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.

Letter to President Franklin D. Roosevelt [August 2, 1939] (the letter that resulted in the assignment of government funds for developing the atom bomb)