F-110 frigates’ anti-submarine capabilities

The F-110 frigates have the difficult mission of replacing the F-80s, which have provided such a good service, giving back to the Armada some of the anti-submarine capabilities that we have neglected for decades. To do so, they are relying on an anti-submarine suite provided by Thales and SAES, which includes top-level equipment on a par with navies such as the US Navy and the French Marine Nationale. As a result, they will form the core of a force that will be supplemented in the future by the capabilities provided by S-80 submarines and future maritime patrol aircraft, manned or unmanned. Although the years ahead are far from rosy, as there is much work to be done – as much as there has been institutional neglect – the F-110 frigates are a great first step.

In January 2013 the Military Capabilities Goal 2013-2016 (Objetivo de Capacidades Militares 2013-2016) was published, which included the need for five new frigates to replace the six of the Santa María class. By then they had more than 20 years of service and already affected by the cutback in defence investment following the 2008 crisis. This was the consequence of a need identified both by the Armada and by the rest of the NATO navies, as one of the key factors in naval warfare in the coming years and beyond will undoubtedly be the proliferation of submarines of all types and conditions.^[1] This is why the five ships have been designed to be multi-purpose ocean escorts, but with the emphasis on anti-submarine warfare (ASW) and optimised. According to the Ministry of Defence the purpose is to operate in high-intensity scenarios as well as for littoral warfare.

From the outset, the programme has been considered strategic, in the broadest sense of the term. This is logical, as its success is essential both for the Armada to be able to fulfil its tasks, and for Navantia to maintain its unique know-how and capabilities. More broadly, for the Spanish naval-military industry as a whole to continue to be a benchmark. For Navantia alone, this means around 20 million working hours, which translated into jobs is equivalent to maintaining a substantial part of the almost 4,000 workers on the payroll for several years. In fact, according to the company, the construction of the series will involve more than 500 Spanish companies, ensuring 9,000 jobs over the course of the decade.^[2] Let’s not forget that the direct investment in the programme is valued at more than 4.3 billion euros.^[3] Furthermore, 64% of the platform is the responsibility of Spanish companies, and this percentage rises to 87% if we extend the range to European companies.^[4] This percentage is quite high in both cases, because although technological and industrial sovereignty is necessary, complete autarky is as impossible as it is undesirable.

Following the usual process in the Armada in 2012 the operational need to replace the F-80 was identified.^[5] In 2012, the operational need to replace the F-80s had already been identified and a prospective study was carried out of the strategic scenario that should be faced by their replacement between 2025 and 2060. Three mission profiles were established: 1) High intensity missions (protection of a naval force); 2) Medium intensity missions (crisis management and protection of maritime traffic); and 3) Low intensity missions (maritime security operations).^[6] Subsequently, in September 2013, a team dedicated to the drafting of the Military Staff Requirements (MSR) was organised, supported by dozens of EMA and JAL officers, which culminated in the aforementioned document in December of the same year. However, it was deemed insufficient, so from January to July 2014, up to five revisions were carried out before the final version was approved by te AJEMA on 16 July.^[7] Thereafter, the programme suffered a certain hiatus before the technical definition was finalised and the Contract Specification was drafted.

Already in April 2019 the Execution Order was formalised with Navantia, while at the same time the purchase of all the key components from the United States was negotiated with the US Navy. Let us not forget that, despite the fact that the F-110 frigates will have a high degree of national technology, the collaboration between Navantia and Lockheed Martin is being maintained. Indeed, a collaboration that has been so successful in the past and which our flagship company hopes to repeat in the coming years despite the setbacks suffered in recent international competitions, such as the Australian and the American ones. The crisis caused by the pandemic, which hit Navantia hard as it prevented its personnel from working normally, led the company to request a delay in the delivery dates of the design reviews, both preliminary and critical, from the Ministry of Defence and the Navy in mid-2020. It was not the only project affected by COVID-19, as the S- 80 class submarines also accumulated further delays for the same reason.^[8]

Thus, on 21 May 2021, the Preliminary Design Review (PDR) was finally approved, after the documents were examined by different working groups formed by representatives of the Ministry of Defence and Navantia.^[9] These working groups had to deal with aspects such as cybersecurity, the integrated services system, the multi-mission space or the famous “digital twin”, to which we will devote a full article in the near future. After all, the F-110 frigates will be the first Armada ships to be equipped with this tool, which promises significant savings in maintenance, as well as minimising mechanical problems and increasing the availability of these ships. Subsequently, between 21 and 22 June 2022, the same was done with the Critical Design Review (CDR).^[10] The CDR was held in a series of plenary sessions attended by representatives from the Ministry of Defence, the Armada and Navantia, but also from the US Navy, as well as some top-level suppliers such as Lockheed Martin, Indra, Thales, Ingeteam and Ferri. The CDR’s approval marked the end of the design phase after three years of work.

However, the construction of the first pilot blocks of the F-111 had previously begun, specifically in April, and the milestone was made official during an event led by the President of the Government, Pedro Sánchez, held in Ferrol. In addition, since a year earlier (May 2021), progress has been made on the construction of the Centre for Integration of Ground Systems (CIST) building for the F-110 frigates, as well as on the manufacture of the prototype of the F-111 prototype.^[11] The same applies for the manufacture of the integrated mast prototype, one of the most complex parts of the ship, which was to be installed in the aforementioned building.^[12] Since then, the construction process has continued normally, although there are still years to go before a more or less tangible result can be seen. According to the latest contractual schedule, the keel laying of the F-111 “Almirante Bonifaz” will not take place until November 2023, while the launching is scheduled for December 2024. If there are no problems in the process, the handover to the Armada should take place in November 2026 in the case of the first unit, and in August 2031 in the case of the F-115 “Barceló”.

