Created: 11/1/1981

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Soviet Intentions and Capabilities for Interdicting Sea Lines of Communicationar With NATO



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This Interagency Intelligence Memorandum was commissioned9 by the Director of Central Intelligence in responseequest by tlie Under Secretary of lhe Navy for an in-depth study of Soviet planning and capabilities for interdicting NATO sea lines ofin wartime. The Secielary of Defense and the Under Secretary of the Navy provided guidance for the terms of reference. Thewas produced under lhe auspices of the NaUonal Intelligence Officei forCeneral Purpose Forces. II wasdraflcdp

jNational Foreign Assessment Center. CIA, with contribulions by the Office of Naval Intelligence, the Defense Intelligence Agency, and the National Security Agency.

The study is special in the senseumber of ,udgments about Soviet interdiction capabilities are based on analyses that involved the simulation and modeling of combat between opposing lorces. These analyses are not an attempt to predict which side woulduture Battle of ther by how much Their purpose is only to highlight iIk* fccy variables lo which Soviet interdiction capabilities are sensitive and to identify trends for those capabilities under various assumptions Interactive combat simulations clarify combat stresses on Soviet forces, and therebyoic meaningful assessment of thc capabilities of those forces These analyses were performed by the Center for Naval Analyses and prov.ded by the Office of the Chief of Naval Operations

This Memorandum was coordinated wiih thc intelligenceof the Departments of Slate and Defense and with the National Foreign Assessment Center, CIA.


This Interagency Intelligence Memorandum addresses the issue of Soviel intcrdiclioti of Western sea lines of communication (SI.OC,eneral NATO-Warsaw Pad war centered in Europe SLOGis denying or hindering by any means an enemy's use of the sea for transporting military or economic cargoes. There are two parts lo tlie issue

Soviel intentions. How does SLOC interdiclion fil into Soviet phoningar with NATO?

Soviel capabililies. To what extent could the Soviets carry out an interdiction campaign inar and what would be the key factors affecting their anli-SLOC potential5

The Soviets note that sea lines can be interdictedariety of forces usedaridy of ways, including attacks on ships at sea. the mining of heavily traveled waters, and the disruption or destrudion of ports of embarkation and destination They clearly believe that itan enemy's ports and harbors with nuclear weapons is the most efficient mean* of SLOC interdiction In this Mernotindum wegenerally on SLOC interdidion in nuclear war, but our concern is mainly with conventional conflict because il would be thc most demanding test of Soviet anli-SLOC capabilities

In general, we confine our analyses to lhe eaily stagesar oronventional conflict lasting less than six months We bcl.eve lhal Soviet anli-SLOC efforts in litis context would be focused primarily onilitary shipping engaged in lhe reinforcement and reiupply of Europe- particularly NATO's Central Region. Disruption of that shipping would have the most impact on the outcome of thc war. We place special emphasis, therefore, on the critical transatlantic shipping lanes between the United Slates and Europe Wc also consider Sovidin other areas such as thc Pacific and Indian Oceans but we Ircal it in less detail

Although wc do not rule nut the possibihtixotraded. conventional war of attrition of indefinitek- Soviets considerar with NATO highly unlikely The nature ol Soviet inlerdic-Imi inar could be similar lo or different from that described in lliK Mndy. deivrxfing nn the eiicumstar. .


I- We believe tlut il is not currently lhe intention of Soviet planners toarge-scale inlcrdiclion campaign against sea lines of communication (SLOG)ajor war with NATO, although we believe ihey intend some interdiction. Ilefote lhe war began, or once il was under way. Soviet inlenUons could change will, the evolving slrategic situation, especially if the combat were protracted. But the Soviets first would have lo bringubstantial weakening of NATO's potential to protect its sea lines before they could expect much successarge-scale, conventional interdiction campaign.

