How Submarine Sonarmen Tirelessly Hunt For Enemies They Can't Even See

The ability to fight and win in the high-stakes game of undersea warfare is all about the art of listening. Here's how it's done.

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DoD photo by Petty Officer 1st class David C. Lloyd, U.S. Navy. (Released)

Sound analysis is a vital tool in naval operations. Sonar operators are a trained group of sailors who are responsible for managing a large amount of real-time acoustic information. They combine some natural ability with yearlong shore-based training before putting on a set of headphones at sea. The means and methods of the sonar operator’s job are one part of science combined with some individual talent to recognize acoustic patterns both audibly and visually. In this article, we will dive into what a sonar team provides the tactical decision-makers on board a vessel and how they go about providing it.

To understand how a sonarman analyzes acoustic detections, we must begin with understanding sound itself. Sound is energy moving through a medium, like water or air. It travels in sinusoidal waves radiating out in all directions from a source. These waves have both an amplitude energy level and a wavelength frequency. A sonar system will detect these waves and display them in different formats to the operator.

Editor's note: For those new to the topic, this is a very basic and brief description of a submarine's sonar. It is dated in a sort of wonderful way, but still worthwhile for a basic primer:

Sonar systems use a variety of arrays to detect energy. A single array is a group of elements that send information to the sonar beamformer. An element is a hydrophone that can be a piezoelectric device that is sensitive to sound or a more modern synthetic element that is much smaller. Smaller elements allow design engineers to add more receivers to an array while also shrinking its overall size.

The sonar array feeds data into signal conditioners like a preamplifier and equalizer. This signal 'cleaning' is carefully done by the processor so as not to strip any contact information from the raw signal. The data passes into the beamformer, where it is 'sorted' in the proper direction. Now the sonar signal is ready for display on the operator's console.

The bow sonar arrays on the Seawolf class attack submarines. In addition to these primary arrays, modern submarines feature conformal arrays and towed arrays, which all contribute to the sonar 'picture' emanating out many miles from the submarines. 

The sonar operator will analyze this signal on two general interfaces: the broadband display and narrowband display. The broadband shows the collective energy received by the array on a bearing over time in a 'waterfall' format, cascading down from top to bottom, like a digital scroll. Broadband sonar displays what areas around the array are louder than others. The sonarman can listen to each bearing and determine if the rise in background noise is a target or not. Modern sonar systems have multiple arrays displaying data at the same time in this format. When multiple arrays are involved, this requires two operators working together to manage the flow of real-time data and make tactical sense of it.

The narrowband processors take the broadband energy and divide it into individual frequencies that cross the full spectrum of the array. The array size and number of elements determine the frequency range of the information displayed. This operator must carefully investigate every bearing and every frequency from every array in real-time. Narrowband sonar displays are a collection of data pages that are examined continuously, zoomed, interrogated, and calculated for possible contact relations.

Sea environments vary greatly and have an enormous impact on sonar performance. Deep-sea oceans have unique characteristics like deep sound channels that trap noise and allow it to travel for hundreds of miles with very little loss of energy. Littoral areas have freshwater run-offs from rivers and snow melts create vertical sound barriers that reflect your own sound. It’s like sailing in a sonic hall of mirrors. Ice caps and marginal ice zones are noisy areas that can mask and reflect sonar signals from moment to moment as you pass beneath ice keels. It’s like walking through a forest blindfolded where you can only detect the tree when it’s at arm’s length.

USN via Seaforces.org

The sonar picture of the area around the platform (ship or submarine) is a tactical puzzle. Small, inconsistent, and unrelated data must be pieced together to determine if a contact is detected. Once one is, the sonar system will begin tracking the noise source for the operators. Several passive ranging techniques, speed calculation, and real-time bearing change formulas are used to generalize the target's position. In a high contact environment, this can rapidly overwhelm an operator.

