PM Files

Report by the Special Committee of the National Security Council to the President 1

top secret

Development of Thermonuclear Weapons

the problem

1. By letter to Mr. Souers dated November 19, 1949, the President designated the Secretary of State, the Secretary of Defense, and the Chairman of the Atomic Energy Commission as a special Committee of the National Security Council to make recommendations

“as to whether and in what manner the United States should undertake the development and possible production of ‘super’ atomic weapons”, and
“as to whether and when any publicity should be given to this matter.”


2. The nature of the decision on which the Committee has been called upon to make recommendations needs to be defined with some precision. Systematic theoretical investigations on the possibilities of a thermonuclear weapon were undertaken at Los Alamos in the fall of 1943, and some work on this problem has been going on since that time (Appendix A).2 … Assuming a continuation of the present [Page 514] program at the present rate, however, it would be many years before a test of a thermonuclear weapon would be possible.

The question presented is whether the United States should undertake at this time an accelerated program to determine the feasibility of a thermonuclear weapon, should continue its research at the present rate, or should place a moratorium on further work in this field.

3. An all-out effort leading to both a feasibility test and quantity production of “supers” would seriously impair the efficiency and output of the fission bomb program, but there appear to be no advocates for this type of effort. Technical studies of the Atomic Energy Commission indicate that an accelerated research and development program to test the feasibility of such a weapon (as distinguished from a quantity production program) would require a minimum time of three years; that with such a target date other weapon developments now under way, principally lighter and smaller weapons aimed at improved deliverability … could probably still be carried out, but not with the care and refinement originally planned; that this probable decrease in refinement would not be sufficiently important to serve as a deterrent to an accelerated effort on thermonuclear research and development (Appendix B).3 The important consideration from a military point of view appears to be that the most advantageous rate and scale of effort would be such as to produce a weapon for testing as soon as possible without significant impairment to the quantity output of fission weapons as scheduled (Appendix C).

4. In the present state of knowledge, it appears that there is at least a 50–50 chance that a thermonuclear weapon will be feasible, but this cannot be determined except by actual test (Appendix B, par. 1 and par. 17).

5. It is estimated on the basis of technical studies made by the Atomic Energy Commission and the Department of Defense that an accelerated program, including ordnance and carrier development, is within the capabilities of the United States from the point of view of money, materials, and industrial effort.

6. Knowledge as to whether the thermonuclear bomb is or is not feasible and knowledge as to its potentialities and limitations, if feasible, are of importance to military planning and foreign policy planning (see Appendix C). It should be recognized, however, that the failure of any given test may not conclusively demonstrate that other methods might not be feasible.

7. It must be considered whether a decision to proceed with a [Page 515] program directed toward determining feasibility prejudices the more fundamental decisions (a) as to whether, in the event that a test of a thermonuclear weapon proves successful, such weapons should be stockpiled, or (b) if stockpiled, the conditions under which they might be used in war. If a test of a thermonuclear weapon proves successful, the pressures to produce and stockpile such weapons to be held for the same purposes for which fission bombs are then being held will be greatly increased. The question of use policy can be adequately assessed only as a part of a general reexamination of this country’s strategic plans and its objectives in peace and war. Such reexamination would need to consider national policy not only with respect to possible thermonuclear weapons, but also with respect to fission weapons—viewed in the light of the probable fission bomb capability and the possible thermonuclear bomb capability of the Soviet Union. The moral, psychological, and political questions involved in this problem would need to be taken into account and be given due weight. The outcome of this reexamination would have a crucial bearing on the further question as to whether there should be a revision in the nature of the agreements, including the international control of atomic energy, which we have been seeking to reach with the U.S.S.R.

8. There is evidence which leads to the belief that the Soviet Union prefers to put its chief reliance on winning the cold war rather than precipitating a hot war. There is also ground for the belief that the Soviet Union would prefer not to use weapons of mass destruction except in the event of prior use by others. These assumptions might appear to argue for renunciation by the United States of work in the field of thermonuclear weapons. We cannot safely assume, however, that these hypotheses are correct. Even if they are correct, it cannot be assumed that the Soviet Union would forego development of this weapon any more than she has been willing to forego the development of the fission bomb. Sole possession by the Soviet Union of this weapon would cause severe damage not only to our military posture but to our foreign policy position.

