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Three decades ago, only a handful of major powers had effective submarine capabilities but, today, fleets in operation around the world are growing rapidly. Emerging superpowers, like China, can add naval capacity equivalent to a European country’s in the space of a few years. The threat from submarines is serious and ever-more difficult to counter. They can block a key trade corridor, destroy a high-value asset, and deliver devastating land strikes. What’s more, streamlined designs and quieter propulsion encourage forays into previously impenetrable zones.
Anti- Sumarine warfare (ASW) is becoming increasingly important for national security. Anti- Sumarine warfare (ASW) is becoming increasingly important for national security. Anti-submarine warfare (ASW) is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, and/or destroy enemy submarines. Such operations are typically carried out to protect friendly shipping and coastal facilities from submarine attacks and to overcome blockades.
Anti-submarine warfare (ASW) has always been a game of hide and seek, with adversarial states looking to adopt and deploy emerging technologies in submarine stealth or detection to give them the strategic edge. A number of submarine threats have advanced stealth and weapon delivery ability. ASW developments are being stressed by the improvements required to detect these threats.
Modern nuclear and diesel electric submarines have become very stealthy and quiet. Work done over decades has resulted in some remarkable advances in radiated noise management to make detection by passive sonar more difficult. Against active sonars, submarine stealth is achieved by anechoic tiles and clever design to reduce the strength of reflected signals. Today’s submarines are many decibels quieter than their predecessors and present lower target strengths to active sonars. But ultimately, large submarines are large, and there’s a limit to what can be done to reduce propeller and flow noise, and target strengths can’t be reduced below some physical limits—especially at low frequencies.
A modern diesel-electric boat operating on AIP is, quite simply, too dangerous to attempt to counter with a passive-sonar approach. Another challenge is diesel-electric submarines operating in littoral waters which generate high false alarm rates (FAR). The risks of operating large submarines in contested spaces will likely be higher in the future than is the case today.
ASW traditionally relies on a limited number of costly manned platforms such as attack submarines (SSNs and SSKs), frigates and maritime patrol aircraft fitted with a variety of sensors. Sonar detection is one of the most important techniques for the detection of overwater and underwater vessels. Acoustic techniques comprise active and passive sonar which requires the insertion of sensors into the water either to detect sound waves produced by the vessel’s propulsion systems (passive) or detect reflected sound waves emitted by the sensor system itself (active). But with the development of noise reduction and stealth material, the overall noise of some advanced warships is close to ocean background noise level, resulting in traditional sonar detection ability of this kind of “quiet” type ship have been on the verge of the limit. Therefore there has been rising importance of non-acoustic detection techniques. Besides visual detection, the primary non-acoustic method is Magnetic Anomaly Detection (MAD).
Today, there’s evidence of a move away from this model towards unmanned aerial vehicles (UAVs), unmanned surface vehicles (USVs), and unmanned underwater vehicles (UUVs) fitted with equivalent sensors, which are more expendable and are becoming cheaper to develop, produce, modify and deploy at scale. Detected information gathered by passive and active sonars is transmitted back to an air or seaborne platform where processing is carried out.
Acoustic detection over a wide area requires the extensive deployment of sonar buoys or towed arrays and the data fusion of their responses to provide a surveillance picture. Elevated sensors on a Low Earth Orbit (LEO) satellite, or aboard an Uninhabited Aerial Vehicle (UAV), provide improved capabilities for conducting wide area surveillance (WAS) within the spatial and temporal requirements.
Of the primary ASW platforms; submarines, ships, and aircraft; the aircraft alone operates outside the ocean environment. This feature promotes the development of ASW hardware unique to the airborne element. In addition, while the ocean’s environmental principles remain the same for all platforms, the aircraft’s agility and speed permit the exploitation of fields of sensors and, by default, multiple simultaneous acoustic propagation paths and active multi-statics. All of this serves to highlight the versatility of the airborne platform and makes it extremely friendly to technology enhancements.
Choosing an appropriate ASW solution is highly deendent on environment, Deep environments have a different ASW solution set from shallow littoral areas, and that includes not just the available acoustic propagation paths but the RF environment in which our sensor
systems must operate. Denied area environment are yet another complication in search of a solution.