To help manage the flow of information, the Sonar Supervisor stands behind the operators where they can see all the displays. They act as a second set of eyes looking for things the operators may have missed. He or she is typically the most experienced operator on the team and can help classify and localize a new detection. 

The Sonar Supervisor is the liaison between the raw acoustic data and the Approach Officer. The Approach Officer is typically the Captain, but can be any commissioned officer. The Sonar Supervisor is responsible for providing a clear picture of the real world tactical situation outside the submarine and to make sure that it matches the tactical fire control system's report. There is a team of people working the fire control computers, this is the Fire Control Tracking Party, they set the target solution. This is the solution a weapon will be given before it’s launched. The sonar supervisor has an independent solution he calculates from the raw acoustic data. He is the check between the reality outside the submarine and what the fire control tracking party believes is happening. 

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The sonar system assists in target detection and classification. Automated and manually designated threat events are preloaded into the sonar computers. If the requirements are met, the sonar display will mark the detection to bring the operator's attention to it. The automated tracking system tracks and stores contact history without operator action. When the sonarman assigns his tracker, the sonar computer already has the recent history of the target and offers it to the operator for analysis.

Let’s go through a hypothetical mission where all this comes together. Before we get underway we swing by the squadron building and pick up our package. It contains the latest weather projections for our operating area and any units that are not in port and maybe in the area. We get underway and update the sonar search plan with the probable threats we expect to encounter. 

During our transit time, we are receiving radio traffic updating us with unit locations, both NATO and otherwise, that may be in our area. We attend daily ‘Warfighter Councils’ in the wardroom where we brief the Captain about our current environment and expected encounters, if any. This is were we deconflict the operating schedule of the submarine’s mission assignments. We can’t conduct noisy evolutions on the mission, so we get that done early while underway. Intelligence updates are discussed here and changes to the sonar search plan are discussed.

Just before the mission begins, we will pull into the nearest NATO or Pacific Fleet port and pick up a fresh pack of food, drop off any trash, and most importantly pick up the ‘Spooks.’ Spooks are crypto-radio sailors who spend most of their time locked inside the radio room’s exclusion area, but are vital to mission success. The Office of Naval Intelligence will also send us two or three specially trained sonarmen to assist us in tracking and recording the mission targets from the sonar perspective. A Submarine Group or admiral’s representative will ride with us as well.

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Once on station, the sonar team manning is increased. We switch to eight hours on watch, eight hours off watch ‘Port and Starboard’ rotations. Half the 14-man sonar division is on watch at any time. This is required for recording verification, annotation, and documenting the events that are about to unfold. Each sonar operator is wearing headphones, listening to the low volume static-like white noise of the ocean. The watches are long and intense as each new update is vigorously scrutinized for detection. Patterns are matched and measured with onscreen tools and cursors. Automatic artificial intelligence algorithms flag potential targets for the sonar operators to verify. 

Target acquisition in sonar begins a series of events. Trackers are assigned to the target from every array that correlates to the detection. Initial movements are closely monitored because no one is sure how close the new contact is to their own ship. ‘Quick quiet’ is announced silently by cycling the lights around the submarine. No one moves. The engine room watch stands in place with their logs in hand. The cooks in the galley are like statues with mitten gloves and serving pans. No one moves.

Generally speaking, Sonarmen are trained to detect changes in patterns. A sharp, metallic transient object is out of place in the natural undersea world. A narrowband frequency shift or a distant active sonar can be subtle, but the experienced sailor can quickly identify these changes. These are the audio and visual cues the trained sonar operator hunts for tirelessly while on watch.

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Contact classification is done in two steps: First, the initial classification is the impression the operator gets when he first hears the target. General categories are biologics (fish and sea life), seismic (earthquakes), merchant, aircraft, trawler, warship, and submarine. It can also be a transit detection like a sharp metallic sound that is heard out of the blue or active sonar that lights up a display like it's the holidays. 