An increasingly worrying scenario

In recent years the military differential north and south of the Strait of Gibraltar has only narrowed. If a few decades ago Spain’s military superiority over Morocco or Algeria, especially in the air and naval sphere, was overwhelming, today it is much more questionable, as we have explained on occasion.^[13] Moreover, since 2008 a sort of “perfect storm” has been taking place, in which the effects of three different phenomena have combined to bring Spanish arms to their lowest level in decades.

The first of these has to do with the political balances within our state, the result of a society that has not yet internalised the importance of defence. The political class – although there are obviously notable exceptions in all parties – is rarely interested in this area and ignorance, even among those who are most interested, is patent. This makes it difficult to reach political agreements on such a sensitive issue, which is used as a campaign issue rather than the rallying point it should be. It is not surprising, therefore, that on too many occasions it is industrial reasons – easy to capitalise on politically because of the jobs generated – that drive Defence Policy and not the other way around. Nor is it surprising that the level of expenditure has remained at minimum levels since 1986, when it reached its peak.

The second factor has to do with the 2008 crisis and its consequences. They have been felt for more than a decade and have prevented the planning and investment cycles from being met, delaying some programmes – the F-110 frigates are a good example of this – and causing the decommissioning of many systems with no replacement in sight. Consequently, provoking a loss of capabilities. In fact, as these lines are being written, the last of the P-3 Orion maritime patrol aircraft is being decommissioned, leaving Spanish waters even more unprotected than they already were.

The third element in this terrible equation is alien to us, but it affects us enormously. We are talking about the arms race between Morocco and Algeria and their competition for hegemony in the North of Africa. A competition that, although it has endogenous causes, is sponsored by the transition from a unipolar and stable world to one in which competition between powers will be the norm. In this sense, a Morocco that is an increasingly close ally – and client – of the United States, and relies on funding from the Middle East, is the vector used to compete against Russian or Chinese influence in the Maghreb. As a result, in recent years both rivals have embarked on a series of procurement and modernisation programmes that have undermined Spain’s military superiority and undermined strategic stability in the Strait of Gibraltar. This term, which is specific to Strategic Studies and which we have explained above, is key to understanding what is happening in the Strait of Gibraltar^[14] is key to understand what is to come. Strictly speaking, a situation of strategic stability is one in which none of the actors has incentives to attack the others.

In this case, while Spain maintained great superiority, Morocco had no incentive to pursue military objectives such as annexing the autonomous cities. It made a very tenuous attempt during the Perejil crisis in July 2002, when Spain’s show of force convinced it that it was not to get anywhere taking that path. Since then, it has been waging an escalating campaign in the grey zone, while investing in its armed forces. As a result, we have reached a situation where Morocco has less and less to fear from the Spanish response and, as a consequence, more incentive to opt for a military solution. This obviously does not necessarily mean that Rabat will order an invasion of Ceuta and Melilla, but it does change the scenario and complicates Spain’s options enormously, as would an open war between Morocco and Algeria, which is far from impossible.^[15]

The most pressing issue, however, has nothing to do with the possibility of war, but with Spain’s loss of control over the waters of the Balearic-Estrecho-Canary Islands axis, our main concern no matter how much we emphasise multinational missions and collective defence.^[16] Fortunately, this is something that has already begun to change with documents such as the Defence Policy Directive 2021^[17] and the Concept for the Employment of the Armed Forces 2021 (CEFAS 2021), which speak of the “search for “a more reasonable degree of strategic self-sufficiency and national resilience” and the consideration of “non-shared threats” – those that are perceived and must be confronted by Spain in an autonomous manner. ^[18]

Despite this, the harsh reality is that while our neighbours are arming themselves and investing huge amounts of money in equipping themselves with new capabilities, Spain has only renounced some of the criticisms and it will take years to recover them, given the time gap between awareness of the problem, the approval of measures to alleviate the situation and the time needed to implement them. This is incomprehensible for a country through whose coasts pass some of the busiest and most important maritime routes in the world, several of the submarine cables on which communication between Europe and America depends, or the undersea pipelines on which our energy supply depends, among many other things.^[19] – let us not forget that there are open disputes with Morocco over the Exclusive Economic Zones.^[20]

However, our southern neighbours are not the only source of concern. In recent years the Russian Navy has significantly strengthened its presence in the Mediterranean, recovering a mock-up of what was once the Soviet 5th Eskadra. It has also increased investment in its submarine weapon, equipping itself with modern and capable vessels. Thus, despite the blow to its credibility caused by the war in Ukraine, in which it lost the flagship of the Black Sea Fleet, its arguments in the submarine field are still considerable. Moreover, incidents such as the attack on the Nord Stream gas pipeline, suspected to be conducted by elements of the Northern Fleet’s 29th GUGI and although attribution is impossible, force us to be even more vigilant. Not surprisingly, in an age of improved ISR (Intelligence, Surveillance and Reconnaissance) due to the proliferation of patrol aircraft, drones and both military and commercial satellites, it will be below the surface that naval forces will try to do their job, as that is where they have the best chance of success.

All of the above forces Spain to react quickly and forcefully, especially in the maritime domain and, in particular, in everything related to submarine and anti-submarine warfare. To this end, it will have to equip itself with new maritime patrol aircraft, both manned and unmanned, increase the S-80 series or seek a complement to them – as four units are frankly insufficient. Perhaps also by installing underwater listening systems at key points in our waters and maybe by taking advantage of the MLU of the F-100s. In this vein, equip them with towed sonar, even if it is less capable due to the space and weight available than that of the F-110 frigates. In addition to all this, the F-110 programme will have to be brought to a successful conclusion, as the Armada’s ability to patrol below the surface in the coming decades will depend to a large extent on them and their anti-submarine suite.

F-110 frigates: between continuity and revolution

Before getting into the subject and tackling the anti-submarine issue, it would be appropriate to dedicate at least a few lines to discussing both the concept of the ship chosen for the F-110 programme. Also, its main technical characteristics and the new features it offers compared to the F-100, which it will complement until the latter is withdrawn from service in the middle of the century.

