The combat system of the S-80 submarines

The heart of the warrior

S-81 Isaac Peral. Source - Navantia
S-81 Isaac Peral. Source - Navantia

It is difficult to explain the complexity inherent in platforms such as the S-80 submarines. This type of programme is often compared to space programmes, partly for marketing reasons, but also to try to summarise, in a few words, the enormous number of systems and subsystems that make them up. Over the next three articles we will explain one by one the systems that, vertebrated by the Combat System, will allow the S-81 “Isaac Peral” and its twins to be among the most capable conventional submarines in the world. To this end, in this first article, we will talk about the sonar suite. Subsequently, in a second publication, we will focus on the surface sensors, communications systems, platform control and navigation systems, and countermeasures systems. Finally, a third article will be devoted to armament, as this is such a complex and controversial subject that requires specific treatment.

When a person interested in warships, and in particular submarines, looks for books that deal with the subject, beyond those that talk about tactics or tell stories of daring attacks, it is almost inevitable to come to the work of Ulrich Gabler. A German author that served as chief engineer on the design of the U-121 and U-564. Later, he devoted his career to business, founding Ingenieurkontor Lübeck (IKL), and to lecturing at the University of Hamburg, as well as to the foundation that bears his name. His book “Submarine Construction”[1] has been a bedside book for many and is still consulted by amateurs and professionals alike. However, given that this book was written in 1982, when the Revolution in Military Information Affairs was still in its infancy and at a time when submarines, although very sophisticated, were still far from today’s submarines, it fails to represent the great complexity of a platform such as the S-81 “Isaac Peral”. Neither the enormous challenge of its design. To give an example, when Gabler refers to detection systems, he includes in this category “all features that serve for the detection and identification of the opponent”.

Another illustrious author who has spoken on the subject is the British nuclear physicist and military communicator Frank Barnaby, director of SIPRI in the 1970s[2] and author of nearly a dozen books on military technology, nuclear warfare and the future of warfare. In “Future Warfare” (1985)[3] he explained that a sensor is “a device used to detect the presence of matter or energy and to determine its position. Among other things, automated battlefield sensors can be sensitive to light, sound, magnetic fields, pressure and infrared radiation”. The latter is a narrower definition than Gabler’s and also includes a fundamental concept, that of the “automated battlefield”. Hence, anticipating one of the basic characteristics of the Military Revolution we are witnessing, and whose implications were not yet clear at the time.

Gabler’s and Barnaby’s examples were not chosen at random. Both were reputable specialists in their respective fields and their statements were themselves perfectly valid at the time they were written. To be fair, one could turn to many other authors and come up with similar definitions. However, even if some of them are still acceptable today, they must be put in context, as at the time they were written, submarines – and military platforms in general – were very different from today in one key aspect: complexity.

In the case of submarines, they included only active and passive sonar, radar and optical periscopes (both observation and attack). Moreover, each of these systems acted and operated independently of the others. In contrast, the S-80 Plus includes – in addition to the above – everything from obstacle detection sonar to systems for monitoring the submarine’s own emissions, signals intelligence systems (SIGINT) and electronic warfare, not to mention communications systems. We are talking about some thirty systems and subsystems, each and every one of which permanently sends data to the Lockheed Martin and Navantia Integrated Combat System, which manages and filters them through two ARES S-80 servers and sends them to the seven multifunction consoles so that the operators who attend to them can act accordingly. In short, a set made up of kilometres and kilometres of cables and hundreds of microchips that is the result of a huge amount of coordination and integration work carried out by engineers and specialists from around twenty companies to give shape to a system that truly rivals some spacecraft in terms of complexity.

It is true that the design and construction of submarines has always been a difficult undertaking and that in each era the technologies involved were what is commonly known as “state of the art”. In this sense, there is not much difference between Monturiol’s “Ictíneo”, Isaac Peral’s “Peral”, the Nazi Type XXI or the Soviet Typhoon. However, there are aspects that have changed and are worth mentioning. This is because what not so long ago could be tackled by a relatively small group of engineers, now involves hundreds of engineers, requires advanced design software and requires programme management know-how that is not within the reach of every country. In fact, probably the most notable change between the original S-80 Programme and the S-80 Plus stems from the latter: the S-80 submarines were designed following procedures inherited from the collaboration with DCN that today would be considered archaic, while after the contracting of General Dynamics Electric Boat in 2013[4] others were imported that are much more suitable for managing a programme of this calibre. In other words, the redesign offered Navantia and the Navy the opportunity to acquire programme management and systems engineering know how that they would otherwise never have been able to acquire.

