Observations on the Development of the H-Bomb
by Hans A. Bethe

Published as Appendix II in the 1989 version of The Advisors, Oppenheimer, Teller, and the Superbomb, by Herbert F York, Stanford University Press, 1976, 1989, with a historical essay by Hans A. Bethe

Introduction by Herbert York, 1988:

In addition to the original text of this book, I have included as Appendix II an essay written by Hans Bethe in 1954 but declassified only in 1980. I was unaware of its existence at the time I wrote my text. It covers much of the same ground that I covered in Chapter 5, but from the perspective of someone who had been much longer and more deeply and directly involved than I had been.

To help readers relate Bethe's observations to my text, I note that Bethe's "Method A" is the classical super, the experiment on "Part 2 of Method A" is the George shot of Operation Greenhouse, "Method C" is the booster device also frequently referred to by Bethe as "the new concept, "Method D" is what I call the Teller-Ulam invention. "Method B" is an intermediate idea I ignored as not being essential to an understanding of the story.

I also note that at one point Bethe says the Soviets might have "already engaged in a thermonuclear program by 1949," but he believes an opposite conclusion is equally justified." We now know they did begin their thermonuclear program in 1949 if not earlier, but that information was not available in 1954.

Introduction by Hans Bethe, 1988:

This essay is adapted from one written in 1954, in response to a book by James R. Shepley and Clay Blair, Jr., which gave a completely distorted view of the history of the H-bomb, giving the Los Alamos Laboratory no credit for its technical development. Norris Bradbury, then director of Los Alamos, gave an interview to The New Mexican of Santa Fe on September 24 and 26 of that year, setting the record straight; his interview is quoted repeatedly in my article. Earlier in 1954, the Atomic Energy Commission conducted proceedings against Robert Oppenheimer, the wartime director of Los Alamos, with the intent of depriving him of his security clearance. The testimony in these proceedings was published and is referred to as the Oppenheimer hearings. The present article was classified in 1954, declassified about 1980, and published in the magazine Los Alamos Science in 1982. It is reprinted here with minor wording changes and with certain superfluous passages eliminated.

Text of Bethe document, 1954:

1. Los Alamos During Wartime

After the Los Alamos Laboratory was started in the spring of 1943, it became clear that the development of a fission bomb was far more difficult than had been anticipated. If our work was to make any contribution to victory in World War II, it was essential that the whole Laboratory agree on one or a very few major lines of development and that all else be considered of low priority. Teller took an active part in the decision on what were to be the major lines. Before any specific work of an engineering or design nature could be taken up, it was necessary that theoretical investigations be brought to the stage where they could provide some detailed guidance. A distribution of work among the members of the Theoretical Division was agreed upon in a meeting of all scientists of the division, and Teller again had a major voice.

In the early summer of 1944. the Laboratory adopted as its main line the development of the implosion, a method since described publicly, e.g., in the testimony in the David Greenglass trial and in instructions to U.S. customs and postal officials for the purpose of helping them detect clandestine import of atomic bomb parts.

As soon as the implosion method was proposed by Neddermeyer, Teller advocated that the Laboratory devote a major effort to its development. In 1944 he was given the responsibility for all theoretical work on this problem. Teller made two important contributions. He was the first to suggest that the implosion would compress the fissile material to higher than normal density inside the bomb. Furthermore he calculated, with others, the equation of state of highly compressed materials, which might be expected to result from a successful implosion. However, he declined to take charge of the group that would perform the detailed calculations of the implosion. Since the Theoretical Division was very short-handed, it was necessary to bring in new scientists to do the work that Teller declined to do. Partly for this reason, some members of the British Atomic Energy team, already working in the United States on other aspects of the Manhattan Project, were brought to Los Alamos and asked to help with this problem. The leader of the British theoretical group was Rudolf Peierls; another very hardworking member was Klaus Fuchs.

With the pressure of work and lack of staff, the Theoretical Division could ill afford to dispense with the services of any of its members, let alone one of such brilliance and high standing as Teller. Only after two failures to accomplish the expected and necessary work, and only on Tellers own request, was he, together with his group, relieved of further responsibility for work on the wartime development of the atomic bomb. This was done by me, as Leader of the Theoretical Division, not by Oppenheimer, the Director of the Laboratory.

It is difficult to judge another mans personal feelings toward a third, even if you see both of them almost daily. But as far as I could see, the personal relations between Teller and Oppenheimer were very good at the beginning of Los Alamos. Later on, Tellers attitude toward his own work and toward the program of the Laboratory created a strain in his relations with Oppenheimer, and, to a lesser degree, in his relations with me. At the start, I had regarded Teller as one of my best friends and as the most valuable member of my division. Our relation cooled when Teller did not contribute much to the work of the division. More important, perhaps, in disturbing relations was his wish to spend long hours discussing alternative schemes he had invented for assembling an atomic bomb or arguing about remote possibilities for the failure of our chief design. He wanted to see the project run like a theoretical physics seminar and spent a great deal of time talking and very little time doing solid work on the main line of the Laboratory. To the rest of us who felt we had a vital job to do, this type of diversion was irksome.