The title chosen for this heading is not the result of chance. At first glance, the future Bonifaz class is not too different from the F-100 or any other frigate launched between the end of the 20th century and the beginning of the 21st century. Its lines are perhaps a little cleaner, especially on the foredeck and superstructure, but otherwise, there are more similarities than anything else. Despite this, it is a very different ship from its predecessors, both in terms of the type of propulsion chosen and the SPY-7 radar that will be installed in the integrated mast, the inclusion of a “digital twin” and the superlative capabilities of its anti-submarine suite, all of which speak of a ship of a very different generation.

The F-110 frigates, according to each and every one of the brochures and presentations published to date, have been designed at least on paper for oceanic and littoral operations, to operate with a small crew, to benefit from low operating and life-cycle support costs, to have a high level of survivability, modular capability and great versatility. Hence, promising to be the perfect vessel. To this end, in addition to resorting to automation, which will enable it to reduce its crew by 65 souls compared to the F-80, it will have a multi-mission space with modular capacity. It will be therefore in line with ships from other navies, such as the Type 26 from BAE Systems, the SIGMA 11515 from DAMEN or the FTI (Frégate de Défense et d’Intervention) from Naval Group. Moreover, it will integrate anti-aircraft sensors and electronic warfare equipment or top-level anti-ship armament, even though its main function will be that of an anti-submarine vessel.

The feasibility of the integrated mast began to be studied as early as 2012, with a 1.69 million euro contract awarded to Indra and Navantia.^[21] Subsequently, a new contract for 135.3 million euros was awarded to the PROTEC 110 joint venture, – formed by both companies -, for the development and integration of sensors in the mast and the SCOMBA combat system which would undergo several modifications to add new capabilities. From the integration of machine guns to that of a second commercial navigation radar, to the integration of the ScanEagle UAV or the direction of torpedo launching, among others.^[22] It will therefore allow, in a structure that offers much greater discretion than others such as those fitted on the F-100, the integration of everything from IFF interrogators to lightning rods and from electronic warfare equipment to communications, positioning and SPY-7 radar antennas. Obviously, this is the jewel in the crown, although we will not dwell on it here as there is an article on the subject in preparation.

In addition to this, there is the famous “digital twin”, which will allow Navantia’s engineers to manage the platform’s critical systems from the company’s facilities, providing support to the crew in case of need. It will also enable the vessels to be perfectly monitored at all times, anticipating possible mechanical problems thanks to predictive maintenance. This, in turn, will increase not only the reliability but also the availability of the vessels, a crucial aspect given that there will only be five of them – compared to six F-80s – and there is no prospect of this changing for the time being.

In short, although in principle their appearance is certainly conventional, without aesthetically striking solutions such as inverted bows or multihulls, the F-110 frigates will be far superior to previous generation ships, incorporating cutting-edge technologies.

F-110 frigates’ anti-submarine capabilities

After this lengthy but necessary introduction, it is time to explain what the components of the anti-submarine suite of the future F-110 frigates will be and, based on them, their capabilities. To do so, we will first list the components of the Anti-Submarine Warfare (ASW) suite, which is largely the responsibility of the Spanish company SAES and the French company Thales. Afterwards, it will explain what is known about them, bearing in mind that much of the information, for obvious reasons, is not public. What is known is that the investment in sonars exceeds 160 million euros, as this is the amount of the contract signed between Navantia and Thales.^[23]

BlueMaster Hull Sonar (UMS 4110)

The BlueMaster (UMS 4110) cylindrical bow sonar is part of the family of hull sonars offered by the French giant Thales. It is the most powerful option in a range that also includes the BlueHunter (or KINGKLIP Mk2) used on the Gowind corvettes or the future French frigates FDI (Frégate de Défense et d’Intervention) and the BlueWatcher (UMS 4120) installed on the French frigate “Surcouf” and on several corvettes acquired in recent years by various Asian navies.^[24] In total, more than 150 units have been delivered in recent years, which gives an idea of the level of market acceptance.

Although it is an original design by France’s Thales Group, thanks to a Technology Transfer (ToT) programme signed with Spain’s SAES – in which Thales participates, linking both industries – it will be manufactured in Spain. This is not the only aspect in which the two companies are collaborating, as the agreement will allow SAES to be responsible for the integration of the entire sonar suite, as well as participating in the development of some of the sonar processing software functions and the development, testing and training services, for which it has had to make a significant financial investment. In addition, thanks to the contract, key underwater acoustic technology will be transferred to Spanish industry, particularly in relation to the TUUM-6 underwater digital communication system and acoustic sensors.

The selection of the French system, over other possibilities such as L3Harris (Edo Corporation) – which was responsible for the cylindrical bow sonar of the S-80 submarines, itself a relative of those installed on the Arleigh Burke^[25] – was completed in 2019, after several years of talks with the French manufacturer.^[26] It made perfect operational and industrial sense, since as aforementioned Thales owns part of the capital of SAES, which facilitates transfers that would otherwise be difficult to achieve. Moreover, Spain has been using the French firm’s products for decades, and its sonar systems are in service or have been chosen by Spain’s main naval allies (United States,^[27] France, United Kingdom, Italy…). Furthemore, in all cases, they have demonstrated outstanding capabilities. Thus, the F-110 frigates will be comparable in all respects to the FREMM ASW, perhaps the best anti-submarine vessels to date, as they have used similar systems, or to the US Navy’s future Constellation class frigates.

Regarding its construction, SAES will be in charge of the complete manufacturing of the transducers, the assembly and integration of all of them forming the cylindrical sonar, the acceptance tests and the delivery to the shipyard of each of the five sonars. All of this in accordance with the Training Plan agreed with the company Thales.

