DARPA’s effort to track undersea life’s behavior as a means to detect enemy submarines has just entered its second phase. In the first phase, DARPA’s Persistent Aquatic Living Sensors (PALS) program sought to prove that sea life would respond to the presence of a submarine in a measurable way. With that seemingly confirmed, the second stage of the program will focus on developing sensors that can identify that behavior and relay a warning back to manned locations aboard a ship or onshore.

While the science is complex, the premise behind the PALS program is fairly simple. Undersea life tends to behave in a certain way when it senses the presence of a large and foreign object like a submarine. By broadly tracking the behavior of sea life, PALS aims to measure and interpret that behavior to make educated guesses about what must be causing it. In other words, by constantly tracking the behavior of nearby wildlife, PALS sensors can notice a significant change, compare it to a library of known behaviors, and predict a cause… like an enemy submarine, even if a submarine was stealthy enough to otherwise evade detection.

Artist’s rendering of DARPA’s PALS Program. (DARPA)

With enough data about how animals react to the presence of an enemy vessel as compared to how animals react to the presence of a large predator or more common undersea threat, PALS could serve as an early warning system when enemy subs approach.

“Because marine organisms are ubiquitous in their environments, self-replicating, and largely self-sustaining, sensing systems that use marine organisms as their foundation would be discreet, cost-effective, and provide persistent undersea surveillance with a minimal logistical footprint,” Dr. Lori Adornato, PALS’s program manager said.

Encroaching enemy submarines are extremely difficult to detect, even with modern surveillance technology. The ocean is vast, and even America’s massive Navy can’t hope to police all of it. The U.S. Navy is currently developing crewless surface ships in a variety of forms, including the ACTUV Sea Hunter. These will eventually be tasked with hunting submarines — but even with a fleet of drone ships, the Navy will still need highly effective underwater sensors to catch the attention of these vessels. DARPA’s PALS program would theoretically leverage existing wildlife to that end.

The Sea Hunter program is another sub-hunting initiative originally championed by DARPA. (DOD image)

DARPA made the following press release:

“Raytheon BBN is working with snapping shrimp for use in a passive bi-static sonar system; Northrop Grumman Systems Corporation is also working with snapping shrimp, using the snap as the input pulse for a 3D acoustic imaging system; and a third team from Florida Atlantic University uses Goliath Grouper as their biological sensor. Naval Undersea Warfare Center – Newport Division is a government partner on the program, using an ecosystem approach to determine if an unmanned underwater vehicle has passed by a reef.”

The need for a reliable means of submarine detection has grown in importance in recent years, as Russia diverts military funding toward its submersible fleet, and China continues the production of subs like the Jin-class Type 094. With China’s rapidly growing Navy posing a threat to American interests in the Pacific and Russia’s sub fleet operating in the Atlantic, the United States has a greater need for a reliable means of submarine detection than it has had at any point since the Cold War.

The Pentagon recently released a map showing the travel paths of Russian and Chinese naval vessels, alongside important undersea cables. The release was part of the Pentagon’s 2021 National Defense Authorization Act request, commonly referred to as the DOD’s budget. The map clearly shows the heavy traffic in both the Atlantic and Pacific oceans, with Russian subs encroaching on America’s eastern seaboard and Chinese submarines creeping up in the west.