The second step in classification requires analysis. It takes 30 to 45 seconds to get a look at a new detection and discover what kind of engine she’s running, what kind of hydraulic pumps are online, and what screw blade configuration she is using. This second step is what confirms the initial classification or changes it to the correct one.

The analysis of information is a large part of the sonar team’s responsibility. Data is not just directed from the array to fire control. The experienced sonar team analyzes each detection for the contact’s characteristics. Target classification is a stepped process of assigning a general rating like biologic or merchant, then refining it into a specific classification as more information is available. The target solution begins with a general direction of motion and is improved to a particular course, speed, and range. Today's military algorithms can solve these questions quickly, but they still must be verified by the sonar team.

Just outside our submarine, our target unknowingly passes along our port side. We wait as the contact passes through CPA (closest point of approach) and opens range. During this time, sonar data is sent to the fire control computers and a solution is set. When the Captain is ready, he will order us to come around and begin to trail the target.

In the control room, the target solution is laid down on a Fusion Plot. The Fusion Plot combines all the targets from every array on a single image anyone on the Tracking Party can use to get the contact picture around our submarine. Information like detailed frequency analysis from the target’s mechanical and electrical sources are also plotted and used to help confirm the solution. Target frequencies are recorded and plotted over time. As the target moves, the frequency shifts slightly due to its Doppler effect. Watching this Doppler shift is one method sonar ‘sees’ the contact and plots its position. A well-trained team will do this without direction. Contact classification and other updates are passed over sound powered circuits that allow quiet communication between stations.

At the sonar consoles, some operators are tasked with finding new contacts. Just because we found our high-value target doesn’t mean he’s alone. In fact, he’s probably not. Few countries outside NATO operate independently. 

The hunt continues.

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Tracking contacts while searching for new targets requires a disciplined operator. Contact maneuvers, changes in the environment, and automated tracker failures must be recognized immediately as not to ruin the contact solution with false data. The search for new contacts continues while the operator ensures a solid contact track is maintained. Every direction, elevation, frequency, and automated detection must be verified on each array. Then the search cycle begins again and is repeated for up to six hours at a time. 

A sonar watch is exhausting and deserves a good shower afterward.

The intense cooperation of the sonar team and the sonar algorithms are necessary to be successful in the high data flow of today's complex sonar environments. The sea is full of noise. Fishing trawlers, long voyage merchant ships, wind, rain, tectonic and biological activity is a constant backdrop the sonar operator must use their tools to peer through the deepsea veil and find the target.

Sonar employment is a hunt. Underway, the sonar team is planning tactical positions, taking advantage of the environment and topography to catch their prey. The target knows they are being hunted. They are planning their own ambush and have a lot of the same tools we have. This hunt is also addictive and keeps sonarmen coming back for more—studying the environment, looking for that acoustic advantage that may be the difference between success and being detected. 

It’s a tactical game where the board is constantly changing. There is no procedure or checklist to follow at this point. When the sonarman dons their headphones, they must use initiative, intuition, and individual ability to execute their role within the sonar team in order to catch the target. 

This is what it’s like to hunt on a submarine.

Dominating an engagement with superior ability and tactical execution is the reward that keeps these undersea hunters coming back. Once you experience victory at sea, nothing else can give you a similar feeling. It makes the hard work in the training simulators, hours of lecture, reading, and study worth the effort. Improved knowledge and practical experience give today’s sonarmen the confidence and ability to fight and win the next hunt.

Aaron Amick is a retired U.S. Navy submarine sonarman. He served in both Atlantic and Pacific Oceans on 688 Los Angles Class Fast Attack and Ohio class ballistic missile submarines. He has published two audiobooks on Cold War-era submarines, Akula SSN Project 971 Sub Brief and USS Nautilus SSN-571 Sub Brief. Now, Aaron manages a small Patreon page and contributes to The War Zone.

Contact the editor: Tyler@thedrive.com