The helicopter-dropped torpedo is the primary method employed by navies to prosecute submarine contacts. As underwater threats are increasing and diversifying, at the same time new technology offers alternative ways to counter the submarine. Here we examine some of the options for the Royal Navy.
The evolving threat
Anti-submarine doctrine is having to be revised as the capability of underwater platforms and weapons are developing fast. Manned submarines: SSBNs SSNs, SSGNs and SSKs continue to become quieter but will also able to deploy their own UUVs that complicate the picture with additional sensing, deception and attack capabilities. Particularly in shallower littoral waters other short-range platforms; midget submarines, UUVs, swimmer deliver vehicles and semi-submersibles also threaten surface ships forced to operate or transit closer to the shore or through choke points. Underwater weapons are also improving with increased range and AI-enhanced sensing/homing and counter-countermeasures logic.
In the littoral, the slower submerged speeds of older submarines allowed protection of High-value Units (HVU) to be conducted using a multi-layered screen that was forward-looking. It could be assumed the submarine had limited lines of approach and would probably be lying in wait for the task group. Theoretically, the MPA or frigate with towed array sonar would detect the threat and a helicopter would be set to localise and destroy the adversary submarine. The RN lacks ASROC or an equivalent and its ability to prosecute submarines is heavily dependent on the time taken to launch the helicopter, its speed and range. MPAs are not always available and locating the threat with sufficient accuracy to cue the helicopter may be limited to what can be provided by the active towed array sonar. Alternatively, multiple dipping sonar-equipped helicopters must be expensively kept airborne for extended periods.
Modern underwater threats may present on any bearing and from longer ranges. Increased situational awareness and area denial techniques are needed to sanitise wider areas. Clearly, additional detection methods are desirable and other ways to neutralise submarines are needed.
The RN’s vision for its Future Maritime Aviation Force (FMAF) of the 2030s includes the provision for MARITIME PROTECTOR playing a role in underwater warfare. The RAF will take delivery of its first PROTECTOR, a Medium Altitude Long Endurance (MALE) Remotely Piloted Air System (RPAS) this year. Protector is a modified MQ-9B SkyGuardian UAV made by General Atomics and used for armed ISTAR, carrying Brimstone missiles and Paveway IV Laser Guided Bombs. The Integrated Review confirmed the RAF will receive 16 Protectors to replace its legacy Reaper fleet and the UK contract with GA includes the option for a further 13, probably with a view to buying the maritime variant.
GA has developed the SeaGuardian derivative of the MQ-9B with a range of 6,000nm, able to stay on station for up to 25 hours, it has nine hard-points for a sensor or weapon payload of up to 2,100 kg. SeaGuardian can be equipped with a variety of maritime radar and EO sensors, being able to conduct many of the same ISR missions as SkyGuardian.
The future development path includes the ability to drop sonobuoys and lightweight torpedos (main image above). Four podded sonobuoy dispenser systems (SDS) hold 10 A-size or 20 G-size buoys in each pod, run by a dedicated sonobuoy management and control system (SMCS). SeaGuardian could act as a communications node sharing sonobuoy and other sensor data with other platforms in including Poseidon and Merlin. Maritime Protector/SeaGuardian would be limited to flying from land but the RN sees it as a potential ASW force multiplier, supplementing the stretched Poseidon fleet, especially in the North Atlantic.
The FMAF vision also includes PROTEUS – a medium Rotary Wing UAS for use in the ASW ‘find’ role. Essentially the RN is seeking proposals from industry for a mid-sized RWAS capable of hunting submarines via sonobuoy and dipping sonar to supplement the Merlin Mk2. Proteus will need to be a sizeable aircraft as is also intended to provide surface search functions and contribute Maritime Intra-Theatre Lift (MITL). The requirement is only an outline at this stage, but there are already projects underway that might provide an RWUAS ASW ‘find’ solution.
The RN interest in medium-sized RWUAS goes back as far as 2013 when a Capability Concept Demonstrator (CCD) contract was awarded to Leonardo. A CCD Phase 2 contract was let in 2017 and flying trials and experimental work was conducted with an SW-4 Solo demonstrator. Development seems to have petered out but Proteus may provide new momentum. (Incidentally, why the RN has not already bought a few small, affordable RWUAVs for reconnaissance work, such as the Leonardo AW Hero or Schiebel’s Camcopter S-100 is difficult to understand).
UK-based specialist sonobuoy manufacturer Ultra electronics is looking at ways of conducting uncrewed ASW using an MQ-8C Fire-Scout RWAS equipped with a sonobuoy dispenser. There are similarities with the SeaGuardian concept, but for shorter range ASW missions launched from the flight deck of a frigate. Northrop Grumman in partnership with Ultra Electronics conducted a trial in Feb 2021 with a manned Bell 407 (acting as a Fire Scout surrogate) and successfully completed a large area multi-static acoustic search with the system.
