geekyThe nuclear race began with the discovery of nuclear fission by German chemists Otto Hahn and Fritz Strassmann in 1938. German physicists Lise Meitner and Otto Frisch postulated that the development of an atomic bomb was a theoretical possibility. Fears were raised that a German atomic bomb project would emerge. Scientists who were refugees from Nazi Germany raised these fears and in August 1939, Hungarian-born physicists Leo Szilard and Eugene Wigner drafted the Einstein–Szilard letter, in which they warned of the potential development of "extremely powerful bombs of a new type". They urged the United States to take steps to acquire stockpiles of uranium ore and accelerate the research of Enrico Fermi and others into nuclear chain reactions. One of the signatories of the letter was Albert Einstein. The letter was delivered to President Franklin D. Roosevelt.
Roosevelt chose Lyman Briggs of the National Bureau of Standards to lead the Advisory Committee on Uranium. Briggs was tasked with investigating the issues raised in the letter. Briggs called a meeting on October 21, 1939, which was attended by Szilárd, Wigner and Edward Teller. The committee reported back to Roosevelt in November. The informed the President that uranium "would provide a possible source of bombs with a destructiveness vastly greater than anything now known."
The U.S. Navy provided Columbia University with $6,000 in funding. Physicists Enrico Fermi and Szilard used the money to purchase graphite. A group of Columbia professors that included Fermi, Szilard, Eugene T. Booth and John Dunning were the first to create nuclear fission reaction in the United States. They built a series of prototype nuclear reactors at Columbia, but they were not able to achieve a chain reaction.
Roosevelt's Advisory Committee became known as the National Defense Research Committee on Uranium (NDRC) on June 27, 1940. Briggs proposed spending $167,000 on the uranium-235 isotope at the University of California. A year later, an June 28, 1941, Roosevelt signed Executive Order 8807, which created the Office of Scientific Research and Development (OSRD). He picked Vannevar Bush as its first director. The OSRD was given the power to hold large engineering projects in addition to research. The NDRC Committee on Uranium became the S-1 Section of the OSRD. They decided to drop the word "uranium" from the name for security reasons.
The OSRD began working with British scientists at the University of Birmingham had made a breakthrough investigating the critical mass of uranium-235 in June of 1939. The British calculated that an atomic bomb could be created that was small enough to be carried by a bomber. In July of 1940, Britain had offered its scientific research to the United States. One of the members of the Birmingham team, the Australian physicist Mark Oliphant, flew to the United States in late August 1941 and discovered that his committee's findings were being ignored by the Americans. He met with the Uranium Committee and then visited Berkeley, California, where he was able to convince American physicists of the potential power of an atomic bomb.
On October 9, 1941, President Roosevelt approved the atomic program after meeting with Vannevar Bush and Vice President Henry A. Wallace. He created a Top Policy Group that included himself, even though he never attended a meeting. The committee was composed of Wallace, Bush, Conant, Secretary of War Henry L. Stimson, and the Chief of Staff of the Army, General George C. Marshall. Roosevelt chose the Army to run the project rather than the Navy, because the Army had more experience with management of large-scale construction projects. He also agreed to coordinate the effort with that of the British, and on 11 October he sent a message to Prime Minister Winston Churchill, suggesting that they correspond on atomic matters.
The Manhattan Project resulted in the production of the first nuclear weapons. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs. The Manhattan Project grew to employ more than 130,000 people. Atomic bombs were used in August of 1945 in the bombings of Hiroshima and Nagasaki.