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Albert Einstein spent the summer of 1939 in a rented cottage on the north fork of eastern Long Island, across the Great Peconic Bay from the villages of the Hamptons. He sailed his small boat Tinef, bought sandals from the local department store and played Bach with the store’s owner. And he met with Leó Szilárd, a charming and slightly eccentric Hungarian physicist, who sought his aid in a matter of grave and urgent concern.

Szilárd taught and conducted research in nuclear physics at Columbia University, where he was working on ways to create a nuclear chain reaction. When he learned that German scientists had discovered nuclear fission the year before by splitting the uranium atom, he concluded that uranium was an element that could be capable of sustaining a chain reaction with huge explosive potential. Szilárd discussed this possibility with his close friend Eugene Wigner, also a refugee physicist from Budapest, and they began to worry that the Germans might try to buy up the uranium supplies of the Congo, which was then a Belgian colony. But how, they asked themselves, could two Hungarian refugees in America find a way to warn the Belgians? Then Szilárd recalled that Einstein was a friend of that country’s queen mother. On Sunday, July 16, 1939, Szilárd and Wigner embarked on their mission to Long Island, with Wigner at the wheel (Szilárd, like Einstein, did not drive).

Sitting at a bare wooden table on the screen porch of Einstein’s rental cottage, Szilárd explained the process of how an explosive chain reaction could be produced in uranium layered with graphite by the neutrons released from nuclear fission. “I never thought of that!” Einstein interjected. He asked a few questions, went over the process for 15 minutes and then quickly grasped the implications. Instead of writing to the queen mother, Einstein suggested, perhaps they should write to a Belgian minister he knew.

Showing some sensible propriety, Wigner suggested that perhaps three refugees should not be writing to a foreign government about secret security matters without consulting with the State Department. In which case, they decided, perhaps the proper channel was a letter from Einstein—the only one of them famous enough to be heeded—to the Belgian ambassador, with a cover letter to the State Department. With that tentative plan in mind, Einstein dictated a draft in German. Wigner translated it, gave it to his secretary to be typed and then sent it to Szilárd.

A few days later, a friend arranged for Szilárd to talk to Alexander Sachs, an economist at Lehman Brothers and a friend of President Franklin D. Roosevelt. Showing a bit more savvy than the three theoretical physicists, Sachs insisted that the letter should go right to the White House, and he offered to hand-deliver it. “It could not do any harm to try this way,” Szilárd wrote Einstein. Should they talk by phone or meet in person to revise the letter? Einstein replied that he should come back out to the cottage.

Wigner couldn’t make the trip, so Szilárd enlisted, as driver and scientific sidekick, another friend from the amazing group of Hungarian refugees who were theoretical physicists, Edward Teller, to go with him. “I believe his advice is valuable, but also I think you might enjoy getting to know him,” Szilárd told Einstein. “He is particularly nice.” Another plus was that Teller had a big 1935 Plymouth.

Szilárd brought with him the draft from two weeks earlier, but Einstein realized that they were now planning a letter far more momentous than one asking Belgian ministers to be careful about Congolese uranium exports. The world’s most famous scientist was about to tell the president of the United States that he should begin contemplating a weapon of almost unimaginable impact that could unleash the power of the atom.

“Einstein dictated a letter in German,” Szilárd recalled, “which Teller took down, and I used this German text as a guide in preparing two drafts of a letter to the President.” Szilárd sent Einstein two versions, one 45 lines and one 25 lines, both dated August 2, 1939, “and left it up to Einstein to choose which he liked best.”

The longer version was given to Alexander Sachs for delivery to Roosevelt. It read in part:

Some recent work by [Italian physicist Enrico] Fermi and L. Szilárd, which has been communicated to me in a manuscript, leads me to expect that the element uranium may be turned into a new and important source of energy in the immediate future. Certain aspects of this situation which has arisen seem to call for watchfulness and, if necessary, quick action on the part of the Administration. I believe therefore that it is my duty to bring to your attention the following facts and recommendations:

… It may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated. Now it appears almost certain that this could be achieved in the immediate future.

This new phenomena would also lead to the construction of bombs, and it is conceivable—though much less certain—that extremely powerful bombs of a new type may thus be constructed. A single bomb of this type, carried by boat and exploded in a port, might very well destroy the whole port together with some of the surrounding territory….

In view of this situation you may think it desirable to have some permanent contact maintained between the administration and the group of physicists working on chain reactions in America.

The letter ended with a warning that German scientists might be pursuing a bomb. But even though it was obviously of enormous importance, almost two months later Sachs still had not conveyed the letter to Roosevelt. By then, events had turned what was an important letter into an urgent one. At the end of August 1939, the Nazis and Soviets stunned the world by signing their war alliance pact and proceeding to carve up Poland. That prompted Britain and France to declare war, starting the century’s second world war.

