187 Cablegram from Plimsoll to Department of Foreign Affairs

Washington, 21 July 1972

3749. Top Secret Austeo

Underground Nuclear Testing

Since my return from the Stockholm Conference on the Human Environment I have tried to probe further into the real reasons for the United States opposition to a comprehensive test ban treaty.

  1. The United States official position has been that in the absence of on-the-spot verification it is not yet possible in all cases within existing techniques to distinguish with certainty between a nuclear explosion and a seismic disturbance. As you know I had formed the impression that technical advances had reached a point where it was possible to distinguish these explosions with a sufficient degree of accuracy and that it would not be worth it to the Russians to run the risk of conducting a test in violation of the treaty and being found out particularly if there was international monitoring machinery so that detection would not be a matter of relying on the Americans' word alone. I have felt that the real reason was that the United States armed forces wanted to conduct further tests for their own defence reasons and that the Soviet Union similarly wanted to continue tests. My discussions since returning here have reinforced that earlier impression but in a conclusive way.
  2. Today I was given a very good briefing on the SALT Talks1 by Mr Gerard Smith (Director of the Arms Control and Disarmament Agency) a full report of which will be sent in the next classified bag. I took the opportunity to pursue with him the question of underground tests. I said my impression was that capacity to distinguish tests from seismic disturbances had now reached the stage where if that was the only obstacle a comprehensive test ban treaty could be accepted but that the United States had no substantive defence reasons for wanting to be able to continue underground tests. I asked whether he could give me some idea of the importance of those defence interests which I said I assumed were mainly tests of MIRV2 warheads. I asked whether the United States was not so far ahead of the Soviet Union in MIRV warheads that a ban on further tests underground would in fact work to the advantage of the United States by making it more difficult for the Soviet Union to catch up.
  3. Mr Smith replied that it was true that the armed forces wanted to be able to continue tests. This was partly the natural reaction of generals and admirals who never wanted to shut the door on possibilities of technological improvement. Mr Smith did not take up my reference to MIRV warheads but mentioned that the services were interested in future tests to develop cleaner tactical weapons. But he said there were also very genuine problems about distinguishing a nuclear test. It was not only in relation to seismic disturbances. He said that many persons had hopes of using nuclear explosions for peaceful purposes (though he thought personally that the potentialities of those was exaggerated) and it would be possible to use for such a peaceful explosion a device that was perhaps not identical with but quite close to a nuclear weapon device which a country wanted to test. On-the-spot verification would be useful in such cases.
  4. Smith also made the point that nuclear weapons might deteriorate in storage. The military would like to carry out sample tests from time to time to see if they were still effective. Smith personally would not regard that as an insuperable objection as both sides would face the same problem.
  5. Smith said his personal view was that despite resistance from the services President Nixon would be ready to agree to a comprehensive test ban treaty if he could be satisfied on detection.

[NAA: A1838, 919/10/5 part 25]