According to the designer,^[28] this sonar will provide the F-110 frigates with the ability to detect, locate and classify submarines in both rough sea states and shallow water. It can operate simultaneously on two active channels, one for anti-submarine warfare and one for obstacle search, in addition to passive channels dedicated solely to listening or torpedo tracking.^[29] It is claimed to be particularly efficient at detecting submarines in difficult conditions, such as restricted waters, and the effects of reverberation are very limited, preventing false positives or masking of signals. Furthermore, it has been designed – more on this later – to be fully interoperable with the CAPTAS-4 towed sonar, taking advantage of the benefits of multistability.^[30] To this end, it works in active mode at frequencies between 4.1 and 6.1 kHz, with a pulse length of more than 4 s and FM, CW and COMBO modes. In passive mode, the frequency ranges from 1 to 6.1 kHz. All of the above allows detection distances of more than 35 km under normal conditions. Nevertheless, it is known that anti-submarine warfare is very complex in this respect and in certain conditions the sea state or the enemy’s expertise can reduce these distances, no matter how good the equipment and however prepared the operators may be.

Towed sonar CAPTAS-4 Compact

Like the UMS 4110 bow sonar, the UMS 4200 CAPTAS towed sonar from Thales Underwater Systems has also been a great sales success. Available in three variants (CAPTAS-1, CAPTAS-2 and CAPTAS-4), with different capacities and sizes, the French company has successfully deployed more than 80 systems in recent years.^[31] Among the most significant contracts, in addition to the French Marine Nationale, are the British Type 23 and Type 26, the Chilean T-23 and, of course, the future US Constellation-class frigates.^[32]

The variable depth towed array sonar CAPTAS-4 is an old acquaintance of these pages, since some time ago Federico Supervielle Bergés already dedicated a specific article to it^[33] in which he also explained the basics of underwater acoustic detection. It is a system that operates at low frequencies and in dual mode (active and passive) and that has, at least nominally, a range of up to 150 kilometres, referring to the second convergence zone in the Atlantic Ocean.^[34] This does not mean that it is capable of detecting submarines at those distances in other conditions. In addition, and according to the manufacturer, it is well suited for the detection of modern diesel-powered submarines in littoral water environments. For this purpose, the CAPTAS-4 has active, passive and combined modes, as well as captured emission analysis and torpedo warning functions. Its declared operational limit would be at sea state 6 (very rough, four to six metres of wave), with the ability to extend the antenna cable to depths of more than 200 metres if deemed necessary by its operators. Taking into account the operational levels of modern submarines and the width of the sound channels, this should make it possible to monitor a not inconsiderable part of the underwater environment.

In the active mode of operation, the CAPTAS 4 sonar covers a frequency range between 0.95 and 2.1, while in the passive mode, frequencies range from 0.1 to 2 KHz, which guarantees a long range as the range is longer the lower the frequency and vice versa. The tow cable and the handling system have been designed to minimise problems due to surface layers. Finally, sophisticated algorithms are used to cope with the reverberation conditions of shallow coastal waters, as with the proel sonar.

The standard CAPTAS 4 sonar (UMS 4249) measures 2x1x1.2 (LxHxW) metres with a weight of 1250 kg. The towed array is 90 metres long and 85 mm in diameter with a combined weight of 2490 kg. The handling system occupies 6.4×2.1×4.4 (LxHxW) metres with a weight of 15,000 kg. The UMS 4249 uses an omni-directional vertical line array of four free flooded rings (FFR). The heavy towed cable is 264 metres long and the light towed cable is 500 metres long. The towed array sonar can be deployed or recovered in 20 minutes and has a maximum tow speed of 30 knots.^[35]

In the Spanish case, the compact version of the CAPTAS-4 (S2807) presented at Euronaval 2016 has been chosen.^[36] This implies a reduction in the total weight of the assembly of around 20%, as well as a reduction of almost 50% in the space required for its installation and operation compared to the ordinary variant. It actually means a reduction of 84 to 45 cubic metres.^[37] In other words, they have managed to make the CAPTAS-4 occupy the same volume as its little brother, the CAPTAS-2, with a view to its installation on frigates of the order of 4,000 tons (we will not enter into the hackneyed debate about whether the F-100, the F-100 or the FREMM deserve to be classified as frigates or, rather, as destroyers). Another interesting aspect is that the CAPTAS-4 cable can be released and retrieved without human intervention, as there is no need for operators in the stowage compartment. It will therefore help in reducing the number of personnel on board the F-110 frigates.

BlueScan System

France’s Thales is also responsible for supplying the multi-platform signal processing system BlueScan^[38] which is capable of managing the large volumes of information from hull sonar, towed sonar and even the on-board helicopters’ sonar. The aim is to provide the operator with a complete view of the acoustic situation in real time.

According to the manufacturer, BlueScan takes advantage of advances in Artificial Intelligence and Big Data to offer a tactical advantage to naval forces. That is, it is able to analyse each signal it receives from the various sensors in real time, process it by discriminating its different characteristics, compare it with those stored in its libraries and, where appropriate, display the results on the operator’s screen.

As a curiosity, it is the name that the French manufacturer has chosen for a mobile game on anti-submarine warfare made in collaboration with the company Rubika.^[39]

Sonobuoys Acoustic Processor System (SPAS)

As our readers are no doubt aware, as discussed in connection with the detection systems of the S-80 class submarines, the Cartagena-based SAES is the only Spanish company capable of developing sonar and underwater acoustic capabilities in Spain. With a broad international presence, which it has consolidated in recent years, it is also an essential part of major Spanish naval programmes. Thus, in the case of the F-110 frigates and beyond the construction of the hull sonar following the agreement with Thales and the transfer of the associated technologies, it also contributes several of its own developed products that have managed to carve out a niche for it in the foreign market. Among all of them, the Sonobuoys Acoustic Processor System stands out first and foremost, something in which SAES engineers have extensive experience, having installed SPAS systems on P-3B/M Orion aircraft, SH-60 LAMPS helicopters and Visby class corvettes, among others.

