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No Place to Hide: The End of Submarine Stealth?

USS Connecticut Submarine.
USS Connecticut Submarine.

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.” 

Seawolf-class. Image Credit: Creative Commons.

The first of a revolutionary new class of fast attack submarine, the Seawolf (SSN-21). Shown during construction at the Electric Boat Division of General Dynamics Corporation in Groton, Conn. She was christened by Margaret Dalton, wife of Secretary of the Navy John H. Dalton, on June 24, 1995.

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. 

Seawolf-Class Submarine

Seawolf-Class Submarine USS Seawolf. Image Credit: Creative Commons.

“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.

Written By

Kris Osborn is the Military Affairs Editor of 19 FortyFive and President of Warrior Maven - Center for Military Modernization. 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.

8 Comments

8 Comments

  1. Mark Power

    January 26, 2025 at 12:47 pm

    Hi Kris: As the recently retired mechanical designer of the world’s most advanced MAD system, CAE’s MAD-XR, (Magnetic Anomaly Detection-Extended Role), I thank you for your article. I learned a few things I had never heard of. CAE’ S MAD-XR is a dramatic improvement over the previous bulky MAD-508 system, which weighed in, with heavy cables, at about 100 pounds, and required an EMI Capsule to mount it and shield oscillator frequencies from radiating and rendering the un-shielded sensor detectable at up to 100 miles. The new MAD-XR is much smaller and weighs only 6.5 pounds, doesn’t need an EMI Capsule, and can be used inboard on aircraft like helicopters and drones, and unlike the MAD 508 has no moving components. It has even more advanced algorithms built into its software to eliminate signatures that cannot be submarines, which are generated primarily by the aircraft carrying it.
    There is one area of MAD detection modes you didn’t mention. Seawater contains iron, and when submarine propellers stir seawater, a wake of magnetized swirling iron molecules leave a detectable low frequency signature a very long distance behind the submarine which our sensor can detect.
    The next generation of submarine detection will be in detecting gravity waves sent out by the mass of the submarine. The French have one in development and they have a virtually unlimited detection range, and will detect surface vessels at the same time. The are however two orders of magnitude more expensive at present than for example, CAE’s MAD-XR.

    Regards,

    Mark

  2. Jim

    January 26, 2025 at 12:57 pm

    Northrop years ago at an open house show and tell exhibiting a laser that bounced off metal.. detection from above through water and on.

  3. David Collishaw

    January 26, 2025 at 6:02 pm

    The soviets used to degauss their subs in Estonia to defeat the MAD detectors.

  4. scott epstein

    January 26, 2025 at 8:23 pm

    If you’d like to discuss the technology I developed which attenuateds forces that cause turbulence please contact me. I can demonstrate reduced drag and acoustic signature

  5. Robert Conrad

    January 26, 2025 at 9:30 pm

    As a retired U. S. Navy anti submarine
    warfare operator, ( AW ) non-acoustic, with over 9,000 P-3C flight hours and
    numerous deployments, it’s sure nice to hear about new MAD systems & equipment.
    I’m sure your well aware the “new” P-8 may be a configured a little different then
    the older S-2’s, S-3’s and P-3’s.
    Please keep up the great work.
    As a sensor “3,” I did have many missions
    where the MAD system was utilized.
    Those systems were rather old and probably antiquated compared to todays
    non-acoustic suite.
    I look forward to reading more.
    I doubt Mr Jerry Bruce is still around.
    If he is, and it’s not against the rules, please
    tell him I said hello.
    Respectfully submitted, Robert Conrad.
    U. S. Navy CPO, though retired.
    Stay safe…..God Bless !
    Keep after those “Ruskies” ! !

  6. Brian Hughes

    January 27, 2025 at 6:31 am

    Many years ago I read a novel set in a futuristic time, when submarines were built of ceramics rather than metal. The way they detected each other was actually ANTI-acoustic. I.e., there’s always background noise, so sensors were set to detect a ‘hole in the water,’ a place where there was no regular background noise. Interesting concept.

  7. Spuwho

    January 27, 2025 at 7:33 am

    Finally, a 19fortyfive article that was properly researched.

    There are other methods of sub detection. With the rise of real time compute power combined with digital mapping of the ocean floors, sats can relay changes in the floor profile.

    A public use of the technology is when they announce “ocean slides” or the fact their is a growing volcanic mount.

    Of course there is also the fact that the US has digitally mapped every screw made for sea faring. Its acoustic sensor nets and buoys can pick up its profile and alert.

  8. Jiminy cricket

    January 28, 2025 at 12:38 am

    This article is pure rubbish and pure propoganda designed to undermine Australia’s confidence in the Aukus sub program.

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