Soviet Intentions for StOC Interdiction

verall, the Soviets' military writings and exercises indicate that the primary wartime objectives of ibeir general purpose navalat least initially in abe to defeat NATO's nuclear-capable naval strike forces and lo protect Soviet strategic submarines Most Soviet naval forces would be assigned to these tasks. SLOC interdiction wouldess urgent task In the Soviet view, cither Warsaw Pact forces would defeat the main groupings of NATO forces in Cenlral Europe or war most likely would escalate lo [heater nuclear

conflict before NATO's seaborne reinforcement and resupply of Europe

ritical factor

ven though Soviet planners regard SLOC interdictionower priority task, wC believe that they would allocaic some forces to it from the outset ol hostilities. In particular, we believe that the Soviets plan to conduct some attacks on shipping -and probably some mining and attacks on European porls-primarily lo influence local land campaigns, fo disperse and he down NATO naval forces, and to reduce the efficiency of NATO military shipping Such actions in the Soviet view would complicate NATO's operations and facilitate performance of what the Soviets see as iheir more important lasts

he Soviets could increase (heir emphasis on SLOC interdiction before orar wiih NATO in response loerceptionhanging strategic silualionow wwild be difficult for them,ecision tn draw down iwevs allncalrd to oilier mission*


and lo commit (hern lo an anli-SLOC campaign almost certainly would be viewed by the Soviets as risky as long as NATO's naval forces threatened the USSR and Soviet strategic submarines

robably one of the most likely circumstances that would motivate the Soviets lo widen their emphasis on SLOC interdiction would be the lengtheningarrotracted conventional conflict. Another circumstance mightonflict that beganrolonged period of mobilization during which NATO began the reinforcement and resupply of Europe by sea. Inase lhe Soviets might see interdiction as an urgent task at the beginning of hostilities.

Executionoviel Interdiction Campaign

are various forces that thc Soviets could bring tosea lines of communication, depending on the situation.attack submarines probably would be the main forceal sea. although strike aircraft also couldole.regard surface ships as less capable for anti-SLOC attacks,do not believe that they would attempt to use themargesuch attacks in thc open ocean, at least noi in the initial phases olAircraft would be the primary force for attacking Europeana conventional war.uclear war, some ballistic missiles couldfor strikes on SLOC termini.

Convcnlionol War

Action ar Naval Operation. If awar developed roughly as envisaged by Soviet writers^"

^the Soviets would not initiallyarge-scale interdiction operation They probably would, however,maller anti-SLOCtheysystematicthe North Atlantic and possibly in the Pacific and Indian Oceans as well. We believe that such an offensive would be conducted pnneipally by attack submarines It probably would normally involve fewer thanubmarines in lhe sea lanes, bui thc Soviets could increase or decrease tbe number ol submarines on station at selected times. The

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campaign also could involve some mining bv various means. Although thc Soviets would considerampaign important, they would not regard it as critical to thc outcome of the war.

While this interdiction campaign was in progress, the bulk of Soviet naval forces would be engaged in what the Soviets call "the initial navalsimultaneous actions designed primarily to control pivotal maritime areas and to deny NATO's naval strike forces the use of other selected areas' The initial naval operations would be focused mainly in the Norwegian. Baltic. Black, andSeas and in thc northwestern Pacific. The Soviets evidently believe that these naval operations would be likely to span both conventional and nuclear conflict. They probably hope to achieve the goals of these operations within the expected durationround campaign in Central Europe.

If the Soviets increased their emphasis on SLOC interdictiononventional war. for whatever reason, we believe that they wouldto mount an anti-SLOC naval operation.ove would change the nature of an interdiction campaign begunystematicThe Soviets would attempt to concentrate large forces in the sea lanes at certain times for decisive sea denial battles They almost certainly would want to defer such an operation, however, until after they had accomplished their initial naval operations and had weakened NATO's capability to protect its sea tines.