In addition to the above, it should not be forgotten that in recent years a whole series of advances have been emerging that complicate submarine design, as it is not envisaged that a new class can do without them. This is the case, for example, with everything related to electronic warfare. In the previous generation of submarines, it was rare for such systems to be included, and when they were, it was during major refits and mid-life upgrades. As a result, each new system was an add-on that operated independently of the rest and generally transmitted the information to ad hoc processing equipment and from there to a console that collected only the data from that sensor. In other words, systems integration was conspicuous by its absence, except in the commander’s head, which had to merge all the data it received from the sonar operators, what it saw through the periscope, etc. Since then, the digital revolution, the use of open architectures and the inclusion of COTS technologies[5] have made it possible for the combat systems of the most modern submarines to receive information from multiple sensors – even from manufacturers that have no relationship with the person in charge of the combat system. In addition, in relatively few years, a series of technologies have been developed and implemented, such as Big Data and Artificial Intelligence, which is essential for analysing and automating certain functions that were previously performed by human operators and which make a fundamental qualitative difference. On the other hand, detection will increasingly depend not so much on the systems integrated in the main platform – the submarine – but on those distributed among the autonomous systems that accompany and complement it, such as USVs, UUVs and even UAVs/UCAVs in the future. Finally, in just a few decades, the means of electronic warfare (EW) have been generalised and perfected, both for defence, attack and, of course, espionage (ELINT, SIGINT). This is something that can be seen perfectly in the case of the S-80 Plus class.

In other words, a submarine launched in 2022 such as the S-81 “Isaac Peral”, although it bears logical similarities in its external shape or in the distribution of the elements it houses inside with its Agosta- class predecessors, in reality they have very little in common in some key aspects, including the combat system and several of the subsystems it manages. Even simpler: on paper and in the absence of its operational life confirming expectations, comparing an S-70 series submarine with an S-80 Plus class submarine would be the equivalent of comparing a V/STOL AV- 8B+ Harrier II aircraft with one of the new Lockheed Martin F- 35B Lightning IIs.

S-Cube sonar suite.-Source-Thales
Practically all combat system manufacturers offer complete suites to their customers. In the case of the S-80 submarines, a mixed solution was chosen to meet the interests of the Spanish Navy and the Spanish defence industry, seeking to maximise independence from third parties. In the picture, the Thales S-Cube sonar suite. Source – Thales.
Kaleidoscope sonar suite, by Wärtsilä. Source – Wärtsilä.
Atlas Elektronik ISUS 100 sonar suite. Source - Atlas Elektronik.
Atlas Elektronik ISUS 100 sonar suite. Source – Atlas Elektronik.

The choice of detection systems

Before discussing the detection systems on board, the S-80 Plus class submarines and their characteristics, it is worth briefly explaining how each of them was selected, albeit succinctly. A story intimately linked to the choice of combat system and the defunct alliance with the French company DCN, but which also has to do with the needs of the Navy at a specific period and the existence of an industrial base in Spain that had to be maintained, which conditioned some decisions. On the latter, by the way, it should be said that unlike what happened with the anaerobic propulsion system (AIP) or the SUBICS combat system itself, there is no controversy whatsoever, at least in our opinion. It is true that these were not such thorny decisions and in no case could they in themselves compromise the progress of the S-80 programme as a whole.

The first thing to bear in mind is that nowadays, – although opting for a specific combat system usually requires the adoption of certain equipment -, the fact that in most cases it already operates with open architectures means that the supplier of each subsystem can be different. Thus, regardless of whether Spain opted for UDS International, Raytheon, Atlas Elektronik, Kongsberg or, as it finally did, Lockheed Martin, the tender specifications established the obligation to be able to integrate third-party sensors or communications equipment. And, of course, armament as well. This safeguard, which surely contributed to raising the final price compared to what it would have cost to purchase the complete package from a single manufacturer, had its raison d’être. Indeed, there are several arguments that justify it:

  • It maximised independence: By maintaining design authority for critical parts such as the Combat System Core (SCOMBA) and Navantia developing the Combat System together with Lockheed Martin from the one offered by the US company, the possibility of the US government or Lockheed Martin using their right of veto was eliminated. Hence, ensuring technical and industrial independence, but also what is now called “strategic autonomy”. On the other hand, with respect to the systems managed by the Combat System, by not depending on a single supplier, the Navy would no longer be subject to its conditions or to possible vetoes or limitations in the event of changes in the international arena. The reader should bear in mind that something as simple as the bankruptcy of a company – although in the defence sector it is rare for states to allow this – could have dire consequences.
  • It favoured continuity: By opting for a system with an open architecture such as SUBICS, the Navy could on paper have the best of both worlds -literally and figuratively-. It should be borne in mind that our Navy had been operating for decades with some Franco-Spanish designed components, including towed array sonars. Given that under the original schedule the S-70 and S-80 should have coexisted for quite some time, sharing some systems would allow for a less traumatic transition and even the rotation of personnel between one class and the other without the need for lengthy training courses. This could not have been done if the full suite offered by manufacturers such as Lockheed had been chosen, as it would have meant starting from scratch. Moreover, there was also no reason to do without elements that had proven to be very capable and in which Spain also had a part, which brings us to the third point.
  • It benefited the national industry: Unlike other components, such as the combat system itself or the periscopes, for which Spain depended on third parties, in many cases it was necessary to count on the participation of Spanish companies. Be they SAES, Indra, Navantia itself and all its subsidiaries such as SAINSEL (of which Navantia acquired 50% in 2006)[6] or the now defunct FABA Sistemas (now Navantia Sistemas). Of all of them, the most particular case was SAES (Sociedad Anónima de Electrónica Submarina), a company created in 1989, classified as strategic and owned by the State through SAES Capital. The latter, in which Navantia owns 51% and Indra the remaining 49%, holds 51% of the shares of SAES, the other 49% being owned by the French defence giant Thales. The decision was taken to allow the transfer of knowledge from France to Spain, but also to strengthen ties with French industry, which would thus maintain its influence over future Spanish projects. Moreover, it was the right decision, because SAES, despite its small size, has been since its origins a company with a great reputation and which has managed in a short time to open up to the international market, having an enviable position in its segment. Thus, the choice of the towed array sonar was not really a choice at all, as no other option than the SAES Solarsub S-80 was ever seriously considered. It was different in the case of the cylindrical sonar, as well as the sides and the sonar rangefinder, all of which were intimately linked to the combat system and which were ultimately proposed by Lockheed Martin, even though the latter was not the manufacturer of any of them.

