United States, where Fermi and Szilard had both emigrated, this led to the
creation of the first man-made reactor, known as Chicago
Pile-1, which achieved criticality on
December 2, 1942. This work became part of the Manhattan
Project, which built large reactors at the Hanford
Site (formerly the town of
Washington) to breed plutonium for
use in the first nuclear
weapons, which were used on the cities of Hiroshima and Nagasaki.
A parallel uranium enrichment effort
also was pursued.