ttacks onoviet bombing and mining campaign against European portsonventional war probably would be similar to the interdiction campaign at sea Initially it wouldystematicbut it could evolve inlo an operation, depending on thc course of ihe war. At the outset of hostilities, most Soviet medium bombers and tactical aircraft would be committedassive bombing offensive to achieve air superiority and reduce NATO's nuclear capability in Centralthe Soviets relet lo as the "Airtherefore they would be unavailable for early strikes on ports. Only some Naval Aviation bombersew attack submarines might be availableampaign against potlsar

Nuclear War

II. Tlie Suvicls clearly believe lhal the most effective way of interdicting sea lines of communication is to attack an enemy's potts

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and harbors with nuclearuch attacks require the fewest forces, offer thc highest probability of success, and are hardest lo defend against.ATO-Warsaw Pact war began as or escalated to nuclear conflict, thc Soviets almost certainly would focus their anti-SLOC efforts primarily on SLOC termini, although they probably would also conduct nuclear attacks on shipping at sea. Attacks on ports could include strikes with chemical weapons.

imited nuclear war. Soviet nuclear strikes would be restricted to the theaters of military operations. If war escalated to intercontinental conflict, some US ports also ptobably would be attacked.

Soviet Capabilities in the North Atlantic in Conventional War

Sovietsignificant anti-SLOC potential.antt-SlAOC capabilitiesonventional NATO-Warsawhowever, would vary with the scenario, and they would betechnical and operational constraints on Soviet forces.

We do not believeoviet systematic action against North Atlantic sea lines would result in the sinking of many meichant shins because thc Soviet investment in forces would be small and those forces probably would suffer heavy attrition against well-defended shipping. The degree to whichampaign tied down NATO forces and reduced the efficiency of reinforcement and icsupply shippingwould depend on how NATO perceived and reacted lo il.

If the USSRarge-scale operation to seversea lines, its prospects for success would be slim unless NATO's capabilily lo protect them were first subslantially weakened. The Soviets couldajor portion of their naval lorces in an anti-SLOC operation in the face of strong NATO opposition Although Soviet forces might be able lo inflict heavy damageew NATO convoys, rapidly mounting allrilion would quickly diminish their capabilities to inTUct further damage

Prerequtiitos (or on Anli-SlOCOperofion

e believe thaiinimum ihe Soviets would have lo accomplish lhe following tasks before thev wouldikely chance of eutting Norlh Atlantic sea lines of communication

They would have lo gain control ol the Norwegian Sea without excessive losses Suchconlrol would have lo include lIh- neulral-

izalion of NATO's anliair and antisubmarine <ASW) capability based in northern Norway.

They would have lo reduce significantly NATO's air and ASW defenses in the Greenland- Iceland-United KingdomK) gap.

They would have to degrade NATO's wide-area ASWcapabilily in the North Atlantic by attacking orSOS US terminals and lhe SURTASS ships that are to be deployed in thcew yeais.

If the Soviets accomplished these tasks, they would be able to dictate the time and place for an interdiction campaign, and they probably could disrupt the reinforcerncnl and resupply of Europe. Otherwise, they probably would have lo fight an anli-SLOC campaign on NATO's terms, and our analyses indicate thai their capabilities to do so would be marginal.

Tlie first two of the above tasks would be objectives of the initial naval opeiations of the Northern Fleet Detailed analyses of these operations are outside the scope of (his study. We judge, however, thai they would be difficuli for ihe Soviets u> conclude successfully and without heavy lossesonvcnlional war il NATO slrongly conlestcd them

The Soviets might be able toumber of SOSUS arrays earlyar. particularly tliose terminating in Iceland. Norway, and the United Kingdom It would be more difficult for them to sink SURTASS ships, however, especially if (hesc ships were protected. Unless the Soviets significantly weakened both the SOSUS andnetworks. NATO could stilltrong submarine detection capability in the North Atlantic.