9. There is also the question of possible effect on Soviet attitudes and actions of a decision to proceed with a program to test the feasibility of thermonuclear weapons.

a. Would a decision on the part of the United States to go ahead with an accelerated program cause the Soviet Union to press ahead in this field more vigorously? The theoretical possibilities of a thermonuclear reaction have long been known; as early as 1932 there were suggestions by Russian scientists and others that thermonuclear reactions might release enormous amounts of energy (Appendix A). The [Page 516] Soviet Union probably has felt it could not make any other assumption than that the United States is working on such a weapon, especially in view of the public discussion that has already taken place. It is difficult to escape the conclusion that the Soviet Union will make an intensive effort to produce thermonuclear weapons. A decision to accelerate our program may cause the Soviet Union to increase the priority of these efforts. Knowledge by the U.S.S.R. that we had successfully completed development of a thermonuclear weapon might have the effect of increasing the probability that the USSR would successfully develop a similar weapon. These are risks which are difficult to measure, but which we must frankly face up to if a decision is made to accelerate our development program.

b. It does not appear likely that the character of United States military developments will have a decisive effect on Soviet military developments or be the cause of an arms race. The Soviet decision to reequip its armies and devote major energies to developing war potential, after the end of the war and at a time when we were disbanding our armies, was based on considerations more profound than our possession of the atomic weapon.

10. a. The possibility of the Russians’ developing a thermonuclear weapons capability, added to their probable growing fission bomb capability, re-emphasizes the importance of effective international control of the entire field of atomic energy. Even if we can find a new approach to the control of atomic energy which would be acceptable to us and to our allies, and which offers greater prospect than the U.N. plan of being negotiable with Russia, the necessary negotiations probably could not be completed in less than a year and a half to two years. But to delay an accelerated program of development for such a period in the absence of adequate assurance that work in the Soviet Union had been similarly delayed, would measurably increase the prospect of prior Soviet possession of thermonuclear weapons.

b. It has been suggested that a decision should be deferred until an approach has been made to the Soviet Union proposing that both nations forego work in the field of thermonuclear weapons. If such a proposal were coupled with a plan for the necessary safeguards to insure that the renunciation was in fact being carried out—these safeguards necessarily involving an opening up of Soviet territory—it is the view of the Department of State that the proposition would be unacceptable to the Soviet Union to the same degree that the United Nations plan for the control of atomic energy is unacceptable. If not coupled with such safeguards, it is not believed that sufficient assurance would be gained from such an agreement to make it worth while.

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11. In the light of the foregoing considerations, the following recommendations are made:

That the President direct the Atomic Energy Commission to proceed to determine the technical feasibility of a thermonuclear weapon, the scale and rate of effort to be determined jointly by the Atomic Energy Commission and the Department of Defense; and that the necessary ordnance developments and carrier program be undertaken concurrently;
That the President direct the Secretary of State and the Secretary of Defense to undertake a reexamination of our objectives in peace and war and of the effect of these objectives on our strategic plans, in the light of the probable fission bomb capability and possible thermonuclear bomb capability of the Soviet Union;4
That the President indicate publicly the intention of this Government to continue work to determine the feasibility of a thermonuclear weapon, and that no further official information on it be made public without the approval of the President.

[Here follow Appendix A, a historical statement, and Appendix B, a staff study, prepared by the U.S. Atomic Energy Commission.]

Appendix “C”

The Military Implications of Thermonuclear Weapons5

the problem

1. To determine the military implications of weapons employing thermonuclear reactions in deuterium and tritium to obtain energy releases in the order of millions of tons of TNT.


2. That it is within the capabilities of the United States from the standpoint of money, materials and industrial effort to develop for test of feasibility a prototype thermonuclear weapon.

