On 11 October 1939, Franklin Roosevelt received a letter from Albert Einstein. The letter, written on August 2, was prompted by fears that uranium ore in the Belgian Congo might fall into the hands of Nazi Germany. Leo Szilard, the Hungarian-born physicist who first conceived of the possibility of a nuclear chain reaction, suggested his friend Einstein to write a letter to the Roosevelt urging him -- less than a month before war broke out in Europe -- to consider starting a program of federal research into atomic energy. The letter read, in part:
Some recent work by E. Fermi and L. Szilard, which has been communicated to me in 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 the 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:Roosevelt was noncommital. He established a small body known as the "Uranium Committee," but set aside only $6000 to purchase uranium and graphite.
In the course of the last four months it has been made probable -- through the work of Joliot in France as well as Fermi and Szilard in America -- that 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 phenomenon 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. However, such bombs might very well prove to be too heavy for transportation by air.
The committee, which included Szilard as well as representatives from the Army, Navy and Bureau of Standards, issued a brief report to Roosevelt in early November. "If the reaction turns out to be explosive in character," they mused, "it would provide a possible source of bombs with a destructiveness vastly greater than anything now known."