Foreign Relations of the United States, 1969–1976, Volume E–14, Part 2, Documents on Arms Control and Nonproliferation, 1973–1976

203. Memorandum From the President’s Assistant for National Security Affairs (Scowcroft) to President Ford¹

Washington, August 5, 1976.

SUBJECT

• Recent Soviet Nuclear Tests

On July 4 and 29, the Soviets conducted underground nuclear explosions which may have exceeded the 150 kt yield limit on individual explosions under the TTB/PNE treaties. Our preliminary analysis on these tests is as follows:

—The July 4 test was located at the Semipalatinsk nuclear weapons test site and is currently assessed as having occurred in hard rock with a yield range of [number not declassified] with a most probable value of [number not declassified]. However, if our location of the epicenter is off by one or two kilometers, the test would have occurred in looser, sedimentary rock which does not couple as well to the explosion. In this case the range of possible values would be [number not declassified] with a most probable value of [number not declassified]. [less than 1 line not declassified] should be available this weekend and should help us precisely locate the epicenter.

—The July 29 explosion was apparently at least in part a PNE experiment to create a large cavity which could be used for storage of petrochemicals or other products. It occurred in a salt deposit (which is the best material for creating free-standing cavities) and has a preliminary yield range of [number not declassified] with a most probable value of [number not declassified]. Our knowledge of the coupling of nuclear explosions in salt is highly uncertain, however, and the range may be lower.

As you know, even though the PNE Treaty was signed on May 28 and forwarded with the TTB Treaty to the Senate for ratification purposes on July 29, they are not legally binding until ratification instruments are exchanged between the parties. On March 31, the intended effective date of the TTB Treaty, the Soviets announced (Tab A) that they would not “take any actions incompatible with the provisions of the treaty,” and we announced that we had no plans for the immediate future to conduct weapons tests with yields greater than 150 kt (Tab B). These statements were necessary since the PNE negotiations had not been completed, and we had stated that agreement would have to be reached in this area before the TTB Treaty could take effect. The Soviet statement was effectively open-ended, whereas ours referred to “the immediate future” to pressure the Soviets to make progress in the PNE talks.

We will not be able to complete a final estimate of the yield of these two tests for several weeks—in some cases it has taken sixty days just to receive the seismic tapes from our far-flung monitoring stations. [3 lines not declassified]

Once the treaties enter into force, their data exchange provisions should help us in measuring yields, [2 lines not declassified]. For the interim, however, we have delivered a note to the Soviets reaffirming our intention to observe the TTB/PNE yield limits and reminding them that we expect parallel compliance on their part.

1. Summary: Scowcroft informed Ford that the Soviet Union had conducted underground nuclear explosions in July.

   Source: Ford Library, National Security Adviser, Presidential Files of NSC Logged Documents, IF/NS File for the President, Box 43, 7604476, Threshold Test Ban/Peaceful Nuclear Explosions Refresher. Secret. Sent for information. The tabs are not attached and not found. All brackets are in the original except those indicating text that remains classified. Boverie sent the memorandum to Scowcroft under an August 11 covering memorandum, recommenting that Scowcroft sign the memorandum and send it to Ford. A handwritten notation by Scowcroft on the covering memorandum reads: “discussed with President.” Another notation in an unknown hand reads: “No need to send Tab I fwd.” For the text of the note delivered to Dobrynin on August 5, see Document 204.