By 1939 nuclear scientists had begun to delve seriously into the fission of uranium atoms causing a chain reaction, particularly in the U235 isotope. As a result, vast progress was made in the fields of neutron bombardment, the comparative efforts of slow neutrons versus fast neutrons in sustaining chain reactions, and the possible methods of separating U235 from U238 in natural uranium. Moreover, the possibility of an immense atomic explosion was becoming common knowledge, and calculations …showed first 75 words of 1586 total…

…showed last 75 words of 1586 total…George" shot of Operation Greenhouse (May 9, 1951) confirmed for the first time that a fission device similar to Fat Man could produce the conditions needed to ignite a thermonuclear reaction. The "Mike" test of Operation Ivy, on November 1, 1952, was the first explosion of a true two-stage thermonuclear device (Brock). It was the original theory of compressing supercritical materials working in combination with light gases that made possible the fusion bombs of the cold war and beyond.