Foreign Relations of the United States, 1961–1963, Volume VII, Arms Control and Disarmament

299. Proposed Interagency Briefing Paper⁰

Washington, June 22, 1963.

INSPECTION AND THE NUCLEAR TEST BAN

In your forthcoming discussion with Prime Minister Macmillan on the nuclear test ban,¹ the question will undoubtedly be raised as to whether there is a real justification for insisting on a quota of at least 5 inspections instead of accepting the Soviet offer of 3 inspections. The question may also be raised as to whether the complete elimination of the inspection requirement would actually pose a threat to the existing balance of power between the U.S.-U.K. and the Soviet Union.

Aside from domestic political considerations, the argument for a quota of 5 instead of 3 inspections can be reduced to two points. First, is the simple fact that a quota of 5 will approximately double the actual chance of finding a clandestine test or test series and probably contribute more than a doubling to the deterrence against testing for purely psychological considerations. Second, with a quota of only three inspections there is danger that undue caution would be exercised in their use, particularly early in a given year. The increased deterrence provided by the larger quota is important since the level of deterrence of the system is not very high even with 5 inspections; therefore, a further 50 per cent or more reduction in the danger of being found out might provide the necessary confidence for the Soviets to undertake clandestine testing.

In comparing these two quotas one must recognize that a quota of 5 is only equivalent to 4 inspections since one inspection would always have to be held in reserve for use against a very suspicious event at the end of the year, and a quota of 3 is actually equivalent to only 2 inspections, since in this case one inspection would also always have to be held in reserve. (This difficulty would be overcome by the proposal to permit drawing upon inspections from future years. However, in the rest of this paper the calculations are based upon an annual quota with no carry-over, so that the last inspection is not used.) These inspections would have to be allocated among the approximately 75 seismic events which it is estimated would on the average remain unidentified out of the 170 seismic events detected annually in the Soviet Union by the system. To evaluate the effectiveness of the system, it is necessary to assume that the Soviets undertake a significant number of tests since only in this manner could any real progress in weapons development be accomplished. To consider a specific example, if the Soviets undertook a clandestine series of 10 nuclear tests with detectable yields and if we assume no unilateral intelligence is available to assist in selecting events for inspection, a quota of 3 inspections would give a probability of only 22% that at least one of the events inspected would in fact be one of the nuclear tests. A quota of 5 inspections would increase the probability of inspecting at least one test to 40%.

Similarly, against a clandestine series of only 5 tests, the probabilities of selecting at least one test would be 12% and 22% for quotas of 3 and 5 inspections respectively. Actually, the probabilities of finding and identifying a clandestine test in the above examples would be less than half as great as the figures indicated since, even if the inspection method itself were highly effective, it is estimated that there is only a 50% probability that a nuclear test would in fact fall within the region designated for inspection because of the uncertainties in the seismic data used to determine the location of the suspicious event.

It will probably be argued by the British that the number of suspicious events will actually be significantly less than 75, which is now quoted in our interagency position paper, since one can use additional seismic information, judgments on the location of seismic events and intelligence to reduce the number of unidentified events to numbers such as 20-30. If the unresolved residual were as low as 20 events, the probability of selecting at least one test in a series of 5 would be 36% for 3 inspections and 60% for 5. Nevertheless, considering the uncertainties as to whether an event actually falls within the area specified for inspection and the unknown probability that an inspection, if undertaken, would in fact be successful in locating the test site, the probability of detecting an actual event in even a series of clandestine tests would still not be sufficiently high to contradict the basic argument that doubling of the probability of detection would substantially improve the deterrent value of a quota of 5 over 3 inspections.

In addition to the numerical considerations, there is an additional difficulty with a quota of 3 as compared with 5 that is impossible to assess quantitatively, and that is the fact that fear of wasting our assets early in the year would result in our having less flexibility in exploiting the 2 inspections available under a quota of 3 than we would in the case of 4 inspections available in the quota of 5.

Turning to the questions of the implications of the complete elimination of the inspection requirement from a test ban treaty, it is correct that this would almost certainly not change the existing balance of power between the U.S.-U.K. and the Soviet Union. It is a mistake, however, to analyze the requirement for inspection in so narrow a context. The elimination of inspection would permit the Soviets to carry on a much more significant clandestine program than they could reasonably do in the face of even limited inspection. Moreover, of equal or greater significance would be the adverse effects of the elimination of inspection on the confidence-building and precedence-forming aspects of the treaty.

