141. Memorandum From the Director of the Arms Control and Disarmament Agency (Iklé) to the President’s Assistant for National Security Affairs (Kissinger)1
SUBJECT
- Threshold Test Ban/PNE Negotiations
With the next round of the TTB/PNE negotiations now scheduled to begin June 3 and the interagency work nearing completion, I want to convey to you my assessment of the critical choice that is involved.
We still face the main stumbling block from the 1974 summit that prevented us from completing the threshold test ban treaty in the first place, namely the claimed Soviet interest in excavation explosions with individual yields above the 150 KT threshold. In line with President Nixon’s commitment to follow-on negotiations on this problem, the US devised a set of limitations (primarily a limit on fission yield) and corresponding verification requirements to apply to individual excavation explosions larger than 150 kilotons, and these have been under active discussion with the Soviets.
Cutting through the forest of detail, I see two possible outcomes for agreement:
Outcome 1. Soviet Acceptance of U.S. Conditions on Excavation PNEs
If all of our proposed limitations and verification arrangements for large excavation explosives are accepted by the Soviets, we would have placed significant short-term limitations, but not definitive limitations, on the potential for weapon testing through PNEs. We still need to reach agreement with the Soviets on important details in our position [Page 472] on verification modalities: in particular, (1) on collection of “melt samples” at excavation sites, and (2) on verification of geometry and dimensions of any cavities beneath emplacements of explosive devices which could strongly affect or prevent measurement of fission yield. The Soviets have so far been negative toward such provisions.
Outcome 2. Soviet Acceptance of a 150 Kiloton Limit on Individual PNEs In Exchange for U.S. Concessions on Salvo Yield and Verification Provisions
Alternatively, we could respond to Soviet reluctance to accept our required verification measures by offering the following modified terms for a simplified PNE agreement (that would be consistent with our 1974 summit commitment):
(1) Limit the yield of individual excavation explosives to 150 kilotons. (A Soviet concession.)
(2) Permit distinguishable salvo explosions to have a high aggregate yield, up to 500 kilotons or even 1 megaton. (A U.S. concession.)
(3) Remove the fission yield limitation and, hence, the requirement for collection of melt samples. (A U.S. concession.)
(4) Trim down verification provisions to those necessary to establish the fact that the yield of any individual explosion does not exceed 150 kilotons. (A U.S. concession.)
Outcome 2 would handle PNEs in a manner readily understandable to all audiences, including the Senate. It would not involve the U.S. with provisions or observations which could prejudice our position on the LTBT, or on the separability of PNEs from weapons. It would provide an explanation of why the threshold was set at 150 KT—a level considerably higher than the current limit of our detection capability.
Yet, Outcome 2 would also give the Soviets the freedom to carry out large-scale PNE projects through salvo explosions. It would meet our commitment to negotiate special provisions for PNEs by permitting them to exceed the threshold in salvos and by permitting them to be detonated outside of test sites.
Outcome 1, on the other hand, would leave us with an agreement that would still have significant liabilities, even if the Soviets accepted all the provisions critical to verifying restraints on weapons testing through PNEs:
—We would have signed an agreement making explicit provisions for U.S. observation of radioactivity from excavation PNEs, an activity which is likely to be associated with a violation of the U.S. interpretation of the LTBT. We would face the possibility of being placed in the position of participating in an event which we consider a violation of one agreement in order to verify compliance with another one.
—We would have given legal status to a technological distinction between excavation PNEs and advanced weapons tests. While we can [Page 473] insist on the validity of this distinction for countries which long tested nuclear weapons, third countries will, nevertheless, use this to support assertions that PNEs can indeed be distinguished from nuclear weapons.
—We will have lost the possibility of using PNEs as part of the explanation for setting the threshold on weapons tests at 150 KT, considerably higher than the verifiable limit.
—If the weapon test threshold were lowered in the future (Soviet and U.S. domestic pressures might move us in that direction) the separate limitation on PNEs could become an increasingly troublesome loophole for Soviet tests of military significance that would be unavailable to the United States.
Conclusion
On balance, Outcome 2 seems clearly preferable to Outcome 1. If we stick fast to our verification requirements, it seems reasonable to expect that Outcome 2 would also be preferable to the Russians, since it would minimize involvement of U.S. observers in their PNE shots and avoid any risk that we would secure useful information about the design of their devices as a by-product of verification.
Thus, we should make all our concessions towards Outcome 2. We should make no concessions on verification modalities for PNEs above 150 kilotons which would not only steer the Soviets toward Outcome 1 but would actually compound its liabilities by raising doubts about our ability to verify compliance with the agreement.
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Summary: In preparation for the upcoming TTBT/PNE negotiations with Soviet officials, Iklé outlined for Kissinger two possible outcomes for agreement.
Source: Ford Library, National Security Council, Institutional Files—NSDMs, Box 60, NSDM 297—Instructions for the U.S. Delegation to the PNE Negotiations, Moscow, 6/3/75. Secret; Exdis. There is no indication that Kissinger saw the memorandum. Copies were sent to Ingersoll, Clements, Brown, Colby, and Seamans.
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