To come back to the relations between Teller and Oppenheimer, politics certainly played no role in them. Communism in particular was no issue at that time at Los Alamos.

The success of Los Alamos rested largely on its teamwork and the leadership of its Director. It is not the primary function of the director of a laboratory to make technical contributions. What was called for from the Director of Los Alamos at that time was to get a lot of prima donnas to work together, to understand all the technical work that was going on, to make it fit together, and to make decisions between various possible lines of development. I have never met anyone who performed these functions as brilliantly as Oppenheimer.

2. Postwar Development of Fission Bombs

It has been made amply clear in the Oppenheimer hearings and elsewhere that at the end of the war the number of scientists at Los Alamos declined severely, and that this was especially true of the number of senior staff members. The Theoretical Division, which had the main responsibility for the conceptual design of weapons, was reduced from over thirty scientists to eight in 1946. This decline was part of the general movement to "let the boys come home." We all felt that, like the soldiers, we had done our duty and that we deserved to return to our chosen lifes work, the pursuit of pure science and teaching.

The older ones among us felt a heavy responsibility to our teaching. Wartime had shown that this country had a very short supply of competent scientists, and Los Alamos was one of the best examples. The young scientists whose careers had been interrupted by the war wanted to get training under the G. I. Bill of Rights. The largest graduate programs in physics before the war had about fifty graduate students; now this number jumped to a hundred and, in some universities, to over two hundred. The great effort made to train these young people has since borne fruit. Only because of that effort were laboratories like Los Alamos able to gather their large staffs of highly competent scientists in the years since 1948. Only in this way could the Los Alamos Theoretical Division grow to its present [1954] fifty-odd members, not to speak of the important work that other young scientists are doing in industry, in other government laboratories, and in the universities themselves.

For most of the scientists, young or old, who participated in the wartime work at Los Alamos, this was their first experience with work of a secret nature or work having immediate practical military significance. It is in no way surprising that most of them preferred the free interchange of ideas with their colleagues in this country and abroad that goes with pure, nonsecret research. Moreover, it was not obvious in 1946 that there was any need for a large effort on atomic weapons in peacetime. All these factors help explain the exodus of scientists from Los Alamos and other wartime projects in 1946.

The most effective cure for this attitude was the behavior of Russia in the first years after the war. For many scientists one of the most convincing aspects of the Russians behavior was their negative attitude toward our offer to make atomic power and atomic weapons a matter for international rather than national development. Most scientists soon recognized that the Russians were not willing to open the Iron Curtain to an International Atomic Authority, Oppenheimer being one of the first to recognize this, as has been demonstrated amply in the Oppenheimer hearings. The negotiations in the United Nations Atomic Energy Commission, as much as anything else, made many of the wartime members of the Los Alamos Laboratory willing to return to weapons work at least on a part-time basis.

The fact remains that in 1946 the Los Alamos Laboratory was very weak. To demand, as Teller did as a condition for his staying, that Los Alamos tackle the super-bomb on a large scale, or plan for twelve tests a year on fission bombs, was plainly unrealistic to say the least. Dr. Brad-bury, in his statement of September 24, 1954, pointed out that it was not until 1951 that a schedule of twelve test shots could be reached. In only one subsequent year, 1953, was the firing of such a large number again found necessary. It is hardly possible to give enough credit to the small group of scientists who decided to stay at Los Alamos in 1946 without making demands beyond the Laboratorys capacity.

The development laboratory at Los Alamos was not the only part of the atomic energy program to be hard hit immediately after the war. The very production of bombs of the existing models also declined severely.

In 1947, as soon as the AEC took over, it and the General Advisory Committee, under the chairmanship of Oppenheimer, turned to the weapons program as their most important task. This is amply shown in the Oppenheimer hearings. Of course, the advocacy of better A-bombs did not occur in public, but in the privacy of its reports the GAC recommended improved A-bombs from the beginning of its existence, which was shortly after the AEC took over from the military.

Beginning in the interim period of 1946, but especially once it received the full support of the AEC and GAC in 1947, Los Alamos set to work on the improvement of A-bomb design. This work bore fruit as early as 1948 in the "Sandstone" tests.

