Guarding ships against the modern torpedo threat

By Luca Peruzzi

With an enlarging number of conventional and nuclearpowered submarines, the worldwide naval forces’ surface component is increasingly reliant on effective torpedo defence systems (TDSs). © Ultra Electronics

With the increasing number of new submarines or upgraded platforms being put into service and planned for the future, alongside the development of more advanced weapon systems represented by heavy- and light-weight torpedoes, the worldwide naval forces’ surface component is increasingly reliant on effective torpedo defence systems (TDSs). The requested budget devoted to these defence development and acquisition, often neglected to cover the increasing costs associated with new ships procurement programmes, tends to find more space in latest defence budgets. Initially based on noisemakers and signature emulators towed astern to seduce torpedoes away from the hull, TDSs saw technological developments to cope with torpedoes weapon logic improvements and re-attack capabilities. Modern TDSs have evolved from seduction and avoidance to advanced detection, classification and localisation (DCL) of threats, integrating active and passive countermeasures. The DCL concept embraces complex passive detection and automatic resolution of ambiguity – without ship manoeuvres and the presentation of tactical command recommendations – and includes advices for deployment of appropriate soft or hard-kill countermeasures. This analysis covers latest developments in TDSs and soft-kill countermeasures among the western industries, leaving to a follow-on article hard-kill solutions.

The Sea Sentor Surface Ship Torpedo Defence (SSTD), according to Ultra, is an integrated, sense-to-effect solution that offers a comprehensive capability maximising vessel survivability in torpedo engagements. The Sea Sentor is operated by the UK, New Zealand, Turkey and its derivatives by India and Australia. The system was also selected by Canada. © Ultra Electronics

Ultra

Ultra has provided TDSs to the UK and other nations for over 20 years with the first Sea Sentor Surface Ship Torpedo Defence (SSTD) having successfully been delivered to the Royal Navy in October 2004. The Sea Sentor, according to Ultra, is an integrated, sense-to-effect solution that offers a comprehensive capability maximising vessel survivability in torpedo engagements. It employs advanced acoustic processing DCL techniques against torpedo threats at a tactically significant range, with a very low false alarm rate and high probability of correct classification. The high-performance levels achieved stems, according to Ultra, from the dedicated towed sonar designed explicitly for torpedo detection. The SSTD towed assembly line comprises a purposedesigned multioctave torpedo detection array coupled with Vibration Isolation Modules (VIMs) forward and aft, a rope drogue ‘tail’ for stabilization, a spaced apart flexible towed body countermeasure module, and a fibre optic tow cable. The towed array, incorporating the in-line acoustic countermeasure, eliminating the need for a dedicated deployment and recovery system, requires only two operators to deploy it from the compact single drum winch. The Sea Sentor dedicated torpedo classification software determines the weapon make, model and type, adjusting automatically to salvo attack, with involved countermeasure action and vessel manoeuvres being presented by the tactics sub-system. Continuous tracking of the vessel progress against the recommended manoeuvre, enables the towed acoustic countermeasure to be programmed and initiated as required without operator involvement. In a typical configuration, the Sea Sentor is equipped with two decoy launching systems (DLS), one deployed to port and one to starboard, containing eight expendable acoustic countermeasures (EAD). Supplied in an environmental protective casing, each expandable stationary sonobuoy-packaged off-board countermeasure weighs 7.5 kg and is launched by a dedicated, rechargeable pneumatic system. Ultra also offers a mortar launched EAD variant allowing easy integration into existing launcher equipment, such as Mk 36 SRBOC (Super Rapid Bloom Offboard Chaff), Sea Gnat and others. Both the towed and expandable countermeasures can be programmed by the end user in the