3. If the thermonuclear reaction of light elements were proved feasible of attainment, that it would be within the capabilities of the United States to produce these weapons in limited quantities.

4. That no practical factors are known to exist which conclusively eliminate the possibility or probability of Soviet development of a thermonuclear weapon in minimum quantities.

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5. That moral considerations are not germane to the limited objective covered by this problem, i.e., the development and test of the weapon to determine its feasibility. Determination of production and use of the weapon is likewise outside the province of this problem.


6. See Annex 1.


7. The United States military position with respect to the development of the thermonuclear weapon should be:

Possession of a thermonuclear weapon by the USSR without such possession by the United States would constitute a situation fraught with danger to the United States, and must be avoided.
It is imperative to determine the feasibility of a thermonuclear explosion, and its characteristics, at the earliest practicable date. This determination is essential for United States offensive and defensive planning, and direction of research and development.
If a thermonuclear weapon is determined to be feasible, the following considerations pertaining to military requirements are currently evident:
Possession of such weapons by the United States may act as a deterrent to war.
Possession of such weapons by the United States will provide an offensive weapon of the greatest known power possibilities thereby providing increased flexibility and effectiveness to our operations in the event of hostilities.
The cost in money for materials, and the research and industrial effort of this determination of feasibility is estimated at between 100 and 200 million dollars by the Atomic Energy Commission. This is within the capabilities of the United States. The USSR has the same capability.
When used against especially selected remunerative targets the thermonuclear weapon, if feasible, can be utilized in lieu of a greater number of fission bombs. This would enable the delivery of a given amount of damage in less time with less exposure and with greater effectiveness than through the employment of a greater number of fission bombs. Furthermore, the weapon promises to be more efficient in utilization of available ore and production capacity per unit area of damage.
A unilateral decision on the part of the United States not to develop a thermonuclear weapon will not prevent the development of such a weapon elsewhere.
It should be possible to maintain the necessary military secrecy on a subject of such importance to the security of the United States. However, it is believed that development of this weapon as a complete surprise to the USSR is not possible.
In summary, from the military point of view, determination of the technical feasibility of the thermonuclear explosion is essential. This does not imply a “crash” or “all-out” program, but, on the contrary, an orderly and economical solution of the problem.

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Annex 1


1. General. From the discussion of technical considerations by the Atomic Energy Commission, it appears that there is a reasonable chance that a thermonuclear reaction of light elements can be achieved by the United States within the next few years after a special effort in this direction is initiated. Consideration of known Soviet developments in the field of atomic energy reveals a degree of Soviet capability also to develop a thermonuclear weapon. The following discussion explores the implications of the military applications of thermonuclear weapons in order to present pertinent facts which may be of assistance in arriving at a decision as to whether or not a special effort will be initiated at this time to achieve a thermonuclear weapon or to determine conclusively its lack of feasibility.

2. The Potential Military Applications of the Super.

a. Effects.

From the point of view of military usefulness, the only effects which need be given consideration at this time are the blast and thermal radiation. In contrast to fission bombs, the nuclear radiation will be relatively unimportant and for the present need only be considered from a defensive point of view or under special conditions of detonation.

Preliminary studies based on a comparative analysis of effects of a 40,000 KT Super to a 40 KT fission bomb indicate that:

The Super will produce a blast damage area greater than 50 times that produced by a fission bomb.
Under average atmospheric conditions, the Super will produce thermal effects over an area 60–170 times that from a fission bomb.

b. Damage Characteristics of the Super.

While the fission bomb may yield an overpressure of 28 p.s.i. or more out to a distance of 2500 feet, the same pressure level may extend to 23,000 feet in the case of the Super. But there is no comparison between the destructive level which is attained inside these radii; for the super pressure levels near “ground zero” are at least twenty times higher than those for the fission bomb, and the Super bomb pressure level is always higher than the fission bomb pressure level at corresponding points inside the two damage circles. Hence, the damage in the large circle associated with the Super is many-fold more complete than that in the smaller circle associated with the fission bomb. It must be concluded, then, that the Super is not directly comparable to a given number of fission bombs, for the peak pressures attained from the Super cannot be attained with the airburst fission bombs and these Super bomb pressures result in complete demolition of a large area.

