139. Letter from Director of Central Intelligence Raborn to Secretary of State Rusk ¹1. Source: Department of State, S/S-RD Files: Lot 71 D 171. Top Secret; Restricted Data.

Washington, June 17, 1966.

OD-ACDA-2623

Dear Secretary Rusk:

In accordance with your suggestion at today's meeting of the Principals,²2. See Document 138. I am forwarding herewith a few comments, from the intelligence point of view, on the proposed Threshold Test Ban Treaty (TTBT).

[2-1/2 lines of source text not declassified] On the Soviet side, we believe that ABM deployment has begun at Moscow. In our judgment, the chances are about even that the Soviets have developed an exoatmospheric ABM system [2-1/2 lines of source text not declassified]. Our evidence, however, is skimpy, and the Soviets may well be further along. If not, there will be great pressure on them to develop a highly sophisticated system, since they are certainly aware in general terms of U.S. plans for improving warheads and penetration aids, e.g., multiple re-entry vehicles. The Soviets have shown considerable willingness to risk violation of the present test ban treaty, and even one or two tests a year above magnitude 4.75 would give them significant advantages. Thus, the Soviets could forge ahead of the U.S., unless the U.S. were itself willing to violate the TTBT, or at least risk doing so.

I do not believe that the TTBT will have much effect in slowing the proliferation of nuclear weapons. It was agreed at the Principals' meeting that the technical restraints imposed by the treaty would create additional difficulties for non-nuclear states in carrying out nuclear programs meaningful to them, but would not prevent it. On the political side, we are all agreed that China will not sign. Hence, the pressures on the countries being threatened by China will continue to grow as China conducts further tests. I do not believe that the TTBT or even a non-proliferation treaty would deter a country from going nuclear if it felt that its vital interests were threatened.

Regarding verification of a TTBT, there is an important distinction between convincing ourselves that a violation has occurred and proving it to others. There could be endless controversy about the magnitude and especially the nature of events which we believed were over magnitude 4.75. In general, convincing proof of a violation could come only from on-site inspection.

[1 paragraph (6 lines of source text) not declassified]

Sincerely,

W.F. Raborn