Strengths ond Limitations of Soviet Submarines

Submarines. Out analyses show lhat long-rangelltose ofndthe most capable Soviel force for an anti-SLOC campaignNATO defenses. Diesel submarines would be difficuli toof their (juiciness when operating on ballery power Willitaclics. these submarines wouldood chance ofNorth Atlantic sea lines They probably would be most vulnerableprosecution during attucls on convoys, when tlievpresence

(hey can operate quietly, diesel subrnarirvesmobility and they would have to travel long distances toAtlantic sea lines from their Northern Fleet bases. It would takesubmarine more than two weeks, lor example, to reach aat the entrance to the English Channel. Once (here, it couldabout threealf weeks on station before it would have toBecause of these considerations, the Soviets wouldto keep large numbers of diesel submarines continuouslyin the North Atlantic. To maintain six on patrol, forwould have to allocatehan half ofF-lass submarines in the Northern

The long distance to North Atlantic sea lanes would tend to limit thc amount of damage the diesel submarine force could inflict on NATO shipping. Moreover, the anti-SLOC capabilities of the force would decrease as the war lengthened and diesel submarine losses mounted.

Nuclear Submarines. Soviet nuclear submarines arc faster and more mobile than diesel submarines, but they lack the quietness of diesels. Most Soviel nuclear submarines arc noisy relative to their Western counterparts, and they therefore would beonstant disadvantage with respect to NATO submarines. Moreover, the noise radiated by Soviet nuclear submarines can be detected by NATO's wide-area surveillance systems, often at great ranges. Our analyses show that, if NATO's area ASWby SOSUS andnot considerably weakened and performed as expected, Soviet nuclear submarines would suffer heavy attrition in an anti-SLOC campaign in the North Atlantic. Although the Soviets evidently are taking steps to reduce the noise of their nuclear submarines, programed improvements to NATO's ASW systems, if realized, will offset much ol what we believe ihc Soviets will achieve in the foreseeable future.

Nuclear submarines could reach sea lines more quickly than diesel submarines because tbey could transit at higher speeds. Their use of high speeds, however, would heighten iheir radiated noise, thus increasing their vulnerability lo NATO's area ASW lorces.

Olher Factors. There are various other factors that would affect Soviet submarine capabililics in an anti-SLOC campaign in the Norlh Atlantic, including:

Submarine availability. The demands ol the initial naval operations and the requirement to protect strategic submarines

wouldimit lhc availability of Soviel attackfor SLOC interdiction, at least earlyar.

Submarine replenishment. If Soviet submarines couldin the North Atlantic without having lo return to Northern Fleet waters, their anti SI.OC capabilities would beew submarines mighl receive minimal support fromin Cuba or Africa or from deployed merchant or auxiliary ships. Such support would not be adequateajor or sustained campaign, however.

Acoustic environmental conditions. Poor conditions would favor Ihe Soviets by reducing submarine vulnerability. Such conditions can change radically, however, andengthy campaign they probably would even out.

Ocean surveillance. Soviet submarines would need timely intelligence on NATO convoys or their attacks could be piecemeal The Soviet ocean surveillanceis highly susceptible to counterhave to operate without material degradation.

Cruise missile targeting. The availability of targeting data for submarines with lonc-range cruise missiles probably would be ephemeral at best in the North Atlantic. Thus the Soviets probably would have to rely on torpedo attack submarines and those wiih short-range cruise missiles for an anti-SLOC campaign

Aircraft Capabilities

For conventional aitstiikcs against North Atlantic shipping, the Soviets probably would use Backfire bombers. Allhough thc Soviets have modified some heavy bombers lo carry conventional antiship missiles, it is problematic whether ihcv would use ihese aircraft against sea lines of communication Other Soviel bombers would haverange to attack North Atlantic sea lines from Warsaw Pact airfields. except perhaps near some European SLOC termini.