The SPAS system is a simple and intuitive tool to operate, the main capabilities and components of which are detailed below. It should be noted that some of them, such as the powerful detection, identification, tracking, classification and analysis algorithms, the sonar performance prediction system and other tools and operator aids, are unique and exclusive to this system, differentiating it from other similar systems and placing it at the forefront of the market. In the case of the F-110, the acoustic subsystem consists of two main components, namely:

• Sonobuoy Acoustic System (SAS): will be responsible for managing each and every one of the functions related to the sonobuoys used not only by frigates, but also by embarked helicopters. These include:
  • The integration into the SCOMBA Command Management System (SCDS) used by the F-110 frigates of the frigates’ Acoustic Receiving Set (ARS) (also provided by SAES), which will enable communication with the sonobuoys with direct visibility (LOS). The control, processing and analysis of the data collected by the sonobuoys, both active and passive. The generation of detections and tracking of possible contacts. Also, it provides ANM and BT sonobuoy data for performance prediction. Moreover, it offers the recording and extraction of acoustic data (digital and audio), for subsequent printing and playback, as well as data extraction for training purposes and/or second level intelligence analysis in a dedicated analysis centre. It also provides audio generation.
  • Serve as an autonomous combat and training system.

• L3Harris AN/SRQ-4 communications system^[40]: will allow the integration of the helicopter’s on-board sonobuoy receiver into the SCDS. In this way, the AN/SRQ-4 will be connected to the SCOMBA system to allow the Sonobuoy Acoustic System (SAS) to extract information from the sonobuoys launched by the aircraft and, where appropriate, to send commands to them.

Among the capabilities of the SAS, the following should be highlighted:

• Full integration with the SCOMBA system, so that the ship’s Combat Information Centre (CIC) has at all times all data relating to contacts, their classification, the prediction of their future movements, the status of sonobuoys and objects to be tracked or audio data.

• Data recording: all tactical information generated and data acquired by the various sonobuoys during the ASW mission are stored in a digital recorder compatible with the STANAG 4283 standard. The objective is to be able to analyse and confirm on the ground the contacts detected during the mission, as well as to be able to detect other threats that may have gone unnoticed. Post-mission analysis is essential for acoustic intelligence work in order to improve and update the threat database (ACINT).

• The remote configuration of the sonobuoys.

• Automatic detection and tracking of contacts: When one or more of the deployed sonobuoys detect a potential threat, the SPAS system alerts the operator indicating which sonobuoy has made the detection. These mechanisms are based on a database of acoustic signatures and certain detection criteria, which can be consulted and modified by the operator during the mission. Localisation aids include: Target Motion Analysis (TMA), Kalman Filter, Closest Point of Approach (CPA), the possibility to establish operator-generated manual contacts and Automatic Cross Fixing (CFA).

• On-board training, both integrated with other detection elements installed on frigates and in isolation.

• Multi-statics between sonobuoys: Active and Active-Passive at low frequency.

For detection, the SAS system installed on the F-110 frigates, like those the company has installed on other ships and aircraft in the past, will allow different modes of analysis depending on the type of sonobuoy deployed:

• Broadband analysis: displays the results for each directional passive sonobuoy in Bearing/Time/Amplitude (BTAI) and Bearing/Amplitude presentations. In addition, and to facilitate threat location tasks, the system integrates broadband processing on an operator-selected set of directional passive sonobuoys, displaying it in a passive energy plot.

• Narrowband analysis: results are presented for each passive sonobuoy in frequency/time (LFI), frequency/amplitude (ALI) and bearing/frequency (BFI) presentations.

• Transient analysis: showing the results, for each passive sonobuoy, in frequency/time (LFI) presentations.

• Demon and Double Demon analysis: presenting the results for each passive sonobuoy of the Demon analysis in frequency/time presentation (LFI) and of the Double Demon analysis in frequency/frequency presentation (carrier/analysis).

• Processing of CW and FM monostatic and multi-static pings (for directional active pingers): The SPAS system outputs and processes CW, FM Up, FM Down and COMBO pings in both monostatic and multi-static modes. The result of monostatic pings are displayed in Bearing/Range (BRI), Doppler/Range (DRI) and Amplitude/Range (ARI) presentations. In multistatic, the SPAS Acoustic Subsystem integrates the processing of the multistatic ping associated to a group of active sonobuoys configured by the operator, the result of this processing is displayed on a multistatic tactical plot, favouring the localisation of the contact with high precision.

Acoustic Management System (AMS)

Even more important than the system for processing the data sent by the sonobuoys will be the Acoustic Management System (AMS) of the Armada’s future F-110 frigates. On some occasions we have explained, for example with regard to the S-80, that more important than a great detection capacity (i.e. obtaining raw data), is to have a library of signals that allows comparison between what is picked up by the sensors and the emissions captured previously, either in other missions of the ship itself, or by other surface ships and submarines. This is where the Acoustic Management System comes in, which will have the following functionalities:

• Classification of the detections provided by SBY and sonar (HMS and VDS): the detected contacts can be compared with an intelligence database (ACINT) for classification purposes. The classification data will be stored in a database compatible with information from other Spanish platforms such as the S-80 submarine. This compatibility and possibility of working with ACINT (Acoustical Intelligence) from different platforms will be possible thanks to the commonality of the classification software provided by SAES. The company is also developing the EDIA acoustic intelligence data exploitation tool.

• Location of probable contact detection areas by PEFP (Passive Energy Fusion Plot) and AEFP (Active Energy Fusion Plot): these plots are generated from acoustic propagation model data and detections received from SAS, merged in AMS with the passive and active energy received from SS (Sonar Suite), respectively. AMS will allow the acoustic operator to generate acoustic tracks from these PLOTs.

