National Security and FBI Surveillance Enemy Aliens
The Custodial Detention Index (CDI), or Custodial Detention List was formed in 1939-1941, in the frame of a program called variously the "Custodial Detention Program" or "Alien Enemy Control." The Indexes have been arranged not only alphabetically but also geographically, designed to help identify potential threats to the United States from within immigrant communities as quickly as possible in times of national crisis.