Backjire flange Constraints II tlie backfire has thcestimated by CIA. we judge thai lhe range constraints of the aircraft would severely limit its capability againsi North Atlantic shipping The capabilityackfire performing according to DlA. Army, and An Force estimates would be less const rained because of longer range


ulnerability to NATO Air Defenses. Backfire anli-SLOC capabilities also would be restricted by ihc aircraft's vulnerability to NATO air defenses. If NATO maintained its maritime air defense capability in Iceland and the United Kingdom. Backfires would suffer heavy attrition if they attempted to My throughK gap Even ifK air defenses were breached, the Soviets still would have to expect heavy attrition in an anti-SLOC campaign if NATO deployed aircraft carriers lo defend shipping. With such attrition. Backfires would sink relatively few merchant ships. With no threat from carriers and if Backfires could fly freely throughK gap, thc Soviets could inflict major damage on NATO shipping-if not disrupt the remforcement and resupply of Europc-unless NATO took actions to cut its losses.

ther Factors. Backfire anti-SLOC capabilities also would be affected by other factors, including:

Backfirehe- Backfire forceircraft-and il probably would have many missions to performATO-Warsaw Pact war. We believe that the Soviets would tend io use Backfires conservatively for anti-SLOC attacks, except in extreme situations.

Raid size. Large, simultaneous Backfire raids would be more productive than small ones against well-defended shipping. The wave tactics that thc Soviets practice, in which small groups of aircraft fly successively to their targets, could work against thc Soviets. In any event, raid size in most situations would be limited by the availablrlily of tankers.ew tanker is deployed for Backfire missions, most of theankers that suppori the intercontinental bomber force would have to be allocated to the anti-SLOC task

Ocean surveillance. Backfire attacks would requiie limel> and accurate information on the location and diieclion ofof NATO convoys Without such information. Backfire anti-SLOC capabilities would Ih: marginal at best.

Payload. Although Backfires can carry one or two air-to-surface missiles, they probably would be limitedingle missile foi attacks at greal ranges

Attacks on SlOC Termini in Conventional War

and repetitive bombing and mining atlacks. inwould be icciuired to disrupt decisively or to sever sea linesEuropean terminionventional war. The Soviets' capabilitiessuch an oflcnsive would hinge primarily on their abilitythe air en route lo and over the ports.

little or no opposition, the Soviets probablyheavy attacks lhat eventually would close ports orof thc ships that attempted to unload in them Withoutthey might be able toew attacks on ports,could not conduct persistent attacks ol sufficicnl size andfreedom lo bring lasting results. Conlrol of the air wouldeasy for thc Soviets lo achieve. Ultimately, it piobably wouldthe course of the war in Cenlral Europe, allhough thc outcome ofSoviet Air Operation wouldirect bearing onearlyar. There is no consensus within theon lhc likelihood of success of thc Air Operation. Ahas concluded lhal the Air Operation would not achievealthough in CIA's judgment il would doto NATO's air defenses Others believe that the degree toAir Operation would achieve air superiority and affect theto conduct air atlacks on SLOC termini is highlyand cannot be judged with confidencc.,

Aggregate Effects of Systematic Actions

c believe thai the Soviets could decisively disrupt or sever NATO's reinforcemenl and resupply of Europeonventional war only by large-scale air and naval operalions and only after they hadweakened NATO's SLOC delenses Nevertheless, wethat the flow of NATO's reinforcement) and supplies could be impaired if the Soviets could maintain constant pressure on NATO shippingell orchestrated campaign of systematic actions both in thc North Atlantic and at lhe European termini. Presumably, these systematic actions would include regular submarine attacks in the open ocean, selected bombing and mining of ports, and perhaps some antiship ail strikes We cannm judge with confidence, however, the extent to which NATO's reinforcemenl and resupply effort would br impaired by such actions

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ost agencies believe ihat the aggregate effects ol the actions desciibcd above would have to compound over time for thc impairment to become significant. One view is, however, that even temporary interruptions in the flow of critical supplies and rein lor cements in NATO's sea lines of communication probably woulderious impairment in the flow to the European Central Front. According to this view,eiious impairment could be causedelatively small scale bombing, mining, and sabotage campaign aimed at critical nodes such as locks, power supplies, bridges. Classification yards, pipelines, andhe majority believe, however, that limited small-scale attacks probably would no!erious impairment because lhe facilities at the termini are so extensive that thc damagewould not seriously inhibit the use of these ports Moreover, the number of termini ensures that sufficient capacity would be available even in the event of some disruption