Curiously, other important systems, such as some of those installed on the various masts, although they could have been put out to tender, tend to be such specific equipment and with so few manufacturers, that their choice was almost a foregone conclusion. It was therefore entrusted to the Italian company Calzoni, a subsidiary of the US company Kollmorgen Electro-Optical, which was also involved in the S-80 programme and which acquired Calzoni in July 1999.

Finally, for electronic warfare (EW) systems – and electronic espionage – the only logical choice was Indra. Another state-owned company[7] with a strong reputation in the sector, and which in recent years has been responsible for the design of many of the EW systems in service with the armed forces. Thus, the Spanish company is responsible for the adaptation and integration of the “Pegaso” electronic warfare system, which includes Signals Intelligence (SIGINT) capabilities, the Aries navigation radar and the IFF, in terms of sensors. Although we will discuss the “Pegasus” in the next article, it is important to note that it is the chosen system for the new South Korean KS-III submarines[8], which gives an idea of its quality and competitiveness.

Diagram of the SCOMBA Combat System, adapted in this case to heliborne landing ships. The versatility of the SCOMBA means that, with some adaptations, it can also be used as a base for S-80 Plus class submarines. Source – Spanish Navy.[9]
In this case, as can be seen, with a view to its adaptation to Maritime Action Ships, the SCOMBA system dispenses with some elements and adopts others. Source – Spanish Navy.

From the S-80 Programme to the S-80 Plus Programme

As explained at the beginning of the article, modern submarines include more and more sensors. Also, how they are all organised around a Combat System to which they are connected, and which is responsible for converting all the information into data that is easy to interpret by human operators and, as far as possible, relevant.

In the case at hand, that of the S-80 Plus class, it must be made clear that, although nominally the systems integrated in the current S-81 “Isaac Peral” and those contracted before the redesigns are the same, the fact is that along the way they have benefited from significant improvements and upgrades. Indeed, although it is impossible to provide exact figures given the lack of transparency of our Administration – uninterested in putting accounts on the table – none of the companies involved have stopped working in these more than ten years, which would help to explain a substantial part of the cost overruns. It should be borne in mind that, even without incorporating new components, the increase in length and weight associated with the redesign undertaken in 2013 forced a very significant readjustment in some of the detection systems.

The latter would not have affected the towed sonar or the bow sonar, which remain unchanged. However, the flank array sonar, which despite having maintained its size, due to the 10-metre increase in length thanks to the inclusion of three extra rings to compensate for weight and stability problems, has changed its position. In fact, it is placed on rings which are not the ones originally foreseen, which means that, in order to fulfil its mission with all the guarantees, it has had to undergo numerous tests and calibrations[10]. The same applies to the ONMS (Own Noise Monitoring System), which is responsible for monitoring the submarine’s own emissions. Given that this is a much larger vessel than the one originally designed, this system, which is the responsibility of SAES, has had to undergo a major adaptation process. This is due to the fact that the cavitation tendency of the S-80 Plus or the relative position of the propulsion to the ONMS hydrophones has changed along with the size of the submarine. In addition, it should not be forgotten that between the initial entry into service date (2012)[11] and the provisional delivery date to the Navy (February 2023)[12] there is a gap of more than a decade. A time in which the foundations have been laid for a Military Revolution which in the case of submarine warfare is reflected in the incorporation of key processing technologies for analysing submarine signals and classifying them.[13]

In other words, although there is continuity between the programmes and even if the change of name may appear to be a publicity stunt, it hides an important undercurrent of reality.

Librascope’s Loral SUBICS-900 system is the direct predecessor of Lockheed Martin’s SUBICS which equips our S-80 Plus. Source – Librascope.
Proposed multifunction consoles for the Librascope SUBICS-900. In the case of the S-80 Plus, it was decided to integrate the CONAN SUB consoles from the Spanish company SAINSEL. Source – Librascope.

The Integrated Combat System

The Integrated Combat System of the S-80 Plus class submarines is the true “heart of the warrior”, hence the title of this chapter. A prodigy of integration, computing and redundancy designed not only to perform all the functions of sensor fusion, information organisation and control of each subsystem, but to do so in virtually any condition, even if the ship has suffered major damage.