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Preliminary target studies based on the anticipated effects of the Super have borne out this conclusion. From these studies it appears that a limited number of strategic and tactical targets will exist, in the event of hostilities with the USSR, which are peculiarly adapted to the Super. The estimated effects of the Super on heavy materiel and structures and on troop concentrations will permit:

The achievement of certain strategic and tactical objectives at a substantial saving in terms of fission bombs, one Super replacing 10–50 fission bombs, depending on the specific target.
A far higher level of assurance of success against certain strategic and tactical targets of the highest importance.
The accomplishment of a level of destruction against very heavy structures, troop concentrations, and materiel which, though desirable, is not practicable of attainment with fission bombs except by heavy expenditure and accurate placement on target.

3. Delivery Considerations. The violence of the blast and thermal effects of the Super require any manned aircraft to be a minimum of 30 miles from the detonation point. This requirement will dictate an unmanned vehicle to traverse the final 50 to 100 miles to the target. The development of such a vehicle is a problem which remains to be solved in conjunction with the development of the weapon itself, being dependent largely upon the characteristics, physical dimensions and weight of the weapon. It is impracticable at this time to anticipate the exact nature of the eventual carrier. It is apparent that eventually a supersonic unmanned vehicle will be necessary, depending upon the scientific advancement in the field of guided missile ground-to-air weapons. It is also apparent that under such conditions of opposition, a supersonic delivery vehicle is also indicated for fission bombs. Thus a seemingly paradoxical situation may eventually develop wherein the larger, more cumbersome Super may eventually be easier to deliver by virtue of the fact that it may be less demanding for refinements in the guidance system of the final delivery missile. In any event, in consideration of the technical problems in the development of the weapon as compared to the carrier, it is believed that the carrier problem, although difficult, is the lesser of the two.

4. Other Important Military Implications. In consideration of the above military applications for the Super, the potential advantages of which would accrue to a nation possessing these weapons, the following discussion explores additional military implications under several hypotheses of possession.