Immediately after the results of the Sandstone tests were known, the Los Alamos Laboratory began planning further improvements in fission bombs. It was also planned that these improved designs would be tested in another test series in the Pacific, and the approximate date of that series, later known as Greenhouse, was agreed upon. It must be realized that a long interval is required between the first conceptual design and the final test of an improved weapon.

First, theoretical calculations have to be done; then a great deal of experimentation, including non-nuclear explosions, is necessary to test the soundness of the theoretical concept; simultaneously, fabrication techniques may have to be developed; then a final design must be made and the weapon fabricated; and finally, elaborate preparations must be made for observing the performance of the weapon at the test and for the test itself.

No such development can be accomplished in a few months, as has often been implied in newspaper speculations on A- and H-bomb development. It is true that now, with extensive experience and expanded resources, such developments can be carried out much more rapidly than they used to; but planning in 1948 and 1949 for a major test series in spring 1951 then seemed a fairly strenuous time scale.

Advanced-design A-bombs, conceived at Los Alamos in 1948 and 1949 and tested in 1951, included weapons of small diameter. This idea was proposed by Los Alamos and most vigorously supported by the AEC and the GAC. There was little interest in it among the military at first, but now [1954] they are clamoring for more of these weapons.

3. The Development of the H-Bomb

The H-bomb was suggested by Teller in 1942. Active work on it was pursued in the summer of 1942 by Oppenheimer, Teller, myself, and others (see Oppenheimers testimony).

When Los Alamos was started up in the spring of 1943, several groups of scientists were included who worked specifically on the H-bomb. It was soon realized, however, that this was a long-range project and that the main efforts of Los Alamos had to be concentrated on making A-bombs. Teller, working on the H-bomb at Los Alamos, discovered a major difficulty (testimony by Oppenheimer). This discovery made it clear that it would be a very hard problem to make a "classical super" work, as this type of H-bomb was called. I shall refer to the classical super as Method A.

It was decided to set down in writing, at the end of the war, an extensive record of the technical knowledge of the entire Los Alamos project. In line with this effort, it seemed also desirable to record the status of the "super" so that work on it would be resumed more readily when more manpower and other requisites were available. A summary report on this subject, written by Tellers collaborators in 1946, proved to be very useful for later work. I believe (but I am not sure because I was not present at Los Alamos at that time) that the conference on the super in April 1946 also was intended partly to provide a record for the future (particularly since almost all the persons who had been working on this program had made definite plans to return to academic, non-weapons work), and possibly in addition to get some physicists from outside Los Alamos who were attending the conference interested in the problems with the hope that they might continue to work on them, theoretically and rather quietly.

Two new methods of designing a thermonuclear weapon were invented (Methods B and C). Both inventions were due to Teller. Method B was invented in 1946, Method C in 1947. Method B was actively worked on by Richtmyer, Nordheim, and others. At the time, however, there seemed to be no way of putting Method B into practice (as Dr. Bradbury mentioned in his statement to The New Mexican). Teller himself wrote a most pessimistic report on the feasibility of this method in September 1947.

Method C is different from all the others in that thermonuclear reactions are used only in a minor way, for weapons of relatively small yield. This method seemed quite promising from the start, and as early as the summer of 1948 it was added to the devices to be tested in the Greenhouse series.

Theoretical work on the "classical super," Method A, proceeded continuously, since this method was considered the most important of all the thermonuclear devices. New plans for calculations were made frequently, mostly by consultation between Teller and the senior staff of the Theoretical Division. However, as Teller stated in 1946, "The required scientific effort is clearly much larger than that needed for the first fission weapon. In particular, the theoretical computations required were of such complexity that they could not be handled in any reasonable time by any of the computing machines then available. Some greatly simplified calculations were done, but it was realized that they left out many important factors and were therefore quite unreliable. Work was therefore concentrated on preparing full-scale calculations "for the time when adequate fast computing machines become available"-a sentence that recurs in many of the theoretical reports of this period. The plans for such calculations on Method A were laid in September 1948, and the mathematical work was virtually completed by December 1949 -- all before President Trumans directive. But it was not until mid-1952 that adequate computers finally became available, and by that time the most advanced of them were fully engaged in work on the new, more promising proposal (Method D) discussed below.

When Dr. Teller and Admiral Strauss proposed in the fall of 1949 that full-scale development of H-bombs be undertaken, the method in their minds, as well as in the minds of those who opposed the program, was Method A. To accomplish Method A, two major problems had to be solved. I shall call them Part 1 and Part 2. Part 1 seemed to be reasonably well in hand according to calculations made by Tellers group from 1944 to 1946, although nobody had been able to perform a really convincing set of calculations for the reasons discussed in the preceding paragraph. Teller now believed that he had a solution for Part 2. In principle, the resolution of Part 2 had never been seriously in doubt, although the question of whether or not any particular device would behave in the way required could not be settled without experiment.