To successfully hunt submarines using a field of sonobuoys requires considerable computing power and, for now at least, experienced human operators to make sense of the data. This is the key component of an expensive MPA such as the P-8A Poseidon. Like many autonomous systems, a potential vulnerability of Protector and Proteus would be their reliance on available satellite bandwidth in order to pass the raw data back for processing to the controlling platform.
Budget torpedo delivery
Recent exhibitions held by the RN to showcase future technology have featured the Malloy Aeronautics T-150 UAV carrying the BAE Systems Future Lightweight Torpedo (FLWT). For now this is just a concept and does not actually feature in the FMAF plan. However, this simple idea could be a very cheap force multiplier for the Merlin as well as a budget alternative to ASROC. The T-150 has a carrying capacity of up to 68kg so even if FLWT is considerably lighter than the 267 kg Sting Ray it will eventually replace, is likely to be too heavy for this particular aircraft.
In December 2020 the MoD issued a Request for Information (RFI) to Industry for an autonomous, UAV capable of carrying interchangeable payloads up to 200 kg and able to operate over the horizon. Malloy Aeronautics already have their T-400, with a 370kg payload and a range of 12 miles available to customers.
As discussed in our previous article, there are no firm plans to fit the Type 26 frigate with a Torpedo Launch System. (The Australians and Canadians have, however, selected TLS for their Type 26 derivatives, the Hunter and CSC respectively). Lacking the 24/7 availability of the TLS and speed of response, a simple UAV could still be highly effective when delivering a torpedo at short or medium range. Although slower to reach its target, the UAV offers much of the capability of the US Navy’s RUM-139 Vertically-Launched Anti Submarine Missile (VLA) at a fraction of the cost.
By its nature, TLS is a close-in weapon of last resort, the UAV-delivered torpedo would allow the submarine to be engaged at a much safer range. Being small and compact, the system would have a minimal shipboard footprint and several systems could be held at readiness in high threat areas, freeing the Merlin to focus on the ‘find’ mission.
In 2019 BAE Systems revealed their KINGFISHER concept for a naval gun-launched modular carrier system. Essentially the frigate can use its 5inch/127mm gun to fire an ASW payload that could include small depth charges, sonobuoys, hydrographic sensors or acoustic decoys. The most promising, simple and affordable option appears to be the depth charge payload. Anti-submarine mortars delivering depth charges to short-range date back to World War II but gun-launching is a new concept, enabled by the accuracy of modern naval guns. Kingfisher could quickly lay a barrage of charges in response to fleeting sonar contacts out to several Kilometers, without the need for airborne delivery of expensive homing torpedoes. Small and affordable depth charges may also be an ideal antidote to UUVs and several ships could fire patterns to cover a wide area relatively quickly. Multiple small underwater explosions would also temporarily deafen submarine or torpedo guidance sonars. Kingfisher could also be used as a ‘hard kill’ anti-torpedo defence system.
In surface actions there is a flexible ladder of escalation that can be used before opening fire; hailing by radio, illumination by fire-control radar, aggressive positioning or a warning shot across the bows. In undersea warfare there a very few options to discourage or deter an adversary without sinking them. Sending a burst of active sonar reveals the position of the emitter and may involve sacrificing the tactical advantage. Kingfisher offers a scaleable response to warn an adversary by laying small depth charges close by without sinking the target. As the line between war and conflict becomes increasingly blurred, having non-lethal response options assumes greater importance.
Other types of payload for Kingfisher would appear to present many more technical problems. A Sonobuoy would require re-engineering to fit into a 5-inch shell and withstand the huge G-forces created when fired from a gun barrel.
Work on Kingfisher has been underway since 2018, self-financed through BAE Systems’ own innovation fund but there has been some coordination with DTSL and the Maritime Capability (MARCAP) staff at NCHQ. The RN has not issued a formal requirement for the system but purchase of the depth charge version would seem like a very sensible low-cost option to equip the Type 26 frigates.
Future Lightweight Torpedo
The Sting Ray MOD 1 anti-submarine torpedo currently in service with RN is still recognised as a highly effective weapon for use against manned submarines. Diversifying threats and new methods of ASW mean a complete re-design and the Future Lightweight Torpedo entered the pre-concept phase in 2019. BAES is evaluating the options and aspirations for the FLWT include better target detection, AI-enabled discrimination against decoys and the ability to counter UUVs, small submersibles and torpedoes. Improved open architecture and interoperability with a much wider variety of launch platforms will also be desirable.
A significant reduction in weight would also be helpful allowing it to be delivered by small UAVs, although it is likely to retain the same dimensions and form factor as Sting Ray for backwards compatibility with existing launch systems. The ability to accept wing-kits would allow extended-range launch from altitude and compatibility with Poseidon/Maritime Protector. New more power-dense batteries could also increase speed or range and active sonar capability.