• Management of ANM and bathymetric data received from the Sonobuoy Acoustic System (SAS): provided by sonobuoy processing, and bathymetric data acquired from the OS Bathy unit. These data will be stored in a database managed by AMS.

• Multi-static operation between SBY and own ship’s VDS sonar:

• Creation of multi-static networks.
  • Management of the sonobuoys belonging to the multi-static network.
  • Synchronisation of sonobuoy processing with pinging.
  • Monostatic and multistatic performance prediction to find the best network configuration for detection using monostatic and multistatic acoustic propagation models.
  • MSP (multistatic graph) generated from the multistatic operation.

• Recording of Audio data received by the sonar suite during the mission.

In addition, and as with SAS, the AMS will also allow acoustic operators to be trained on these functionalities.

• Integration with SCOMBA: contacts, sorting, prediction, status, audio…

• Integration with Sonar Suite (ISS): contacts, sorting, recording…

• Signal processing of sonobuoys, VDS and HMS sonars for ACINT generation.

• ACINT management.
• Environmental data management: bathythermal, ambient noise, background, sea state…

• Fusion of energy maps: VDS+HMS+Sbys

• Multistatism Sbys – O/S VDS

• Multi-static planning tools.

Another very interesting aspect of the AMS is its ability to merge the energy plots and represent the information about the geographical plot of the ship, as shown in the images below. In this way, the energy levels will be merged with the rest of the tactical information (detections, tracks, tools…) and displayed in a scale of colour tones:

• Orange for sonobuoy detections;

• Green for sonars (HMS and VDS) and;

• Blue for VDS-VDS multistatic events.

This capability is implemented through the Passive Energy Fusion Plot (PEFP) and Active Energy Fusion Plot (AEFP) tools.

Even more interesting is the ability to operate in a variety of modes, including traditional monostatic, bistatic and multistatic, which is undoubtedly the future of underwater acoustic detection. Since not everyone needs to know what each of these modes is, they can be roughly summarised as follows:

• Monostatic: Echo transmission and reception occur on board the same unit (sonar equipment). Two or more monostatic systems operating independently of each other in the same area of operations are called multi-monostatic. The systems can share command level contacts through existing links, such as Link 11.

• Bistatic: used when one naval or airborne unit transmits acoustic energy (e.g. sonar, sonobuoy, explosive charge…) while a second unit is responsible for receiving the target echoes generated by the transmission. Two or more bistatic systems acting independently of each other in the same area of operations are called multi-bistatic.

• Multistatic: in this case, one or more units transmit and other units (possibly including transmitting units) receive the echoes generated by these transmissions. Through a communications link they share low-level contact data for fusion, which is performed by a multistatic sonar processing engine, for example).

The following table shows the combinations of sonar and sonobuoys working in monostatic and multi-static modes:

In the case of the F-110 frigates, as all the processors are installed on the same platform, multi- staging is simplified as they have the same time reference and communications are wired – with the logical exception of sonobuoys, which in any case are received through the data link.

One shall not forget that as simple as it may seem on paper, from the moment that instead of one sensor there are two or more involved in the equation, plus the acoustic management system itself, the exchange of messages between all of them becomes more complicated and new problems come into play, such as latencies, the adaptation of processes to other waveforms, etc. All in all, the F-110s will be able to make the most of the main advantages of multistability, which can be summarised as follows:

• Reduction of noise emissions

• Improved contact tracing and sorting

• An increase in spatial coverage, which goes beyond that which can be provided by each of the individual systems.

• It keeps the receiver-only (RO) platforms covert, as the better-placed – or expendable – ones can be used for pings, while the more valuable ones, such as the frigate itself, are kept on listening.

• Although the monostatic sonar (RT) may receive the echo from the worst aspect of the contact, other receivers will receive the echo from a better aspect, allowing an optimal picture of the contact to be formed.

All of which will provide the F-110 frigates with capabilities in locating enemy submarines that are unparalleled in the history of the Armada and which will have nothing to envy in our neighbouring navies.

Other systems and technologies related to anti-submarine warfare and F-110 frigates

The underwater electric field produced by a ship can be detected with a range comparable to any other ship’s influence signature.^[41] This is why SAES has also been entrusted with the control of the electric field signature, both static and alternating, something that has been carried out since the ship’s definition phase.

During this, the sources of the electric field are identified, which for a surface vessel are basically the currents generated by the ICCP (Impressed Current Cathodic Protection) system, the elements of different material in contact with the water and any rotating element capable of radiating an alternating electrical signature.

Once the sources have been identified, the electrical signature generated by each of them is estimated, both separately and jointly. Furthermore, to control the alternating electrical signature, it is necessary to identify the main frequencies of the rotating machines capable of radiating alternating electric fields. Subsequently, in order to control and mitigate the electrical signature, criticality indexes are established for each source and mitigation and monitoring actions for each of them are established according to the level of this index, as shown in the diagram below.

In addition to the above, in July 2021, Thales started production, under a contract signed in December 2019, of the TUUM-6 underwater communication system, one of the components of the integrated sonar and acoustic suite to be fitted to the F-110 frigates.^[42] Unlike other systems, licensed to third parties, in this case it will be Thales España itself that will be responsible for manufacturing at its Leganés facilities.

On the other hand, to materialise the construction of the hull sonar, although this does not have to do with the capabilities of the F-110, but rather with industrial returns, a new 400 square metre facility has been built on La Palma between June 2020 and May 2021, with the installation of equipment to be completed in March 2022. This facility will manufacture the arrays, each with 480 transducers, each grouped into 5 half-staves of 96 units.

The new plant has a 16-tonne overhead crane, a 10×8-metre acoustic tank with a depth of 8 metres, and different areas for manufacturing, storage or measurement. If all goes according to plan, they will be able to manufacture up to 15 transducers per week, although capacity could be increased to 30 if necessary.

