Foreign Relations of the United States, 1961–1963, Volumes VII, VIII, IX, Arms Control; National Security Policy; Foreign Economic Policy, Microfiche Supplement

185. Memorandum from Kaysen to President Kennedy, May 20¹

May 20, 1963

Mr. President:

Attached is a background paper on the high yield nuclear weapon situation for your 11 o’clock meeting tomorrow. The DoD would like to go ahead with the development decision. AEC has so far been cool. Note that if developed for B–52 delivery, which is what the DoD recommends, the weapons would be available by about 1967.

C.K.

Attachment

HIGH YIELD NUCLEAR WEAPONS (50–100 MT)

BACKGROUND PAPER

The United States, both within the DOD and the AEC, has been considering large yield weapons for at least ten years, but because of the anticipated large size and weight the early delivery concepts were based on the use of ships for delivery to or near harbors, for detonation at sea in deep water to generate tidal waves or large areas of fall-out. With further development of nuclear warheads and improvement of understanding of relevant nuclear effects, other possible approaches have emerged.

During the Eisenhower administration plans for development of [text not declassified] were considered and the decision made not to pursue development of weapons with higher yields [text not declassified]. At that time the objective was to provide for a large yield bomb to be delivered from high altitude. Subsequently because of the improvements in Soviet defenses against high flying aircraft, it became necessary to develop [text not declassified]. The JCS quotes a penetration probability of the Soviet Union [text not declassified].

The JCS, in reviewing the value of a large laydown bomb, have concluded that a valid military requirement exists for a limited number of very high yield weapons. The rationale being that the numbers and hardness of Soviet targets are increasing, that gains are to be made against imprecisely located targets, and finally that psychological and political advantages would accrue. As a consequence of these considerations, the JCS have recommended that we proceed immediately with the development of [text not declassified] compatible [text not declassified]. On 6 March 1963, the Deputy Secretary of Defense, in a letter to the Chairman of the AEC stated a DOD tentative decision (subject to Presidential approval) to proceed with the development of such a bomb and inquired as to maximum yield, time to stockpile, and costs of development and production under the assumption of no nuclear tests.

[text not declassified]

An improved bomb based on new concepts and atmospheric tests could be provided perhaps a year or two later. The costs would be greater perhaps by $20–$30 million than indicated above because of the additional costs of nuclear tests but the yield might be doubled.

The expected effects of [text not declassified] can be summarized as follows:

Crater Dimensions

Radius—[text not declassified]

Depth—[text not declassified]

Expected Areas of Severe Damage

Industrial Urban Complex (6 psi)—[text not declassified]

Hard Targets

300 psi—[text not declassified]

3500 psi—[text not declassified]

Fallout Area

Area to at least 2000 roentgens integrated dose (500 roentgens is median lethal dose) would be [text not declassified].

Electromagnetic Effects

Unknown.

In addition to the possible development of large yield bombs the relevance of very large yield warheads for missiles has been studied. In this case, the controlling factors are the available payloads in the present and projected military booster program. [text not declassified]

Because of the great problems posed for defensive systems to discriminate between decoys and the warhead at altitudes above the re-entry altitude, thought has been devoted to the value of exploding sufficiently large warheads prior to re-entry. [text not declassified] Therefore, we have concluded that unless a larger booster is programmed, large warheads for missiles do not require development.

In the event it is decided to proceed with any very high yield development, with or without test, it must be recognized that a development program of this scope will not escape public attention. The development of [text not declassified] is likely to become known. Inherent in the preparations for testing very high yield devices are certain actions that are being taken now that might reveal our interest in very high yield weapons. For example, [text not declassified] These activities, either collectively or independently, may result in public disclosure of our development interest in very high yield weapons.

However, there is need for the AEC to develop the necessary high yield technology to provide the inputs required in the decision-making process with respect to booster characteristics. In addition, the effects of such large explosions require further evaluation. The AEC should be encouraged to continue the development of concepts appropriate to these objectives and, as nuclear testing policy permits, test them. In addition, the DOD will continue experimental and theoretical work on the effects.

SUMMARY

[text not declassified]	Without NuclearTest	With Tests
Yield	[text not declassified]	[text not declassified]
Length/diameter	[text not declassified]	[text not declassified]
[text not declassified]
Weight	[text not declassified]	[text not declassified]
Costs
Research and Development	[text not declassified]	[text not declassified]
Test	[text not declassified]	[text not declassified]
Unit Production	[text not declassified]	[text not declassified]
Earliest Stockpile Entry	[text not declassified]	[text not declassified]
Missile Warhead
Yield	[text not declassified]	[text not declassified]
Length/diameter	[text not declassified]	[text not declassified]
Weight	[text not declassified]	[text not declassified]
Costs
Research and Development	[text not declassified]	[text not declassified]
Test	[text not declassified]	[text not declassified]
Unit Production	[text not declassified]	[text not declassified]
Earliest Stockpile Entry	[text not declassified]	[text not declassified]

[text not declassified]

1. Provides background information on the high yield nuclear weapon situation and general Defense and ACDA views. The attached background paper discusses feasibility of U.S. developing large yield weapons based on new technology. Top Secret. 6 pp. Kennedy Library, National Security Files, Kaysen Series, High Yield.