It is well known that the Combat System Core (ICSC), i.e., the hardware and essential lines of code, is a development of the former FABA Sistemas (currently Navantia Sistemas). The qualification tests of the first version of this ICSC, called “VC 9.0 SCA”, were carried out in the summer of 2021. Thanks to having opted for a national solution, it shares many elements in common with the rest of the SCOMBA systems (Sistema de COMbate de los Buques de la Armada), starting with the two ARES servers or process cabinets and continuing with the CONAN screens (in this case CONANSUB) of Sainsel. This allows for maximum synergies and compatibility, as well as interoperability with other ships and systems in use by the Spanish Navy.

Therefore, the ICSC provides the Combat System’s set of weapons and sensors with a high level of integration that enables optimal use of operational and command and control centre information. This in turn makes it possible to acquire, evaluate and present all the information necessary for offensive, defensive or intelligence actions, including control of the weapons and countermeasures to be used and their delivery devices.[14] To ensure that all of the above becomes a reality, the Combat System has been equipped with the capability to acquire and track multiple targets in different scenarios, which can be managed simultaneously:

  • Active and passive sonars with short, medium and long range, for exploration, attack and navigation tasks;
  • Electronic, optronic and electromagnetic detection systems for combat missions or intelligence operations;
  • Navigational aids;
  • An integrated communications system, including satellite link and tactical data link with other naval units via Link-11 and Link-22 and;
  • Weapon systems, including submarine-launched anti-ship missiles (although not currently integrated), heavy multi-purpose torpedoes and naval mines.

Of course, this involves integrating a whole series of systems that differ significantly from those found on board a frigate or an amphibious ship, since the main part of its mission is below the surface. Thus, although the SCOMBA system – whose origin is, by the way, in the AEGIS Combat System and also from Lockheed Martin – has served as the core of the Integrated Combat System of the S-80 Plus, the latter has a number of specific features and a very different heritage from that of the Spanish Navy’s surface vessels.

It is also known that just a few months after its birth in 1995, Lockheed Martin acquired the defence electronics division of Loral Corporation in a multi-million-dollar deal. The latter, in turn, had acquired Librascope in 1992 from the Armenian-born speculator Paul Bilzerian, whose activities were bizarre to say the least and who at the time was serving a prison sentence in Florida. The purchase of Loral would eventually serve Lockheed Martin to strengthen its submarine systems business line by building on Librascope’s decades of experience in the design and production of combat systems. Among these, the LORAL SUBICS-900, whose acronym SUBICS (SUBmarine Integrated Combat System) will no doubt be familiar to us and is obviously behind the one used by the system installed in our S-80s, as it is the source from which Lockheed Martin drew for its subsequent developments.

In our case, given that it was necessary to integrate many elements that would not be provided by Lockheed Martin and that Spain wanted to retain design authority, important modifications were made to adapt it to the particular needs of the Spanish Navy. As guidance, we provide the reader with this diagram showing the architecture of the Integrated Combat System of the S-80 Plus submarines, which we have translated into Spanish from a Navy slide shared by IDS in a webinar. Note the similarities with the SUBICS-900, but especially the greater degree of complexity of the Spanish system.

Systems and subsystems controlled by the Integrated Combat System of the S-80 Plus class. Source – Own elaboration from a Navy original published by IDS.

In this way, in addition to software changes, the S-80 Plus Combat System makes use of numerous proprietary components, starting with:

  • Two “ARES S-80” servers: the real nerve centre of the ship, as they not only receive the information from all the detection, communications or weapon and platform control systems, but also run the software that makes up the core of the Combat System and are responsible for processing and distributing the entire data flow.

Since all this information is of no use if it is not made available to the operators of the various systems and the commander in the appropriate format, the control room and various rooms of the S-80 Plus have seven multifunction consoles, two consoles for ship steering and platform control and a large tactical display, as well as various multifunction terminals to do this. Some have purely tactical functions, while others provide the status data of the platform itself. Among these displays and consoles, we find[15]:

  • Large Tactical Display: Presides over the submarine’s control room and provides data on cartography, the submarine’s position, contacts in the immediate vicinity, etc. Simply put, it provides a summary of the most relevant information presented on the multifunction consoles.
  • Seven Multi-Function Combat System Consoles (CONAM SUB or MFCC): Provide an operator working environment combining graphics with sensor information to perform command and control tasks.
  • Multifunction Repeater: rugged units that include the necessary hardware and software to function as a programmable multifunction display connectable via Ethernet to the various displays and provide important information not in the control room, but in various parts of the vessel, e.g., on start-up, drift and dive.
  • Digital Mapping Server: Exports the various types of decrypted navigation charts for use by the Combat System or, more precisely, the ICSC.

