Nuclear Museum Logo
Nuclear Museum Logo

National Museum of Nuclear Science & History

Rotblat Account

Joseph Rotblat reflects here on his decision to leave the Manhattan Project early and return to England. Toward the end of 1944 it became clear that Germany did not have an atomic bomb. Thus Rotblat’s rationale for working on an atomic weapon—to create a deterrent to Hitler’s using one—no longer existed. While he departed before Christmas 1944, he spent the rest of his life working with an international community of scientists to abolish nuclear weapons and renounce war.

Document Type:
Joseph Rotblat

From Leaving the Bomb Project by Joseph Rotblat

In March 1944, I experienced a disagreeable shock. At that time I was living with the Chadwicks in their house on the Mesa, before moving later to the “Big House,” the quarters for single scientists. General Leslie Groves, when visiting Los Alamos, frequently came to the Chadwicks for dinner and relaxed palaver. During one such conversation, Groves said that, of course, the real purpose in making the bomb was to subdue the Soviets. (Whatever his exact words, his real meaning was clear.) Although I had no illusions about the Stalin regime—after all, it was his pact with Hitler that enabled the latter to invade Poland—I felt deeply the sense of betrayal of an ally. Remember, this was said at a time when thousands of Russians were dying every day on the Eastern Front, tying down the Germans, and giving the Allies time to prepare for the landing on the continent of Europe. Until then I had thought that our work was to prevent a Nazi victory, and now I was told that the weapon we were preparing was intended for use against the people who were making extreme sacrifices for that very aim.

My concern about the purpose of our work gained substance from conversations with Niels Bohr. He used to come to my room at eight in the morning to listen to the BBC news bulletin. Like myself, he could not stand the U.S. bulletins which urged us every few seconds to purchase a certain laxative! I owned a special radio on which I could receive the BBC World Service. Sometimes Bohr stayed on and talked to me about the social and political implications of the discovery of nuclear energy and of his worry about the dire consequences of a nuclear arms race between East and West which he foresaw.

All this, and the growing evidence that the war in Europe would be over before the bomb project was completed, made my participation in it pointless. If it took the Americans such a long time, then my fear of the Germans being first was groundless. When it became evident, toward the end of 1944, that the Germans had abandoned their bomb project, the whole purpose of my being in Los Alamos ceased to be, and I asked for permission to leave and return to Britain. Why did other scientists not make the same decision? Obviously, one would not expect General Groves to wind up the project as soon as Germany was defeated, but there were many scientists for whom the German factor was the main motivation. Why did they not quit when this factor ceased to be?

I was not allowed to discuss this issue with anybody after I declared my intention to leave Los Alamos, but earlier conversations, as well as much later ones, elicited several reasons. The most frequent reason given was pure and simple scientific curiosity—the strong urge to find out whether the theoretical calculations and predictions would come true. These scientists felt that only after the test at Alamogordo should they enter into the debate about the use of the bomb. Others were prepared to put the matter off even longer, persuaded by the argument that many American lives would be saved if the bomb brought a rapid end to the war with Japan. Only when peace was restored would they take a hand in efforts to ensure that the bomb would not be used again.

Still others, while agreeing that the project should have been stopped when the German factor ceased to operate, were not willing to take an individual stand because they feared it would adversely affect their future career. The groups I have just described—scientists with a social conscience—were a minority in the scientific community. The majority were not bothered by moral scruples; they were quite content to leave it to others to decide how their work would be used. Much the same situation exists now in many countries in relation to work on military projects. But it is the morality issue at a time of war that perplexes and worries me most.


After I told Chadwick that I wished to leave the project, he came back to me with very disturbing news. When he conveyed my wish to the intelligence chief at Los Alamos, he was shown a thick dossier on me with highly incriminating evidence. It boiled down to my being a spy: I had arranged with a contact in Santa Fe to return to England, and then to be flown to and parachuted onto the part of Poland held by the Soviets, in order to give them the secrets of the atom bomb. The trouble was that within this load of rubbish was a grain of truth. I did indeed meet and converse with a person during my trips to Santa Fe. It was for a purely altruistic purpose, nothing to do with the project, and I had Chadwick’s permission for the visits. Nevertheless, it contravened a security regulation, and it made me vulnerable.

Fortunately for me, in their zeal the vigilant agents had included in their reports details of conversations with dates, which were quite easy to refute and to expose as complete fabrications. The chief of intelligence was rather embarrassed by all this and conceded that the dossier was worthless. Nevertheless, he insisted that I not talk to anybody about my reason for leaving the project. We agreed with Chadwick that the ostensible reason would be a purely personal one: that I was worried about my wife whom I had left in Poland.

And so, on Christmas Eve 1944, I sailed for the United Kingdom, but not without another incident. Before leaving Los Alamos I packed all my documents—research notes as well as correspondence and other records—in a box made for me by my assistant. En route I stayed for a few days with the Chadwicks in Washington. Chadwick personally helped me to put the box on the train to New York. But when I arrived there a few hours later, the box was missing. Nor, despite valiant efforts, was it ever recovered.

The work on the Manhattan Project, as I said at the outset, has had an enduring effect on my life. Indeed, it radically changed my scientific career and the carrying out of my obligations to society. Work on the atom bomb convinced me that even pure research soon finds applications of one kind or another. If so, I wanted to decide myself how my work should be applied. I chose an aspect of nuclear physics which would definitely be beneficial to humanity: the applications to medicine. Thus I completely changed the direction of my research and spent the rest of my academic career working in a medical college and hospital.

While this gave me personal satisfaction, I was increasingly concerned about the political aspects of the development of nuclear weapons, particularly the hydrogen bomb, about which I knew from Los Alamos. Therefore, I devoted myself both to arousing the scientific community to the danger, and to educating the general public on these issues. I was instrumental in setting up the Atomic Scientists Association in the United Kingdom, and within its framework organized the Atom Train, a traveling exhibition which explained to the public the good and evil aspects of nuclear energy. Through these activities I came to collaborate with Bertrand Russell. This association led to the foundation of the Pugwash Conferences, where I met again with colleagues from the Manhattan Project, who were also concerned about the threat to mankind that has arisen partly from their work.

After 40 years one question keeps nagging me: have we learned enough not to repeat the mistakes we made then? I am not sure even about myself. Not being an absolute pacifist, I cannot guarantee that I would not behave in the same way, should a similar situation arise. Our concepts of morality seem to get thrown overboard once military action starts. It is, therefore, most important not to allow such a situation to develop. Our prime effort must concentrate on the prevention of nuclear war, because in such a war not only morality but the whole fabric of civilization would disappear. Eventually, however, we must aim at eliminating all kinds of war.


More Historical Resources: