The interrogation centers and PRUs were developed by the CIA'sSaigonstation chief Peer de Silva. DeSilva was a proponent of amilitary strategy known as "counter terror" which held that terrorismwas a legitimate tool to use in unconventional warfare, and that itshould be applied strategically to "enemy civilians" in order to reducecivilian support for the Viet Cong. The PRUs were designed with this inmind, and began terrorizing suspected VC members in 1964.

Between 1968 and 1972, Phoenix "neutralized" 81,740 people suspected of NLF membership, of whom 26,369 were killed. A significant number of NLF were killed, and between 1969 and 1971 the program was quite successful in destroying NLF infrastructure in many important areas. By 1970, communist plans repeatedly emphasized attacking the government’s pacification program and specifically targeted Phoenix officials. The NLF also imposed quotas. In 1970, for example, communist officials near Da Nang in northern South Vietnam instructed their assassins to “kill 400 persons” deemed to be government “tyrant[s]” and to “annihilate” anyone involved with the pacification program.