The screens are the visible face of the system, the element that allows all the data to be represented in such a way that the operator can understand them and if possible, without seeing his attention diverted by irrelevant information. Nevertheless, or this to be possible, several key elements are needed, which have been entrusted to the Spanish company SAES:

HMI – Human Machine Interface

The first of these is the graphic interface (HMI – Human Machine Interface) of the sonar array of the S-80 Plus class submarines and other related systems (Stimulator Simulator, Classification, Self and Radiated Noise Detection…) whose data are represented on the submarine’s multi-function consoles. This interface allows the integration of all acoustic and non-acoustic information and its presentation to the operator in a coherent and structured way. To achieve this, SAES has been participating in the integration of all the sonar systems, of course, but also in that of the submarine navigation systems, the C4 equipment (Radar, Electronic Warfare, Periscopes…), the weapons system, communications, the development of systems to aid decision making and command of the vessel and those related to signal processing, among others.

The graphical interface is displayed via SAINSEL’s CONAN SUB consoles. Source – Sainsel.

SICLA (Acoustic Classification System)

Based on multiple and simultaneous contact analysis, graphical tools and an acoustic intelligence database (ACINT), it allows the operator to quickly and accurately obtain the classification of the contact. According to the company’s engineers, SICLA has a great flexibility of adaptation to different applications, both to meet different operational needs and to allow the implementation of new functionalities. Hence, being able to achieve various levels of communication and/or integration with other systems, depending on the requirements of the Combat System. Operating with SICLA ensures uniform levels of detection and classification over time. It should be borne in mind that, unlike the early days of sonar use, in which the analysis and classification of acoustic signatures depended on the operator’s ear, today there are huge databases fed both by the acoustic signatures collected by the submarine itself and by information from other Spanish Navy vessels or even from allied navies, with which information is shared. For the recognition and classification of the signals, which are mostly extracted by passive sensors (side and towed sonar) in the low frequency range, it generally works by recognising patterns, so that the information collected – and we are talking about thousands of sound sources – is translated into numerical or symbolic values that the classification system recognises and sorts.[16] In this way, the classification function is performed by means of a visual presentation of the processed signals and by interactively comparing them with a library of signatures called the ACINT Contact Database (ACINT CDB) stored in SICLA itself. In the case of the S-80 Plus class, the system is fully integrated within the submarine’s ICSC. It has been designed to provide the following Sonar System operation aids:

  • To provide a computerised, interactive, contact classification tool with the highest level of confidence in the shortest possible time.
  • Obtain maximum performance, in terms of detection range and sonar tracking capability, especially in particular operating conditions such as: weapons employment, snorkelling and combined unit work.
  • Equalise Sonar performance, increasing operator experience and training.
SICLA is able to obtain data from any of the acoustic detection systems installed on the submarine. Moreover, based on the data in its library, classify them to determine their typology and provide the sonar operator with valuable information about the source of the sound. Source – SAES.

SEAPROF (Submarine Acoustic Environment Modelling System)

This is an acoustic performance prediction system developed by SAES based on the RAM and BELLHOP sound propagation models, validated and tested by SAES with the collaboration of NURC (NATO Undersea Research Center). Furthermore, this is the second generation of SAES acoustic performance systems installed on board the Spanish Navy’s submarines, as they follow in the footsteps of those installed on the Agosta class. In the case of the S-80 Plus, SEAPROF is fully integrated in the ICSC and its function is to allow the calculation of ray tracing, 2D and 3D sound propagation losses, sonar figure of merit (FOM)[17], detection and counter-detection distances and detection probabilities. The main objective of the system is to provide a user-friendly tool to predict both the sound propagation in highly detailed scenarios and to evaluate the behaviour of the different sonars of a Combat System against any kind of underwater or surface threat.

If all of the above could be considered the mortar that gives consistency to the whole, and which is vertebrated by metres and metres of fibre optic cable that reaches from the servers to the last of the sensors inside and outside the pressure hull, it is of no use without the associated subsystems.

Of all of them, which you can find in the following diagram, in this first article the focus will be solely on the sonar suite. After all, it is the most important, because without detecting the enemy before he does the same to us, great weaponry, a huge immersion range or the best electronic warfare systems are of no use.

SEAPROF system components. Source – SAES.

Sonar Array Suite

If the Combat System is the brain of the submarine, the senses, at least the most important ones, correspond to the various sonars. Submarines, unlike surface vessels, are completely “blind” when they navigate in submerged conditions -unless they do so at periscope level.

The only way for them to know what is going on around them, i.e., to have some situational awareness, derives from the inclusion of an increasing number of sonars. These devices are used to detect other vessels, whether surface or underwater, military or civilian, to locate obstacles or even to measure their own emissions. Only in this way is it possible, firstly, to navigate safely. Secondly, to do so discreetly, so that our presence is not discovered by other enemy submarines, warships or – if possible – maritime patrol aircraft. Last but not least, the assigned missions, whatever they may be, must be accomplished. For these, discretion provides an essential tactical advantage and allows them to be carried out with a certain degree of security, while the ability to detect the other side before it does the same to us makes it possible to attack while maintaining surprise. In the case of the S-80 Plus class, the different sonars are as follows:

SOLARSUB S-80 DTAS & TAHS (Digital Towed Array Sonar & Towed Array Handling System)

