128. Memorandum From the Assistant Secretary of Defense for Systems Analysis (Enthoven) to Secretary of Defense McNamara 1


  • Interaction of U.S. Assured Destruction and Damage Limiting Forces (U)

Last year’s Memorandum to the President on Strategic Offensive and Defensive Forces2 paid particular attention to larger-than-expected threats to our Assured Destruction capability. These threats were postulated without explicit study of their desirability or feasibility from the Soviet viewpoint and without evidence of Soviet trends in those directions from intelligence indicators. Postulation of such threats furnishes an appropriate analytical tool for an extreme test of our Assured Destruction capability; nevertheless there is a risk that it may obscure possible U.S. opportunities to influence Soviet behavior. Taking larger-than-expected threats as “given” fails to credit our Damage Limiting forces with the virtual attrition that they in fact exact of the Soviets in planning their own forces.

The Soviets apparently view our forces, as we do theirs, as a potential first strike threat. They therefore must design their capabilities to protect their own Assured Destruction capability against a U.S. first strike. To the extent that Soviet resources are thus expended, and hence diverted from alternative uses in improving the U.S.S.R.’s Damage Limiting posture, our own Assured Destruction task becomes easier.

It is in our interest for the Soviets to spend sizable sums in guarding their Assured Destruction capability, provided these expenditures are primarily reflected in defensive measures such as missile launch facility hardening, missile dispersal or missile mobility, rather than in increases in their offensive forces’ payloads. Diversion of Soviet resources to defensive measures would reduce the cost of maintaining our relative Assured Destruction position for a given level of Soviet expenditure on strategic programs and would also contribute to U.S. and Allied Damage Limiting by reducing their ability to inflict damage on us.

The implications for U.S. policy concern the value of continuing to maintain a counter-military threat against the Soviet strategic offensive [Page 397] forces; specifically they concern the value of achieving low CEP to force the Soviets to adopt very expensive vulnerability-reducing methods such as mobility and hard point defense. Although Soviet responses cannot be predicted with confidence, a Soviet response that optimized their Assured Destruction capability against a U.S. threat with much lower CEP than we have now, would result in a reduction in Soviet first strike Damage Limiting capability over a wide range of Soviet Assured Destruction budgets.

An illustration of the pressure imposed by U.S. strategic offensive forces on Soviet forces was made in the DDR&E study, “A Summary Study on Strategic Offensive and Defensive Forces of the U.S. and U.S.S.R.” of September 8, 1964.3 The study contains an analysis (p. 68) showing that if the Soviets optimized their Assured Destruction capability against a small U.S. counter-military offensive capability they could purchase large, soft missiles at $1.33 million per kilopound ($M/KP). The cost to the Soviets of the same payload triples—to $4M/KP—if survivability through hardening and dispersal must be purchased. Virtual attrition seems to be exerting major influence on Soviet force planning, as shown by the Soviets’ large scale deployment of SS–11s and by their pursuit of small and mobile missile technology.

My staff has undertaken a further analysis of the pressures that programmed U.S. forces indirectly bring to bear on the Soviet Damage Limiting capability. This analysis proceeds in three steps.

In the first step, a Soviet force is designed to negate the U.S. Assured Destruction capability in a Soviet first strike assuming that the Soviets were not in fact concerned with maintaining an effective Assured Destruction capability. It is basically the approach used in the extreme cases of last year’s Draft Presidential Memorandum.

Then, the programmed U.S. forces are applied against this Soviet posture, and surviving Soviet forces strike U.S. urban targets. Resulting U.S. fatalities are so low that the assumed enemy posture could not constitute a high-confidence (to the U.S.S.R.) Soviet Assured Destruction capability.

Finally, at the same Soviet budget level used in the first step, a new Soviet force is designed for first strike Damage Limiting, subject to a constraint on Soviet second strike Assured Destruction stemming from the pressure exerted by our capabilities. This constraint markedly reduced the Soviets’ ability to erode our Assured Destruction capability within the fixed Soviet budget level.

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Soviet First Strike Only Damage Limiting Threat. A re-examination of SS–9 requirements, taking all reliabilities into account, indicates that the Soviets would need some 350 SS–9s, each carrying 10 Mk-17 MIRV’s, to achieve high expected damage against programmed U.S. land-based forces with high confidence. Assuming the existence of such a Soviet capability, and applying reasonable adjustments to National Intelligence Projections for Planning (NIPP) factors to reflect the assumed introduction of MIRV, the expected damage against U.S. forces is .92 with a 1500 foot SS–9 CEP, but only .77 with a 2100 foot CEP. (We now project a CEP of 3000 feet for the SS–9 in 1970, with no evidence of an appreciable Soviet effort to reduce this figure.) These missiles alone cost some $9 billion (about $1.5 M/KP) beyond the cost of the remainder of Soviet Offensive forces.

Next, we design a least-cost Soviet defense to keep Soviet fatalities at [less than 1 line of source text not declassified] of their total population in the face of a counter-urban attack by the surviving U.S. forces. This fatality level corresponds to the delivery of [less than 1 line of source text not declassified] warheads in the absence of Soviet defenses, and roughly equates to the level that might be expected from leakage through a very good defense against a U.S. retaliatory attack. This defense consists of 1800 area interceptors and 1000 terminal interceptors at 15 cities, at a total five-year cost of approximately $6.4 billion plus a non-recurring cost for research and development, tooling and production facilities, etc., which is irrelevant to this calculation. Of this cost, approximately 80 percent is for area defenses. This is consistent with results obtained in analyses of light Nike-X deployments.