Hypothesis: Sole Possession by the USSR. Aside from the power ratio differential of the Super as compared to the fission weapon and of the psychological potential which automatically exists through enemy exploitation of this ratio differential, there is the added factor that if we fail to develop a thermonuclear weapon and thereby lack [Page 521] knowledge of its positive effects, we shall be unable to counter possible enemy exploitation of the frightening and paralyzing fiction which has become associated from time to time with thermonuclear explosions. Accordingly, it must be anticipated that the development of a thermonuclear weapon by the USSR in advance of the United States, particularly if the announcement follows secret development, would have a demoralizing effect on the American people. It would have psychological and political repercussions which might raise a question concerning the continued unity of spirit, confidence and determination among the nations of the western world. The situation today is strikingly parallel to that of a few years ago when this nation was engaged in a race to develop a fission bomb before Germany. From the Soviet point of view, sole possession of the thermonuclear weapon would place in their hands an offensive weapon of the greatest known power possibilities. It would provide the Soviet leaders, people and satellites with a psychological boost which in peacetime could lead to increased truculence in international affairs and increased political infiltration in nations of the western world. The “blackmail” potential of the thermonuclear weapon would serve the USSR well in its aims to impose its will upon the nations of Europe and to alienate these nations from the Western camp. In time of war, sole possession of the thermonuclear weapon and possession of fission weapons coupled with superiority of conventional military forces would provide the Soviets with the necessary balance to current Western unity and to our superior fission weapon stockpile to enable them to risk hostilities for the rapid achievement of their objectives. The above developments cannot be forecast with certainty; however, the materialization of one or more of these possible developments could have such an unacceptable effect upon our world position as to force a complete re-evaluation of our strategic plans and of our national objectives in peace and in war. It is concluded that possession of a thermonuclear weapon by the USSR without such possession by the United States would constitute a situation fraught with danger to the United States, and must be avoided.
Hypothesis: Sole Possession by the United States. The sole possession of this weapon by the United States would cause all of the practical and many of the psychological advantages of possession of thermonuclear weapons to accrue to our side, and may act as a deterrent to war. From the practical point of view, possession of this weapon would add materially to the striking power of our forces against those important tactical and strategic objectives which are particularly adapted to a thermonuclear weapon. For example, large concentrations of enemy troops and materiel, such as occur frequently in war (the Normandy invasion, the defense of Stalingrad, the Bulge break-through, large dumps, singularly important airplane concentrations, and other such large but lucrative targets) which would now require multiple delivery of fission weapons, could be destroyed or critically disrupted with a single thermonuclear weapon. Since this destruction could be applied throughout the target area with simultaneity, the value of surprise could be exploited to the maximum. Effective destruction of the above target types may well lead to decisive results since such concentrations normally occur in connection with critical operations in war. Moreover, attack of enemy atomic air [Page 522] bases with a thermonuclear weapon may be the only effective defense against enemy atomic attack. If, on the other hand, enemy knowledge of our possession of this weapon causes them so to conduct operations as to avoid concentrations of troops and materiel to a materially greater extent than is now indicated by our possession of fission weapons, we shall have forced them to abandon the source of their greatest strength, employment of mass. There is an additional advantage of the thermonuclear weapon. The thermonuclear weapon promises in the high ranges of energy release to be more efficient in the utilization of available ore and production capacity per unit of damage area.
Hypothesis: Possession by Both Countries. It is clear that under these conditions the world would be precipitated into the atomic age much more rapidly than would otherwise be the case. Such requirements as dispersal of industry, dispersal on the battlefield, avoidance of reliance upon ports, beachheads, large airfields, etc., would become more mandatory and on a considerably larger scale than is now indicated by mutual possession of fission weapons. Under such conditions it can be anticipated that great stress will be placed by each protagonist on the attempt to deliver as the initial act of hostilities a paralyzing blow on the offensive atomic capabilities of the enemy, such as air bases for the atomic carrier force. Accordingly, it appears reasonable to forecast that great effort must be made to allow the development of suitable techniques of operational employment under conditions of dispersion which will achieve an adequate degree of invulnerability of retaliatory attack force.
Hypothesis: Firm Determination of Infeasibility. Because of the above military implications which are associated with the development of a thermonuclear weapon, it is imperative to determine conclusively the feasibility of a thermonuclear explosion and its characteristics. Such determination is essential for United States defense planning, preparations for retaliation, and direction for our research and development programs. There are undoubtedly a number of possible social, psychological and moral objections which may be considered to argue against research and development by the United States leading to the development and test of a thermonuclear weapon. The above considerations outweigh such objections. In addition, it is difficult to escape the conviction that in war it is folly to argue whether one weapon is more immoral than another. The United States has enjoyed and relied upon a measure of technological advantage over the USSR. This advantage lies principally in our industrial capacity, our stockpile of atomic weapons, and our ability to deliver these weapons. We no longer have a monopoly of atomic weapons, which fact lessens our degree of technological advantage. There are indications that the USSR also has some capability of producing a thermonuclear weapon. To stop arbitrarily our atomic research at the frontier of thermonuclear reactions would guarantee the loss of our technological advantage and further would not prevent development of this weapon by the USSR as long as war remains a possibility. If we do not determine the feasibility of a thermonuclear weapon before a war, we would be forced to make this determination on a “crash” basis upon the initiation of hostilities. In view of the above, it is considered that the cost involved in a determination of feasibility of a thermonuclear explosion [Page 523] is insignificant when compared with the urgency to determine more accurately the ceiling on atomic development.

