology Permits
Current Hardware Subsequent
Schedule Availability Construction
Technology IOC/FOC8 During Rate

MX missile 1986/1989 1983 70/yr

MPS 1986/1989 1985 1610/yr
Endoatmospheric 1991/? 1985 1000/yr
defense b
Exoatmospheric Not scheduled 1987 100/yr
defense
“IOC = initial operational capability; FOC = fully operational capability.
bLow Altitude Defense system.
Note: MX and MPS schedules taken from Ref. 8. Ballistic missile defense
projections assume an accelerated, aggressive, but not crash ap­
proach to technology preparation. Endoatmospheric defense sched­
ules are based on the Congressional testimony by Major General
Grayson D. Tate, Jr., Ballistic Missile Defense Program Manager,
cited on page 8. Exoatmospheric defense schedules are our own
projection and appear realistic to us, but they have been criticized as
unduly optimistic by others.

deterrence by 1988. This would be accomplished with a the United States cannot respond promptly with defense
deployment of 130 missiles, 3000 shelters, and far fewer systems of its own.
than the scheduled inventory of interceptors. According to our model, low-altitude defense of
Our model suggests that layered defense of MX MX-MPS, or layered defense of MX missiles in silos, or
missiles in silos could not be effective much before both, offers the earliest recovery of ICBM survivability
1988-1989, due to the expected availability dates of in the near term. Obviously, we have not accounted for
exoatmospheric defense components. Operating by itself other elements of our triad. Thus, in the near term,
in defense of silos, the endoatmospheric component of degradation of our deterrent capacity should not be as
layered defense could be enhanced to protect silos before great as that suggested here.
the availability of the exoatmospheric technology
(dashed curve of Fig. 6a). This must be considered at b. Long term. To counter possible continued Soviet
best an interim solution because terminal defense by threat growth, continued growth of American strategic
itself is easily overwhelmed as the threat grows. inventories is also necessary. The extent of that growth
If the Soviets were to add area defenses, the date when relative to Soviet investments in strategic inventories, in a
the American ICBM force could deliver the desired sense, influences Soviet incentives to proliferate weapons
retaliatory force on Soviet targets would be further systems. If our costs are much higher than theirs,
delayed by 3 to 5 years (or more) as shown in Fig. 6b. continued Soviet proliferation may exceed our will or
We again project deterrent recovery to be most delayed capability to respond. This might be a powerful incentive
with undefended MX-MPS and to occur soonest with for the Soviets to continue proliferating. If, on the other
defended MX-MPS. But even in this best case, deterrent hand, our costs can be much smaller than theirs, an
recovery is delayed until about 1990. The contrast equally powerful incentive may exist for them to limit
between Figs. 6a and 6b quantifies concerns about proliferation.
Soviet ballistic missile defense breakouts, particularly if

17
 WITHOUT SOVIET AREA DEFENSE WITH SOVIET AREA DEFENSE

3000 3000
□ mx-mps + loads
at ^
Ck: t—
LU LU O LAYERED DEFENSE □ mx-mps + Loads
t- o OF SILOS
O LAYERED DEFENSE OF SILOS
Q < A MX-MPS
2000 UNDEFENDED 2000 A MX-MPS UNDEFENDED

CO Z
yo
>-
& £Q
o <

< <

CO
3
85 87 89 91 85 87 89 91

CALENDAR YEAR

Fig. 6.
Modeled recovery of United States ICBM retaliatory deterrent if various American strategic forces are emplaced according
to technology-limited schedules (Table III): (a) delays in ICBM recovery if the Soviets install 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
available in the United States.

