In December 1938 two German physicists, Otto Hahn and Fritz Strass-
mann, working in a Berlin laboratory, discovered that the heavy element
uranium upon bombardment by neutrons had split, or fissioned, into sepa-
rate, lighter elements with a consequent production of both high energy
and additional neutrons. It seemed possible that under proper control the
additional neutrons might continue to split other atoms, producing a contin-
uous process of chain reaction. Thus in 1939 (and possibly in 1934 in Italy)
the atom had been split, but not in America.

Refugee scientists fleeing Hitler's Germany and Stalin's Russia soon
brought the revolution in physics to America. In early 1939 the Hungarian
physicist Leo Szilard, a reader of H. G. Wells's prophetic book, learned of
the Hahn-Strassmann fission experiment and became concerned. Szilard,
then a refugee living in New York, correctly anticipated that a new world of
atomic weapons would be "headed for grief," especially if such weapons
came into the hands of Adolf Hitler's Nazi Germany.

In 1939, with the support of influential patrons such as the banker Lewis
Strauss, Szilard and another young Hungarian refugee, Edward Teller, per-
suaded the world-famous refugee physicist Einstein, living in Princeton,
New Jersey, to sign a letter to President Franklin Delano Roosevelt warning
him of the dangers of nuclear weapons and of the possibility that Hitler
would soon acquire the valuable Joachimsthal uranium mines in Czechoslo-
vakia. The letter was conveyed to Roosevelt shortly after World War II
began with the German Blitzkrieg against Poland on September 1, 1939.

Despite a proliferation of committees on "the uranium question," little
was accomplished in the United States until after Pearl Harbor. The initial
key theoretical work on the possibility of building an atomic bomb was
performed in England in 1940 and 1941 at Birmingham by two refugee
German physicists, Rudolf Peierls and Otto Frisch. In the spring of 1940
they produced a working paper for the British government, then fighting for
its life against aerial attacks by the Luftwaffe, on the theory of an atomic
bomb. In it they concluded that a relatively small amount of uranium could
constitute a "critical mass," which, if properly brought together at sufficient
speed, could yield an explosion equivalent to many thousands of tons of
TNT. The conclusions of Frisch and Peierls were reinforced by a second
study carried out in 1941 by a secret British government working group
known as the "MAUD Committee."

For further information on the early history of nuclear energy, see Ron-
ald Clark, The Greatest Power on Earth: The International Race for Nuclear
Supremacy from Earliest Theory to Three Mile Island ( New York: Harper
& Row, 1980). The papers and correspondence of Leo Szilard have been
collected by his widow, Gertrude Weiss Szilard, and Spencer R. Weart as

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