With more than 405,000 American casualties and Japan rejecting unconditional surrender, the United States begins testing the atomic bomb in New Mexico. This is some of the only footage recorded of ...

The first atomic bomb ever exploded was a test device, insouciantly nicknamed the Gadget. In mid-July 1945, American scientists had trucked the five-ton mechanism from their secret laboratory at ...

Photo: Atomic bomb test explosion in Alamagordo, New Mexico, July 16, 1945. AP/Wide World Photos In 1932, James Chadwick discovered the neutron, a small atomic particle with mass but no charge.