Successful ASW operations typically involved a combination of sensor and weapon technologies, along with effective deployment strategies and sufficiently trained personnel. Sonars are one of the primary systems for detection and tracking of submarines in Anti Submarine warfare. Sensors are therefore a key element of ASW. Common weapons for attacking submarines include torpedoes and naval mines, which can both be launched from an array of air, surface, and underwater platforms. ASW capabilities are often considered of significant strategic importance, particularly following provocative instances of unrestricted submarine warfare and the introduction of submarine-launched ballistic missiles, which greatly increased the perceived lethality of submarines.
ASW Armament
The ASW armament carried today by maritime aircraft and helicopters includes lightweight torpedoes, depth charges and bombs.
Air Dropped Depth Charges have again come into focus because of the ASW threat in littorals. These can be very effectively utilised for flushing out the lurking diesel submarines. The MK-11 depth charge was developed by British Aerospace (now BAE Systems) for air delivery from maritime aircraft and helicopters. The Mod 3 version incorporates a 4mm mild steel outer case and nose section, which is designed to withstand entry into the water at high velocities without distortion.
The BDC 204 depth charge was developed by Bofors Underwater Systems (now Saab Dynamics) for air delivery from maritime aircraft and helicopters of the Swedish Navy. The depth charge can be deployed in patterns, with different depth charges set to detonate at different depths to achieve profound shock and damage to submarines.
Air Launched Torpedoes
Stingray is a LWT manufactured by BAE Systems. It has a diameter of 324mm, weight of 267 kg, and length of 2.6 metres. Its speed is 45 knots with a range of 8 km and its warhead is 45 kg of Torpex. It can dive up to 800 metres. Stingray is fed with target data and other associated information prior to its launch, after entering water it searches for target autonomously in active mode and on acquiring the same attacks it. It is carried by Nimrod aircraft. Stingray Mod 1 is reported to have a shaped charge warhead and improved shallow water performance.
The MK-54 lightweight torpedo is a hybrid of technologies taken from MK-46, MK-48 and MK-50 torpedoes. It is supposed to have homing and warhead of the MK-50 and propulsion package of the MK-46 torpedo. It has incorporated COTS processing technologies for an advanced guidance and control system. It is stated to have sophisticated shallow water capabilities for littoral threats. The MK-54 torpedo has been finalised for P-8I aircraft by India.
Low Cost Anti Submarine Weapon (LCAW) A200/A is a miniature torpedo developed by WASS. LCAW has been developed as an intermediary between air launched torpedoes and conventional depth charges. It is a low-cost option, which provides propulsion and guidance to a depth charge without the costs of a torpedo. The air dropped version A200/A is deployed from aerial sonarbuoy dispensers. The weapon is primarily designed to engage targets in shallow water, like midget submarines. The A200/A version has a length of 914.4mm, weight of 12 kg, and a diameter of 123.8mm. The warhead is a 2.5 kg PBX shaped charge and the LCAW has an operating depth from 15 metres to 300 metres. It has a speed of about 18 knots with a range of 2 km.
Airborne ASW Sensors
In ASW operations, diverse sensor suites have been and will continue to be used. This reflects the variable detection performance and accuracy of these sensors, with variations in submarine signatures and sea state conditions. Typically less accurate sensors may be used to establish the presence of a contact, and more accurate sensors establishing exact position and identity, to prosecute an attack.
Typically, sophisticated sonar equipment is used for first detecting, then classifying, locating, and tracking a target submarine. Typically an Aircraft deploys a radio sonobuoy, the sonobuoy deploys a hydrophone sensor, and finally, acoustic data is transmitted from the buoy to an aircraft where it is analyzed for submarine signatures.
Passive Sonar Technology
Passive sonar techniques remain a mainstay of ASW systems, and have benefitted strongly from advances in digital processing and advances in array beamforming techniques over the last two decades. The preferred passive sonar configuration for surface warships and submarines is a towed array sonar, where a cable carrying an array of hydrophones is towed behind the vessel. With digital beamforming techniques, a towed array can produce high sensitivity but also highly accurate bearing tracks. If a series of accurate bearing measurements are made, the location of a submarine emitting screw and machinery noise can be determined.
