No professional group in the United States benefited more from World War II than the scientific community. After the atomic bombings of Hiroshima and Nagasaki, scientists enjoyed unprecedented public visibility and political influence as a new elite whose expertise now seemed critical to America's future. But as the United States grew committed to Cold War conflict with the Soviet Union and the ideology of anticommunism came to dominate American politics, scientists faced an increasingly vigorous regimen of security and loyalty clearances as well as the threat of intrusive investigations by the notorious House Committee on Un-American Activities and other government bodies.