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Nuclear Deterrence (1)

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  • Nuclear Origins: Einsteins letter to FDR

  • Nuclear Origins (cont.)Manhattan Project: $$$ to scientists,based on the expectation (or fear) that Germany was also developing A-bomb. Apparently Germanys nuclear program never got very far.Germany surrendered before the A-bomb was ready in the summer of 1945, but Japan had not yet surrendered.Potsdam Conference and Site Trinity (successful A-bomb test, July 16, 1945)Potsdam Declaration: We call upon the government of Japan to proclaim now the unconditional surrender of all Japanese armed forces, and to provide proper and adequate assurances of their good faith in such action. The alternative for Japan is prompt and utter destruction. The bomb was used to compel early Japanese surrender (prior to invasion).Also for atomic diplomacy vs. Soviet Union?The US, which had been anxious for the SU to act on its pledge to enter the war against Japan, presumably regarded an early Japanese surrender as additionally advantageous since the SU then could not claim as large a role in post-war East Asia.Was the US also trying to intimidate the SU by actually using the A-bombs?

  • Strategic Implications of Nuclear WeaponsBernard Brodie: The Absolute Weapon: Atomic Power and World Order (1946)The most basic implication:destructive power on an unprecedented scale was now possible, and it could be inflicted almost instantaneously.The second implication: combined with strategic delivery vehicles (long-range bombers and missiles), destruction could be visited on an adversary at a distance, and thereforewithout first defeating that opponent militarily.The third implication: if more than two nations possess nuclear weapons,mutual destruction is possible.The fourth implication: nuclear weapons cannot defend, butcan support deterrent (and possibly compellent) threats.

  • From Allies to AdversariesThroughout WWII, US (+UK) and SU viewed each other warily.There was doubt that the alliance could be maintained after defeat of Axis powers.Victorious alliances regularly fall apart after the common enemy is defeated, andthe Grand Alliance between the West and the SU was hardly based on common political ideals and institutions.East-West tensions emerged in last months of WWII and became profound within a few years.Eastern Europe was communized behind an Iron Curtain.There was political instability in Western Europe (with powerful Communist parties in France and Italy).While all allied powers substantially demobilized after WWII,the SU did so less than US and UK.Many Soviet troops remained in forward positions in Eastern Europe, whilefew US troops remained in Western Europe (only on occupation duty in Germany).Western powers had fears of potential Soviet aggression or, more likely, of Soviet compellent threats against Western EuropeRecall Appeasement Theory vs. Spiral Model accounts of the origins of the Cold War

  • The US Atomic MonopolyWestern defenses in Western Europe vs. SU were very weak.But maybe the US had an ace up its sleeve, i.e., its atomic monopoly,which seemed to provide the basis for a Western deterrent threat vs. the SU.However, it is not clear that this was really true, because at the time the US had very few nuclear weapons, andrather few long-range bombers, whileSU had excellent air defenses.In any event, the SU broke the atomic monopoly in 1949, when it tested an A-bomb.It was not a surprise to the US that this happened, butit was a surprise that it happen so quickly.This first Soviet bomb was evidently based on atomic espionage, butlater Soviet nuclear advances were based on their own excellent scientific capabilities.Another surprise a year later: the outbreak of the Korean war,to which US responded with WWII-style military forces.Some official statements suggested nuclear weapons might be used,but evidently no serious consideration was given to their use.

  • Eisenhowers New Look at Defense PolicyLesson of Korea seemed to be: no more Koreas.The response to future aggression would be: massive retaliation by means and at places of our choosing.The problem was the SU was developing its own nuclear capabilities and delivery systems and seemingly doing this at as least as fast a pace as the US.However, its exact pace was unknown, as there was almost no way to monitor what was happening in the SU.In the 1950s, there were many instances of US over-flights of Soviet borders, andin the late 1950s, U-2 planes secretly flew over much of the SU.The Soviets know about the U-2 over-flightsbut initially could not shoot them down, anddid not complain publically because they would in effect be admitting they could not shoot them down.All this changed when the SU was able to shoot down Francis Gary Powers U-2 in May 1960.

