Discovered by James Chadwick
Enrico Fermi added a neutron to Uranium in an attempt to create a new element.
Lisa Meitner and Otto Frisch repeat Fermi's experiment, determine he broke down Uranium instead of creating a new element, and gave nuclear fission as the name for the new process.
First successful chain reaction of nuclear fission
First test of atomic bomb in New Mexico
Atomic bombs are dropped in Japan.