As a consequence of the nature of earthquakes, the inspections under our proposed treaty would in fact be applied against a relatively narrow yield range of potential clandestine nuclear tests. The detection threshold of the proposed external detection system would vary between 1/4 and 10 KT, depending on the medium in which the test occurred. We believe it is generally agreed that a prudent violator would probably have to test below about 3 KT in order to be confident of evading detection. While the number of detected but unidentified events is relatively large (estimated at about 75 in the present interdepartmental position paper), the number of unidentified events falls off very rapidly with increasing seismic magnitude. The principal reason for this effect is that the number of seismic events decreases very rapidly with increasing size. For example, the existing U.S. Atomic Energy Detection System, which has a threshold of magnitude 4.0 (equivalent of about 1.5 KT in tuff) detected some 260 seismic events in the Soviet Union in the year beginning mid-1961, and only 37 of these events were of magnitude 4.7 (about 20 KT in tuff) or above. Above magnitude 5.4 (roughly 100 KT in tuff) there would probably be only in the range of 10-20 seismic events in an average year. In addition, the ability to identify a given seismic event as an earthquake increases rapidly with increasing magnitude or equivalent yield. While confidence of identification is poor in the neighborhood of the detection threshold of the detection system, it is estimated that it would be possible to identify practically all events above magnitude 5 (approximately 40 KT in tuff) by the proposed external detection system. Combining all these factors, it can be argued that a monitoring system without inspection would identify with fairly high confidence by a purely technical means a significant clandestine series above a threshold of some 50 to 100 KT, taking into account possible adverse environmental factors. In addition, such a system would undoubtedly provide important but nonconclusive technical inputs for the identification of clandestine tests above 20 KT or possibly even lower. On the basis of these considerations, the British may argue that, since the Soviets can test clandestinely under 3 KT in any event and since the external detection system would deter them from testing above 50-100 KT, the only value of the entire inspection process is to eliminate the possibility that the Soviets will test in the relatively narrow yield range between 3 and 100 KT.

The possibility of testing in the range between 3 and 100 KT would give the Soviets the opportunity to carry out a number of reasonably significant weapons development and effects programs that cannot be successfully conducted below 3 KT. However, it is very difficult to argue that any of these developments would, in fact, change substantially the existing balance of power with the U.S.-U.K. and the Soviet Union. In the strategic area, the Soviets could, by testing at a fraction of full yield, probably develop an improved family of low-yield thermonuclear devices [1-1/2 lines of source text not declassified]. This would permit the Soviets to develop multiple warheads for existing missile systems and possibly new smaller strategic missile systems. Such multiple warheads would be of value as a penetration aid against a future AICBM system. Given the large payload of existing Soviet rockets, the Soviets will be able to use decoys and nuclear blackout as well as multiple warheads as penetration aids against an AICBM system. However, a low altitude AICBM system such as Nike X could probably be made to discriminate between heavy warheads and decoys weighing appreciably less than the actual warhead. This situation would place a major premium on the reduction of the size of warheads either to permit closer matching of decoys and warheads or the use of multiple warheads instead of decoys. If we decide to deploy Nike X, the possibility that the Soviets might be able to develop much smaller warheads than they now possess would require us to deploy our Nike X batteries on a larger scale to achieve a given level of defense than would otherwise be the case. Similarly, in this yield range important work could be undertaken by the Soviets to reduce the vulnerability of their thermonuclear weapons to nuclear explosions against potential U.S. AICBM systems. However, this will probably not be a critical factor in determining the effectiveness of an AICBM system in view of the very close miss distances anticipated. Obviously, none of these penetration aids or reductions in vulnerability are even relevant to the balance of power situation unless we do in fact undertake a massive deployment of an AICBM system. With respect to very high yield strategic weapons, the Soviets [1 line of source text not declassified] would advance the state of their weapon technology in the event the treaty were broken and high yield atmospheric tests were resumed. The Soviets could not, however, by testing in the 3 to 100 KT range, actually develop new high yield weapons that would be suitable for stockpile. The ability to conduct clandestine tests with relative impunity in the 3 to 100 KT range would allow the Soviets to maintain their laboratories in a higher state of readiness for large-scale testing, including more substantial continuing development and test experience for the scientific staff.

With regard to AICBM capabilities, the Soviets could by testing in the 3 to 100 KT range develop a better designed AICBM warhead than is now available to them or could be developed in yields below 3 KT. This probably would not affect the Soviet Union’s decision on whether or not to deploy an AICBM system but, if they do so, could reduce the drain of the system on their stockpile of fissionable material and might thereby speed the rate at which the AICBM system could be deployed. Testing in this range would also permit more elaborate effects tests to determine the vulnerability of AICBM warheads to neutron heating and X-ray effects. While certainly not critical, this information would be very useful in supplementing data that could be obtained by theoretical calculations and lower yield tests. Additional information on radar blackout, which is the most important effect influencing AICBM system design and which cannot be easily calculated, could not be obtained by testing underground since useful data can be obtained only by high altitude testing and cannot be simulated underground.