  • Implications of Nuclear DuopolyOne seeming but erroneous implication:Under the US monopoly, the US could destroy SU and therefore could deter it from aggression.Given a US-SU duopoly, each side could destroy (and therefore deter) the other:deterrence as an automatic consequence of possessing nuclear weapons;mutual deterrence;balance of terror. Winston Churchill: It may be that we shall by a process of sublime irony have reached a stage in this story where safety will be the sturdy child of terror, and survival the twin brother of annihilation.

  • Implications of Nuclear Duopoly (cont.)But there was a second less obvious implication,which was not recognized and acted upon for some time.In the basic Western scenario, the SU invades Western Europe, andthe US responds with massive nuclear retaliation on the SU,the prospect of which should deter the SU in the first place.But now that the SU is also a nuclear power, the US now has a choice of targets for its retaliation:Its nuclear strike can be either essentially punitive (or countervalue), directed at Soviet cities, industrial capacity, etc., (as it could only be under the monopoly) ordirected against Soviet nuclear forces (or counterforce), in an attempt to destroy them or render them inoperable, thereby (perhaps) precluding Soviet counter-retaliation.Clearly the second option seems more sensible, at least in far as it offers any prospect of success.

  • Implications of Nuclear Duopoly (cont.)But the duopoly relationship is symmetric:If, in the event ofsome US provocation (in Soviet eyes), orin the expectation of a US nuclear attack, orin some intense US-SU crisis, or perhapsout of the blue the SU were to launch a nuclear attack against the US,by the same considerations, it would presumably be directed against the US capacity for retaliation, i.e.,Strategic Air Command (SAC) bases, andrelated communications, command and control, etc., facilities.However, the dominant scenario discussed in the media, etc., in the 1950s, was of Soviet bombers appearing (Pearl Harbor style) not only out of the blue but also over a civilian target like New York City, etc. ,even though it clearly would not have made sense for the SU to initiate a nuclear attack against such unthreatening civilian targets.

  • Vulnerability of Strategic ForcesRAND Report (led by Albert Wohlstetter) on The Selection and Use of Strategic Air Bases, 1953-54How should SAC bombers be deployed?In particular, to what extent should SAC rely on foreign bases relatively close to the SU?Advantages:From such bases, SAC bombers could reach targets more quickly and cheaply. B-47 (medium range) bombers, which were plentiful, could be used instead of B-52 (intercontinental range) bombers (just coming into service),and prospectively IRBMs rather than ICBMs.Disadvantages:Communications, etc.Many host countries, even if present US allies, were politically unstable.

  • Vulnerability of Strategic Forces (cont.)The RAND Report noted that putting SAC bombers at forward bases close to SU has both positive and negative implications:it was easier for SAC to attack the SU, but alsoit was easier for the SU to attack SAC bases, quite likely destroying bombers on the ground, orthe airfields they need to get off the ground, etc.This recognition led to an appreciation of the significance of the vulnerability of SAC forces in general.This RAND report was an example of a systems analysis, and in particular, of opposed systems design.Cf. games against nature vs. games against rational adversaries.

  • Vulnerability of Strategic Forces (cont.)This conclusion led the RAND researchers to examine SAC bases within the US:SAC bombers were concentrated at relatively few bases,including some foreign bases close SU; the nuclear weapons themselves were concentrated in separate and even fewer locations; andcommunications, command, and control between Washington, SAC headquarters, and individual SAC bases were relatively primitive and most likely would not survive an attack.

    It became clear that (even though the SU was behind the US in the mid-1950s) the US was highly vulnerable to a Soviet attack, especially a surprise counterforce attack with little or no warning,which, if the Soviets were to attack, was presumably the kind of attack they would launch.