After President Truman made the decision to go ahead with a full-scale thermonuclear program, Los Alamos made plans to add to the Greenhouse series an experiment intended to test a particular proposal relating to Part 2. Teller played a large part in the specification of this device, and as it turned out it behaved very well. However, as on previous occasions, Teller did not do so well in directing the detailed theoretical work of his group. Only in January 1951, a month or so before the test device had to be shipped to the Pacific, was the full theoretical prediction of the (probably successful) behavior of the device available. But even while complete theoretical proof was lacking, most of us connected with the work at Los Alamos were confident that the Greenhouse experiment would work. As far as I could make out, at a meeting at Los Alamos in October 1950 which I attended as a guest, this was also the opinion of the GAC, including Dr. Oppenheimer.

The major discovery of the year 1950, however, was the discovery that Part 1 of Method A was by no means under control. While Teller and most of the Los Alamos Laboratory were busy preparing the Greenhouse test, a number of persons in the Theoretical Division had continued to consider the various problems posed by Part 1. In particular, Dr. Ulam on his own initiative had decided to check the feasibility of aspects of Part 1 without the aid of high-speed computing equipment. He and Dr. Everett, who assisted him, soon found that the calculations made by Tellers group in 1946 were wrong. Ulams calculations showed that an extraordinarily large amount of tritium would be necessary. In the summer of 1950, further calculations by Ulam and Fermi showed additional difficulties with Part 1.

That Ulams calculations had to be done at all was proof that the H-bomb project was not ready for a "crash" program when Teller first advocated such a program in the fall of 1949. Nobody blames Teller for the erroneous calculations of 1946, especially because adequate computers were not then available. But he was blamed at Los Alamos for leading the Laboratory, and indeed the whole country, into an adventurous program on the basis of calculations that he must have known to have been very incomplete. The technical skepticism of the GAC, on the other hand, had turned out to be far more justified than the GAC itself had dreamed in October 1949.

We can now better appreciate the attitude of the GAC, and indeed of most of the members of Los Alamos, toward the Greenhouse thermonuclear test. They did not expect it to fail, but they considered it irrelevant because there appeared to be no solution to Part 1 of the problem. An accurate description of this attitude is given by Oppenheimer in his own testimony.

The lack of a solid theoretical foundation was the only reason why the Los Alamos work might have seemed to some to get off to a slow start in 1950. Purely theoretical work may seem slow in a project intended to develop "hardware," but there was simply no basis for building hardware until the theory had been clarified. I visited Los Alamos around April 1, 1950, and tried to defend the point of view of the GAC in their decision of October 1949. 1 encountered almost universal hostility. The entire Laboratorv seemed enthusiastic about the project and was working at high speed. That they continued to work with full energy on Tellers Greenhouse test, after Ulams calculations had made the success of the whole program very doubtful, shows how far they were willing to go in following Tellers lead.

Teller himself was desperate between October 1950 and January 1951. He proposed a number of complicated schemes to save Method A. none of which showed much promise. It was evident that he did not know of any solution. Even so, he urged that the Laboratory be put essentially at his disposal for another year or more after the Greenhouse test, at which time there should then be another test on some device or other. After the failure of the major part of his program in 1950, it would have been folly on the part of the Los Alamos Laboratory to trust Tellers judgment, at least until he could present a definite idea that showed practical promise. This attitude was strongly held by most of those on the permanent staff of the Laboratory who were responsible for its operations. As might be expected, the many discussions of aspects of this situation bred considerable emotion.

Between January and May 1951, the new concept (which I call Method D) was developed. After the major effort the Laboratory had made to prepare the Greenhouse test of Part 2, which everyone understood to have been rendered largely pointless before the test was fired, there might have been some hesitation about immediately becoming committed to a large-scale effort along a new line of inquiry. In addition, it should be remembered that between January and May both tests in Nevada and the Greenhouse series in the Pacific took place, that they required many senior members of the Laboratory to be at the test sites for prolonged periods of time, and that the attention of many others was engaged in study of results of these tests.

In january 1951, Teller obviously did not know how to save the thermonuclear program. On March 9, 1951, according to Bradburys press statement, Teller and Ulam published a paper that contained one-half of the new concept. As Bradbury has pointed out, Ulam as well as Teller should be given credit for this. Ulam, by the way, made his discovery while studying aspects of fission weapons. This shows once more how important ideas may come not from a straightforward attack on the main problem, but indirectly.

Within a month, the very important second half of the new concept occurred to Teller, and was given preliminary checks by DeHoffman. This immediately became the main focus of attention of the thermonuclear design program.