Szilárd went to see Sachs in late September and was horrified to discover that he still had not been able to schedule an appointment with Roosevelt. “There is a distinct possibility Sachs will be of no use to us,” Szilárd wrote Einstein. “Wigner and I have decided to accord him ten days grace.” Sachs barely made the deadline. On the afternoon of Wednesday, October 11, he was ushered into the Oval Office carrying Einstein’s letter, a memo from Szilárd and an 800-word summary he had written on his own.

Sachs worried that if he left the memos and papers with Roosevelt, they might be glanced at and then pushed aside. The only reliable way to deliver them, he decided, was to read them aloud. Standing in front of the president’s desk, he read his summation of Einstein’s letter, parts of Szilárd’s memo and some other paragraphs from assorted historical documents.

“Alex, what you are after is to see that the Nazis don’t blow us up,” the president said.

“Precisely,” Sachs replied.

That evening, plans were drawn up for an ad hoc committee, coordinated by Dr. Lyman Briggs, director of the Bureau of Standards, the nation’s physics laboratory. The committee met informally for the first time in Washington on October 21. Einstein was not there, nor did he want to be. He was neither a nuclear physicist nor someone who enjoyed proximity to political or military leaders. But his Hungarian émigré colleagues—Szilárd, Wigner and Teller—were there to launch the effort.

The following week, Einstein received a polite and formal thankyou letter from the president. “I have convened a board,” Roosevelt wrote, “to thoroughly investigate the possibilities of your suggestion regarding the element of uranium.”

Work on the atomic project proceeded slowly. Over the next few months, the Roosevelt administration approved only $6,000 for graphite and uranium experiments. Szilárd grew impatient. He was becoming more convinced of the feasibility of chain reaction and more worried about reports he was getting from fellow refugees on the activity in Germany.

In March 1940, Szilárd went to Princeton, N.J., where Einstein worked at the Institute for Advanced Study, to see him again. They composed another letter for Einstein to sign, again intended for Sachs to convey to the president. It warned of all the work on uranium they heard was being done in Berlin and urged the president to consider whether the American work was proceeding quickly enough.

Roosevelt reacted by calling for a conference designed to spur greater urgency, and he told officials to make sure that Einstein could attend. Einstein did not want to get more involved. He replied by saying he had a cold—somewhat of a convenient excuse—and did not need to be at the meeting. But he urged the group to get moving: “I am convinced of the wisdom and urgency of creating the conditions under which work can be carried out with greater speed and on a larger scale.”

On December 6, 1941, the United States launched the secret program to build an atomic bomb that would become known as the Manhattan Project. It was just over two years after Einstein and his colleagues had brought attention to the possibility of building atomic weapons and, fittingly enough, was the day before Japan launched its attack on Pearl Harbor that brought the nation into the war.

Because so many fellow physicists, including Szilárd, Wigner and Teller, had disappeared to obscure towns, Einstein surmised that the bomb-making work he had recommended was now proceeding with greater urgency. But he was not asked to join the Manhattan Project, nor was he officially told about it. He continued to stay involved from the sidelines, however.

The physicist Otto Stern, who had been one of Einstein’s friends since their days in Prague, had been secretly working on the Manhattan Project, mainly in Chicago, and sensed by the end of 1944 that it would be successful. That December, he made a visit to Princeton. What Einstein heard upset him. Whether or not the bomb was used in the war, it would change the nature of both war and peace forever. The policymakers weren’t thinking about that, he and Stern agreed, and they must be encouraged to do so before it was too late.

Einstein decided to write to Danish physicist Niels Bohr. He and Bohr had sparred over quantum mechanics, but Einstein trusted his judgment on more earthly issues. Einstein was one of the few people to know that Bohr, who was half-Jewish, was secretly in the United States. When the Nazis overran Denmark, he had made a daring escape by sailing with his son in a small boat to Sweden. From there he had been flown to Britain, given a fake passport with the name John Baker, then sent to America to join the Manhattan Project at Los Alamos, N.M.

Einstein wrote to Bohr, using his real name, in care of Denmark’s embassy in Washington, and somehow the letter got to him. In it Einstein described his worrisome talk with Stern about the dearth of thinking about how to control atomic weapons in the future. “The politicians do not appreciate the possibilities and consequently do not know the extent of the menace,” Einstein wrote. He argued that it would take an empowered world government to prevent an arms race once the age of atomic weaponry arrived. “Scientists who know how to get a hearing with political leaders,” Einstein urged, “should bring pressure on the political leaders in their countries in order to bring about an internationalization of military power.”

Thus began the political mission that would dominate the remaining decade of Einstein’s life. Since his days as a teenager in Germany, he had been repulsed by nationalism, and he had long argued that the best way to prevent wars was to create a world organization that had the authority to resolve disputes and the military power to impose its resolutions. Now, with the impending advent of a weapon so awesome that it could transform both war and peace, Einstein viewed this approach as no longer an ideal but a necessity.