  • Vulnerability of Strategic Forces (cont.)Would the SU ever choose to attack in this way?If the choice were war vs. no war, probably not.But what if, especially in some crisis situation, the Soviets saw their choice as between a Soviet first strike vs. waiting for a US first strike?

    It seemed likely that,if US were figuring out that US retaliatory forces were vulnerable to Soviet attack,the SU would also be figuring out that SU retaliatory forces were (at least) equally vulnerable to US attack, sothe US would be in the same dilemma.

  • Vulnerability of Strategic Forces (cont.)In other words, it appeared as if the US and SU were entering a situation in which there would be a strong reinforcing incentive for nuclear pre-emption,that is, a situation in which both sides might have a strong incentive to launch a nuclear attack, because they could not be sure the other side wasnt thinking along the same lines, andboth sides recognized that the side that struck first might gain a decisive advantage.

    Cf. Reciprocal fear of surprise attack (Schelling)

  • The Delicate Balance of TerrorAlbert Wohlstetter, The Delicate Balance of Terror, Foreign Affairs, January 1959 [updated and sanitized version of RAND report], outlined the stringent requirements for nuclear deterrence, that isthe undoubted capability to retaliate after and despite an all-out surprise attack by the SU directed at the elements of that US capability.Such deterrent systems must overcome all six of the following hurdles:a stable, safe and not prohibitively expensive "steady-state" peacetime operation; and in addition they must have the ability tosurvive enemy attacks;make and communicate the decision to retaliate;reach enemy territory with fuel enough to complete their mission;penetrate active enemy defenses (especially fighters and surface-to-air missiles); and destroy the target in spite of any passive civil defense in the form of dispersal or protective construction or evacuation of the target itself.

  • Nuclear CapabilitiesNation A has a non-preclusive first-strike capability if: A can inflict (perhaps great) damage on B by striking first, butonly by striking first, and even thenA cannot thereby preclude retaliation by B, andIf B strikes first, A will not be able to retaliate.

    Nation A has a preclusive first-strike capability if:[B has no nuclear capability in the first place, or]A can destroy Bs retaliatory capability by a counterforce first strike.

    Nation B has a secure second-strike capability if:A can inflict great (countervalue) damage on B even striking second, and A can do this even after absorbing and all-out counterforce first strike by B.

  • The Strategic Nuclear BalanceClearly there are logical interconnections among these capabilities.

    If A has non-preclusive first-strike capability only, it follows that B has both a preclusive first-strike capability, and a secure second strike capability.While A can inflict (perhaps huge) damage on B by striking first, if A makes a nuclear threat against B, B has a strong incentive to pre-empt.So if A looks ahead and reasons back, it should be clear that Ashould not be threatening but conciliatory, and make every effort to persuade B that A has no intention of launching a nuclear attack.

  • The Strategic Nuclear Balance (cont.)Therefore, As non-preclusive first-strike capability provides little basis for a deterrent (let alone compellent) threat,except perhaps through the rationality of irrationality gambit (or the reality thereof),or perhaps through existential deterrence,But these factors may also induce a pre-emptive strike by B.On the other hand, Bs nuclear capacity provides it with a strong basis for deterrent (perhaps even compellent) threats.The nuclear balance is stable in thatA has no incentive to pre-empt, andB has no incentive to pre-empt unless A behaves irrationally, butthis stability is very favorable to B.

  • The Strategic Nuclear Balance (cont.)If both A and B have a preclusive first-strike capability, the story is both different and much more scary.Suppose B believes that A is about to attack B (for whatever reason):Then (as before) B has an incentive to pre-empt.When A looks ahead,A sees (as before) that B has an incentive to pre-empt.But now when A reasons back,A realizes that A also has an incentive to pre-empt,rather than an incentive to conciliate. So the nuclear balance is very unstable (or delicate) [it exhibits fearful symmetry].We must both live together, or one of us will die the more trigger-happy one of us lives and the other dies.

  • The Strategic Nuclear Balance (cont.)Finally, if A and B each has a secure second-strike capability, the story is distinctly less scary.Neither A nor B has an incentive to pre-empt.The nuclear balance is stable [it is still symmetric but in a much less fearful way].We must both live together, or both of us will die. This may be cold comfort, but it is comforting none the less,as the common interest of A and B in avoiding nuclear war is easier to realize.

    The following chart summarizes these different relationships, andlinks (approximate) historical periods of the Cold War nuclear balance to particular combinations of nuclear capabilities for the US and SU.

  • The Strategic Nuclear Balance During the Cold War

  • The Incentive to Pre-emptClearly the preceding either/or distinctions among different nuclear capabilities are never so clear in practice.

  • Securing a Second-Strike CapabilityMost obvious quick fixes for the delicate balance problem in the 1950s were expensive andineffective, and/ordangerous.Ineffective -- buying more bombers/missiles, etc. (closing the bomber gap/missile gap, etc.):Such a merely quantitative increase enhances first-strike capability, but does little or nothing to increase second-strike capability, if the additional vehicles are equally vulnerable. Dangerous high-alert status: e.g., keeping a large fraction of the SAC force on airborne alert at all times; orlaunching bombers on warning (even with a failsafe system).Tradeoffs: greater dispersion of weapons and vehicles:This reduces vulnerability, butincreases communications, command, and control problems,

  • Side Point: Nuclear War by Accident The possibility of accidental nuclear war was a focus of much attention (in the popular media as well strategic planning) in the late 1950s and early 1960s.Dr. Strangelove (farce) and Failsafe (serious) moviesbased best-seller novels (Red Alert and Failsafe respectively).This probability of accidental nuclear war is essentially the product of two probabilities:the probability of an accidental missile firing, etc., timesthe probability that such an event would trigger general war.Both probabilities are relatively large in a delicate balance situation in which both side have an incentive to pre-empt, and much lower in a mutual deterrence situations in which both sides have a secure second-strike capability.

  • Securing a Second-Strike Capability (cont.)Moreover, the immediate next generation of technology involvedliquid-fuel ballistic missiles that would supplement (and perhaps replace) bombers.This looked to worsen the situation.First generation liquid-fuel ballistic missiles: would sit in fixed above-ground positions;could not be moved around like bombers;would take a long to fuel and prepare for launch (and had a tendency to blow up on the launch pad); in the meantime, would be highly vulnerable to any kind of attack, especially IRBMs in forward bases (e.g., US missiles in Italy and Turkey, Soviet missile in Cuba); andonce launched, could not be recalled (like bombers),though they could in principle be destroyed in flight.

  • Securing a Second-Strike Capability (cont.)JFK campaigned on the missile gap theme,that had been made politically salient by Sputnik and Mr. Ks boasts and threats.President Eisenhower knew from U-2 photography that these were indeed boasts,but he could not refer to U-2 evidence to support this view. JFK and his Defense Secretary Robert McNamara soon recognized that the missile gap, if it ever existed, was not the main problem.The immediate problem was to secure a second-strike capability.Fortunately, second-generation solid-fuel missiles had much more benevolent implications for escaping the delicate balance problem.

  • Securing a Second-Strike Capability (cont.)First priority: obtaining a secure second-strike capability:

    Redundancy: the triad (or unholy trinity) with three legs:long-range bombers (B-52s) based in US but dispersed;long-range solid-fueled land-based (Minuteman) missiles placed in blast-resistant and dispersed silos;medium-range solid-fueled missiles in nuclear submarines (Polaris, Poseidon, Trident).

    Emphasis on Communications, Command, and Control (CCC)Permissive Action Links (PALs)

  • Securing a Second-Strike Capability (cont.)Evidently, the Kennedy Administration attempted (with considerable success) to instruct the SU in nuclear strategy (and perhaps even shared some technology with it), particularly concerningthe importance of having a secure second-strike capability, and especiallythe importance of effective and secure CCC systems, PALs etc.Shortly after the Cuban Missile Crisis (when US-SU relations were exceptionally friendly),Sec. of Defense McNamara gave an extraordinarily detailed and candid talk to a select US audience on these issues, andThe US government notified Soviet Ambassador Anatoly Dobrynin (died 4/6/10) and Soviet Embassy staff in advance and urged them to read and digest what McNamara said, and to report the information to their government.

  • Mutual Assured Destruction (MAD)When the SU acquired a secure second-strike capability (in the mid- to late-1960s), a stable balance of Mutual Assured Destruction between the US and SU was achieved.The was achieved largely by several technological accomplishments:the development of small reliable solid-fuel ballistic missiles;The development of small nuclear warheads that could be fitted onto such missiles;the development of nuclear submarines (in addition to land-based silos) that could carry such missiles; and the development of guidance systems that could direct such missiles to targetseven from mobile under-water launch platforms.

  • Type II (or Extended) Nuclear DeterrenceTo this point, we have been discussing what was once called (by Herman Kahn) Type I Deterrence, i.e., the ability to deter an all-out nuclear attack.A necessary, though perhaps not sufficient, condition for Type I Deterrence was a secure second-strike capability.But this capability did not necessarily deter any less extreme act of aggression, e.g.,a Soviet invasion of Western Europe, ora Soviet nuclear attack on Western Europe, ora limited Soviet nuclear attack on the U.S.As we have noted, in the 1950s the US was officially committed to a policy of (all-out nuclear) massive retaliation to deter such aggressive acts,a policy that became increasingly unrealistic as Soviet (and US) nuclear capabilities increased.

  • Type II Deterrence (cont.)When he became Defense Secretary, Robert McNamara was briefed by General Thomas Power, the head of SAC, on the official U.S. nuclear war plan, called SIOP (Strategic Integrated Operational Plan). Under this plan, if the Soviets invaded any part of the free world even without firing a single nuclear weapon,SAC would retaliate by launching its entire arsenal of nuclear weapons (3,423 bombs and warheads, totaling 7,847 megatons), which was expected to kill 250-300 million Russians and Chinese and injure 40 million more, along with uncalculated casualties caused by radioactive fallout all over the world (including the US).

    Bill is William Kaufman; the text is from his recent obituary in PS: Politics and Political Science

  • Type II DeterrenceIn addition to being horrified by SIOP, McNamara believed it was an unwise [insane?] policy, becauseit had never been publicly announced in such stark terms (for understandable reasons),so the Soviets probably were not fully aware of it.In so far as it might be carried out automatically, it was, in effect, an unannounced Doomsday Machine,like the Soviet Doomsday Machine in the Dr. Strangelove movie.Herman Kahn characterized SIOP as spasm war,which was not intended to be a compliment.

  • Type II DeterrenceEven if the Soviets were (or became) aware of the US policy embodied in SIOP,they might not be deterred,because they would not believe that the US would carry out such a horrendous and disproportionate threat,as it reserved for the US the last clear chance to avoid what would be pretty much be the end of the world.In any case, if the Soviets had aggressive intentions, they would use salami tactics, i.e.,their aggression would come in small incremental steps, no one of which would justify massive retaliation,as explained by the Scientific Advisor in Yes, Prime Minister.

  • Flexible ResponseThe Kennedy-McNamara alternative to Massive Retaliation against less than massive aggressive by SU was Flexible Response, with two components:Rebuild conventional (non-nuclear) military capabilities to defend against , and thereby perhaps also deter, conventional aggression,especially a Soviet/Warsaw Pact attack on Western Europe; andPrepare for limited or controlled (less than all-out or spasm) nuclear war.This was the idea that William Kaufman had tried to explain in his interview with General Power.Rebuilding conventional capabilities:Maybe more Koreas after all (instead of No More Koreas), i.e., fight WWIII much like WWII.European nations were unenthusiastic about Flexible Response and tended to advocate (Nuclear) Deterrence Only.Flexible response gave the US the flexibility not to respond, andWWII all over again meant something different to Europeans and Americans.