To evaluate this situation, we used our model to of shelters. For example, against a threat of 2000 Soviet
estimate American inventories needed to counteract missiles, we would need about 700 missiles and about
threats much larger than those achieved in the short-term 19 000 shelters.
projection. Our short-term threat projection ended in With terminal defense installed with MX-MPS (Fig.
1992 with arriving threats of fewer than 10 000 war­ 7b), estimated inventories would be significantly re­
heads. For the long term we considered threats of up to duced; for the same example as above, the United States
40 000 warheads (that is, the payloads of 4000 missiles could maintain deterrence with 300-350 missiles,
with 10 warheads each). We then added an approximate 8000-9000 shelters, and approximately 1500 termi­
cost model for comparisons among the strategic options. nal-defense interceptors.
Inventories. Estimated American inventories re­ With layered defense of MX missiles based deceptive­
quired to establish assured-destruction deterrence against ly in silos, the estimated inventories depend on whether
potential long-term threats were computed with our the Soviets also install an area defense. If they do not
model. We do not present results for missiles based (Fig. 7c), the United States can maintain its ICBM
nondeceptively in silos because the estimated inventories deterrent with the minimum inventories of any of the
are too large to be considered achievable. In Fig. 7, we options considered. For the 2000-missile threat, we
plot inventories for the other three options, and contrast would need 115 missiles, 660 exoatmospheric intercep­
them with Soviet missile inventories needed to launch the tors, and 775 silos and endoatmospheric interceptors.
threat. We also show (as dots) inventories for the If the Soviets choose to install an area defense, the
cooperative-symmetric case given earlier. United States layered defense inventories needed to
Figure 7a shows inventories for undefended maintain our ICBM deterrent (Fig. 7d) would be larger
MX-MPS. In this case, the United States would need to than without such Soviet defenses. To assess American
install roughly one-third as many missiles as the Soviets, inventory growth, we assumed (as before) that the Soviet
but would have to emplace them among a huge number defense inventories mirror our own. For the 2000-missile

18
 MX-MPS-UNDEFENDED MX-MPS-LoADS

100000 r

US SHELTERS

US SHELTERS
INVENTORIES

10000 -

SOVIET MISSILES SOVIET MISSILES

US ENDOS

US MISSILES
US MISSILES

2000 4000 2000 4000

LAYERED DEFENSE LAYERED DEFENSE

WITHOUT SOVIET DEFENSE WITH SOVIET DEFENSE

100000
INVENTORIES

10000
SOVIET MISSILES SOVIET MISSILES

EXO INTERCEPTORS
EXO INTERCEPTORS

US MISSILES US MISSILES

2000 4000 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-MPS
undefended; (b) MX-MPS with low-altitude defense; and layered defense of MX based deceptively in silos, without
equivalent Soviet defenses (c), and with them (d). Dots show inventories given earlier for the cooperative-symmetric
solutions.

19
threat, the American inventories would be: 270 missiles, would favor the nonnuclear ballistic missile defense
930 exoatmospheric interceptors, and 1200 silos and responses relative to the other responses.
endoatmospheric interceptors. The Soviet force would Cost curves are presented for the modeled strategic
also have 930 exoatmospheric interceptors, and would options, giving the emplacement costs as a function of
specify 2930 silos and endoatmospheric interceptors. threat, in Fig. 8. All three American options we con­
This option also has the stabilizing feature that the best sidered cost about the same at the low end of the Soviet
American response to increased Soviet threat growth is threat spectrum. However, the costs of the three options
to add dominantly exoatmospheric interceptors, with but become very different as the threat grows.
a few additional missiles. MX-MPS, undefended, consistently costs twice as
Costs. The economic comparisons among strategic much as the Soviet threat because of the large number of
options were based on two functions: the initial installa­ shelters needed. This cost behavior suggests that ex­
tion costs, and the way costs would grow as the threat panded Soviet arms build-ups might eventually cause the
grows. A system whose initial cost exceeds that of the United States to reach limits of national resolve or
threat, and whose cost continues to grow faster than that capacity to respond. This certainly violates the spirit of
of the threat, is less effective by this definition than a any arms-control climate ever proposed. By adding
system that consistently costs much less than the threat terminal defenses to MX-MPS, United States costs
it faces. decrease to approximate Soviet costs; this offers neither
Costs were based on dollar estimates of development side marginal incentive for or against arms limitations.
and inventory expenses of the various components. The Layered defense of MX missiles based deceptively in
same estimates were used for equivalent Soviet and silos appears to offer stabilizing economic advantages
United States systems—for example, Soviet missiles and that tend to deny incentives for continued Soviet arms
MX missiles—as a basis for comparing Soviet and build-up. The lower curves of Fig. 8b represent cost vs
American costs. The cost data from which estimates threat estimates if the Soviets do not install an area
were derived are given in Table IV. defense but the United States does. Here, our estimated
There are additional costs associated with nuclear costs exceed the Soviets’ at the low end of the threat
warheads that cannot be quoted in an unclassified spectrum; costs are equal at moderate threats; and
format. Including warhead costs would make all respon­ American costs remain significantly below Soviet costs
ses appear more cost-effective relative to the threat, and thereafter. The economics of introducing layered defense

