298. National Security Action Memorandum No. 2500


  • The Director of Central Intelligence
  • The Secretary of State
  • The Secretary of Defense
  • The Chairman, U.S. Atomic Energy Commission


  • Contingency Plan for Dealing with Possible Low-Yield Soviet Atmospheric Tests1

The President has approved the following procedures for dealing with the current evidence of low-yield Soviet tests.2

At present there should be no announcement and every effort should be made to prevent leaks with respect to the current evidence.

In the event of a leak, the Atomic Energy Commission would promptly issue the following statement, with any amendment made necessary by the specific circumstances of the situation at the time:

“The Commission’s attention has been called to press reports of Soviet nuclear testing. The Commission reports that in recent weeks there has been evidence of events in the Soviet Union which may be [Page 737] nuclear tests of very low yield. The evidence remains inconclusive, and it is expected that more definite conclusions must await further evidence and analysis.”

At the same time, the Department of State would announce that there is no change in the plans for the Harriman-Hailsham mission.

Throughout the Government senior officials would be authorized to inform the press on a background basis of the following relevant facts:

The phrase “very low yield” means what it says and refers to evidence in the range of 1 KT.
The U.S., in its underground series, is currently conducting tests much more numerous than anything of which we have any signal from the Soviet Union and the yields of some of the U.S. tests are substantially higher than those of which there is a question now in the Soviet Union.
The President is of course fully informed and does not consider that this inconclusive evidence of very low-yield tests should be regarded as invalidating his American University position against resumption of atmospheric tests until others do the same.
Even if the U.S. atmospheric testing were approved,3 the forward planning of AEC and DOD would not call for a major series of tests until 1964.
The reason for avoiding any earlier public announcement was the fact that there was still genuine uncertainty as to whether the evidence justifies a final conclusion as to just what the Soviet Government is doing. For example, evidence to date is consistent with very large non-nuclear explosions.


In the event that there is more conclusive evidence on the nature of these or later events, the AEC would issue the following statement, adjusted to fit the exact situation:

“The AEC announces that analysis of evidence recently received shows that the Soviet Government has resumed nuclear testing in the atmosphere, with explosions of (very low) (low) yield.”

The State Department would then announce that these events did not change the plans for the Harriman-Hailsham mission, but merely made that mission more urgent and its prospects more uncertain.

Officials of the U.S. Government would inform the press on a background basis of the following position:

We are disappointed that the Soviets are resuming atmospheric testing. Of course, the tests in question are very small and are more nearly comparable, both in technical purpose and in fallout effects, to our [Page 738] underground tests and certain cratering tests we have conducted in Nevada than to the large atmospheric test series that the Soviets and we conducted last year. Nonetheless, we may wish to review the President’s American University position. Even if the President were to decide to resume atmospheric testing, on technical grounds, it is unlikely that we would wish to test before 1964.
Some information on the current level of U.S. underground tests, in terms of numbers and size, should be offered as a comparison for interpreting the Soviet level of testing.

If we receive evidence of Soviet testing in the atmosphere on a larger scale, we will need to reconsider our position urgently. A large scale will mean tests of 100 KT or over or several tests of 20 KT or over.4
McGeorge Bundy
  1. Source: Kennedy Library, National Security Files, Meetings and Memoranda Series, NSAM 250. Top Secret; Restricted Data.
  2. A telephone call from Kaysen to Harriman on June 13 indicates that Kaysen had learned about one of these possible tests on June 12. “Harriman said it was a direct slap. He said it was quite startling; the [American University] speech was two days before.” The two men agreed to wait to see if there was another test. Another call to Harriman on June 21 indicates that Kaysen had learned of another test. They discussed the possibility of U.S. disclosure of the tests or a possible inquiry to the Soviets. (Both memoranda in Library of Congress, Manuscript Division, Harriman Papers, Box 581, June-July Telephone Conversations)

    In a talk with Seaborg on June 14, Kennedy asked if the indication of Soviet “atmospheric tests of one kt. was valid” or “an underground shot that vented.” Seaborg said that “the acoustic and electromagnetic signals that were used in a case like this can only come from an atmospheric event, and there is no indication of debris as yet.” Seaborg “expressed some doubt that this could be a real atmospheric test” because of its small size and its occurrence soon after the American University speech. Kennedy also indicated that the United States should not make preparations for atmospheric testing that would attract attention until after Harriman’s Moscow trip. (Seaborg, Journal, vol. 5, pp. 630-631)

  3. In a June 22 memorandum titled “Possible Recent Soviet Nuclear Tests,” McCone stated that there were a number of indicators that a Soviet test program of low-yield devices was taking place, but that many indicators were inconclusive and that final proof depended on securing radioactive debris from the atmosphere. A note on that memorandum states that McCone handcarried it to a meeting with the President and Bundy on June 22. (Central Intelligence Agency, DCI Memos for Record, 6/5-7/20/63) Kennedy’s Appointment Book has no record of this meeting. (Kennedy Library)
  4. A June 19 memorandum of decisions taken at a White House meeting held June 18 states that no underground event with a yield of over 50 kilotons was to be scheduled prior to September 1, and that the “scheduled work” could continue through July. (Kennedy Library, National Security Files, Subjects Series, Nuclear Weapons Testing, 1/63-7/63) See the Supplement.
  5. Kennedy wrote Macmillan on this subject, although it is not certain Macmillan’s reply reached Kennedy prior to issuance of NSAM No. 250. (Unnumbered White House telegram, June 21; British telegram PMUK 1248 Zulu received 1:11 p.m. June 22; both in Kennedy Library, National Security Files, Departments and Agencies Series, ACDA, Test Ban Correspondence Kennedy-Khrushchev-Macmillan) Both are in the Supplement.