Operation Wandering Soul was a propaganda campaign exercised by U.S. Forces during the Vietnam War. The operation played off the belief of many Vietnamese in the "wandering soul":
It is the Vietnamese belief that the dead must be buried in their homeland, or their soul will wander aimlessly in pain and suffering. Vietnamese feel that if a person is improperly buried, then their soul wanders constantly. They can sometimes be contacted on the anniversary of their death and near where they died. Vietnamese honor these dead souls on a holiday when they return to the site where they died.
U.S. engineers spent weeks recording eerie sounds and altered voices - which pretended to be killed Vietcong - for use in the operation, with the intended purpose of instilling a sense of turmoil within the enemy, the desired result being for the soldier to flee his or her position. Helicopters were sometimes employed to broadcast recordings; the voices called on their "descendants" in the Vietcong to defect and cease fighting.
This is fucked up. Wiki.