The Acoustics of War

By the early 1990s, the United States was reassessing its self-image. The major conflicts of the last century—the two World Wars and Vietnam—had, for the most part, already been consigned to history (for a younger generation, they were only more media kitsch). But a protracted Cold War had kept the United States in a defensive posture for decades; now that the USSR had dissolved, the US no longer worried about the threat of a nucle­ar attack. The military wanted weapons that reflected the US’s new international role. What to do? In 1991, the Pentagon issued a directive to test an emerging class of arms: Called “non-lethals,” these weapons were meant to disable their targets “in such a way that death or severe permanent disability was unlikely.”

Most international policy was, at that point, riot control. The US had become a peripatetic interventionist, dabbling in United Nations sanctions and adjudicating regional skirmishes as if they were protests at a college rally. For an optimistic military administration, non-lethals were the humanitarian antidote to atom bombs. By 1996, the US had invested nearly $37 million in research for non-lethal weapons.

The ideology behind “non-lethal” weapons was not new. Police had used chemical sprays and rubber bullets, to name just two, to quell domestic riots in the US throughout the 1960s. A second-wave of non-lethals were introduced in the Gulf War and then, later, in Somalia in 1994: sticky foams to adhere a person to an object or another person; caustics to dissolve tires and roadways; lasers to disorient and temporarily blind; acoustic weapons that used high-decibel noise to cause pain, or infrasound to cause unbearable nausea. The US had already discovered, while dropping bombs over Vietnam, that sudden, high-decibel noise would deafen people, though this was not what non-lethal researchers had intended. (The 1907 Hague Convention clearly prohibits the use of “arms, projectiles, or materials calculated to cause unnecessary suffering.”) But it presented an interesting question: Was it possible to project sound at a precise decibel level that caused pain without permanent ear damage? Furthermore, there was anecdotal evidence suggesting that at the right frequency, infrasound would “liquefy [people’s] bowels and reduce them to quivering diarrheic masses.”^[1]

By the mid-1990s, most of the major papers had reported on the emergence of non-lethal technology. A Lexis-Nexis search with the keywords “acoustic weapons” and “acoustic warfare” turned up a cluster of articles from 1994 to 1999. International papers reported that acoustic weapons were “close to becoming reality.” In 1997, a US News & World Report feature on non-lethals quoted the CEO of SARA [Scientific Applications & Research Associates, the Pentagon’s leading acoustics research arm] as saying that they had already built prototypes for acoustic fences, and that acoustic cannons would be available in as little as one to two years. By 1999, Human Rights Watch issued a memorandum suggesting that a new protocol dealing with acoustic weapons be added to the Convention on Conventional Weapons.

This was the last reference to non-lethal weapons in the media at large. I assumed that the Pentagon was in its last stages of development and had bumped the project up to top-secret mode, but a SARA press agent cagily informed me on the phone that they were no longer involved in non-lethal acoustics research. “We couldn’t find an appropriate mechanism to pursue,” I was told. “Acoustics didn’t prove out.” When I called Penn State’s Institute for Non-Lethal Defense Technologies, I was directed to Dave Swanson, an acoustician sent in by the Pentagon to assess the acoustics research being done.

Swanson told me that the Pentagon decided to stop acoustic funding to SARA largely on the basis of his findings. High decibel sound could inadvertently deafen its target, he explained, and the US had not figured out how to build a portable weapon with enough energy to power and direct low-frequency infrasound across any considerable distance. Swanson thought that it would remain physically impossible to do so because of the huge energy demands of low-frequency sound. In his experiments, Swanson had not found a single repeatable case of low-frequency sounds affecting a large population the way the Pentagon had hoped. “Their attitude was, ’If we can’t put them on the ground, we don’t want to hear about it.‘”

In addition to requiring large quantities of energy and being difficult to use with a portable device, infrasound works poorly in air where sound waves tend to reflect off the body.^[2] Low-frequency sound travels in all directions and is hard to direct. (Infrasound is measured at 20 Hz and below, ultrasound at 20 KHz and above.) Wavelength is in a ratio to the aperture of the device that is directing it, so that infrasound needs a very large aperture. As a matter of contrast, ultrasound uses a very small aperture. It is cheap to generate and relatively easy to direct, but ultrasound burns surface tissue and destroys organs (medical ultrasound is used to break up kidney stones) and therefore has not been adapted for non-lethal purposes.

Infrasound is an amazingly effective weapon under the right conditions. A small percentage of the population is so unbearably sensitive to infrasound that they become nauseous near the ocean (which naturally generates low-frequency signals) and can sense, or “hear,” earthquakes hundreds of miles away. Ultra-low frequencies will nauseate and disorient most people under the right conditions (that is, if the sound can easily couple with their bodies, which it does under water or in a high-pressure chamber).

There are notable cases of people encountering low-frequency sounds under such conditions. In one case, Walt Disney and his team of cartoonists slowed down the 60-cycle tone of a soldering iron in a short cartoon. At a low-frequency 12 cycles, they became sick for days afterwards. The inventor Nikola Tesla experimented with low-frequency vibrating platforms that he motored using simple “eccentric” wheels. He found that standing on the platform for a minute created a pleasant buzz through the body. Remaining on the platform for any longer than a minute aggravated his subjects’ hearts and dangerously raised their blood pressure. His friend Mark Twain once got on the platform and refused to descend. As the author Gerry Vassilatos writes, “Tesla’s concern was drowned out by both the vibrating machine and Clemens’ jubilant exaltations and praises. Several more seconds and Clemens nearly soiled his white suit.”^[3]