Inlerdiclion in the Pacific ond Indian Oceans

a NATO-Warsaw Pact war the Soviets could mountanti-SLOC systematic aciion against Pacific sea lines as partsea denial mission, but we believe that the anli-SLOC taskof lower priority than in the Atlantic. The focus of any systematicprobably would be military shipping, although the Sovietsrandom attacks on economic shipping in an ailempl toUnited States to allocate additional scarce resources loDepending on the course of thc war. the Soviets couldlarge-scale operations against certain sea lines at specificgeneral. Soviet capabilities for SLOC interdiction in thebe less lhan in thc Atlantic theater because the Sovietsforces in lhe Pacific Fleet.

anti-SLOC campaign in the Indian Ocean probablythe formystematic action conducted by the Soviet foicesat lhe start of theikely target for the campaign wouldcrucial tanker traffic to Western Europe and the United StalesSoviet force of lour to five submarines and severalships probably could disrupt undefended tanker trafficattacks and mining of the Strait of Honnuz Tbe Sovietsampaign against significant opposition or if theyIn rrsupply their Indian Ocean forces

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c do not expect the Soviet concept ol SI.OC interdictionATO-Warsaw Pact war to change radically over thc next few years Over the next decade or longer, the Soviets could gradually modify their view of and approach to interdiction iu response to their changing perceptions of the courseATO-Warsaw Pact war or to changes in NATO's force structure or strategy for the reinforcement and resupply

of Kurope. Thc Soviets' capabilities to interdict sea lines ofwill improve throughs new submarines, aircraft, and

weapon systems enter their inventory Such improvements could be

offset if NATO continues to upgrade its naval strike forces and its

ability to defend its sea lines.

robably the most likely factor that would affect the status of interdiction in Soviet planning would be an evolving Soviet perceptiononventional period ol war with NATO would be more protracted than the Soviets currently envision. I

oviets begin to view conven-

tional conflict with NATO as likely to lasl fur several months or longer, ihey probably would place new emphasis on SLOC interdiction. Itecause they would be unlikely to decmphasize the importance of countering NATO's naval strike forces and protecting their strategic submarines, they could encounler problems in allocating their forces, and Ihey probably would have to expand current building programs or introduce new ones

he Soviet conceptOC interdiction also could change in response io changes in NATO's force structure. The reiirement ol US aiicraft carriers without replacement, for ciarnple.izableof NATO's general purpose naval lorces wouldATO deterrentoviet anti-SLOC campaign The Soviets probably would sec fcwci impediments lo early SLOC interdiction mid ihey probably would deploy additional foices lor distant sea denial operations againsi both meiehant ships and naval forces

idespread deploy irvent im NA TO swfacfand siihtna-mho ul loiigiaiige. miclcai callable CTUtar inisoiles foi land attack

would lend to restrict the Soriet allocation of forces for SLOC interdiction. Sucli deployment would greatly complicate the overriding Soviet objective of quickly destroying NATO's nuclear*capable strike forces in the initial navalarge-scale effort against cruise missile-equipped submarines and surface ships could bankrupt Soviet capabilities for SLOC interdiction, if not some other lasks as well.

f in the coming years the Soviets establish major naval and air facilities in Africa. South or Southeast Asia, the Caribbean, or other distant areas, their capabilities for SLOCwell as otherbe significantly improved. At present there is little likelihood that they will develop extensive overseas facilities in lhe near future to support large forces. The overseas facilities to which live Soviets currently have access would not be adequate forustained interdiction campaign without further development and the prc-positioning of substantial combat stores, fuel, and munitions.

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