Bohr was unnerved by Einstein’s letter, but not for the reason Einstein would have hoped. The Dane shared his desire for the international control of atomic weaponry, and he had advocated that approach in meetings with Churchill, and then with Roosevelt, earlier in the year. But instead of persuading them, his arguments had prompted the two leaders to issue a joint order to their intelligence agencies saying that “enquiries should be made regarding the activities of Professor Bohr and steps taken to ensure that he is responsible for no leakage of information, particularly to the Russians.”

Upon receiving Einstein’s letter, Bohr hurried to Princeton. He wanted to protect his friend by warning him to be circumspect, and he also hoped to repair his own reputation by reporting to government officials on what Einstein said. Bohr told Einstein that there would be “the most deplorable consequences” if anyone who knew about the development of the bomb shared that information. Responsible statesmen in Washington and London, Bohr assured him, were aware of the threat caused by the bomb as well as “the unique opportunity for furthering a harmonious relationship between nations.”

Einstein was persuaded. He promised that he would refrain from sharing any information he had surmised and would urge his colleagues not do anything to complicate American or British foreign policy. And he immediately set out to make good on his word by writing a letter to Otto Stern that was, for Einstein, remarkable in its circumspection. “I have the impression that one must strive seriously to be responsible, that one does best not to speak about the matter for the time being, and that it would in no way help, at the present moment, to bring it to public notice,” he wrote.

Einstein’s only intervention before the end of the war was prompted again by Szilárd, who visited in March 1945 and expressed anxiety about how the bomb might be used. It was clear that Germany, now weeks away from defeat, was not making a bomb. So why should the Americans rush to complete one? And shouldn’t policymakers think twice about using it against Japan when it might not be needed to secure victory?

Einstein agreed to write another letter to President Roosevelt urging him to meet with Szilárd and other concerned scientists, but in it he went out of his way to feign ignorance. “I do not know the substance of the considerations and recommendations which Dr. Szilárd proposes to submit to you,” Einstein wrote. “The terms of secrecy under which Dr. Szilárd is working at present do not permit him to give me information about his work; however, I understand that he now is greatly concerned about the lack of adequate contact between scientists who are doing this work and those members of your Cabinet who are responsible for formulating policy.”

Roosevelt never read the letter. It was found in his office after he died on April 12 and was passed on to Harry Truman, who in turn gave it to his designated secretary of state, James Byrnes. The result was a meeting between Szilárd and Byrnes in South Carolina, but Byrnes was neither moved nor impressed.

The atom bomb was dropped, with little high-level debate, on August 6, 1945, on the city of Hiroshima. Einstein was at a cottage on Saranac Lake in the Adirondacks, taking an afternoon nap. His secretary, Helen Dukas, informed him when he came down for tea. “Oh, my God,” was all he said.

Three days later, the bomb was used again, this time on Nagasaki. The next day, officials in Washington released a long history, compiled by Princeton physics professor Henry DeWolf Smyth, of the secret endeavor to build the weapon. The Smyth report, much to Einstein’s lasting discomfort, assigned great historic weight for the launch of the project to the 1939 letter he had written to Roosevelt.

Between the influence imputed to that letter and the underlying relationship between energy and mass that he had formulated 40 years earlier, Einstein became associated in the popular imagination with the making of the atom bomb, even though his involvement was marginal. Time magazine put him on its cover, with a portrait showing a mushroom cloud erupting behind him with E = mc2 emblazoned on it.

In a story that was overseen by an editor named Whittaker Chambers, the magazine noted with its typical prose flair from the period:

Through the incomparable blast and flame that will follow, there will be dimly discernible, to those who are interested in cause & effect in history, the features of a shy, almost saintly, childlike little man with the soft brown eyes, the drooping facial lines of a world-weary hound, and hair like an aurora boreali….Albert Einstein did not work directly on the atom bomb. But Einstein was the father of the bomb in two important ways: 1) it was his initiative which started U.S. bomb research; 2) it was his equation (E = mc2) which made the atomic bomb theoretically possible.

It was a perception that plagued Albert Einstein. When Newsweek did a cover on him, with the headline “The Man Who Started It All,” Einstein offered a memorable lament. “Had I known that the Germans would not succeed in producing an atomic bomb,” he said, “I never would have lifted a finger.”

Of course, neither he nor Szilárd nor any of their friends involved with the bomb-building effort, many of them refugees from Hitler’s horrors, could know that the brilliant scientists they had left behind in Berlin would fail to unlock the secrets. “Perhaps I can be forgiven,” Einstein said a few months before his death in a conversation with the American chemist Linus Pauling, “because we all felt that there was a high probability that the Germans were working on this problem and they might succeed and use the atomic bomb and become the master race.”

Originally published in the June 2007 issue of World War II Magazine. To subscribe, click here