In 1957, inventor/robot scientist Vladimir Gavreau, attempted to build a low-frequency weapon after accidental exposure to infrasound. While working in a concrete building that housed his laboratory, he and his fellow researchers periodically became debilitatingly nauseous. He discovered that the nausea ceased when certain windows in the building were blocked. Eventually, engineers traced the problem to an improperly installed motor-driven ventilator that activated an infrasonic resonance in a large duct where it sat. The motor, coupled with the rest of the concrete building, itself a large enclosure, formed an infrasonic amplifier. Shutting the windows altered the resonance of the building and shifted its infrasonic pitch. Gavreau, convinced he had discovered a new weapon, created several replicas of the original air duct. He pumped different frequencies of sound through massive ducts 6 feet in diameter and 75 feet long. When exposed to the infrasound, the researchers felt a “pressure against the eyes and ears...their internal organs were filled with continual painful spasms...and every pillar and joint of the massive structure [on which the duct rested] bolted and moved.”^[4]

While every military project has its conspiracists, I found hundreds of Internet stories suggesting that the US government has been testing acoustic weapons on its citizens. The US government has its own conspiracy theories as well. Major Joseph Cook III has suggested in his handbook, Nonlethal Weapons, that the Russians have a gun that shoots 10-Hz acoustic bullets the size of baseballs from hundreds of yards away. It has been claimed for years that the Nazis developed a sonic cannon so powerful it could fell a B-17 bomber out of the sky. But these appear only as anecdotal stories. Of the acoustic prototypes that actually exist, several have actually proved viable. In his 1981 book Riot Control, Colonel Rex Applegate showcased a blueprint for a curdler (which he aptly nicknames “the people repeller”), which looks like a British police club and emits a shrieking, pulsating sound equal to 120 decibels at 30 feet. Swanson directed me to two weapons: a Compression Air Device [CAD] and a Ring Vortex Cannon. The CAD generates energy at a specific low frequency from a combustion engine at its base, and directs the sound out of a long tube. The Ring Vortex Cannon, which Swanson thinks is the most viable of the acoustic weapons, is actually an acoustic and kinetic cannon that sends out an infrasound donut-shaped shock wave combined with a toxic chemical spray. The vortex ring travels at hundreds of miles per hour, and hits its target with the force of a rubber blanket.

Ultrasound also has its adherents. For years, self-proclaimed futurologists such as the husband-wife team Janet and Chris Morris have been prophesying a different kind of ultrasound weapon: acoustic voice plants that can make the target imagine to be hearing voices inside his or her head. A powerpoint slide from a talk Swanson had given in 1999 explained the technology in more detail: Two high-frequency sound beams are mixed, producing a “difference tone” that is audible with “laser-like directivity.” (Audible sound, in the 20 Hz to 20 KHz range, tends to dissipate in all directions like infrasound.)

On 15 May 2001, the New York Times reported that a graduate student named F. Joseph Pompei had created the first acoustic beam using ultrasound: “The result is that the audio spotlight doesn’t directly generate the audible sound. It generates a beam of ultrasound that acts like a long, thin loudspeaker and releases audible sound—a secondary effect.” Pompei told the reporter that people had written to him worried about the beam’s “insidious mind control uses.” The Times also mentioned that American Technology Corporation (a research organization similar to SARA) had already sent out evaluations to military contractors.

Audible, psychologically disturbing sounds have also been used with mixed results. In 1990, loud music forced Noriega out of the Vatican Embassy in Panama, and at the Waco stand-off in 1993, Janet Reno played Tibetan chant music and heavy metal. Swanson explained that a problem with using music as a dispersal tool is that there is no single type of music that people dislike, as is also the case with malodorants—smells so noxious that they would force people to evacuate an area. When they were tested as potential non-lethals, researchers discovered that some people had become aroused by several of the headier aromas. Swanson suggests research into sounds that are universally disorienting, such as nails scraping against a blackboard. “If you lay out their frequencies,” he said, “they spread out in much the same way a symphony does. So what makes them so distressing?”

Ultimately, however, Swanson is more wary of infrasound and high-decibel acoustic testing. When I asked SARA’s point man if it had ceased acoustics research because of the difficulty in directing low-frequency sound, I was told, “No. You can direct it pretty well. There just wasn’t a real dial-in capability.” He explained that a weapon dialed in at, say, 137 decibels and meant for a target 100 feet away could easily cause deafness in someone ten feet away. Non-lethal technology can turn “worse-than-lethal,” in the words of Harvey Sapolsky, head of Security Studies at MIT and one the first people to look at non-lethals in the US. When I spoke to Sapolsky over the phone, he told me stories he heard of Israelis stripping rubber off bullets and Americans using lasers to illuminate Somali targets in order to shoot them.

“Our ears are our primary sensor,” Swanson tells me. “Sound can cause anxiety and stress, but a loud sound won’t put you on the floor and keep you there. It won’t make 100% or 70% [of people] sick the way it will work for 1% or .01% of the population. Nausea is not a repeatable effect for the general population, but deafness is. If you make everybody deaf, your weapon doesn’t work that well.”

Sapolsky agrees: “In third world countries, illiteracy means that hearing loss could be a worse handicap than amputation. If you made everybody deaf, you’re better off killing them, better off killing women and children than sending them home blind.” Sapolsky believes that people will eventually use earplugs to protect themselves. “I’m coming in from the policy side of things, and this technology won’t get you far. It’s great for civilians and for riot control, but eventually people get defenses against them. It’s only good if you face enemies that don’t have weapons.” For Sapolsky, using acoustics raises the issue of intervention in the first place. “You should be asking whether the situation is worth doing at all. My idea? You’re going to think I’m crazy. Leave them presents, for example: On the border of North and South Korea, leave all sorts of stuff from shopping malls, stuff they’ve never seen before. Wrap it up really well so it takes a long time to unwrap. Slow them down—that’s the logic behind landmines.”