  • Limited Nuclear War (No Cities Doctrine)Robert McNamaras No Cities Doctrine speech, June 1962.Given a secure and plentiful second-strike capability, in the event of an all-out Soviet conventional attack on Western Europe ora less than all-out Soviet nuclear attack on Western Europe, or other allies, or the US itself,respond with controlled and limited (rather than all-out or massive) nuclear retaliation,directed at some Soviet military targets, probably including Soviet nuclear forces (counterforce),while deliberately avoiding Soviet cities and other civilian or value (as in countervalue) targets.

  • No Cities Doctrine (cont.)This controlled response nuclear strike would somewhat degrade the ability of the Soviets to retaliate, but would not entirely destroy it, because the US expected (perhaps wanted) the SU to also have a secure second-strike capability.Most US nuclear forces would be held in reserve, and most of Soviet society (most value targets) would remain unharmed.Thus deterrence would continue to operate even after (limited) nuclear war begins.Contrary to General Power, the point isnt to kill the bastards as quickly as possible, but to enhance US bargaining power by being able to credibly threaten to kill some of them.

  • No Cities Doctrine (cont.)That US threat and bargaining power is lost oncethe US has expended all its firepower, and/orthe US has killed all its hostages.Note that an all-out (SIOP-style) US nuclear attack on the SU may or may not disarm the SU (depending how secure its second-strike capability was),but it certainly disarms the US.Recall the Hostage-Holding Game:It is certainly not expedient for the hostage holders to kill all their hostages at the first sign of trouble from the authorities.The US and SU in effect held [and, incidentally, still hold] a large fraction of each others population hostage, somewhat in the manner of the ancient practice of exchanging hostages for security.

  • The Arms Race as an On-Going Prisoners DilemmaRemember that in the 1950s the US could not reliably monitor Soviet technological and military developments. Being uncertain as to what the SU was doing, the US (unsurprisingly) tended to fear the worst.More generally, the US-SU arms race was like an on-going Prisoners Dilemma, in which cooperating meant exercising restraint in the technological arms race, whiledefecting meant going ahead full blast.In a single-shot PD, we know that defect is each sides dominant strategy,even though this produces a worse outcome for both sides than if both cooperate.

  • On-Going Prisoners Dilemma (cont.)But in a repeated PD with perfect information from one iteration of the PD to the next, if A defects while B cooperates,B can retaliate by defecting on the next round,and the prospect of this retaliation should deter A from defecting in the first place.By like argument, B is also deterred from defecting.

    Thus ongoing cooperation should be possible in a repeated PD with perfect information, even though it is not in a single-shot PD.

  • On-Going Prisoners Dilemma (cont.)But (more or less) perfect information is essential for this cooperation.If A repeatedly defects but B does not find out about As defections until many rounds later (i.e., if successive rounds of the PD are played with imperfect information),it may be too late for B to catch up,so A is actually encouraged to defect rather than being deterred from defecting.And of course B has a similar incentive to defect.So cooperation is as difficult in the repeated PD with imperfect information as in the single-shot PD.

  • Strategic Intelligence and the Arms RaceAt the first post-Potsdam East-West Summit Conference in Geneva in 1955,Eisenhower proposed an open skies agreement to the SU,which the SU (very unsurprisingly) rejected.The SU could find out a great deal about US technological and military developments just by subscribing to the NY Times, Aviation Week, etc.As noted previously, the US attempted a unilateral open-skies gambit with the U-2.In the late 1950s, US initiated the CORONA reconnaissance satellite project.One political/legal problem:Would the SU strenuously object to US satellite orbiting over Soviet territory (at an altitude of 100-200 miles)?

