While most americans celebrated the accomplishments and heroism of our Soviet allies during World War II, reveling in the Red Army's pulverizing of Nazi forces and hoping that the United States, Britain, and the Soviet Union would continue their cooperation into the postwar world, counterintelligence agencies were less sanguine. Although the FBI had focused much of its wartime activities on Nazi and Japanese activities, by 1943 it was unable to ignore growing signs that America's Soviet ally covertly was behaving in an unfriendly manner.

Neither the Soviet Union's joining the fight against Hitler nor Stalin's dissolution of the Communist International (Comintern) during the war could erase the long-standing hostility to communism that animated many Americans or the suspicion of some that Communist subversion was a continuing problem. While the Communist Party, USA (CPUSA) had abandoned its rhetorical denunciations of capitalism, proclaimed its absolute commitment to winning the war, and, by 1944, forsworn even a postwar effort to transform America into a socialist society, a series of events and investigations convinced FBI chief J. Edgar Hoover and other high government officials that communism remained a danger to American security.

Only a small fraction of the evidence that Communists and communism remained a threat became public before 1947. What did become known, moreover, was often fragmentary and confusing, occasioning angry claims from admirers of the USSR that mendacious forces in the government were intent on undermining American-Soviet cooperation.