nuclear chain reaction was achieved, during 1942. Szilárd became a naturalized citizen of the United States during 1943. J. Robert Oppenheimer (1904–1967) was appointed the scientific director of the Manhattan Project, the World War II project that developed the first nuclear weapons. He is often referred to as the "father of the atomic bomb". Oppenheimer was born to Julius S. Oppenheimer, who had immigrated to the United States from Germany in 1888 with his parents and become a wealthy Jewish textile importer, and Ella Friedman, a painter. Among other German scientists forced to flee Germany were fourteen Nobel laureates and 26 of the 60 professors of theoretical physics in the country. Among the scientists who came to the United States or its Allies were Edward Teller, Niels Bohr, Enrico Fermi, Otto Stern, Victor Weisskopf, Hans Bethe, and Lise Meitner, many of whom worked to ensure that the Allies would develop nuclear weapons before the Nazis. With so many Jewish scientists forced to live in the United States, where they often worked together, Einstein wrote to a friend, "For me the most beautiful thing is to be in contact with a few fine Jews—a few millennia of a civilized past do mean something after all." In another letter he writes, "In my whole life I have never felt so Jewish as now." Einstein was offered a position at the Institute for Advanced Study at Princeton, New Jersey, an affiliation that lasted until his death in 1955. In the summer of 1939, a few months before the beginning of World War II, Einstein was persuaded to write a letter to president Franklin D. Roosevelt and warn him that Nazi Germany might be developing an atomic bomb. Einstein helped strengthen the letter, and he recommended the U.S. begin uranium enrichment and nuclear research. According to F.G. Gosling of the U.S. Department of Energy, Einstein, Szilard, and other refugees including Edward Teller and Eugene Wigner, "regarded it as their responsibility to alert Americans to the possibility that German scientists might win the race to build an atomic bomb, and to warn that Hitler would be more than willing to resort to such a weapon." Gosling adds that "the President was a man of considerable action once he had chosen a direction," and believed that the U.S. "could not take the risk of allowing Hitler" to possess nuclear bombs. Other weapons historians agree that the