In airborne ASW operations, sonobuoys remain the technology of choice. In its simplest form, the sonobuoy is a compact, self-contained package of electronics designed to be dropped from an aircraft, enter the water, separate into an underwater acoustic sensor and an on-the-surface radio transmitter, and relay the underwater acoustic signals it detects to the aircraft, where the radio frequency (RF) transmission is received and processed to detect, locate, and track submarines at sea.
The most important current advances in technology are the introduction of satellite navigation receivers on sonobuoys, and advanced digital beamforming techniques to exploit the improvements in sonobuoy position measurement. With exact three-dimensional positioning data for
every sonobuoy in an array dropped in the water, range measurement accuracy to a contact is improved. More importantly though, the ability to use beamforming techniques which aggregate data collected by all dropped buoys, if in close proximity, permit accurate bearing measurements and increased sensitivity as the array of hydrophones is in effect acting as a single large steerable hydrophone.
Current technology research and development effort appears mostly focused on beamforming research, with Capon and Bartlett beamforming algorithms preferred. Given the enormous potential in the use of tomographic algorithms for this purpose, there is considerable long term growth potential in satellite navigation receiver equipped sonobuoys, combined with high power digital
processing.
Active Sonar Technology
Like passive sonar techniques, active sonar techniques have a long and colourful history, and active sonars are carried by surface warships,
submarines, helicopters on dunking tethers, but also used in active-passive sonobuoys. The most important developments in active sonar
are high power digital signal processing, and at the sensor end of the system the shift to Low Frequency Active (LFA) sonar technology operating in the 100 Hz to 1 kHz bands. There are two imperatives, one being the prodigious range performance of LFAs less affected by propagation mechanisms that scatter high frequency signals, but also its ability to defeat thin anechoic coatings or cladding on target
submarines.
Airborne Multistatic Anti-Submarine Warfare
Multistatic sonar technologies are emerging as an important strategy for ASW. Multistatic operations can potentially improve ASW effectiveness in challenging shallow-water environments while allowing critical assets to remain acoustically covert or at a safe standoff distance. The Navy uses multistatic acoustic sensor systems with aircraft and surface ships, in network-centric ASW surveillance missions.
But, for all its potential, multistatism is no panacea. The challenges are immense. All the sonar in use must be fully interoperable; they must be able to seamlessly exchange information for synchronisation and processing; and environmental conditions (like salinity and temperature) must be known over large areas if data is to be interpreted accurately.
In the face of this, sonobuoys can offer an advantage: fixed in position and able to transmit information to a single aircraft, they can, among other things, easily solve synchronisation issues. It’s perhaps no surprise that, with increasing submarine activity and advancing technology, navies are taking a keen interest in sonobuoy multistatism.
Multistatic sonobuoy fields for air ASW search mission are becoming more complex. The ability to utilize more sources, more receivers, and the resulting higher transmission rates provide an influx of information. As a result, the detection capabilities and data rate for contact reports (automatic detections produced by the received signal processing) is increasing dramatically. It is no longer practical for a sonar operator to be able to sift through detections one-by-one to find the target.
Techniques and tools which consolidate information from the contact reports and provide the operator with the capability to rapidly find and focus on target detections are sought. Typical active contact reports provide time difference of arrival (TDOA), bearing, signal-to-noise ratio (SNR), and, Doppler , depending on the waveform type. Geographical locations based on these measurements and the positions of the sonobuoys are also typically displayed to the operator, along with a target probability surface based on Bayesian inference from the observations. Innovations in graphical display of data that ease the operator’s workload, ranking of contacts to bring target detections to the forefront, and automatic suppression of clutter are potential topics of interest.
Electro-Optical Sensors
Thermal imagers and stabilised high definition television telescopes have been widely integrated on LRMP aircraft and ASW helicopters but have mostly been used for the identification and tracking of surface vessels. The technology has been proposed for use in tracking submarines by bioluminescence in surface wakes, or to track minute temperature increases in a surface wake. Both applications would be more suitable for an infrared hyperspectral imaging sensor.