TABLE IV

ASSUMED COSTS AND SCALING FACTORS OF OFFENSIVE AND

DEFENSIVE SYSTEMS AND COMPONENTS

Development Quantity Cost<,)

Component Syrtibol ($M) ($M)

Missile M 8000(b)|
7000 ) 60 (M+X)'18^
Exo interceptor X
Endo interceptor N 5000 16 N 78
Silo H 0 6 H(d)
Shelter (MX-MPS) H 5000(b) 3 H(b)

<a|The scaling function N 78 for the cost of N units, as applied to missile and interceptor hardware, was
suggested by McDonnell Douglas Aircraft Corporation.
(b>Based on MX development costs obtained from Congressional Budget Office Budget Issue Paper, Ref. 8.
(c>Figuring the exoatmospheric interceptor to use missile hardware.
(d,Silo cost assumed to be twice that of shelter cost due to added complexity.

20
 MX-MPS LAYERED DEFENSE
MX-SILOS

SOVIET MISSILES USED IN STRIKE

Fig. 8.
Estimated costs of strategic options configured 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 thus As Secretary Brown noted in his 1981 Posture State­
inhibits Soviet expansion of its ICBM force by placing ment:1
the Soviet forces at a substantial cost disadvantage.
For deterrence to operate successfully, our. poten­
However, what if the Soviets were to implement a
tial adversaries must be convinced that we possess
comparable area-defense concept, one that we assume
sufficient military force so that if they were to start
would force them to incur development and inventory
a course of action which could lead to war, they
costs mirroring our own? The results are shown as the
would be frustrated in their effort to achieve their
upper curves of Fig. 8b. In this case, an especially
objective or suffer so much damage that they
favorable arms control setting would ensue. As the
would gain nothing by their action. Put differently,
Soviet threat level increases, American costs to maintain
we must have forces and plans for the use of our
its deterrent posture would increase as well; but the
strategic nuclear forces such that in considering
incremental costs needed to offset Soviet investments
aggression against our interests, our adversary
and reestablish the strategic balance would strongly
would recognize that no plausible outcome would
favor the United States. In this setting, Soviet arms
represent a success—or any rational definition of
limitations would be driven strongly by the economics; a
success. The prospect of such a failure would then
treaty might well be superfluous.
deter an adversary’s attack on the United States or
our vital interests. The preparation of forces and
plans to create such a prospect has come to be
B. Additional Considerations: Countervailing Strategy
referred to as a “countervailing strategy.”

By concentrating on ICBM survival and as­ To achieve this objective we need, first of all, a
sured-destruction deterrence, our analysis has so far survivable and enduring retaliatory capability to
ignored much of the real-world complexity of deterrence. devastate the industry and cities of the Soviet
l
21
 Union. We must have such a capability even if the Small attacking forces might be expected in a number of
Soviets were to attack first, without warning, in a scenarios, for example,
manner optimized to reduce that capability as • attack by a superpower in the early nuclear phases
much as possible. What has come to be known as of the escalation ladder;
assured destruction is the bedrock of nuclear • attack by a superpower on selected, critical compo­
deterrence, and we will retain such a capacity in nents of the national command authority and force
the future. It is not, however, sufficient in itself as a structure;
strategic doctrine. Under many circumstances • attack by an enemy with limited nuclear resources,
large-scale countervalue attacks may not be ap­ including attack by a third party in an attempt to
propriate—nor will their prospect always be suffi­ initiate a superpower exchange (“catalytic launch”);
ciently credible—to deter the full range of actions and
we seek to prevent. • accidental launch.
Against such limited attacks, interceptor inventories
Secretary Brown went on to discuss the role of damage would be so large compared to the threat that they could
limitation in the countervailing strategy:1
be flown redundantly to reduce leakage. Against very
Our goal is to make a Soviet victory as improbable limited attacks there might be a high probability of
(seen through Soviet eyes) as we can make it, over totally successful defense. The availability of a non­
the broadest plausible range of scenarios. We must nuclear defensive response thus adds elements of crisis
therefore have plans for attacks which pose a more stability not available without defensive systems.
credible threat than an all-out attack on Soviet However, even against massive attacks, area-defense
industry and cities . . . We could . . . attack, in a systems would provide additional means to limit damage
selective and measured way, a range of military, to targets of a Soviet attack. Warheads attacking targets
industrial, and political control targets, while re­ of value could be intercepted directly. Such defense
taining an assured destruction capacity in reserve. would not be perfect, but it would offer much improved
chances for military, industrial, and urban survival. A
But Secretary Brown did not emphasize defense in his significant fraction of the defended targets would be
strategy. The Department of Defense was constrained by available to deny Soviet objectives in any subsequent
concerns about instabilities associated with ballistic conflict. This capability of ballistic missile defense seems
missile defense (see quote cited in Sec. I) and by the to meet in an optimal way a criterion specified for the
Anti-Ballistic-Missile Treaty of 1972. Secretary Brown countervailing strategy by Secretary Brown:1
noted (Ref. 1, p. 99):
. . . leave open the possibility of ending an
Our current programs of active defense reflect exchange before the worst escalation and damage
these constraints and the emphasis we place on
had occurred, even if avoiding escalation to mutual
offensive forces for deterrence. destruction is not likely.
If the concerns felt by the Department of Defense Such a prospect seems, at best, much less likely to be
could be alleviated, what then would be some of the possible for strategic systems without ballistic missile
potential roles for ballistic missile defense in support of defenses.
the countervailing strategy? Enhanced capability against limited attack, seen as an
We have already shown how ballistic missile defenses asset by the United States, may be perceived differently
might economically ensure the survival of enough by our allies. They have limited nuclear missile arsenals
land-based missiles to achieve assured-destruction deter­ whose effectiveness might be seriously degraded in the
rence. More of our land-based missiles would be needed presence of an extensive Soviet area defense. This
for damage-limiting roles in support of the countervailing concern is one of many such political/strategic questions
strategy; the optimal way to ensure their survival would regarding the assets and liabilities of ballistic missile
very likely also include missile defenses. This remains to defenses in our strategic posture. They must all be
be confirmed.
considered in the coming debate on ballistic missile
Missile and area defenses structured to limit damage
defense. Our quantitative results, and this brief quali­
from a massive nuclear attack would probably be even
tative discussion of some elements of damage limitation
more highly capable against limited nuclear attacks.

