137. Memorandum From the Director of Defense Research and Engineering, Department of Defense (Foster) to Secretary of Defense McNamara 1


  • Transmittal of Study Report—Penetration Capability of U.S. Missile Forces versus Soviet ABM Defense 1967–1973


  • (1) Memorandum, Secretary of Defense to DDR&E dated 21 May 1966 requesting study of U.S. Missiles ability to penetrate Soviet Defenses2
  • (2) Memorandum, DDR&E to Secretary of Defense dated 8 June 1966 outlining study approach3

Attached are Summary Volume I and Volume II of the Penetration Study4 prepared by my staff in response to your request of May 21, 1966. Volumes III and IV are separate reports prepared as inputs to my staff for the purpose of this study by CIA and DIA respectively, entitled “Soviet Anti-Ballistic Missile Capabilities” and “The Soviet Anti-Ballistic Missile Program and Deployment”;5 these are available through Special Activities Office control.

The results of the study, for a “high” estimate of the projected number of Anti-Ballistic Missile interceptors show that the U.S. can maintain approximately [less than 1 line of source text not declassified] in the Soviet Union through 1973, in agreement with studies presented by ASD(SA) in the draft 1968–1972 Strategic Offensive and Defensive Forces Presidential Memorandum,6 if a simple, unsophisticated model of defense capability is assumed. On the other hand, if the Soviets are assumed to have the capability to operate these forces in a coordinated manner, using “preferential” defense of some locations at the expense of others and to operate some of their long range interceptors in a precommitted “loiter” mode to intercept reentry objects [less than 1 line of source text not [Page 417] declassified], then they may limit their fatalities to about [number not declassified] through 1971 and to substantially less than that thereafter against the presently programmed U.S. Missile Forces.

As indicated in the Introduction and Threat discussions in the report, the study results are strongly influenced by the Threat projection, about which there remains considerable uncertainty. These uncertainties involve questions as to: 1) which of the two systems that the Soviets are building that can have ABM capability will be proliferated as the main ABM component; 2) what the rate of interceptor build-up will be; 3) what mode of defense (as discussed above) their interceptors will operate in; 4) how effective their first strike on U.S. Missile Forces will be (including the possibility of MIRV or Terminally Guided Reentry Vehicle), and 5) the success of the U.S. in continuing to have accurate intelligence on interceptor deployment.

The study results, in general, are U.S. conservative in that the choice of assumptions regarding the reference case ABM deployment rate, the lack of defense command and control constraints, the Soviet Offense effectiveness, and the effects of simplifications needed to model the engagements for computation all tend to provide an upper bound to Soviet ABM effectiveness. Alternatively, changes in certain key assumptions could reduce the level of Soviet7 fatalities significantly, under certain circumstances. These assumptions are 1) that the U.S. penetration aids will be effective in drawing interceptors; 2) that the Soviets do not have mobile interceptors about which we are unaware and that we will continue to obtain intelligence regarding their fixed sites and 3) that the U.S. will develop changes to its SIOP to have a planned option for nearly 100% utilization of Missile Forces for Assured Destruction by 1970.8 In the early 1970’s, when the major part of the U.S. reentry systems can be in the form of small warheads, the dependence on penetration aids effectiveness can be reduced.

The U.S. does not presently have in its inventory any missile payloads that individually “penetrate” Soviet Defenses. Our “penetration aids” are in reality [8–1/2 lines of source text not declassified].

There are other penetration aids that can potentially “penetrate” if the details of the defense are known and which therefore are not particularly sensitive to the numbers of interceptors. Penetration in this way involves [6 lines of source text not declassified]. Thus while U.S. defense design has had to worry in detail about these tactics, the offense has not yet been able to plan to use them with confidence. As the Soviet defense [Page 418] design matures and as we begin to get sufficient intelligence about their systems to probe for weak spots, such “penetration” tactics will probably become available with confidence and be cheaper to apply than is the exhaustion tactic. These penetration concepts are undergoing exploratory development under the ABRES program and the bus deployment techniques now being developed for payload dispersal on Minuteman III and Poseidon are both well suited for quick adoption of payload variants.

As soon as you have had a chance to review the contents of the report, I would be glad to set up a meeting with you, Cy, Alain and Harold to discuss its implications.

John S. Foster, Jr.
  1. Source: Washington National Records Center, OSD Files: FRC 330 70 A 4662, 471.94 Penetration 1966. Top Secret.
  2. See footnote 4, Document 130.
  3. Not found.
  4. These two volumes, entitled “U.S. Strategic Missile Force Penetration Capability versus Soviet ABM 1967–1973,” August 1, and four annexes are not printed.
  5. Not found.
  6. Reference may be to a July 26 (for comment) draft. (National Archives and Records Administration, RG 200, Defense Programs and Operations, Draft Memoranda to the President, 1968–72, Tab 8, Box 71) For text of a later draft, September 22, see Document 139.
  7. McNamara inserted the word “Soviet” by hand.
  8. In the margin next to this third assumption, McNamara wrote: “aren’t all the calculations based on this assumption?”