As explained above, Spain already had significant experience in the design, production and life cycle support of towed sonars. In this case, the DTAS SOLARSUB S-80 is already the third generation of towed digital passive array sonar (DTAS) developed by SAES. Its predecessors were previously installed on board the S-70 submarines of the Spanish Navy, so the experience of our submariners in its use is important. On the S-80, however, it has been installed and integrated into the ICSC using a TAHS deployment and collection system that is also the responsibility of the Murcian company. The SOLARSUB S-80 is made up of the following elements:

  • Digital Towed Sonar (DTAS). This sonar is composed of three basic units:
    • Towed Antenna Unit (Unidad Antena Remolcada, UAR)
    • Signal Conditioning Unit (Unidad Acondicionadora de la Señal, UAS)
    • Operator’s Console Unit (Unidad Consola del Operador, UCO)
  • Towed Array Handling System (TAHS), whose integration tests were completed in 2017[18] and which in turn contains:
    • Winch Unit (Unidad Chigre para despliegue y recogida, UCDR)
    • Custom Unit (Unidad Adujadora del DTAS, UAD).
    • Cutter Unit (Unidad Cortadora del DTAS, UCD).
    • Enhancement Water Pump Unit (Unidad Bomba de Agua para mejorar el despliegue del DTAS, UBAD).
    • Deployment and Collection Unit (Unidad de Despliegue y Recogida del DTAS, UDRD).
  • Winch Control Unit (Unidad de Control del Chigre, UCC).

As far as the Digital Towed Sonar (DTAS) is concerned, the Towed Antenna Unit (TAU) contains the hydrophones that pick up the signals from the contacts to be detected. Remember that this is a passive sonar, so it does not emit any signal, but picks up the signals that other ships or submarines (and, of course, marine fauna) leave in their wake.


These signals are digitised in the Towed Antenna itself and sent to the Signal Conditioning Unit (UAS), which is located inside the submarine and is responsible, on the one hand, for feeding the hydrophones of the UAR Antenna. On the other hand, for collecting the digitised signals from the hydrophones, sorting them and sending them to the Operator Console Unit (UCO), which receives the digital signals from the UAS and processes them, thus presenting the detected contacts to the operator. The main objectives of this DTAS towed sonar are, among others:

  • Increase the submarine’s effectiveness capabilities in terms of surveillance, detection, tracking, analysis and classification assistance.
  • Avoid submarine noise.
  • Detect at low frequency.
  • Perform triangulation with other sensors on board due to its position being far away from the submarine.
  • Detect surface contacts.
  • Obtain acoustic intelligence.
  • Assist in conducting Target Motion Analysis.

Regarding the Towed Array Handling System (TAHS), the winch unit (UCDR) has the function of adducing the Towed Antenna (UAR) by means of the Customs Unit (UAD). To prevent entanglement or any other problem from compromising the safety of the vessel, in the event of an accident, the Cutter Unit (UCD) has two blades that act out of phase with each other to safely cut the antenna. It may seem unnecessary, but given historical examples, the possibility of the very long antenna cable getting caught in the propeller of another submarine[19] or surface vessel[20] cannot be ignored. For its part, the Water Pump Unit (WBU) allows the UAR to be deployed, using water as a lubricant, and assisted by the Deployment and Recovery Unit (UDRD), which has a belt operating under pressure that pulls the UAR. Finally, the whole system is powered and synchronised by the Control Unit (CCU), located inside the resistant hull of the submarine.


As for the DTAS Towed Antenna (UAR), a couple of clarifications are in order. Firstly, it is a system that can be operated, as on the S-80 Plus, by means of the TAHS (S-80 submarines) Deployment and Collection System, but it can also be installed as a clip-on type, as was done in its day with the S-70 class. The UAR Towed Antenna consists of the following modules from stem to stern:

  • Un Módulo de Estabilización de Cola (MEC)
  • Un Módulo Antena Acústica (MAC)
  • Dos Módulo Cables de Remolque (MCR)
  • Un Módulo Caja de Juntas (MCJ) (Solo para el tipo Clip-on)
Basic characteristics of the TAS towed antenna. Source - SAES.
Basic characteristics of the TAS towed antenna. Source – SAES.
Diagram of the TAS & TAHS assembly. Source – SAES
Diagram of the TAS & TAHS assembly. Source – SAES

Flank Array & Passive Ranging Sonar (FASLPRS)

A responsibility of the US Lockheed Martin, flank sonar is, like towed sonar, a passive system. The first thing to clarify is that the inclusion of this type of system is relatively new. Previously, submarines had only bow sonar and, at best, a bow sonar and a towed sonar. However, the bow sonar has certain limitations due to, among other things, the position in which it is installed, while the towed sonar cannot be used in all conditions, such as in coastal areas.

This is why hydrophone arrays began to be installed on the submarine flanks, making use of a substantial part of them. In fact, this is one of their main limitations, since the longer the length, the greater the number of hydrophones that can be installed. In the case of the S-80 Plus, -for unknown reasons and which have not been made clear to us, but which are probably monetary -, it was not decided to extend the length of the FASLPRS, which remains at 27 metres, thus increasing its sensitivity. Compared to what is possible with the towed antenna, which is several hundred metres long, the aperture of this sonar is rather limited. Nonetheless, more than sufficient for most situations where the use of the TAS is not required. On the other hand, TAS and FASLPRS can be used in unison, creating a passive array with a much larger aperture than if they were used individually[21]. In the case of this system, there is hardly any information available, not even for US Navy submarines. The only system that could be linked to is the AN/BQG-5 installed on the Los Angeles-class SSNs, designed in 1995 by Loral[22] , which has already been discussed in the history of the S-80 Plus Combat System.[23] Henceforth, the US Navy changed its approach and for the Virginia-class SSNs they turned to competitor systems, specifically the Light Weight Wide Aperture Array (LWWAA)[24] from Raytheon. Interestingly, the last recorded delay in the programme announced on 12 November was reportedly related to this system, although officially due to “Combat System adjustments”.[25] Apparently, although this has yet to be confirmed and the information must be treated with caution, it seems that it has suffered a corrosion problem that must be rectified in dry dock. This has therefore forced the first dive of the S-81 “Isaac Peral” to be delayed until January.

The following computer graphic shows perfectly the location of the flank sonar, from a few metres behind the bow dome to a little further behind the sail. Source - Navantia.
The following computer graphic shows perfectly the location of the flank sonar, from a few metres behind the bow dome to a little further behind the sail. Source – Navantia.

Cylindrical Array Sonar (CAS)

Also responsibility of the American company Lockheed Martin, this is a dual system (active/passive) capable of both detecting emissions from the environment and launching pings that are analysed on their return once they bounce off the surrounding vessels. As with the rest of the Bethesda giant’s systems, there is little public literature. Indeed, for this particular system the gaps are even greater, as the CAS was not built by Lockheed Martin, but by another company, EDO Corporation, which specialises in this type of product. EDO Corporation is now part of L3Harris, but around the same time as the S-80s were being built, it went through some turbulent years.[26] Founded Edo Aircraft Corporation in 1925, it became a defence contractor during World War II and diversified even further during the Cold War,[27] eventually creating a subsidiary specialising in submarine warfare. Among the flagship products that would be directly related to the cylindrical sonar of the S-80 Plus are the AN/SQS-53C hull sonars of the US Arleigh Burke destroyers, which are fitted as part of the AN/SQQ-89 anti-submarine suite[28] even though these are surface-based. In any case, despite the lack of documentation, given the references, there is every reason to believe that the cylindrical sonar characteristics of the S-80 Plus are more than adequate. Furthermore, tests on this fundamental system were completed in 2009, as it was a relatively mature system by then, although it has since been upgraded. The brackets and fairings were supplied by Goodrich.

S-80 Plus class cylindrical sonar. Source - Lockheed Martin.
S-80 Plus class cylindrical sonar. Source – Lockheed Martin.
S-80 Plus class cylindrical sonar during testing at Salt Lake. Note that it does not have all its elements connected. Source - Lockheed Martin.
S-80 Plus class cylindrical sonar during testing at Salt Lake. Note that it does not have all its elements connected. Source – Lockheed Martin.

Acoustic Intercept Sonar (AIS)

Developed as well by the American Lockheed Martin, it is responsible for intercepting active enemy sonar signals – i.e., pings sent by the sonars of other ships – as well as carrying out directional and identification operations, mainly used to detect both hostile vessels and submarine weapons. Since many torpedoes already use an active seeker on the bow, the AIS can detect the emissions from the seeker. From this, it determines the course and speed of the torpedo and thus the time to impact, so that evasive manoeuvres can be carried out or countermeasures can be launched at the appropriate time.

Inside the S-80 Plus Tactical Simulator (SIMTAC). Operators receive information from each of the systems through Sainsel's 7 CONAN SUB consoles, including data provided by the AIS. Source – Spanish Navy.
Inside the S-80 Plus Tactical Simulator (SIMTAC). Operators receive information from each of the systems through Sainsel’s 7 CONAN SUB consoles, including data provided by the AIS. Source – Spanish Navy.

Mines Obstacle Detection Sonar (MODS)

Also provided by the Bethesda giant, the MODS is located at the bow, slightly above the cylindrical sonar and is capable of detecting very small objects at short distances, due to its greater definition. The main function, as its name suggests, is to provide safety for the submarine itself during navigation, avoiding contact with mines, be they of any kind (bottom, drifting, mooring…) or objects that could get in the way of navigation, posing a danger, such as a drifting container, a wreck or anything else that does not appear on the charts.

Computer graphic showing the layout of the main systems that make up the S-80 Plus class submarines. Author – HI Sutton.

Own Noise Monitoring System (ONMS)

Another primary system that has been entrusted to the Spanish company SAES. It provides the Combat System with alarms and levels for the control of the ship’s noise and vibrations, the maintenance of its acoustic signature and the cancellation of its own noise in the sonars. In this case, the ONMS installed on the S-80 Plus submarines is a third-generation system and, therefore, more modern, and capable than, for example, those installed on the Spanish Navy’s Segura-class minehunters, which use an equivalent, but second-generation system.