LIDAR Sensors
LIDAR (laser radar) technology has been used successfully in depth sounding systems for seabed mapping, and has also been very effectively
employed for the detection of seabed and tethered mines in the US Navy Airborne Laser Mine Detection System (ALMDS). It has also been raised at various times since the 1970s as a potential ASW sensor.
LIDAR works by emitting laser (or LED) pulses and measuring the return time and strength of the reflected light. When deployed on space, aeronautic, or naval platforms, LIDAR can track a submarine’s disturbance to the ocean surface or directly image a vehicle. LIDAR is presently limited to sensing depths up to 200 m—projected by some to reach 500 m.
Emitter Locating Systems
Like electro-optical sensors, ELS/ESM (Emitter Locating System / Electronic Support Measures) have been widely integrated on LRMP aircraft and ASW helicopters, but have mostly been used for the identification and tracking of surface vessels, as surfaced submarines seldom employ radar. However, satellite uplink antennas may produce sufficient sidelobe emissions to render them detectable to more sensitive ELS/ESM type equipment.
Diesel Exhaust Sniffers
The diesel exhaust gas ‘sniffer’ was introduced during the 1940s, and uses techniques similar to contemporary household smoke detectors to
locate the exhaust plume residues from snorkelling diesel-electric submarines. The AN/ASR-3 Diesel Submarine Exhaust Gas Detection System was introduced during the 1950s and widely installed on NATO LRMP aircraft, including the P-2, P-3, S-2 and Canadian Lancaster.
As the Soviets replaced blue water diesel-electric submarines with nuclear powered replacements, the usefulness of the sniffer declined and they were not replaced when newer LRMP aircraft were built. In operation sniffer equipped aircraft would fly a meandering
search pattern to establish the direction of the exhaust trail, and then follow it until they found the submarine. In littorals and heavily trafficked shipping lanes, false alarm rates were high.
Diesel exhaust sniffers have not featured in any recent high visibility ASW programs yet their utility is much higher today than at any time since the 1940s. A new generation sniffer would be based on DIAL (Differential Absorption LIDAR), a form of laser radar in which the laser colour is tuned to excite specific chemical species in the exhaust gas. A LIDAR based design could sweep a circular footprint of hundreds of square kilometres around an aircraft in a matter of tens of seconds, generating a radar like image of all exhaust trails in reach.
Photoacoustic airborne sonar system
Engineers at Stanford University have developed a new hybrid technique combining light and sound. Aircraft, they suggest, could use this combined laser/sonar technology to sweep the ocean surface for high-resolution images of submerged objects. The proof-of-concept airborne sonar system, presented recently in the journal IEEE Access, could make it easier and faster to find sunken wrecks, investigate marine habitats, and spot enemy submarines.
“Our system could be on a drone, airplane or helicopter,” says Amin Arbabian, an electrical engineering professor at Stanford University. “It could be deployed rapidly…and cover larger areas.” Airborne radar and lidar are used to map the Earth’s surface at high resolution. Both can penetrate clouds and forest cover, making them especially useful in the air and on the ground. But peering into water from the air is a different challenge. Sound, radio, and light waves all quickly lose their energy when traveling from air into water and back. This attenuation is even worse in turbid water, Arbabian says.
So he and his students combined the two modalities—laser and sonar. Their system relies on the well-known photoacoustic effect, which turns pulses of light into sound. “When you shine a pulse of light on an object it heats up and expands and that leads to a sound wave because it moves molecules of air around the object,” he says.
The group’s new photoacoustic sonar system begins by shooting laser pulses at the water surface. Water absorbs most of the energy, creating ultrasound waves that move through it much like conventional sonar. These waves bounce off objects, and some of the reflected waves go back out from the water into the air. At this point, the acoustic echoes lose a tremendous amount of energy as they cross that water-air barrier and then travel through the air.
To detect the weak acoustic waves in air, the team uses an ultra-sensitive microelectromechanical device with the mouthful name of an air-coupled capacitive micromachined ultrasonic transducer (CMUT). These devices are simple capacitors with a thin plate that vibrates when hit by ultrasound waves, causing a detectable change in capacitance. They are known to be efficient at detecting sound waves in air, and Arbabian has been investigating the use of CMUT sensors for remote ultrasound imaging. Special software processes the detected ultrasound signals to reconstruct a high-resolution 3D image of the underwater object.