With regard to tactical nuclear weapons, it is recognized that the Soviets could undertake a considerable amount of work on very small yield weapons, including enhanced radiation and pure fusion devices, [1 line of source text not declassified]. Nevertheless, in view of our existing capabilities in the field of tactical nuclear weapons, it has been generally agreed that such clandestine activities by the Soviets would not significantly change the balance of power. In fact, since they could develop such weapons at a rapid rate in the absence of a test ban, a test ban would undoubtedly prolong the time of our advantage even if the Soviets tested clandestinely. Testing in the 3 to 100 KT range would certainly make it easier for the Soviets to improve the quality of their intermediate yield tactical weapons. However, this is a yield range in which the Soviets already have a significant capability. It would be possible for the Soviets to develop a family of clean tactical weapons such as those in which the Livermore Laboratory at present has considerable interest. However, it is not clear what motivation the Soviets would have to do this or that any adverse effects would result from such an action.

The argument against complete elimination of the inspection requirement goes much further than the simple fact it would allow the Soviets to carry out important, though admittedly not critical, nuclear tests. One important objective of a test ban treaty is to create confidence between this country and the Soviet Union by reducing tension and suspicion and to provide a first step to more substantive measures. The external monitoring system that we propose will detect a large number of unidentified events which could in fact be nuclear tests in the range from a fraction of a KT to 100 KT. Unless the inspection process is retained, there will be no mechanism whereby the uncertainty associated with these unidentified events can be resolved. This problem will exist whether there are 75 unidentified events annually as we have concluded on purely technical grounds or whether in fact the number can be reduced to only some 20 really suspicious unidentified events, as the British maintain, by employing other information in the identification process. Moreover, it is probable there will always be a few events which because of location and associated circumstances will appear particularly suspicious whether or not the Soviets are in fact testing.

The inspection procedure also provides a clear mechanism whereby the treaty can be terminated if the Soviet Union does in fact undertake clandestine testing. While it is true that we always have the option to denounce the treaty if we are satisfied that there is good evidence that the Soviet Union is cheating, the denunciation of such a treaty would in fact not be easy as long as the evidence was ambiguous in the eyes of the world. The fact that an actual test was discovered in the course of an inspection, or more probably that the Soviet Union would refuse to permit an inspection because we had selected an event for inspection that was in fact a clandestine test, would provide a clearcut issue on which we could terminate the treaty if we so desired.

It is not possible to predict at what threshold, if any, the Soviet Government will feel that the pressures and opportunities of testing are sufficiently great to cause them to undertake clandestine tests. Clearly, the higher the threshold below which tests can be conducted without danger of detection, the wider the spectrum of possible weapon developments and the greater the pressure to attempt to exploit them. Since the fact of such clandestine testing, which we would probably ultimately learn of in any event through unilateral intelligence, would have bad effect on the relations between this country and the Soviet Union, it is important for us to minimize the Soviet incentive to undertake such testing. To this end, the inspection process contributes substantially to holding down the threshold below which clandestine testing could be attempted.

Finally, one of the reasons for undertaking a nuclear test ban is to establish the principle of inspection as part of an arms limitation and control agreement. While we should never ask for more inspection than we really need, if we abandon the requirement entirely in this case where the need for at least some level of inspection exists on technical grounds, we will seriously jeopardize our argument for reasonable inspection in connection with any more substantive disarmament and arms limitation agreements that we hope to negotiate in the future with the Soviet Union.²

0. Source: Kennedy Library, National Security Files, Subjects Series, Nuclear Weapons Testing, Status of US/USSR Nuclear Technology 6/63. Top Secret. There is no drafting information on the source text. The paper printed here contains material modified or inserted after June 22. A June 25 White House telegram from Kaysen to Bundy (who was traveling with the President in Germany), which was drafted by Harold Brown, Wiesner, and AEC Commissioner Leland Haworth, proposed a change which is incorporated in the text printed here. The telegram concludes: “At present, McNamara proposes that after we have gone through the formal process of getting an agreed memorandum on this subject, he would be glad to have a Brown-Haworth-Wiesner comment and interpretation of it as a document bearing his endorsement for the President’s advice.” (Telegram Sitto No. 12; ibid., Kaysen Series, Harriman Instructions) No further information has been found on the use made of this paper.
1. In a June 20 memorandum to the President, Kaysen stated that it was dear that one of the President’s problems during the talks with Macmillan would be “to prevent the British from undermining our position on the number of inspections for a test ban treaty.” (Ibid.)
2. With a brief note dated June 21, Macmillan forwarded to Kennedy a memorandum by “our scientists” on underground testing, which Macmillan believed made “a pretty powerful case.” The 6-page memorandum concluded that underground tests were “not a consideration which, in themselves, should prevent agreement on a test ban treaty.” (Ibid., Departments and Agencies Series, ACDA, Test Ban Correspondence, Kennedy-Khrushchev-Macmillan, 3/63-6/63)