22
and crisis stability potentially available through active • The resultant mix between ballistic missile defense
defense, suggest that such analysis not be delayed. and offensive weapons is stabilizing in that the
effects of Soviet cheating, were a new SALT
agreement in force, would be comparatively small.
IV. CONCLUSIONS • Arms-control objectives are satisfied; the system
also provides a limited capacity to reduce damage
Strategic arms control is a national priority. Recent to urban/industrial targets. Exoatmospheric in­
Soviet and third-world aggression has underscored the terceptors can be used to defend both value and
requirement to limit United States strategic investments counterforce targets without denying the second
so as to free effort and funds for needed conventional striker his ability to retaliate.
forces. • Similar economic and stability advantages are ex­
Paradoxically, the goal of significant arms reduction hibited in non-arms-control settings.
has appeared inconsistent with the deterrence objectives • In contrast with other proposed measures for reduc­
on which our military planning is based. Although often ing ICBM vulnerability, ballistic missile defense
termed “unthinkable,” we must face the possibility that does not depend on maintaining deception in basing.
deterrence by threat of assured retaliation may fail. Some • Crisis stabilizing measures are introduced by allow­
means of damage limitation would then be America’s ing for nonnuclear interceptor launch under real or
only recourse: preparation of such means is also seen by apparent attack.
many to strongly enhance deterrence. • Environmental problems posed by alternative MX
Our purpose has been to investigate alternative tech­ schemes are avoided.
nological and force-structure opportunities that could • Availability of exoatmospheric technology is the
simultaneously achieve mutual assured destruction and critical path constraining the implementation of
contribute to damage limitation. We feel that ballistic such a system.
missile defense, when deceptively based along with • In the search for near-term solutions, survival of the
missiles in ICBM silos, may offer the opportunity for United States ICBM force could be significantly
• reducing armaments substantially; enhanced, with reduced environmental impact, if
• filling the gap between competing security and low-altitude terminal defense were installed concur­
arms-control goals; rently with MX-MPS.
• thwarting limited ICBM attacks including acciden­ This preliminary analysis has given many indications
tal or catalytic launches against missile fields or of the potential value of a hybrid ballistic missile
urban targets; defense/deceptive MX-basing system. The subject clear­
• supplementing an inadequate theater nuclear force ly warrants further analysis. We will need detailed
by maintaining a strategic force structure and models, including large-scale computer simulations of
balance, which would be relatively insensitive to the targeting, time-phased attacks, defense-suppression at­
limited use of our strategic forces against theater tacks, and game theory.
targets; and Our analysis was based on assured-destruction deter­
• offering additional crisis management and stabiliza­ rence, modeled by a 1000-warhead retaliatory force.
tion tools to the United States and the Soviet Union. Deterrence by this definition can be achieved even if
We emphasize the preliminary nature of our results, there are large departures from missile parity, as
but they do suggest profound effects that should not be evidenced by Soviet/United States inventory differences
ignored. Credibility of the concept—even at the expense for layered defense of silo-based MX. However, our
of reopening the anti-ballistic missile controversy—has capability to achieve elements of war-fighting deterrence
been demonstrated. But much more analysis and very would be degraded if our forces were much smaller than
involved simulations are mandatory if the presenfresults the Soviets’. The actual American strategic forces needed
are to withstand scrutiny. against very large Soviet threats would be structured by
Specifically, the models provide these suggestions. striking a compromise between the large forces needed to
• Layered defense of ICBMs based deceptively in achieve war-fighting goals and the smaller forces suffi­
silos may provide an exceptional opportunity for cient for assured-destruction deterrence. Ballistic missile
strategic arms reduction.