Researchers have presented a proof-of-concept system which bridges the gap between electromagnetic imaging in air and sonar imaging in water through the laser-induced photoacoustic effect and high-sensitivity airborne ultrasonic detection. Here, we use air-coupled capacitive micromachined ultrasonic transducers (CMUTs) which is a critical differentiator from previous works and has enabled the acquisition of an underwater image from a fully airborne acoustic imaging system – a task that has yet to be accomplished in the literature
The system should work in murky water, Arbabian says, although they haven’t tested that yet. Next up, they plan to image objects placed in a swimming pool, for which they will have to use more powerful laser sources that work for deeper water. They also want to improve the system so it works with waves, which distort signals and make the detection and image reconstruction much harder. “This proof of concept is to show that you can see through the air-water interface” Arbabian says. “That’s the hardest part of this problem. Once we can prove it works it can scale up to greater depths and larger objects.”
Magnetic Anomaly Detection
MAD (Magnetic Anomaly Detection) sensors were introduced during the 1940s and until the P-8A Poseidon have generally been a standard sensor on all airborne ASW platforms. Typically, fixed wing aircraft carry their MAD sensor in a nonmagnetic tail boom while helicopters tow it on a drogue equipped non-magnetic tether. MAD was sufficiently effective that the Soviets constructed some submarines with non-ferrous Titanium hulls to defeat MAD sensors.
MAD sensors are in technical language, termed ‘Magnetic Gradiometers’ as they measure variations in the local magnetic field of the earth. A
large object made of a ferrous metal, such as steel, will distort the local shape of that magnetic field, an effect which can be detected and localised, if the aircraft flies a systematic search pattern. These sensors have generally performed best in ‘blue water’ operations, in littorals sunken wrecks and variable magnetic properties of the seabed can generate false alarms. There is also limit of range of the detection technique due to the nature of the physical phenomena being sensed. For example, MAD detects the local disturbance in the
earth’s magnetic field caused by a concentrated ferromagnetic body (e.g. a vessel’s hull). However, given that magnetic field strength reduces with the cube of the distance, the range of such sensors is limited; current sensors are only effective out to a few thousand feet.
Legacy MAD sensors used 1930s fluxgate technology, with electrical coils wrapped around a magnetic core. More recent MAD sensors such as the ASQ-81 and derived ASQ-208 use an optically pumped helium atom detector device. The most important advancement has been the development and trialling of SQUID (Superconducting Quantum Interference Device) MAD sensors, which remain amongst the most sensitive sensors.
Focus Areas / Elements of Consideration
Signal processing
ASW relies on separating tiny submarine signals from background ocean noise, primarily by using active and passive acoustic sensing (sonar) and magnetic anomaly detection (MAD), and it looks likely that these will remain the most important signals in the near future. However, the range of signals may grow as sensor resolution, processing power and machine autonomy reach the necessary thresholds to reliably separate other, ‘quieter’ kinds of signal. As Bryan Clark notes, ‘While the physics behind most [non-acoustic detection] techniques has been known for decades, they have not been exploitable until very recently because computer processors were too slow to run the detailed models needed to see small changes in the environment caused by a quiet submarine.’ However, he adds there’s now ‘the capability to run sophisticated oceanographic models in real time’.
No breakthroughs have been publicly disclosed, though an independent investigation by British Pugwash in 2016 identified light detection and ranging, or LIDAR, using blue–green lasers; anti-neutrino detection; and satellite wake detection as signal types that may merit further examination.
Information Superiority; the ability to gather, process, integrate, disseminate, and display information together with a corresponding increase in the ability to use that information.
Data Fusion; combining track information from a variety of sources into a single best picture of the tactical operational area.
Situational Awareness / Assessment; continually monitoring the dynamic picture for impacts to the plan (recognizing potential limitations in the mission plan). Higher processing power can also enable digital sensor fusion, whereby different kinds of signal are synthesized and analyzed together, and better simulations of the baseline ocean environment, which would show up anomalies in greater contrast.