It is worth noting that the entire new concept was developed before the thermonuclear Greenhouse test that took place on May 8, 1951. The literature is full of statements that the success of Greenhouse was the direct cause of the new concept. This is a misrepresentation of history. Teller was probably influenced by thinking about the Greenhouse design when he developed the new concept, but the success of Greenhouse (which was anticipated) had no influence either on the creation of the new concept or on its quick adoption by the Laboratory or later by the GAC. The new concept stood on its own.

As early as the end of May 1951, I received from the Associate Director of Los Alamos a detailed proposal for the future program of the Laboratory in which Tellers new concept figured most prominently. By early June, when I visited Los Alamos for two weeks. everybody in the Theoretical Division was talking about the new concept. Thus not only was the acceptance of the new concept not slow, but the realization of the development was a sensationally rapid accomplishment, in the same class as the achievement of Los Alamos during the war.

The immediate acceptance of Method D by the AEC and GAC has been described in the Oppenheimer hearings. Many scientists besides Teller took part in explaining the method. The meeting by no means started out in gloom because most participants (including some members of the GAC) had some advance knowledge of the new concept. It did not require much persuading to make the GAC accept the new concept. "If this had been the technical proposal in 1949," [the GAC] "would never have opposed the development" (Oppenheimer hearings). Now at last there was a sound technical program, and now the GAC and everybody else connected with the program immediately agreed to it. Testimony at the Oppenheimer hearings shows that the GAC went beyond the Los Alamos recommendations in allocating money for the support of the new concept.

It is difficult to describe to a nonscientist the novelty of the new concept. It was an entirely unexpected departure from the previous development. It was also not anticipated by Teller, as witness his despair immediately preceding the new concept. I believe that this very despair stimulated him to an invention that even he might not have made under calmer conditions. The new concept was to me, even as someone who had been rather closely associated with the program, about as surprising as the discovery of fission had been to physicists in 1939. Before 1939, scientists had a vague idea that it might be possible to release nuclear energy, but nobody had the remotest idea of a way to do it. If physicists had tried to discover a way to release nuclear energy before 1939, they would have worked on anything else rather than the field that finally led to the discovery of fission, namely radio-chemistry. At that time, concentrated work on any "likely" way of releasing nuclear energy would have led nowhere. Similarly, concentrated work on Method A would never have led to Method D, a method that nobody, including Teller, could have foreseen or did foresee when the Greenhouse tests were first being planned. By a misappraisal of the facts, many persons not closely connected with the development have concluded that the scientists who had shown good judgment concerning the technical feasibility of Method A were now suddenly proved wrong, whereas Teller, who had been wrong in interpreting his own calculations, was suddenly right. The fact was that the new concept had created an entirely new technical situation. Such miracles do happen occasionally in scientific history, but it would be folly to count on their occurrence. One of the dangerous consequences of the history of the H-bomb may well be that government administrators, and perhaps some scientists, too, will imagine that similar miracles should be expected in other arenas.

By the end of the summer of 1951, the Los Alamos Laboratory was putting its full weight behind attempts to realize the new concept. However, the continuous friction of 1950 and early 1951 had strained the personal relations between Teller and a number of other scientists at Los Alamos. In addition. Teller insisted on an earlier test date than the Laboratory deemed possible. There was further disagreement between Teller and Bradbury on personnel, in particular on the person who was to direct the actual development of hardware. Bradbury had great experience in administrative matters like these. Teller had no such experience and had in the past shown no talent for administration. He had given countless examples of not completing work he had started; he was inclined to inject new modifications constantly into an on-going program, a habit that beyond a certain stage in engineering development becomes intolerable; and he had shown poor technical judgment. Everybody recognizes that Teller contributed more ideas at every stage of the H-bomb program than anyone else, and this fact should never be obscured. However, as an article in Life on September 6, 1954, made clear, nine out of ten of Tellers ideas are useless. He needs men with more judgment, even if they be less gifted, to select the tenth idea which often is a stroke of genius.

It has been loosely said that the other people at Los Alamos "couldnt get along" with Teller, and it might be worthwhile to clarify this point. Both during the difficult days of the wartime period and again in 1951, Teller was on excellent terms with the vast majority of the scientists at Los Alamos with whom he came in contact in the course of the technical work. On both occasions, however, friction arose between him and some of those responsible for the organization and operation of the Laboratory. In each case, Teller, who was essentially alone in his opinion, was convinced that the situation was hopeless and that nothing would go right unless things were arranged quite differently. In each case, the Laboratory accomplished its mission with distinction. In September 1951, when the program for a specific test of the new concept was being planned, Teller was strongly urged to take responsibility for directing the theoretical work on the design of Mike. But he felt sure the test date should be a few months earlier; he didnt like some of the people with whom he would have to work; he was convinced they weren't up to the job; the Laboratory was not organized properly and didnt have the right people. Teller decided to leave and he left. The Mike shot went off on schedule and was a complete success.