In addition to the towed array, winch, processing cabinet and control unit, a typical configuration of the Sea Sentor includes two decoy launching systems, each containing eight expendable acoustic countermeasures. © Ultra Electronics

field with up to ten different settings stored simultaneously. The torpedo detection and countermeasures system is based on a two-console stand-alone full configuration including the dedicated processing cabinet, the two countermeasure decoy launchers and their control unit, and weighs overall around 5,000 kg. Ultra’s Sea Sentor is operated by the UK, New Zealand and Turkey, with derivatives provided to India and Australia. Sixteen systems have been initially delivered to the UK Royal Navy and are being used on both front line and support ships when required. Although no further information was released on the inventory of the Sonar 2170, as the SSTD is known in the Royal Navy, in May 2022 the UK MoD announced to have awarded Ultra a contract for the provision of three additional Sonar 2170 SSTD Fit-to-Receive (FTR) kits to be integrated onto the new Type 31 frigates. The Sea Sentor is also equipping the ANZAC frigate in service with the New Zealand Navy while a related system is deployed from the Hobart-class destroyers of the Australian Navy, which selected the Sea Sentor also for the new Hunter-class frigates under construction. Turkey brought the Sea Sentor under contract with Haselsan as prime in a dedicated version for its Ada-class corvettes. The Indian Navy, which calls it New Torpedo Defence System (NTDS), installed the Sea Sentor with the winch and launcher made by Mahindra Systems on a number of surface platforms. The Ultra TDS was also selected by the Canadian Navy for the new Canadian Surface Combatant (CSC) programme’s frigate platforms, a supply contract being awaited.

In January 2022 Ultra, in partnership with Mahindra Defence Systems Limited, announced the award of the Integrated AntiSubmarine Warfare Defence Suite (IADS) programme for selected frontline warships of the Indian Navy. The IADS is a new system that combines a powerful multi-sensor ASW capability using an in-line active and passive towed low-frequency variable-depth sonar and a torpedo defence suite with embedded DCL to defeat detected torpedo threats. With a contract worth approximately £ 60 million, deliveries are due to commence in 2024 to be completed by 2030.

Leonardo

Leonardo proposes a new TDS based on the solutions developed for the Italian Navy and sold on the international market. The package, known as Morpheus, includes the Black Snake towed array sonar, a reaction management sub-system (RMS), the current family of C310 effectors or the new Mobile Jammer Target Emulator (MJTE), the dedicated trainable 8 or 12 barrels DLS or the multi-purpose and multi-spectral OTO Decoy Launching System (ODLS) 20, in addition to the new B358 single lightweight launch tube. Specially designed for torpedo detection, the Black Snake towed array sonar operates in “passive” mode and features a patented

The Leonardo Black Snake towed array sonar operates in “passive” mode and features a patented innovative device that allows solving the left/right ambiguity in a very short time without using hydrophones-triplets or asking the towing ship to execute manoeuvres to induce movements on the towed array. © Leonardo The Leonardo MJTE (Mobile Jammer Target Emulator) combines in a single body the capabilities of current stationary jammers and mobile target emulators, reducing the number of decoys in a salvo from 5 to 2-3, nearly doubling the number of defensive actions. © Luca Peruzzi