Mission Planning; recommending updates / changes to the operational plan to ensure the highest probability of detection is possible.
Execution Aides, assisting the crew in executing the operational plan / mission.
Automation, how the information is provided within the elements of the decision-making. The Tactical Decision Aides (TDA) should be prosthesis, adding additional capabilities to the operators, or simply as a tool available to the operators. The TDA shall assist, or replace, the operator when the situation causes an excessive workload that cannot be managed by the human capabilities. These approaches are not mutually exclusive, but complementary, depending on situation context, the specific nature of the TDA element and the operator’s role.
US ASW Platforms
The Boeing P-8 Poseidon is a military aircraft developed for the US Navy by Boeing Defense, Space and Security. The P-8 conducts ASW, ASuW and shipping interdiction, along with electronic signals intelligence role. The P-8 can carry torpedoes, depth charges, SLAM-ER missiles, Harpoon anti-ship missiles, and other weapons. It is able to drop and monitor sonobuoys. Indian Navy has acquired eight P-8I which have been adapted as per India’s operational requirement.
The Indian navy was the first and is the largest international customer for the P-8 with delivery of 9th Patrol Aircraft and recently completed seven years of operating the fleet. In addition to maritime reconnaissance and anti-submarine warfare capabilities, P-8I have been deployed to assist during disaster relief and humanitarian missions.
P-8A Poseidon is equipped with a host of sensing and surveillance equipment which make it well-adapted for maritime patrol and submarine hunting. This includes an APY-10 radar by Raytheon for high-resolution mapping. The APY-10 radar makes it possible to detect and track vessels above and below water (Raytheon Intelligence & Space, 2020). This model is an improvement on the previous APS-137 due to its reduced size and weight, increased target tracking capability and color weather avoidance mode. This advanced radar is capable of detection, classification, and identification of small stationery vessels on water using the synthetic aperture radar (SAR) mode. This provides the crew with detailed battle damage assessment.
Small fast-moving vessels and surfaced submarines can be detected, classified and tracked using the high-resolution imaging synthetic aperture radar (ISAR) mode (Raytheon Intelligence & Space, 2020). The P-8A uses an acoustic sensor rather than the magnetic anomaly sensor used on the previous iterations due to the high operating altitude of the P-82 (41000 feet). It uses an active multi-static and passive acoustic sensor.
The P-8A Poseidon surveillance system also includes gyro-stabilized MX-20HD digital electro-optical/infrared multispectral sensor turrets capable of housing seven sensors; these sensors include CCDTV, laser range finder, image intensifier, and laser illuminator. The MX-20 HD is a modular HD imaging system with large-aperture lenses for high magnification and a solid-state inertial measurement system for effective stabilization. This allows for long-range target optimization.
The P-8A achieves advanced sensing capabilities using passive and multi-static Sonobuoys, which can be deployed at high altitudes. A Sonobuoy is an expendable sonar detection system that is ejected from the P-8A. The P-8A deploys the Buoys in a canister and the inflatable float expands upon impact with the water to keep the buoys afloat.
Detection is carried out using hydrophone sensors deployed below the surface of the water, they contain a Piezoelectric transducer which generates an electric potential when subjected to a change in water pressure. This information is used to detect submarines in its vicinity and is then relayed back to P-8A via a radio UHF/VHF radio transmitter.
The P-8A advances its sensing capabilities using a UAV which can be launched from P-8A equipped with a Magnetic Anomaly Detection (MAD) sensor. Submerged submarines are detected by measuring small variations in the earth’s magnetic field caused by the vessel. In cases where hostile vessels are detected, the P-8A is capable of deploying a Mark 54 torpedo at an altitude of about 3000 ft by initially turning it into a glide bomb before impact. This is enabled by the High Altitude Anti-Submarine Warfare capability air launch accessory. The P-8A proves to be a key and necessary addition to the nation’s maritime patrol fleet due to its advanced sensing and assault capabilities.