It took much more than the idea of the new concept to design Mike. Major difficulties occurred in the theoretical design in early 1952, which happened to be a period when I was again at Los Alamos. They were all solved by the splendid group of scientists at Los Alamos.

At this time more than half of all the development work of the Los Alamos Laboratory went into thermonuclear weapons and into the preparation of the Mike test in particular. Almost everyone in the Theoretical DiviSion was thinking about this subject. In addition, a group of theorists in Princeton under the direction of Professor johi A. Wheeler were working iii collaboration with the theoretical group at Los Alamos.

Teller at this time was engaged in intensive agitation against Los Alamos and for a second laboratory. This agitation was very disturbing to the few leading scientists at Los Alamos who knew about it. Much precious time was spent trying to counteract Tellers agitation by conveying the true picture to Washington. I myself wrote a history of thermonuclear development, which was mentioned in the Oppenheimer hearings, and sent it to Chairman Dean of the AEC. This loss of time could be ill afforded at a time when the technical preparations for Mike were at a critical stage.

Nevertheless, the theoretical design of Mike was completed by June 1952, in good time for the device to be tested on November 1. In addition, in the same period, much work was done leading to the conceptual design of the devices that were to be tested in the Castle series in the spring of 1954. The approximate date for the Castle tests was also set at that time, and it was planned then that they should lead to a deliverable H-bomb if the experimental Mike shot was successful. It is necessary always to plan approximately two years ahead. Between summer 1952 and spring 1954, theoretical calculations on the proposed thermonuclear weapons proceeded; they were followed and in some cases paralleled by mechanical design of the actual device, and finally followed by manufacture of the hardware.

In July 1952, the new laboratory at Livermore was officially established by the AEC. Its existence did not, and in fact could not, accelerate the work of Los Alamos because in all essentials the work for Operation Castle had been planned before Livermore was established. In August 1952, an additional device was conceived at Los Alamos that might possibly have been slightly influenced by ideas then beginning to be considered at Livermore. In addition, Los Alamos decided to make a few experimental small-scale shots in Nevada in the spring of 1953, and this program may have been slightly stimulated by the existence of Livermore. Livermore did assist in the observation of the performance of some of the devices tested in the Castle series.

Concerning the performance of Livermores own designs. I will simply quote Dr. Bradburys 1954 statement to the press: "Every successful thermonuclear weapon tested so far has been developed by the Los Alamos Laboratory." This statement has not been contradicted. This shows that the GAC was right when it said in 1951 that the facilities of Los Alamos were (quite adequate for both H-bomb and A-bomb development. However, the staff of the Los Alamos Theoretical Division had doubled between 1949 and 1951, much progress on the A-bomb had been achieved, and the new concept, as well as the advent of high-speed computers, had made H-bomb development far easier than could have been anticipated in 1949.

Note added in 1982: In the intervening 28 years, Livermore has contributed greatly to nuclear weapons development. Some weapons programs are assigned to Livermore, some to Los Alamos, and the talents of the two laboratories complement each other.

4. Requisites for the Thermonuclear Program

The requirements for a successful thermonuclear program were four. First, there had to be an idea; second, there had to be many competent people who could work together as a team to carry out this idea; third, there had to be well-developed, highly efficient fission bombs; fourth, there had to be high-speed computers.

The development of the idea has been dealt with in the last section. As far as competent people were concerned, Dr. Bradbury showed in his press conference that during 1950 the number of scientists in the Theoretical Division increased from 22 to 35. Today [1954], this number has increased to over 50. That all this was possible was due to the extensive training programs for graduate students in physics at our universities in the years following the war.

The third requirement, an excellent fission bomb, is perhaps the most important of all. It is well known that a fission bomb is needed to create the high temperatures necessary to ignite an H-bomb. Since in such a process it is obviously necessary to adapt the fission bomb to the particular requirements of the situation, a much more detailed understanding of the fission explosion process is required, as well as much more flexibility in the design of the fission weapon itself, than was needed to develop the first fission weapon. Not until 1950 or 1951 did we begin to have the capability required to meet this important prerequisite for a real attack on the thermonuclear problem.

The primary obligation of Los Alamos and the AEC after the war was to develop advanced models of the fission bomb. I tried to show in section 2 above that this was done with competence and speed. But even if our secondary aim had been to develop the H-bomb, we probably would not have proceeded along a very different path than the one we took. As far as experimental and hardware development were concerned, the fission bomb simply had to come first. It is therefore clear that the fission bomb requirement precluded the successful development of an H-bomb substantially earlier than we actually got it, even if Tellers new concept had been available much earlier. There simply are no "three lost years" from 1946 to 1949.