innovative device that allows solving the left/ right ambiguity in a very short time without using hydrophones-triplets or asking the towing ship to execute manoeuvres to induce movements on the towed array. According to Leonardo, this provides two main advantages: reduced dimensions of the towed body and consequently of the winch system, and reduced time to obtain the torpedo-classification information. The use of a patented, innovative beamforming algorithm within a suitable working frequency bandwidth allows achieving good performance in terms of detection distances and bearing measurement accuracy even against modern very silent torpedoes. According to the company, the Black Snake is the only passive sonar on the market able to achieve a detection range higher than 6 km, despite its compact dimensions, and to be operated up to Sea State 5. It provides a full panoramic acoustic coverage around the ship, ensuring permanent surveillance also during the escape manoeuvre, enabling a second reaction to torpedo re-attack. The passive array sonar has a 55 mm diameter, is 4 meters long, and is towed by means of an electromechanical cable of around 16 mm diameter and up to 600 meters long. It includes the stern stabilizing system, the towed array and the electronic sensor module to convert the acoustic into electronic digital signal to be passed to the ship via fibre optic, a vibration insulation module to prevent vibration to be transmitted to the towed array, and the towing cable. The latter is deployed and recovered through a reduced-footprint winch and sledge with an overall weight of less than 3.8 tonnes. The Black Snake is directly interfaced with the reaction management sub-system to carry out the optimized reaction with a mix of escape manoeuvres and the launch of dedicated decoys. It will equip the new Italian Navy’s Trieste-class LHD and although both Fincantieri and Leonardo haven’t disclosed or commented, the system is reported to equip the new Al Zubarah-class corvettes and the amphibious ship for the Qatar Emiri Naval Forces (QENF). In addition to the family of current C310 anti-torpedo countermeasures including stationary jammers and mobile target emulators (MTE) and sold worldwide, Leonardo is conducting the at-sea qualification trials of the new generation MJTE (Mobile Jammer Target Emulator), based on Italian Navy requirements and procurement programme. As an evolution of the MTE, the MJTE combines in a single body the capabilities of current stationary jammers and mobile target emulators, reducing the number of decoys in a salvo from 5 to 2-3, nearly doubling the number of defensive actions. The MJTE body is 1.3 meters long and has a 127 mm diameter, weighs 21 kg, and features a transmitter front section, battery, electronics and a rear motor section with a towed receiver. Being capable to be launched at a shorter distance compared to current systems, it also comes in an exercise configuration, the MJTE decoy buoying at the end of the mission allowing recovery. While the MJTE has already conducted initial at-sea trials, due to the pandemic and personnel/ platform availability, the qualification phase is expected to be concluded at the beginning of 2023 when the effective performances will be verified in operational-like scenarios. In addition to the Italian Navy, while Leonardo do not confirm or comment, EDR Magazine understood the MJTE already found success with worldwide customers. The new decoy can be launched from both current dedicated trainable 8 or 12 pneumatic-actuated barrels launch subsystems from Leonardo, as well as from the Euroslat consortium 12-barrel antitorpedo launch system, two such modules being installed on board French and Italian FREMM frigates and Horizon destroyers, alongside the Charles de Gaulle aircraft carrier. The MJTE can also be used in any type of anti-air warfare decoy launcher by using a pyrotechnical canister, including the new ODLS 20 launcher from Leonardo. EDR Magazine understood that the company has already sold internationally its lightweight B358 single launch tube for the MJTE and current C310 decoys, which can be grouped

in two separate three-barrel groups to offer the best protection on smaller naval platforms.

Aselsan

Indigenously developed by Aselsan for surface combatants, the Hizir TDS is a soft-kill countermeasure system that localizes torpedos and advises the appropriate countermeasure tactics utilizing state-of-the-art technologies. The Hizir configuration features the torpedo detection array that, together with the acoustic decoy module, are accommodated and part of a single towed array, lowered and recovered by a single towing winch. It is characterized by a triple array to resolve left/ right ambiguity. The Hizir also includes an electronic cabinet hosting the signal processing unit and electronics, and two DLS, each hosting eight expandable decoys with a launcher remote control unit and a user control panel. Zoka programmable expandable decoys and jammers, also provided by Aselsan, create respectively deception and confusion (the former) and a noise barrier against torpedoes (the latter), working alongside the programmable towed acoustic decoy to provide critical time to perform tactical evasive manoeuvres. In addition to long range threat detection with precise detection and classification by the support of a threat database, the system has defence capabilities against simultaneous multi-torpedo attacks, and is able to track at least six different targets. In addition to a fully automatic mode, it detects and chooses the optimum countermeasure tactic from its database and waits for approval to initiate the operation. During sea trials carried out in the first half of 2018 with the manufacturer, the HIZIR TDS successfully detected and classified the DM2A4 heavy weight exercise torpedo approximately 1012 km away and managed to deceive/jam it. In addition to being deployed from the third Ada-class corvette and newest Turkish Navy’s surface combatants, in the latter case as part in the future of an anti-submarine suite, the Hizir is also set to equip both the Pakistan Milgem/ Babur class and Ukrainian corvettes platforms still in construction.