5. Consideration of Current Policy on International Control. The military is in strong support of the United States position in the United Nations on international control of atomic energy. Preliminary studies indicate that the possible existence of a thermonuclear weapon does not appear to warrant change of the attitude of the military, with the exception that serious consideration must be given to the probability that adequate control would be more difficult and that successful violation of control would be much more significant. Detailed studies by the United States in this regard are indicated and should be undertaken without delay.

6. Considerations of Timing and Intensity of Effort. The overriding considerations which indicate a necessity for the development and test of a thermonuclear weapon occur in conjunction with the analysis of the situation which would exist if the USSR had sole possession of a thermonuclear weapon. Accordingly, our plans must be on such a scale that we do not lose an appreciable amount of time in determining the feasibility of such a weapon. From the military point of view the following minimum program should be undertaken at this time:

The determination of the technical feasibility of a thermonuclear explosion as a matter of top priority.
Studies of the necessary delivery vehicle and ordnance problems should proceed concurrently with a above and should not necessarily await trial of a thermonuclear assembly.

7: Considerations Regarding Security. There are many facets to the question of whether it should be made a matter of public knowledge that the United States is engaged in an active effort to develop a thermonuclear weapon. It is considered that public discussion once initiated and encouraged is extremely difficult to control and inevitably leads to a greater disclosure than originally intended. An additional factor of military significance is the divergence of opinion among scientific circles in this country relative to the feasibility of a thermonuclear explosion. It can be expected that such divergence of opinion exists in the USSR on at least an equivalent parity. If the United States announces that we are engaged in an active effort to develop a thermonuclear weapon, such positive knowledge would give added credence and ascendancy to the Soviet group sponsoring development in this field and may result in an earlier start or greater impetus to the Soviet program. For the above two reasons, it is considered that any decisions or actions pertaining to United States effort to develop a thermonuclear weapon or any determination of its feasibility is military information of the highest security classification.

  1. The body of this report is based on a working paper dated January 24, 1950, prepared by R. Gordon Arneson, Special Assistant to Under Secretary of State Webb for atomic energy policy. The working paper is printed in large part in Arneson, “The H-Bomb Decision” (part ii), Foreign Service Journal, June 1969, pp. 25–26. On January 24, Secretary Acheson approved the working paper as a draft report to the President and transmitted it to Secretary Johnson and Commissioner Lilienthal.

    The Special Committee (Acheson, Johnson, and Lilienthal) considered and approved the working paper at a meeting of January 31, making a limited number of modifications. The session is described in Lilienthal, pp. 623–632, and in Acheson, pp. 348–349. The Special Committee immediately proceeded to the White House where President Truman indicated his approval of the report. The White House meeting is not documented in the files of the Department of State, but is described in Lilienthal, pp. 632–633, and in Acheson, p. 349.

    Later on January 31, the President released the following statement:

    “It is part of my responsibility as Commander in Chief of the Armed Forces to see to it that our country is able to defend itself against any possible aggressor. Accordingly, I have directed the Atomic Energy Commission to continue its work on all forms of atomic weapons, including the so-called hydrogen or super-bomb. Like all other work in the field of atomic weapons, it is being and will be carried forward on a basis consistent with the overall objectives of our program for peace and security.

    “This we shall continue to do until a satisfactory plan for international control of atomic energy is achieved. We shall also continue to examine all those factors that affect our program for peace and this country’s security.” (Public Papers of the United States: Harry S. Truman, 1950, p. 138)

  2. Appendix A, a historical statement prepared by the U.S. Atomic Energy Commission, is not printed. The statement summarized past research and development in the field of thermonuclear weapons.
  3. Appendix B, a staff study prepared by the U.S. Atomic Energy Commission, is not printed. The study discussed the requirements for and feasibility of construction of the hydrogen bomb, as well as the characteristic of the weapon.
  4. Interdepartmental efforts pursuant to this recommendation resulted in the preparation of NSC 68, “United States Objectives and Programs for National Security,” a report to the President, April 7, 1950. For the text of NSC 68 and related documentation, see pp. 234 ff.
  5. Prepared by the Department of Defense.