Sikorsky Aircraft SH-60B
Sikorsky Aircraft SH-60B carries a complex system of sensors including a towed magnetic anomaly detector and air-launched sonobuoys. Other sensors include the APS-124 search radar, ALQ-142 ESM system and optional nose-mounted forward looking infrared turret. It carries the MK-46, MK-50, or MK-54 torpedo, AGM-114 Hellfire missile, and a single cabin-door-mounted M60D/M240 7.62mm (0.30 in) machine gun or GAU-16 .50 in (12.7mm) machine gun.
MH-60R Seahawk multi-mission naval helicopter
Sikorsky Aircraft developed the MH-60R Seahawk multi-mission naval helicopter, also called ‘Romeo’, in order to replace the US Navy’s legacy SH-60B and SH-60F helicopter fleet. The MH-60 R integrates advanced mission systems and sensors developed by Lockheed Martin Mission Systems and Training (MST). The helicopter is intended to carry out a range of missions, including anti-submarine warfare (ASW), anti-surface warfare (ASuW), surveillance, communications relay, search and rescue (SAR), naval gunfire support (NGFS), personnel transport, vertical replenishment (VERTREP) and logistics support. It can be launched from aircraft carriers, destroyers, cruise ships, frigates and amphibious ships. The MH-60R helicopter can be armed with Mk 54 lightweight torpedoes for ASW missions. It can carry a number of weapons, including eight Hellfire anti-surface missiles and .50 calibre guns for ASuW missions.
The MH-60R Seahawk naval helicopter incorporates new Telephonics APS-147 multimode radar, which employs inverse synthetic aperture radar (ISAR) technique to perform imaging and periscope detection at short / long ranges. The rotorcraft utilises Raytheon-developed AN/AQS-22 airborne low frequency sonar (ALFS) subsystem for littoral and underwater warfare missions. The ALFS subsystem is integrated with a dipping sonar and sonobuoy processing capability. The Advanced ALQ-210 electronic support measures (ESM) system is also installed to detect, locate and identify threats. It is complemented by an ESM autoloader and the development of mission data loads.
India in Feb 2020 cleared the purchase of 24 Sikorsky MH-60R naval multirole helicopters through the U.S. Foreign Military Sales program, according to a Ministry of Defence official.
GA-ASI Completes Unmanned Aircraft Anti-Submarine Warfare Demonstration of Sonobuoy Dispensing & Remote Processing, reported in Jan 2021
General Atomics Aeronautical Systems, Inc. (GA-ASI) recently completed development and test of the world’s first self-contained Anti-Submarine Warfare (ASW) capability for an Unmanned Aircraft System (UAS).
In Nov 2020, GA-ASI successfully demonstrated an ‘A’ size sonobuoy carriage, release, process and control from a company-owned MQ-9A Block 5 on a U.S. Navy Pacific test range. Using a SATCOM link, GA-ASI remotely processed bathythermal and acoustic data from deployed ‘A’ size Directional Frequency Analysis and Recording (DIFAR-AN/SSQ-53G), Directional Command Activated Sonobuoy System (DICASS-AN/SSQ-62F) and Bathythermograph (BT-AN/SSQ-36B) sonobuoys and accurately generated a target track in real time from the Laguna Flight Operations Facility located at Yuma Proving Grounds.
The MQ-9A Block 5 successfully deployed one BT, seven DIFAR, and two DICASS buoys to initiate prosecution and continuously track a MK-39 EMATT (Expendable Mobile ASW Training Target) over a three-hour period. Target track was generated using General Dynamics Mission Systems-Canada’s industry-leading UYS-505 Sonobuoy Processing Systems. GA-ASI is developing this first-of-its-kind capability for its new MQ-9B SeaGuardian UAS in partnership with the U.S. Navy under a Cooperative Research and Development Agreement with Naval Air Systems Command, Patuxent River, Md.
“This demonstration is a first for airborne ASW. The successful completion of this testing paves the way for future development of more Anti-Submarine Warfare capabilities from our MQ-9s,” said GA-ASI President David R. Alexander. “We look forward to continuing collaboration with the U.S. Navy as they explore innovative options for distributed maritime operations in the undersea domain.”
