Foreign Relations of the United States, 1964–1968, Volume X, National Security Policy

25. Memorandum From the Joint Chiefs of Staff to Secretary of Defense McNamara¹

JCSM–260–64

Washington, March 27, 1964.

SUBJECT

• Development of Very High-Yield Nuclear Weapons (U)

1. By memorandum, dated 4 March 1964,² subject as above, the Assistant to the Secretary of Defense (Atomic Energy) expressed your desire for the views and comments, as appropriate, of the Joint Chiefs of Staff on a draft of a proposed memorandum for the President on the above subject. The Joint Chiefs of Staff note that while the proposed memorandum would no longer support the recommendation made in JCSM–117–63, dated 11 February 1963,³ that the development of a very high-yield laydown bomb [less than 1 line of source text not declassified] to be compatible with the B–52 aircraft be initiated immediately, it does not preclude reconsideration of this subject at a later date.

2. In view of the Limited Nuclear Test Ban Treaty, the Joint Chiefs of Staff consider the following factors to be pertinent to this decision at this time:

a. The development, without atmospheric testing, of the proposed [less than 1 line of source text not declassified] laydown bomb for B–52 delivery would not advance appreciably the nuclear state-of-the-art in the yield-to-weight ratios.

b. It is too early to know, in detail, what can be accomplished through the redirection of weapons development effort necessitated by the restriction against testing in the prohibited environments. Significant advancement in the development of very high-yield nuclear weapons may be attainable without atmospheric testing.

c. The effort to be expanded in very high-yield weapons development could be directed toward advancing the state-of-the-art so that knowledge and new weapon designs are available to permit rapid advancements should the decision be made to resume testing in the prohibited environments.

d. Future large boosters potentially available could provide a capability for delivery of very high-yield warheads. The facilities for missiles such as Atlas F and Titan II conceivably could be modified to accept such large boosters.

3. The Joint Chiefs of Staff conclude that:

a. A [less than 1 line of source text not declassified] weapon should not become for the indefinite future the largest yield weapon available for military application.

b. Although the [less than 1 line of source text not declassified] laydown bomb for the B–52 would have met the recommendations set forth in JCSM–117–63 referred to in paragraph 1, above, the effort and expenditure of resources for its development would be better oriented toward the advancement of the state-of-the-art directed toward the attainment of very high-yield weapons with advanced technology, i.e., [less than 1 line of source text not declassified] and higher yield of aircraft laydown delivery and/or missile delivery.

c. Because of the uncertainties in high-yield weapons effects and in requirements for nuclear weapons during the 1970s, research, experimentation, and testing in the area of very high yields should be conducted by the Atomic Energy Commission to the maximum extent possible within the constraints of the Limited Test Ban Treaty.

d. Development should not be undertaken at this time of a [less than 1 line of source text not declassified] high-yield warhead for present missile systems.

4. The Joint Chiefs of Staff recommend that the draft of the proposed memorandum for the President, as changed by the line-in, line-out rewrite in the Appendix hereto,⁴ be submitted as the response to National Security Action Memorandum No. 245.⁵

For the Joint Chiefs of Staff:

Maxwell D. Taylor

Chairman Joint Chiefs of Staff

1. Source: Washington National Records Center, OSD Files: FRC 330 69 A 7425, A–471.61 (25 Jan 64). Top Secret; Restricted Data.
2. Not found.
3. Not found, but this JCS paper led to a Department of Defense initiative in early 1963 to persuade the Atomic Energy Commission to sign a joint DOD-AEC letter to President Kennedy proposing the development of a multi-megaton nuclear weapon. AEC Chairman Glenn Seaborg had reservations about the proposal, however, and prevailed in having the issue referred first to the White House for thorough study. For background, see Journal of Glenn T. Seaborg, Chairman, U.S. Atomic Energy Commission, 1961–1971 (Lawrence Berkeley Laboratory, University of California, 1989), vol. 5, pp. 258, 410, 436, 501, 525.
4. Not printed.
5. The study Seaborg requested (see footnote 3 above) was authorized in NSAM No. 245, “High Yield Nuclear Weapons,” May 21, 1963. (Johnson Library, National Security File, National Security Action Memoranda, Box 2)