Einstein Urges FDR: Build the Atomic Bomb

Two physicists, one famous and one obscure, sat down on Long Island to compose a letter that would redirect the course of the twentieth century. Albert Einstein signed his name to a warning drafted largely by Hungarian physicist Leó Szilárd on August 2, 1939, urging President Franklin Roosevelt to investigate the military potential of nuclear fission before Nazi Germany could do the same. The letter, just two pages long, described the possibility of creating "extremely powerful bombs of a new type." Szilárd was the driving force behind the effort. He had fled Europe ahead of the Nazi rise and understood both the physics and the politics with unusual clarity. Having recently learned that German scientists had achieved uranium fission at the Kaiser Wilhelm Institute, he recognized the danger immediately. But Szilárd was unknown to Roosevelt. He needed Einstein's signature, the most famous name in science, to ensure the letter would reach the president's desk and be taken seriously. Einstein, a lifelong pacifist, agreed to sign because the prospect of a Nazi atomic weapon was more terrifying than the weapon itself. The letter reached Roosevelt through economist Alexander Sachs in October 1939. Roosevelt's response was measured but decisive: he established the Advisory Committee on Uranium, the bureaucratic seed that would grow into the Manhattan Project. The Manhattan Project ultimately employed more than 125,000 people, cost nearly $2 billion (roughly $28 billion today), and produced the weapons that destroyed Hiroshima and Nagasaki in August 1945. Einstein, who played no role in the project itself, later called signing the letter "the one great mistake" of his life. The two-page document remains one of the most consequential pieces of correspondence ever written, a moment when theoretical physics crossed irreversibly into geopolitics.