The important thing about this facility, in terms of Spain’s interests, is that there are very few companies in the world capable of producing this type of component. Therefore, it opens up the opportunity to capitalise on the investment, not only by producing for the Navy’s needs, but also for the contracts that SAES may win abroad in the future.

On-board helicopter

A frigate such as the future F-110 has, as follows from the above explanations, an important capability based on its own sensors, in terms of locating submarines that may be operating in its vicinity. However, it cannot do without the airborne element, which not only provides it with greater coverage, but also the possibility of investigating the most suspicious contacts and, if necessary, even attacking them with torpedoes launched from the air.

In this regard, the F-110 frigates will initially employ an MH-60R helicopter, supposedly as a prelude to future NH90 HSPN ASWs, which may never arrive. It is precisely because of Airbus’ delays that the Armada has been forced to turn again to the United States – although this has always been its preference, which it has never hidden – to purchase eight Sikorski MH-60R helicopters, spare parts and a host of equipment, including four sonar guns, as well as various types of sonobuoys, all for $950 million.^[43]

The “Romeo” is a multi-purpose helicopter, powered by two General Electric T700-GE-401C engines, each with 1,800 hp. Although its first flight dates back to July 2001 and its first operational deployment took place in January 2009, it has not ceased to be updated, nor has it ceased to improve aspects such as the avionics or the mission system, provided by Lockheed Martin. The cockpit has four 8×10-inch (20.3 x 25.4 cm) full-colour displays. The communications suite is the Rockwell Collins AN/ARC-210, while Northrop Grumman provided the LN-100G dual navigation system (INS/GPS).^[44] Multiple sensors include a FLIR Raytheon AN/AAS-44C(V) and a Telephonics AN/APS-147 or AN/APS-153(V) radar. It also includes different countermeasure systems.

For what matters here, both its choice and the choice of its calibrated sonar will allow the Armada to continue to interact with those of the main allies on equal terms for many years to come. From the US Navy to the Royal Australian Navy and the French Marine Nationale, many of the top navies have opted, if not for this aircraft, then for some of the ASW equipment it mounts, the most important of which is Raytheon’s AN/AQS-22 ALFS (Active Low Frequency Sonar). This is actually the FLASH from France’s Thales, produced under licence. A system that is already certified on the MH-60R, obviously, but also on the NFH90 “Cayman”^[45], so there would be no problem if it was decided to change the platform in the future.

In terms of cargo capacity and exclusively for anti-submarine warfare, which is what we are interested in, the “Romeo” can carry 3 MK 50 torpedoes and up to 25 sonobuoys of various classes.

F-110 frigates’ anti-submarine armament and countermeasures

After talking about the signal detection and processing systems and even the air wing, it is necessary to talk about the anti-submarine armament that the Bonifaz class ships will carry. Of the whole panoply, the ASW armament is relatively scarce, although sufficient in number and of proven capacity, with the F-110 frigates mounting two MK-32 Mod. 9 fixed twin launchers for MK-54 torpedoes, about which we will not dwell too long, as we have already explained everything necessary in a specific article.^[46]

The latter, developed from portions of the MK-50 guidance system and warhead in combination with the MK-46 propellant, offer high performance in shallow water as well as reasonable cost. They have been in service since 2004 and have since achieved significant sales figures abroad.

With a length of 2.71 metres and a diameter of 320 mm, their mass is 276 kilograms of which 44.6 kilograms belong to the warhead. In terms of performance, they are capable of a maximum speed of 45 knots at 500 feet (150 m), dropping to 40 knots at 1,500 feet (457 m). Their range is 11.1 km at 50 ft (15 m), but only 5.6 km at 1,500 ft (45 m).

Curiously, the use of ASROC (Anti Submarine Rocket), which would allow a substantial increase in the range of these torpedoes, has not been chosen for the moment, entrusting the attack at long distances to the on-board helicopter. Apparently, the aim was to avoid increasing displacement and cost, as well as complicating the ship’s sustainment, and the idea was discarded at a very early stage of the design. However, it could be implemented in the future, if the decision is made to do so.^[47]

As far as countermeasures are concerned, the F-110 frigates will use a Pairie-Masker^[48] which generates a bubble curtain around the hull that distorts the speed of sound emitted by the ship towards the outside, making it difficult for enemy detection systems to classify the radiated noise.^[49]

In terms of decoys, the well-known AN/SLQ-25 Nixie, used by both the US Navy and a number of allied navies, will be used. This is a device that generates signals similar to those emitted by the ship in its ordinary operation and which is dragged at a prudent distance from the ship so that enemy torpedoes operating in passive mode confuse the target.

Conclusions

On paper, as construction is just beginning, the Bonifaz class frigates will be the most capable anti-submarine vessels the Armada has ever had in its long history. The choice of the various systems leaves no room for doubt, as the best the market has to offer has been chosen.

More importantly, a high degree of nationalisation and transfer has been achieved in the case of foreign systems, which will allow the domestic industry to continue to develop in the future on the basis of what has been learned.

Although there are still some aspects to be specified, such as the future use of ASROC or whether the “Romeo” will finally be replaced by the specific variant of the NH90, the ingredients are good and the F-110 frigates will make it possible to recover a critical capability that, at present, the F- 80s in the state in which they are in, cannot fulfil with guarantees.

However, not everything is positive, despite the steps taken in recent months. The overall situation of the Spanish Armed Forces, as far as anti-submarine capabilities are concerned, remains critical, especially in the air domain. Without a short-term replacement for the P-3s – the last of which was decommissioned on 16 December – the only thing left to do is wait for the Ministry of Defence to purchase four C-295 MPAs in 2023.