Naval Group’s Canto countermeasures is an all-inone broadband active acoustic emitter acting both as a jammer, for dilution effect, and as false target generator, for confusion effect. © Naval Group

Naval Group

In March 2022, Naval Group announced the contract award by the Greek MoD for the three defence and intervention frigates for the Hellenic Navy. The anti-torpedo defence of these ships will be provided by Canto decoys supplied by the same shipbuilding company. According to the latter, unlike the sedution-based decoys, Canto acts completely independently from attacking torpedoes, being based on the dilution/ confusion concept. The decoy is capable of defeating previous and new generations torpedoes combining complex signal processing and high endurance, against which the seduction-based decoys are no longer efficient, the company says. Canto is an all-in-one broadband active acoustic emitter acting both as a jammer, for dilution effect, and as false target generator, for confusion effect. It generates hundreds of false targets, permanently and randomly renewed on a 360° coverage area, aiming at saturating the torpedo sonar and data processing. The decoy constrains the torpedo to repeat computations to elaborate a coherent tactical picture, forcing it to reiterate search patterns. The extremely confused tactical picture forces the attacking torpedoe to waste time finding the real target, thereby exhausting its energy. Thanks to these capabilities, the number of Canto decoys to be launched by salvo is drastically limited to two munitions, says Naval Group. Canto is associated with the Contralto software reaction module that computes the most efficient evasion manoeuvre and deployment sequence. The Contralto software reaction module is customized to each platform, and is embedded into the control unit of the decoy launching system and can be displayed on the CMS operator console. With a 123.8 or 130 mm diameter, a length of less than 1,150 mm and a weight under 20 kg, with a shelf life of 20 years, Canto employed by surface vessel is compatible with any decoy launcher at 123.8 mm (pneumatic) and 130 mm (mortar) standards. Canto has been integrated with Terma’s C-Guard DLS thanks to the Chemring Countermeasures launch module, alongside the Lacroix Defense Sylena Mk2 DLS thanks to SEALAT pyrotechnic mortar allowing to fire any anti-torpedo solution, and is being proposed as part of the Rheinmetall Defence MASS (Multi Ammunition Softkill System) DLS. In addition to France for both surface and submarine applications, Canto has been supplied or ordered by a total of 10 customers without specifying between surface and submarine or both applications. The system is known to have been supplied or ordered for surface applications by Egypt and the Philippines, in addition to Greece.

The AN/SLQ-25 Nixie is the US Navy’s primary Surface Ship Torpedo Defense (SSTD) system and is the most widespread among NATO and allied navies with at least over 20 customers over the years. It is a modular, digitally controlled electro-acoustic soft-kill countermeasure towed decoy. © US Navy

In December 2020, Ultra Naval Systems and Sensors was awarded a $ 186.4 million contract by the US Navy’s Naval Systems Command for the supply of the latest version of AN/SLQ-25 Nixie TDS. The US Navy is also funding AN/SLQ-25 engineering changes providing for hardware and software configuration modifications to in-service decoy baselines. © US Navy