As its name suggests, the ONMS can provide the submarine’s operators and commander with an estimate of the noise radiated by the vessel itself. This is thanks to the fact that it constantly measures:

  • Vibrations and ship hull noise generated by noise sources whose vibrations are transmitted throughout the ship, such as machinery, thrusters, cavitation, main engines, auxiliary generators, refrigerators, air conditioning, transients, etc. These vibrations are measured by accelerometers strategically distributed along the vessel’s structure.
    • Outer hull noise in specific areas where the external noise source is of major importance such as dynamic flow noise around the hull or thruster cavitation noise.
    • The noise generated around the hull of the submarine, caused by hydro- dynamic flow or mechanical elements installed on the outside of the hull strength, by means of hydrophones installed between the external hull and the hull strength of the submarine.
    • The noise generated by the submarine’s propulsor and in particular cavitation, measured by specific hydrophones and accelerometers installed close to the propulsor.

Accordingly, whenever the ONMS detects something out of the ordinary, i.e., out of the parameters it has programmed or that have been set by its operator, it automatically sends noise alarms to the Combat System and provides the vessel’s sonars with information for own-noise cancellation. For this purpose, the ONMS works integrated with the Combat System, being controlled from one of the seven multi-function consoles. Thus, each of the information sent by the acceleration sensors (accelerometers) to measure the vibration of the ship’s hull and noise sensors (hydrophones) to measure the noise radiated on the external hull are digitised in the Acquisition Units (AU) and sent to the Operator Control Unit (OCU), through the Distribution Units (DU), for processing, noise monitoring and supply of information to the operator and the Combat System.

Regarding the accelerometers, they are distributed inside the hard hull for the purpose of providing continuous measurement of hull vibrations. On their part, hydrophones are installed between the hard hull and the outside of the submarine for the purpose of providing continuous measurement of radiated noise in areas not covered by the accelerometers. In the case of cavitation hydrophones, they are placed outside the outer hull and near the stern of the submarine to monitor propellant noise, especially to trigger alarms when cavitation is detected.

The Acquisition Units (AU) are responsible for feeding the sensors connected to them, digitising the signal from these sensors (at 32 KHz sampling rate) and transmitting them via the Distribution Units. These units are different for accelerometers or hydrophones, due to the differences in connection and adaptation between the two types of sensors, but the rest of their functions and connection with the ONMS are the same in both cases. Finally, the Distribution Units (DU) are responsible for powering the AUs and distributing data to the Operator Control Unit (OCU), where the signal processing (DSP, Digital Signal Processing) and human interface (HMI, Human Machine Interface) are performed.

On the other hand, the ONMS has a second function that is rarely addressed. It serves as an extra tool for maintenance, monitoring the effectiveness of the vibration dampers or any event that allows anomalies to be detected in the operation of the machinery, thus forming part of the predictive maintenance system of the S-80 Plus. The operating principle is simple in this sense, since under optimum conditions, elements such as the transmission should generate a certain level of noise at certain frequencies. If a higher noise level or anomalies of any kind are detected, this indicates the presence of parasitic vibrations, degraded parts, or problems of some sort. Thanks to the sensitivity of the system, these can be detected before they fail and  remedial action can be taken. It therefore results in improved maintenance and cost savings and avoiding mission-threatening breakdowns.

The following figure shows an overview diagram of the physical components of the ONMS for a submarine, including accelerometers and hydrophones. Source - SAES.
The following figure shows an overview diagram of the physical components of the ONMS for a submarine, including accelerometers and hydrophones. Source – SAES.


The S-80 Plus class Combat System will ultimately be the element that will allow these submarines to stand toe-to-toe with the world’s best upon entry into service. Regardless of whether the AIP is not installed for some years, whether it is replaced or supplemented by lithium batteries in the future, the youth problems that there will undoubtedly be and any other factor, the S-81 “Isaac Peral” will be equipped with first-class sensors.

Among all of them, the sonar suite is the main component. A suite provided by SAES and Lockheed Martin that has sufficient arguments to be confident of the good performance of these submarines in any conditions, ensuring both the ability to detect potential enemies at great distances – thus making the most of the weaponry – and the discreetness itself, thus maximising security.

Finally, and fortunately for Spain, a substantial part of the components discussed in this article are in-house developments, in what was one of the best decisions taken during the initial stages of the S-80 programme. This last point is important, because although the S-80, as a platform, may never be an export success the possibilities in the international market do not end there, as we explained when discussing the industrial impact of the programme[29]. In this vein, there are several SAES or Indra products that are already achieving success abroad. Therefore, they are opening a path that we as a country cannot abandon, which also makes it necessary to give continuity to the S-80 Plus series.

Bibliography and sources

[1]  Gabler, U (1982) Submarine construction. Madrid. San Martín.


[3] Barnaby, F (ed.) (1985) La guerra del future. Madrid. Debate.



[5] Commercial off-the-shelf in reference to commercial components. A good example of this is the SCOMBA PC system simulators, which allow Spanish divers to be trained with little more than a desktop computer and slight adaptations. See: (p. 2-3).










[14] del-submarino-s-80



[17] The Figure of Merit (FOM) of the sonar is the maximum value of loss that a signal can suffer while maintaining a 50% chance of being detected.














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