23
defense appears to give the greatest latitude for such a propriations, United States Senate, March 12, 1980,
compromise. pp. 49-51.
Arms control will continue to be a basic national goal,
now emphasized by the need to modernize both strategic 2. Some analysts report this action is already under
and conventional forces with limited funds. The prospect way. See, for example, J. K. Davis, R. L. Pfaltzgraff,
of using exoatmospheric defense to achieve this goal will Jr., U. Ra’anan, M. J. Deane, and J. M. Collins, “The
surprise many arms-control advocates who will need Soviet Union and Ballistic Missile Defense,” Institute
time to rethink the ballistic missile defense issue. The for Foreign Policy Analysis, Inc., Special Report
extensive analyses needed to corroborate and extend the (March 1980), pp. 6-7.
present results will take many months. The 1982 review
3. “The MX Missile Debate,” Bill Moyers’ Journal
of the present Anti-Ballistic-Missile Treaty is imminent.
broadcast by the Public Broadcasting System, April
Prompt, vigorous action on these issues is needed.
24, 1980.
Even if the analytic results hold, and even if our
layered defense concept proves politically viable, we may 4. Major General Grayson D. Tate, Jr., Ballistic Missile
find ourselves without the needed technology to imple­ Defense Program Manager, “Status of the Ballistic
ment the concept. It would seem prudent, therefore, to Missile Defense Research and Development Pro­
engage in accelerated research and prototype develop­ gram,” (Prepared Statement) Congressional Record,
ment of ballistic missile defense systems so that technolo­ Committee on Armed Services, United States Senate,
gy limitations do not constrain future decisions. testimony of March 12, 1980, p. 2869.

5. W. Schneider, Jr., D. G. Brennan, W. A. Davis, Jr.,

ACKNOWLEDGMENTS and H. Ruble, “U. S. Strategic Nuclear Policy and
Ballistic Missile Defense: The 1980s and Beyond,”
A Los Alamos National Laboratory team assembled Institute for Foreign Policy Analysis, Inc., Special
by E. O. Chapin was responsible for the brief assessment Report (April 1980), p. 42.
of ballistic missile defense technology upon which this
analysis is based. R. G. Shreffler was the source of the 6. Major General Grayson D. Tate, Jr., testimony in
idea that MX-missile/exoatmospheric interceptor similar­ response to questions by Senator John W. Warner,
ities could offer advantages for deceptive basing. We Ref. 4, p. 2923.
thank D. R. Westervelt, T. W. Dowler, and S. A.
Maaranen for critical review, Rongriego for preparing 7. R. H. Kupperman and H. A. Smith, “Deterrent
the figures, and J. W. McDonald and H. Frauenglass for Stability and Strategic Warfare,” in Mathematical
editorial comments. We thank K. K. Fenner for process­ Systems in International Relations Research, J.
ing the multiple drafts of this document. Gillespie and D. Zuines, Eds. (Praeger Publishers,
Inc., New York, 1977).

REFERENCES 8. “The MX Missile and Multiple Protective Structure

Basing: Long-Term Budgetary Implications,” Con­
1. Secretary of Defense Harold Brown, 1981 Posture gressional Budget Office, Budget Issue Paper for
Statement, Congressional Record, Committee on Ap­ Fiscal Year 1980 (June 1979).

24