Thus, for a total increment of some $15 billion over a base U.S.S.R. budget, the Soviets can reduce the Assured Destruction capability of our programmed missile forces to a highly unsatisfactory level through 1969–1974. The base budget is the cost of their R&D program, their missile programs, their SLBM programs, their bomber program and their air defense programs.

Assured Destruction Capability of the Soviet Force. We have analyzed a pre-emptive U.S. strike as a Soviet planner might do, in evaluating the Soviet Assured Destruction capability. The programmed U.S. forces are laid down in a pre-emptive strike against the Soviet intercontinental strategic military target system designed above (i.e., the MIRVed SS–9s plus the other Soviet ICBMs, SLBM bases, intercontinental bomber bases, etc.). If the Soviet area defenses did not cover their SS–9 missile fields, as would be the case with the present locations of the SS–9 silos, U.S. fatalities would be less than 10%. If the Soviet area missile defense is assumed to protect Soviet military targets and to operate without [Page 399] leakage residual Soviet forces are estimated to inflict 22% U.S. fatalities (200 equivalent one MT weapons) in the absence of U.S. ABM. Thus the Soviet deterrent would depend entirely on the precise siting and effectiveness of their ABM as a component of hard point defense. (Even a very light U.S. ABM deployment would be able to negate the remaining Soviet forces.)

Soviet First Strike Damage Limiting with Assured Destruction Constraint. As a last step, the Soviets take measures to maintain their Assured Destruction capability. They are allowed to replace the forces assumed above with more survivable forces at the same cost as the Soviet Damage Limiting force. The resulting posture (shown in table below is very similar to the missile force predicted in the NIPP), but the SS–9s are assumed to carry MIRVs. Additional mobile missiles and an area only defense are also purchased at the expense of Soviet terminal defenses. The SS–9s and the area defenses can be considered as the Damage Limiting increment added to the Assured Destruction backbone of their posture.

If this entire force is sent against the U.S. in a Damage Limiting first strike (i.e., no part is withheld for a later Assured Destruction capability), the residual U.S. missile forces can still deliver more than [less than 1 line of source text not declassified] equivalent weapons against the U.S.S.R. instead of the [less than 1 line of source text not declassified] equivalents that the U.S. could deliver against the Soviet Damage Limiting only posture. Again, this figure exceeds the [less than 1 line of source text not declassified] equivalent criterion for an effective U.S. Assured Destruction capability that was suggested in last year’s Presidential Memorandum.

TABLE 1: Soviet Intercontinental Forces of the Damage Limiting Posture (#1) and of the Assured Destruction Posture (#2)

Launchers 69 70 71 72 73 74
Posture #1
Soft SS–7 (1x2) 102 80
Hard SS–7 (1x3) 70 70 70 70 55 30
Hard SS–9 MIRV (1x1) 300 350 350 350 350 350
Posture #2
Soft SS–7 (1x2) 102 80
Hard SS–7 (1x3) 70 70 70 70 55 30
Hard SS–9 MIRV (1x1) 125 125 125 125 125 125
Hard SS–11 (1x1) 300 375 425 475 525 550

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The Soviets, by viewing our forces as a first strike threat to their Assured Destruction capability, must spend much more to achieve a first strike Damage Limiting capability. This does not argue that the Soviets are incapable of achieving both a satisfactory (to them) Assured Destruction capability and a Damage Limiting capability. But it does mean that, by carefully designing our own forces, we can foreclose any “easy” roads to Damage Limiting for the Soviets. Furthermore, low U.S. CEPs prevent simple proliferation of hard ICBM silos from being a useful Soviet response; Soviet mobility or defense would be required. Thus, a simple increase in total Soviet offensive payload is not a likely response to the strong U.S. counterforce capability.

Characteristics of U.S. Damage Limiting forces that place this constraint on Soviet forces should, therefore, receive continued attention. For example, the high accuracy attainable with the Mk-17 (rather than the Mk-11A) can be thought of as making an indirect contribution to Assured Destruction.

Proposed changes in U.S. forces (such as the addition of large payload missiles) should be evaluated in light of possible Soviet responses, and especially in light of the constraints they impose on the Soviet mix of Assured Destruction and Damage Limiting. Analyses not based on such consideration are likely to be incomplete, and the decisions based on such incomplete analyses, misleading.

In this year’s Presidential Memorandum, I propose to include an interaction analysis. Thus, in addition to postulating Soviet threats and finding what forces would be required to overcome them, various possible new U.S. systems—both for Assured Destruction hedges or for Damage Limiting—will be considered in terms of the effects they would be likely to have on the U.S.S.R.

Alain Enthoven
  1. Source: Washington National Records Center, OSD Files: FRC 330 70 A 4662, 381 SRF 1966. Top Secret. “Sec Def has seen, 24 May 1966” is stamped on the memorandum.
  2. Document 103.
  3. This 192-page study and Appendix are not printed. (Washington National Records Center, OSD Files: FRC 330 69 A 7425, 381 Strategic Retaliatory Forces (9 Jan 94) Sep-Nov 1964)