Key Points and Summary: Advances in non-acoustic submarine detection could undermine traditional stealth advantages. Technologies exploiting magnetic field disturbances, bioluminescent organisms, submarine-generated waves, thermal anomalies, and laser detection offer adversaries new tools to detect submerged submarines.
Key Point #1 Magnetic anomalies reveal metal-hulled subs, while boundary-layer effects trigger detectable bioluminescence. Surface waves generated by shallow-depth or high-speed transit and temperature changes also present new vulnerabilities. Blue-green laser detection, capable of penetrating seawater and reflecting off subs, might become the most potent non-acoustic method.
Key Point #2 – These emerging threats may significantly influence submarine design and tactics, forcing navies to evolve their undersea warfare strategies in response to improved detection capabilities.
Are Submarines Losing Their Stealth? How New Technologies Could Detect Subs
Acoustic systems have driven detection, innovation, and new generations of quieting technologies in the undersea warfare realm for decades, as they have become more precise, better networked, and extended range.
In recent years, the US Navy has made significant progress in developing emerging technologies capable of capturing higher-resolution images and connecting manned submarines to drones and unmanned underwater vehicles.
Innovations in this area are a key part of why the US Navy has continued to operate with what many regard as undersea superiority, a tactical and strategic advantage too large and significant to calculate.
Unlike surface ships or aircraft, more easily detected by satellite surveillance, enemy radar, and line-of-sight detection technologies, submarines can quietly and secretly lurk in high-threat areas to hold enemies at risk without being easily detected.
No More Stealth Submarines?
Sonar systems and acoustic detection will likely be here for decades into the future, yet a series of non-acoustic detection technologies may be changing this equation.
A significant essay from the Navy Submarine League called “Non-Acoustic Means of Submarine Detection” analyzes several key non-acoustic detection measures that are improving rapidly and are likely to be implemented by potential adversaries.
One central area of exploration relates to detecting disturbances in the earth’s magnetic field, something devices can measure.
“As a large piece of ferrous metal, the steel-hulled submarine causes a local disturbance in the earth’s magnetic field,” the essay explains.
Significantly, the essay explains that if a submarine is built with “non-magnetic” materials, its signature is decreased but not eliminated entirely.
“Submarines contain a large amount of metal that becomes magnetized in the course of normal operations. The permanent magnetic field associated with the submarine remains until active measures are used to demagnetize it,” the Naval Submarine League essay explains.
The U.S. currently deploys two types of MAD equipment on its ASW aircraft. The essay says these systems can detect the submarine magnetic field at no more than a few thousand feet.
Boundary Layer Water Flow
But other threats to the submarine are also possible. There are “bioluminescent” organisms beneath the sea that generate a natural “light,” something submarines can detect. This detection possibility is caused by “boundary layer” phenomenology, referring to the water flow surrounding a moving submarine. This water movement generated as the submarine transits the undersea realm can also generate movement of undersea organisms, including ones that create detectable light.
“These organisms can generate light when they are physically stimulated in the boundary layer of a submarine or in its wake. This phenomenon has been studied as a method for detecting submarines from the air or space,” the essay explains.
Wave Submarine Detection?
Another method of non-acoustic detection pertains to somewhat self-evident or easily observable variables such as “submarine-generated waves on the surface of the Ocean.”
When submarines move at shallow depths or travel at high speeds, they generate detectable surface waves. However, larger wind-generated surface waves can obscure or hide these waves.
Internal waves of great significance generate surface signatures that are not visible to the human eye. Radar systems, however, can detect some changes in moving surface water generated by undersea oscillations and water movements caused by submarines.
However, much like surface wind, there are many reasons why water can move beneath the surface, so there are also some limitations to this kind of detection method.
Temperature Submarine Detection?
Also, not surprisingly, thermal sensors can detect small changes in the water temperature caused by submarine movements.
Like how an infrared sensor would detect a heat signature emitting from an enemy fighter or engine vehicle, temperature-detecting technology can quickly discern differences likely to indicate the presence of a submarine.
“A moving submarine may also change the temperature of the sea surface by mixing lower cooler water with upper water, thereby leaving a trail of cool surface water that could be detected with infrared (heat) sensors,” the essay says.
Laser Detection
The Navy Submarine League essay further explains that “laser detection” may emerge as the most promising area of non-acoustic submarine detection.
Overall, electromagnetic signals have little ability to travel underwater except in some “ultra-low-frequency” waveforms.
Yet, the sea is “transparent” to blue-green light, which electromagnetic light “pings” from a laser can detect.
“The sea is relatively transparent to blue-green light. A burst of blue-green laser light could penetrate the sea, reflect off an object, and return to the sensor. The round-trip travel time of the laser burst indicates the depth of the object, but cannot discriminate, for example, between a large whale and a submarine,” the essay says.
Since the speed of light is a known or fixed quantity, and the length of travel time can be determined, algorithms can then discern the exact distance of an object. The travel time can be determined like a laser rangefinder on land.
Once the exact travel speed and time are known, an algorithm can quickly calculate the distance. In these cases, a blue-green laser light might be able to “see” or “find” a submarine at specific depths.
About the Author: Kris Osborn
Kris Osborn is the Military Technology Editor of 19FortyFive and President of Warrior Maven – Center for Military Modernization. Osborn previously served at the Pentagon as a highly qualified expert in 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.