There was a great deal of theoretical exploration during those three years, as discussed in section 3 above. One might have wished that still more theoretical work had been done, but this would have required more manpower, which was perhaps the scarcest commodity in the early postwar years. But even supposing the manpower had been available, the work would undoubtedly have been concentrated on Method A, which proved futile. As far as one can imagine such a hypothetical history, we might then have known by the fall of 1949 that Method A would most likely not work. Even had we reached that stage at that time, there is no reason to think that Method D would consequently have been uncovered earlier than it was. Of course it might have been, since in principle there was nothing to prevent someone from conceiving of this approach. But even if it had been invented somewhat earlier, the time from invention to realization would necessarily have been considerably longer than it was as things turned out. The size of the Los Alamos Laboratory, the experience of its staff, and the sophistication of their control over fission bomb design were all enormously greater in 1951 than they had been a couple of years before. In addition, there is the matter of the revolutionary change in computing facilities and techniques between 1947 and the present time [1954], which was just beginning to take real effect about the beginning of 1951.

Immediately after the war at many places in the United States, work was started to design and build high-speed computers. This work was pursued with great vigor and enthusiasm. The first machine of the modern type which was used in connection with the weapons program was the ENIAC, and from early 1948 on, persons at Los Alamos had made considerable demands on this machine. It was, however, of very limited capacity by modern standards. The IBM Companys SSEC in New York began to operate sometime in 1948, and though it had a very large capacity, it was very slow by modern standards. No fast computer existed at either Los Alamos or Princeton at the time, and the two machines existing elsewhere were not adequate for the calculations that had to be performed.

The first major improvement in this situation occurred during 1951, when the SEAC began to operate at the Bureau of Standards in Washington. Not long after this machine was running, a large fraction of its time was taken over for calculations required by the thermonuclear program. Later in 1951 large blocks of time were taken over on various models of the UNIVAC. Early in 1952 the MANIAC at Los Alamos came into operation and was immediately put to work in the thermonuclear program. This machine had been built with thermonuclear calculations specifically in mind. In the program leading to Mike and later to Castle, the resources of the new machines were taxed to the limit. This was true even though these machines could accomplish in days calculations that would have required weeks to handle on the ENIAC and months to handle with the means available at Los Alamos in 1947.

5. Was the H-Bomb Necessary?

To this point I have tried to give a factual history of the development of fission and H-bombs. The vast majority of the scientists connected with this development will agree with me on the history. What I have to say now is entirely my own responsibility, and my views may not be shared by many of my colleagues.

It seems to be taken as an axiom nowadays [1954] that the H-bomb simply had to be developed. The possibility that the Russians might obtain an H-bomb was of course the most compelling argument for proceeding with our thermonuclear program. It was, in my opinion, the only valid argument. It is interesting in this connection to speculate whether the Russians were indeed already engaged in a thermonuclear program by 1949. Mr. Strauss has stated in a speech that the Soviet H-bomb test, coming as early as August 1953, indicated that they had started work on the thermonuclear bomb much in advance of the United States. I believe that the opposite conclusion is equally justified.

We have seen that even in the worst cases, i.e., if the Russians had developed their H-bomb and we had not developed ours, our present situation would not be untenable. The best case, on the other hand, would have been if neither country had developed such a weapon, and if the mortal peril in which the whole world now finds itself had thereby been avoided.

When I started participating in thermonuclear work in the summer of 1950, I was hoping to prove that thermonuclear weapons could not be made. If this could have been proved convincingly, this would of course have applied to both the Russians and ourselves and would have given greater security to both sides than we can now ever achieve. It was possible to entertain such a hope until the spring of 1951, when it suddenly became clear that it was no longer tenable.

The GACs minority plan of 1949, which proposed that we try to reach an agreement between Russia and the United States so that neither side would proceed with H-bomb development, still does not seem to me utopian, a point I will discuss later.

Having considered the worst and best case, let us consider our present [1954] situation. The balance of power is now much more in our favor than it would have been under the assumptions of the worst case. Clearly this is to be welcomed. However, it must always be kept in mind that the advantage we now enjoy through the greater power of our H-bombs may not last. I will not venture a prediction of the time it will take for the Russians to catch up with us again.

While we have a temporary advantage in the armament race, we now have the H-bomb with us for all time. We can now only rely on the sanity of the governments concerned to prevent an H-bomb holocaust.

