Sound has long been known to have a deep, psychological effect. This is why every year, grade school science fairs are filled with projects about the effect music has on plants/hamsters/fish/little brothers. Loud music is frequently used to cause sleep deprivation in POWs, and the United States notoriously used round-the-clock recordings of Van Halen to force Manuel Noriega to surrender in 1990. But back in the 1960s, the Air Force was working on something much more psychologically damaging.
Called Pyrotechnic Harassment Devices, or PHDs, these noise bombs were developed to sound like human screams in order to terrify the enemy, break their morale, and confuse the opposing forces. The United States had used loudspeakers to confuse the Germans during World War II, and blared propaganda messages during the Korean conflict, but these PHDs were specifically designed to instill fear with the sounds of human screams.
The Air Force hired a company called Special Devices, Inc. to build the prototype “bombs.” The goal was to have devices that could be placed into pods, dropped from airplanes, and emit noises for up to six hours. Engineers recorded a bunch of different sounds: male and female screams; different types of gun fire; and a “neutral scream” consisting of a mix of the male and female screams, and the cries of elephants and panthers. Each PHD would be fitted with a small, one pound explosive that would detonate once its audio cycle finished, or earlier if it was tampered with.
The PHDs never came to fruition. The pods were easy to see on the ground, yet too small to allow the sophisticated mechanics necessary to create realistic sounds. At best, the PHDs could let out shots, whistles, whines, and other white noises. Annoying, yes, but not psychologically damaging. The PHDs never saw combat.