Nevertheless, it will still not be sufficient. To maximise control over the Balearic-Estrecho-Canary Islands axis, as well as to comply with international commitments, it will have to be complemented with more manned and unmanned aircraft, with fixed listening systems installed on the seabed and also with more ships with significant ASW capabilities. Whether or not the F- 110 series of frigates is extended, the MLU of the F-100 should be fitted with the necessary equipment to make them more multi-purpose vessels, with a view to anti-submarine warfare. The same could be done, as there are very compact systems such as CAPTAS-2, with one of the BAMs or with the future European Patrol Corvettes (EPC), which could install towed sonar in a mission module instead of resorting to a fixed mounting.

Be that as it may, Spain, given its responsibilities, potential and growing threats, cannot neglect an area it has long neglected. Some of the mistakes have begun to be corrected, but there is still much work to be done.

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^[22] Ministerio de Defensa. (8 April 2019). Documento administrativo de modificación de contrato “Desarrollo e integración de sensores en mástil-SCOMBA F-100”. Expediente núm. 1003215005900. https://contrataciondelestado.es/wps/wcm/connect/9bf79cb5-5e3c-49a6-9187-a8aa1084f983/DOC201904101312532019+04+08+DOC+ADM+MODIF+9+PARA+PUBLICAR.pdf?MOD=AJPERES

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^[24] Thales. (s.f.). Hull Mounted Sonars. https://www.thalesgroup.com/en/markets/defence-and-security/naval-forces/underwater-warfare/bluescan/hull-mounted-sonars

^[25] Villanueva-López, C. (2022). El Programa S-80 – El sistema de combate (I). Ejércitos, 42. https://www.revistaejercitos.com/2022/11/28/el-programa-s-80-el-sistema-de-combate-i/

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^[28] Thales. (s.f.). Thales UMS 4110. https://es.scribd.com/document/361996004/Thales-UMS-4110

^[29] https://docplayer.fr/52224160-Thales-a-bord-des-fregates-fremm.html

^[30] Thales. (4 March 2020). Thales à bord des frégates FREMM. http://calderon.cud.uvigo.es/bitstream/handle/123456789/428/González%20del%20Tánago%20Land%C3%ADn%2C%20José%20Luis%20-%20Memoria.pdf?sequence=1&isAllowed=y

^[31] Vavasseur, X. (10 February 2022). US Navy Looks Again At VDS Options For New Frigate. Naval News. https://www.navalnews.com/naval-news/2022/02/us-navy-looks-again-at-vds-options-for-new-frigate/

^[32] Thales. (s.f.). CAPTAS Family. https://www.thalesgroup.com/en/markets/defence-and-security/naval-forces/underwater-warfare/bluescan/captas-family

^[33] Supervielle, F. (2020). CAPTAS-4. El sonar de las futuras fragatas F-110 y la acústica submarina. Ejércitos. https://www.revistaejercitos.com/2020/01/02/captas-4/

^[34] Ibid. 

^[35] Deagel. (s.f.). UMS 4200 CAPTAS. https://www.deagel.com/Sensor%20Systems/UMS%204200%20CAPTAS/a002134

^[36] Roa, A. (21 October 2016). Thales diseña una versión compacta de su sonar ‘Captas-4’. Infodefensa. https://www.infodefensa.com/texto-diario/mostrar/3078387/thales-disena-version-compacta-sonar-captas-4

^[37] Nugent, B. (2017). Naval ASW Sonar Review. European Security & Defence, agosto, 74-78.  https://amiinter.com/pdf/NavalASWSonarReview.pdf

^[38] Gobierno de España. (29 June 2021). Thales refuerza sus capacidades industriales en España. https://www .investinspain.org/content/icex-invest/es/noticias-main/2021/thales-espana.html

^[39] Thales. (11 February 2022). Bluescan, the Game.https://www.thalesgroup.com/en/worldwide-defence-naval-forces/underwater-warfare/magazine/bluescan-game

^[40] L3Harris. (s.f.). CDL Hawklink AN/SRQ-4 Radio Terminal Set. https://www.l3harris.com/all-capabilities/cdl-hawklink-an-srq-4-radio-terminal-set

^[41] Electrónica Submarina (SAES). (s.f.). SET-200/P – Sensor de Campo Eléctrico Submarino. https://electronica-submarina.es/medicion-submarina/sensor-campo-electrico-submarino/

^[42] Thales. (16 June 2021). Thales strengthens its industrial capacity in Spain due to production start-up of the TUUM-6 Underwater Digital Communication System. https://www.thalesgroup.com/en/spain/news/thales-strengthens-its-industrial-capacity-spain-due-production-start-tuum-6-underwater

^[43] Defense Security Cooperation Agency. (15 de marzo de 2022). Spain – MH-60R Multi-Mission Helicopters with Support [Press release]. https://www.dsca.mil/press-media/major-arms-sales/spain-mh-60r-multi-mission-helicopters-support

^[44] Forecast international’s Aerospace Portal. (s.f.). MH-60R Seahawk. http://www.fi-aeroweb.com/Defense/MH-60R-Seahawk.html

^[45] Thales. (s.f.). Sonares de Inmersión de Baja Frecuencia para Helicópteros. https://www.thalesgroup.com/es/markets/defence-and-security/naval-forces/underwater-warfare/bluescan/familia-flash

^[46] Conte de los Ríos, A. (2022). La evolución de los torpedos. Ejércitos, 35. https://www.revistaejercitos.com/2022/04/19/la-evolucion-de-los-torpedos/

^[47] González del Tánago, A. (2018). La fragata F-110, una apuesta de presente y futuro. Revista General de Marina, abril. https://armada.defensa.gob.es/archivo/rgm/2018/04/rgm042018cap08.pdf

^[48] Buques de Guerra. (24 November 2018). Fragatas Clase Fridtjof Nansen. https://www.buquesdeguerra.com/es/buques-armada-espanola/fragatas/fragatas-f-110/tag/AEGIS.html

^[49] Prairie-Masker (31 October 2022). In Wikipedia. https://en.wikipedia.org/w/index.php?title=Prairie-Masker&oldid=1119306687