In the course of time, the present conflict between communism and democracy, between East and West, is likely to pass, just as the religious wars of the sixteenth and seventeenth centuries have passed. We can only hope that it will pass without thermonuclear war. But whichever way it goes, the H-bomb will remain with us and remain a perpetual danger to mankind. Some day, some desperate dictator like Hitler may have the bomb and use it regardless of consequences.

To anyone with such knowledge and with any imagination, the decision to start full-scale development of an H-bomb is a tremendous step to take, one that must not be taken lightly. This was a decision for which the scientists, inside and outside the GAC, could not take the responsibility on themselves. It was also too big a responsibility for the AEC. One of the arguments of the GAC and of the AEC majority was that the decision had to be made at higher levels of government. Furthermore, they felt it their duty to tell the President and his close advisors of the implications of this step, which they saw so clearly, while members of the government, less familiar with the potential power of an H-bomb, could not visualize these consequences to the same extent.

I never could understand how anyone could feel any enthusiasm for going ahead. I could well understand that President Truman and his close advisors were forced to a positive decision by the potential threat of Russian H-bomb development. But I am sure that they came to this decision with a heavy heart, and that most of the scientists who went to work on this project also had heavy hearts. I certainly had the greatest misgivings when Teller first suggested in October 1949 that I return to Los Alamos full-time to work on this project.

Yet there seemed to be some scientists who apparently had no scruples on this account. This unquestioning enthusiasm for the thermonuclear program looks to me very much like the enthusiasm many Germans felt in 1917 when the German government declared unrestricted submarine warfare. This gave the Germans a temporary advantage in the war but later brought the United States into the war against Germany and thus caused the German defeat.

To most of us the important question seemed not how to build an H-bomb, but whether one should be built. The conference that was to be held at Los Alamos on November 7, 1949, was to discuss this problem at length as much as the technical problem. Nearly every scientist felt the way Oppenheimer did in his letter (of October 21, 1949) to Conant: "It would be folly to oppose the exploration of this weapon. We have already known it had to be done; and it does have to be done But that we become committed to it as the way to save the country and the peace appears to me full of dangers.

The GAC report concluded: "We all hope that by one means or another, the development of these weapons can be avoided. We are all reluctant to see the United States take the initiative in precipitating this development. We are all agreed that it would be wrong at the present moment to commit ourselves to all-out efforts toward its development."

The report of the GAC might well be considered as a prayer for some solution to the dilemma, not as an answer. Scientists are not especially qualified to find a solution in the domain of statecraft. All they could do was to point out that here was a very major decision and it was worth every effort to avoid an irrevocable, and perhaps fatal, step. (An intermediate step, which would have left time for careful consideration of the problem by the government and yet not have lost time in technical development, might have been to direct intensified theoretical work on the H-bomb at Los Alamos, but not to take any immediate steps toward any major hardware development.)

Although the GAC was seeking a solution rather than offering one, the proposal of its minority still seems worthwhile, even as seen from today's [1954] viewpoint. The proposal was to enter negotiations with Russia with the goal that both countries commit themselves not to develop the H-bomb. If such an agreement could have been reached and had been kept, it would have gone far to avoid the peril in which the world now stands. At that time neither we nor presumably the Russians knew whether an H-bomb could be made. In this blissful state of ignorance we might have remained for a long time to come. Since the technical program was a very difficult one, it could never be accomplished without a major effort. It is possible, perhaps likely, that the Russians would have refused to enter an agreement on this matter. If they had done so, this refusal would have been a great propaganda asset for us in the international field and would in addition have gone far to persuade the scientists of this country to cooperate in the H-bomb program with enthusiasm.

Many people will argue that the Russians might have accepted such an agreement but then broken it. I do not believe so. Thermonuclear weapons are so complicated that nobody can be confident that he has the correct solution before he has tested such a device. But it is well known that any test of a bomb of such high yield is immediately detected. Therefore, without any inspections, each side would know immediately if the other side had broken the agreement.

It is difficult to tell whether or not the Russians would have developed the H-bomb if we had not. I am not sure what would have happened if we had followed the recommendations of the GAC majority and had merely announced that for such and such reasons, we would refrain from developing the H-bomb. Once we announced that we would go ahead, the Russians clearly had no choice but to do the same. In the field of atomic weapons, we have called the tune since the end of the war, both in quality and in quantity. Russia has to follow the tune or be a second-class power.

In summary, I still believe that the development of the H-bomb is a calamity. I still believe that it was necessary to pause before making the decision to consider this irrevocable step most carefully. I still believe that the possibility of an agreement with Russia not to develop the bomb should have been explored. But once the decision had been made to go ahead with the program, and once there was a sound technical program, I cooperated with it to the best of my ability. I did and still do this because it seems to me that once one is engaged in a race, one clearly must endeavor to win it. But one can try to forestall the race itself.