Imagine a small recon unit of Army soldiers was advancing through hostile terrain on a high-risk scouting mission to find points of entry for a major follow-on armored ground assault. What if it was suddenly hit, even overwhelmed, with a massive array of enemy small arms fire? The soldiers take casualties, run for cover and immediately engage the enemy, yet the attackers are obscured from view. Where exactly is the enemy fire coming from? What if soldiers could immediately know the source of incoming fire?
Perhaps a sniper is, by design, hidden in leaves, brush or other kinds of camouflage? Wouldn’t it be useful to destroy the attacker before more soldiers were hit? If a small area of attacking fire were precisely identified, perhaps the recon unit could call for immediate air support to blanket the enemies with suppressive fire from above?
These prospects are now a reality.
Traveling at supersonic speeds, a bullet exiting a gun barrel generates acoustic “shock waves” propagating through the air from the tip of the projectile, producing a sound “signature” which can be detected by specially engineered sensors, according to Raytheon BBN engineers.
This technical process, simply put, saves lives as it enables soldiers to instantly know the exact location of incoming enemy small arms fire, offering an opportunity for a precise and lethal counterattack amid high-intensity combat. A technology which does this, made by a Raytheon subsidiary called BBN, already exists and has been deployed with U.S. Army soldiers. It’s called Boomerang, and a set of six different sensors can instantly find the source of incoming bullets from moving vehicles and stationary locations.
“The way a shock wave works is it generates and propagates at the speed of sound. While the bullet is moving, a stream of waves comes off the tip of the bullet that propagates through the air. From six sensors I can locate exactly where it came from,” Brad Tousley, President at Raytheon BBN, told Warrior in an interview.
Now part of Raytheon, Boomerang-maker BBN began with innovative ideas from three MIT professors who envisioned a way to engineer these kinds of advanced acoustics years ago.
“As a bullet travels down range, it generates a shock wave. The sensor locates the shock wave from the muzzle blast and the shock wave from the bullet,” Tousley added.
A second variant of the technology, called Boomerang II, can locate enemy fire from moving vehicles by using sensors on top of the vehicle and small sensor box processor compartment underneath the passenger side or rear of the vehicle. The acoustic signature is converted into a small 5-inch by 5-inch display providing audible warning of shots fired. A Warrior X variant is carried by an individual soldier, wherein sensors and processors are worn by the soldier.
“As the source of sound, a shock wave travels through free space. A sensor detects it and converts the acoustic energy into an electrical signal. We have a set of algorithms that know where the sensor is located and we take the data feeds from those sensors and fuse those...convert those into an algorithm which is fed into a processor,” Tousley explained. “The shock wave expands as a cone behind the bullet, with the wave front propagating outward at the speed of sound.”
Interestingly, Tousley’s description of the sensor analysis of supersonic shock waves aligns with a 2006 Montana State University essay written about acoustic gunshot detection, which explains that shock-wave detection is more accurate than purely tracking a muzzle blast.
“The supersonic projectile causes an acoustic shock wave that propagates away from the bullet’s path. The shock wave expands as a cone behind the bullet, with the wave front propagating outward at the speed of sound,” the essay, called “Modeling and Signal Processing of Acoustic Gunshot Recordings,” states.
Extending its analysis, the essay explains that a muzzle blast alone is not necessarily as reliable source for analysis.
“For most firearms the sound level of the muzzle blast is strongest in the direction the barrel is pointing, and decreases as the off-axis angle increases. The blast may also be obscured by barriers and other obstacles blocking the direct path between the firearm and the microphone location,” Maher writes in the essay.
Also, Maher makes what might be a lesser known point, that an acoustic suppressor such as a silencer might remove or decrease a muzzle blast, yet not interfere with the shock waves described by Maher and Tousley.
Kris Osborn is the new Defense Editor for the National Interest. Osborn previously served at the Pentagon as a Highly Qualified Expert with the Office of the Assistant Secretary of the Army—Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at national TV networks. He has appeared as a guest military expert on Fox News, MSNBC, The Military Channel, and The History Channel. He also has a Masters Degree in Comparative Literature from Columbia University.