GA-ASI first demonstrated a sonobuoy remote processing capability in 2017 from an MQ-9A. Since then, GA-ASI has added a Sonobuoy Management & Control System (SMCS) to monitor and control deployed sonobuoys, and developed a pneumatic sonobuoy dispenser system (SDS) capable of safely carrying and deploying 10 U.S. Navy compliant ‘A’ size or 20 ‘G’ size sonobuoys per pod. The MQ-9B SeaGuardian has four wing stations available to carry up to four (4) SDS pods, allowing it to carry and dispense up to 40 ‘A’ size or 80 ‘G’ size sonobuoys, and remotely perform ASW anywhere in the world.
In a standard Maritime ISR and ASW configuration, SeaGuardian’s endurance exceeds 18 hours, encompassing a mission radius of 1200 nautical miles with eight hours of on-station time for submarine prosecution, providing a low-cost complement to manned aircraft for manned-unmanned teaming (MUM-T) operations. GA-ASI has already received orders for this MQ-9B SeaGuardian ASW capability from two separate foreign customers, and anticipates demand to be extremely strong for the MQ-9B SeaGuardian with its high-end maritime capabilities and low cost relative to legacy manned Maritime platforms.
France commits to SonoFlash active/passive sonobuoy, reported in March 2021
France’s Direction générale de l’armement (DGA) has contracted Thales for the full development, qualification, and production of the SonoFlash combined active/passive A-size sonobuoy to meet the anti-submarine warfare (ASW) needs of the French Navy. The development and fielding of SonoFlash is intended to meet the French Navy’s future airborne ASW requirements by affording increased flexibility for future multistatic operations. At the same time, the programme re-establishes a sovereign onshore source of supply for sonobuoy production. France currently relies on US-manufactured sonobuoys.
According to Thales, the SonoFlash’s innovative design and advanced technology incorporate several key features that deliver unmatched performance. Today’s buoys are either active (transmitting) or passive (receiving)., but the SonoFlash combines the two modes in a single sonobuoy: an optimal, powerful low-frequency transmitter and a passive receiver with a high directivity gain. The combination of these two capabilities with high endurance makes the SonoFlash buoy very versatile.
The active component, based on four compact high-power transducers, ultilises hardware sourced from Thales’ underwater business in Rydalmere, Australia. The frequency band is compatible with the company’s FLASH active dipping sonar to enable co-operative operations in a multistatic field.
For the passive element, SonoFlash adopts a design that mirrors the concept of the BARRA passive localisation sonobuoy, which deploys a horizontal array of hydrophones mounted on five extending telescopic arms, at a set operating depth. While the array employed by SonoFlash is not as large, it is still able to deliver very good directional performance, according to Thales. The company adds that the SonoFlash buoy can be commanded to change its setting via a UHF command radio link. Maximum battery life is eight hours.
China’s Airborne ASW
China has been working to shore up its ASW capabilities, notably with the development of the Z-20F and the Shaanxi Y-8Q – an ASW version of the ubiquitous Y-8 tactical transport.
The ASW-roled Z-20F bears a close resemblance to the US Navy’s (USN’s) MH-60R, including a chin-mounted surface search radar, stub-wings for weapons and other equipment, as well as an electro-optical/infrared (EO/IR) sensor mounted in front of the cockpit. The Z-20J, which presumably would function in a transport/utility role similar to the MH-60S, lacks the radar, EO/IR sensor, and stub wings.
Similar to their USN counterparts, both rotorcraft have the tailwheel mounted at the base of the tail, to facilitate handling aboard ships. The baseline Z-20 used by the People’s Liberation Army (PLA) has its tailwheel located at the end of the tail boom. The Z-20 also features a five-bladed main rotor, while the S-70 has a four-bladed main rotor. Both the Z-20F and Z-20J are still in development. The baseline Z-20 has entered service with the PLA, and made its public debut during the 1 October 2019 military parade in Beijing.
One unique feature the official mentioned was the Z-20’s fly-by-wire controls. This is rare on Western helicopters, with only the NH Industries NH90 and the considerably bigger Sikorsky CH-53K King Stallion adopting the technology. It is understood that the Z-20 is powered by a pair of locally-developed WZ-10 turboshafts, believed to be rated at 2,400shp (1,790kW) each – about 27% more powerful than the GE Aviation T700s that power the S-70.