US

The AN/SLQ-25 Nixie is the US Navy’s primary Surface Ship Torpedo Defense (SSTD) system, providing towed persistent torpedo countermeasure capability to protect over 180 in-service surface ships and new platforms under construction, including aircraft carriers, cruisers, destroyers, amphibious ships and support ships, and is the most widespread among NATO and allied navies with at least over 20 customers over the years. Having been produced since the mid-70’s by different companies, and enhanced through different iterations, the AN/SLQ-25 is a modular, digitally controlled electro-acoustic soft-kill countermeasure decoy system that employs an underwater towed body acoustic projector deployed by a fibre optic tow cable from the sterns of surface warships. It consists primarily of the TB-14 towed decoy device in a single or twin towed configuration and the shipboard signal generator, and defends ships against wake homing, acoustic homing and wireguided torpedoes. As a result of hardware obsolescence issues with the previous AN/ SLQ-25A/C baselines that precluded the continued production of these variants, in FY 2018 the US Navy began a technical insertion effort as the AN/SLQ-25E. The latter is a government-designed, contractor-fabricated system, characterized by hardware and software architecture to a Commercial-OffThe-Shelf (COTS-based), open, and modular configuration, while keeping the systems Form, Fit, and Function. In FY 22 the latest version of the Nixie is planned to continue to progress through design acceptance criteria, finalizing analysis on the environmental qualification testing, and initiating any engineering changes with the OEM contractor on the new version. Integration and testing of tactical software for the AN/ SLQ-25E using design qualification units previously procured should be ongoing and is planned to include the system’s first atsea test. In addition, proof of manufacturing will begin for the new system’s version. Procurement of AN/SLQ-25E upgrade kits have begun in FY 22 to address AN/ SLQ25C obsolescence with the first three kits being procured from the OEM and prepared for installation in FY 23. In December 2020, Ultra Naval Systems and Sensors was awarded a $ 186.4 million contract for the supply of the AN/SLQ-25E system version. This contract has options that could increase its value to $268.5 million. In parallel, the US Navy is funding AN/SLQ-25 engineering modification providing for hardware and software configuration changes to current

production baselines to resolve emergent hardware obsolescence issues and software updates, these efforts being critical to the system service life extension until upgrade to AN/SLQ-25E is complete.

Israel

Rafael Advanced Defence Systems developed substantial experience in torpedo defence with the Scutter submarinelaunched countermeasure and the surface version called Launched Expendable Scutter (Lescut), alongside the more recent Shade defence suite and Torbuster decoy for submarine applications. Lescut is an intelligent, third generation reactive countermeasure, designed to identify the incoming threat and provide a customized response. Lescut is based on the Ultra Naval Systems and Sensors hardware and Rafael’s proven reactive acoustic module electronics and software. It requires noprelaunch input or tests, shortening the response time and eliminating errors due to incorrect settings or operator mistakes. Designed to respond simultaneously to multiple torpedoes of various types – active, passive and combined modes capable - it is programmed to defeat all types of modern torpedo logic, including range gates, Doppler shift and pulse discrimination. After being launched by the DLS and entered into the water, countermeasure operations start with the decoy suspended to its operating depth. Lescut analyses the environment and the attacking torpedo and then selects from its threat library the appropriate deception signal for emission. As a result, acoustic torpedoes home in on Lescut as the legitimate target, attacking it repeatedly, enabling the ship to evade the attack. It operates for 10 minutes, then self-destructs and sinks. It can be deployed at short range from pneumatic launchers, at medium range using mortar launch (such as the Mk 36 DLS) or to longer ranges (over 2,000 meters) using a rocket. Rafael also developed a towed torpedo countermeasure system known as ATC2 and a mini-line torpedo detection towed array (TDTA). The ATC-2 is a multifrequency active/passive seduction decoy offering two modes of operation to counter the threat, either when the target parameters are known or when there is no specific knowledge and generic parameters are generated. The TDTA uses a triplet array optimised for torpedo DCL, and the short acoustic aperture is claimed to minimise array instability, enabling continuous effective tracking. The receiver array also includes an intercept receiver/processor.

Designed to respond simultaneously to multiple torpedoes of various types – active, passive and combined modes capable – the Lescut decoy can be programmed to defeat all types of modern torpedo logic. © Rafael

The Rafael Advanced Defence Systems’ Lescut is an intelligent, third generation reactive anti-torpedoes countermeasure, designed to identify the incoming threat and provide a customized response. © Rafael

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