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

14. Memorandum From the Joint Chiefs of Staff to Secretary of Defense McNamara⁰

JCSM-221-61

Washington, April 8, 1961.

SUBJECT

• Further Considerations Bearing on a Voluntary US Moratorium on All Underground Testing of Nuclear Weapons (U)

1. The Joint Chiefs of Staff have noted a cable from the Acting Secretary of State to the US Delegation to the Conference on a Nuclear Test Treaty in Geneva (State to Geneva—Nusup 1110, 29 March 1961).¹ This cable indicated that the United States is prepared to continue the voluntary moratorium on all underground nuclear testing, including tests of small yields, for three years from the date of signing of a treaty on control of nuclear testing, if the United Kingdom and the USSR will do likewise. The Joint Chiefs of Staff remain of the belief that the continuation of a voluntary moratorium on tests which cannot be detected by any inspection system would be unwise at this time and could be seriously inimical to the continued security of the United States.

2. There are several considerations bearing on this problem which the Joint Chiefs of Staff believe should be reviewed by the President and the Secretaries of State and Defense before irrevocable steps are taken in negotiations to commit the United States to the voluntary moratorium. The Joint Chiefs of Staff, in consequence, recommend that you request the President to hear a briefing in the near future at which scientific and military experts in the various fields mentioned below can set forth certain factual and potential factors affecting the problem. The Joint Chiefs of Staff would suggest such a briefing be attended, in addition to the President and such members of his staff as he desires, by the Secretary of State, the Secretary of Defense, the Chairman of the AEC, the Director of the CIA, the Advisor to the President for Science and Technology, and the Honorable John J. McCloy.²

3. The several fields which the Joint Chiefs of Staff would recommend be covered in the proposed briefing of the President are as follows:

a. The possible development of pure fusion weapons—[less than 1 line of source text not declassified] or so-called “neutron bomb.”

b. The lack of practical and authoritative data regarding the phenomenon of neutron-flux and x-rays outside the atmosphere.

4. It is only by considering the above subjects in their interrelationships that the possible serious impact on our national security of the continuation of an unpoliced moratorium on testing can be properly evaluated. In brief, these interrelationships, as seen by the Joint Chiefs of Staff, are as follows:

a. The principle upon which a “neutron bomb” may be developed has been known to the Soviet Union, by their own admission, since 1952. [3-1/2 lines of source text not declassified] Inherent in the neutron bomb concept—a pure fusion weapon emitting very high intensities of neutrons—is that the only scarce nuclear component required is tritium [4-1/2 lines of source text not declassified].

b. The major characteristic of the neutron bomb is the extent and range of its lethal instant radiation effect and relatively small other effects as compared to the much larger blast, thermal and residual radiation effects of the fission weapons. This characteristic may make the neutron bomb highly efficient as an anti-personnel weapon without the other destructive characteristics, including radioactive contamination, which are associated with fission weapons. Thus, the new weapon might be classed somewhere between conventional and current nuclear weapons. Possibly more important, however, could be the potentially greatly higher efficiency of the pure fusion weapon in generating at very long distances a neutron-flux in adjacent nuclear and thermonuclear weapons, particularly in space or the higher atmosphere.

c. The Nike-Zeus, and presumably the anti-ICBM weapons which intelligence sources indicate are being developed by the USSR, depend among other effects on neutron-flux to “kill,” i.e., render impotent, the warhead of the incoming ballistic missile against which the anti-missile is directed. If the Soviets have developed, or could develop by surreptitious and undetectable testing, an efficient pure fusion weapon which could “kill” enemy missile warheads at a considerable range, there could result a very high degradation to the credible nuclear deterrent posture of the United States. If the Soviets achieve this capability while the United States remains without it because of inability to test the [less than 1 line of source text not declassified] devices, the result could be catastrophic.

d. Allied with the problem just alluded to is the fact that the United States has very little practical data on the intensities of instant radiation produced by fission or fusion explosions in rarefied atmosphere or space. The Orange and Teak shots in the US nuclear testing program just prior to the current moratorium on nuclear testing provided inadequate data for a full evaluation of this effect at very high altitudes. Additional technical information concerning intensities of radiation at very high altitudes might show that x-rays have a much greater lethal radius for “killing” missile warheads than neutrons. If this were to be the case, we would want to take measures to protect our own warheads and, at the same time, exploit this effect in our own anti-ICBM capability.

5. In sum, the United States plans to deter deliberate initiation of thermonuclear war by the USSR, over the next decade, by the maintenance of an adequately invulnerable nuclear retaliatory capability. If the USSR were able to develop and make practical tests of the effects of the pure fusion weapon, and if the USSR as a result or by other means could develop a highly effective and relatively cheap AICBM, the USSR could conceivably plan a nuclear attack upon the United States without fear of receiving retaliatory destruction to a degree which would be unacceptable to the Soviet leaders. Because the Soviet stockpile may well contain today [1-1/2 lines of source text not declassified] and because of US lack of tested experience in the several fields mentioned above, the continuation of a voluntary moratorium on testing the potential development of a US pure fusion weapon could seriously prejudice the national security.

6. In consequence of the above, the Joint Chiefs of Staff recommend that:

a. The briefing referred to in paragraph 2 above be given the President and his senior officials at the earliest feasible date. The Joint Chiefs of Staff would be prepared to coordinate the preparation of this briefing if it is desired.

b. The United States not commit itself to a voluntary moratorium of underground testing below the level of test explosions which produce a seismic signal of less than 4.75.

c. Further research and development on the pure fusion weapon, [less than 1 line of source text not declassified] or otherwise, be given urgent attention by the AEC.

d. The need for further testing on the pure fusion weapon and the phenomenon of radiation-flux in space be considered of such national importance that no further concessions be made towards extreme Soviet positions in future negotiations on a nuclear test treaty.

For the Joint Chiefs of Staff:

L.L. Lemnitzer³
Chairman
Joint Chiefs of Staff

0. Source: Washington National Records Center, RG 330, OSD Files: FRC 65 A 3464, Atomic 400.112 8 Apr 61. Top Secret; Restricted Data.
1. Not printed. (Department of State, Central Files, 397.5611-GE/3-2961)
2. Gilpatric forwarded this suggestion to Bundy in a letter dated April 20. In a reply to Gilpatric of April 25, Bundy stated that the President had been briefed previously on both fusion weapons and the neutron flux problem. (Ibid.)
3. Printed from a copy that indicates Lemnitzer signed the original.