  • Strategic Intelligence (cont.)Evidently, the Eisenhower Administration was content to allow the SU to be first in space with Sputnik.Werner von Brauns US Army Jupiter-C rocket could have put a US satellite in orbit a year or more before Sputnik.Officially, the US wanted the civilian Project Vanguard to put the first US satellite in orbit. After Sputnik, von Braun was given the go-ahead.

  • Strategic Intelligence (cont.)This following is evidently is the back story [from NOVA, PBS science show].The Eisenhower Administration wanted the SU to put the first satellite in orbit.The US then would conspicuously not object to the Sputniks orbit carrying it over the US.With this precedent set, the SU couldnt later object to the US launching its satellites in orbits carrying them over the SU.These would initially be Explorer and Vanguardbut later CORONA and thenmuch more powerful reconnaissance satellites.The SU in due course would develop its own reconnaissance satellites.

  • Spy Satellites, SALT, and ABM TreatyReconnaissance satellite technology had a benevolent effect the US-SU strategic balance.

    First, it dramatically slowed down the US-SU strategic arms race, since each side could (pretty much) see what the other was doing and then respond on the basis of this information,rather than fearing the worst and then responding on the basis of these worst fears.Second, allowed arms control agreements to be verified by national means of inspection.Devising international inspection systems that would be acceptable to the SU had always been a hang-up.

  • The SALT and ABM TreatiesThe SALT and ABM treaties of the early 1970s essentially ratified the existing strategic balance based ona secure second-strike capability on both sides, andlimited anti-ballistic missile capabilities on both sides.Essentially each side agreed not to try to free its hostages, by depriving the other side of its second-strike capability, orby being able to defend its population against attack.This implicit agreement was dubbed Mutual Assured Destruction or MAD.Some people (on both the left and right) thought the acronym was all too appropriate.

  • Challenges to MADIn the later Cold War period, MAD was challenged by both technology and by strategic thought.

    The principal technological challenges were two:the (extraordinarily) enhanced capability of guidance systems, andthe development of MIRVs (Multiple Independently Targetable Re-entry Vehicles).

  • Challenges to MAD: MIRVsIn the classic (1960s) MAD strategic balance, missiles had single warheads and were not especially accurate.If A targeted a single missile against a specific missile silo of B, As missile would probably not come close enough to Bs silo to destroy the missile (or prevent its launch), i.e., the kill ratio was distinctly less than 1,so A would be disarming itself faster than A would be disarming B.But with greater accuracy, the kill ratio could approach 1.And with MIRVs, the kill ratio could greatly exceed 1.Thus MAD might be undermined as each side potentially regain a preclusive first-strike capability.

    Note: submarine-based (Trident) missiles continued to be regarded as more or less invulnerable.

  • Challenges to MAD: Strategic DefenseMutual Assured VulnerabilitySome strategists noted that, in the early nuclear age, the basic strategic lesson was:Since we cant defend, we must deter.But, in the later nuclear age, this lesson was illogically transformed into:Since we must deter, we cannot (and should not) defend.Strategic defense (ABM systems, etc.) was regarded as potentially undermining MAD and therefore destabilizing.In terms of MAD, strategic defense of nuclear forces could be stabilizing (and perhaps necessary to counteract MIRVs).But strategic defense of cities and other value targets was contrary to MAD.

  • Challenges to MAD: Strategic DefenseHowever, if strategic defense is technologically possible (at reasonable cost, relative to strategic offense), Mutual Assured Defense would seems to be preferable to MAD.Each side would have strong strategic defenses,combined with small (or even zero) strategic (offensive) forces.The defenses (coupled with reconnaissance satellites) could defend against any (including illicit hidden) strategic forces on the other side,and also against third-parties (e.g., Iran, North Korea).The problem is that the effectiveness ABM and other strategic defense technology is very much open to doubt.