In this article, Kamil Sadowski considers how Medium Rotary-Wing Uncrewed Air Systems could be employed in anti-submarine warfare operations.
Utilising RWUAS for anti-submarine warfare is an obvious path for navies, given their low cost compared to conventional means and their rapidly advancing capabilities mirror the growing underwater threat. There is an obvious symmetry between the advance of XLUUVS and their airborne counterparts and a potential balance in the composition of future forces. While UAS are not intended to replace conventional ASW helicopters or Maritime Patrol Aircraft, they can play an important role in extending coverage in vast operational theatres or in smaller areas inaccessible to crewed assets.
Medium rotary-wing UAS exhibit promising payload capacity and endurance, coupled with their compact size and lower maintenance requirements compared to helicopters. The absence of unified NATO UAS classification standards leads to diverse categorisations amongst both defence communities and civilian operators. The term ‘medium rotary-wing UAS’ encompasses a broad family of aerial units, ranging from around 200 kg MTOW (Maximum Take-Off Weight), such as the Schiebel S-100 Camcopter, the Leonardo AW Hero, or USM Skeldar, to heavier aircraft like the Airbus VSR-700 or Schiebel S-300, with MTOW ranging from 600-700 kg. (The Proteus RWUAS in development for the RN can be described as a ‘heavy RWUAS’ being in to 2-3,000 kg class).
Rotary-wing UAVs have already found successful applications in navies, primarily for Intelligence, Surveillance, and Reconnaissance missions when operated from ships. The S-100 is soon to be operational in the RN, known as Peregrine. The integration of ASW ‘find’ capabilities is the likely next step beyond ISR and this is recognised by all the leading manufacturers. During live trials, such as the renowned REPMUS exercise, UAVs equipped with ASW mission modules have demonstrated clear potential. Ongoing efforts are directed towards enhancing the capabilities of medium rotary-wing UAVs, including sonobuoy overwatch (data relay) and deployment capabilities. Leading examples are pictured below.
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Schiebel S-100 with two twin G-size sonobuoy dispensers. An ISR-optimised version of this aircraft will enter service with the Royal Navy in 2024 and will be known as Peregrine (Image: Schiebel). -
Schiebel S-100 with Thales sonobuoy data relay module (Image: Thales). -
Airbus says its VSR-700 RWAS can be fitted with 2 x 4 A-size sonobuoy dispensers. (Image: Airbus) -
The Leonardo AW-Hero is the first in its class to achieve full military certification. The latest iteration includes twin engines for increased efficiency and safety (Image: Leonardo). -
UMS Skeldar V-200 with 3 x twin G-size sonobuoy dispensers (Image: Ultra).
Lightweight dipping sonar
Dipping sonar stands is an effective surveillance sensor for ASW helicopters, but its total weight, including the array, winch, necessary installations, and power supply, surpasses the capacity of even larger UAVs. Additionally, each dipping cycle affects endurance, necessitating a new solution to extend this capability to UAVs. The active sonobuoy, known for its compact size and weighing approximately 16 kg could be adapted as the basis for a lightweight RWUAS-borne dipping sonar. Some of the components such as the transducer array, electronics and UHF/VHF radio modules could be modified to reduce size and mass.
Eliminating elements such as the CO2-filled balloon, battery, and launching container would reduce the overall weight. A compact winch with a cable line would require development to achieve the desired maximum operational search depth. Despite these modifications, power supply remains the principal concern, as generating the necessary energy for active mode during hovering (with the sonar array deployed) could significantly impact endurance. In a multi-static operation, adjusting the emission cycle can mitigate this impact by reducing active periods and transmitting in specific circumstances, such as supporting contact tracking or covering ASW Helo transitions between dipping stations.
The proposed solution offers several advantages:
- Overall simplicity, eliminating the need for an additional acoustic processing system or sub-surface picture compilation tool. The control unit (aircraft, ship, or shore station) processes acoustic data relayed through the existing common sonobuoy RF communication protocol.
- Cross-platform bi/multi-static capability, enabling UAVs to execute searches in bi/multi-static mode through the control unit (ASW Helo, MPA) sonobuoy processing system.
- Small footprint, making it promising for smaller UAVs.
- The dipping sonar is fully reusable, unlike expendable sonobuoys.
Two general options for a compact dipping sonar using sonobuoy components are worth considering:
- Low complexity – simple DICASS (Directional Command Active Sonobuoy System) or DICASS combined with DIFAR/HIDAR (for extended passive surveillance capability)
- High-performance – sonobuoys with Low-Frequency Active (LFA) projectors and advanced receivers, such as 5-arm ADAR (Air Deployable Active Receiver)
High-performance solution would require substantial effort in designing a lightweight, retractable dipping array (as expendable sonobuoys sensors only have deployment ability). In addition to addressing the acoustics through the onboard sonobuoy processor, the mission system of the command aircraft (MPA or ASW Helo) would need an integrated UAV control module. This is crucial for planning and monitoring the UAV trajectory, executing search patterns including dipping positions and sensor allocation in multi-static operations and other essential functions.
The ‘mobile active sonobuoy’ concept should be considered as a viable future UAS sensor option for finding submarines and will undoubtedly suit some operational conditions as part of a wider ASW toolkit.
Kamil Sadowski served as an officer in the Polish Navy for 21 years specialising in ASW and has experience of developing and deploying underwater weapons systems.
An interesting take.
If the sonar buoy electronics are so good then why isn’t there…….? They are probably good enough for active but not for passive.
But I agree that these kind of systems are significant force multipliers and do have a space in the overall panoply of sensors.
Agree, interesting, but still hurdles to overcome.
Sonar buoys are effective bits of kit, but have several constraints. The biggest of which is detection range, which is purely down to the size of the kit (nominally 5″ diameter x 36″ length which everything has to fit into).
As a broad brush range analogy, if a TA sonar 2076/87 detection range against a SM was equivalent to the size of a football pitch, then a slim line array(Krait) might be equivalent to the penalty area, a dipping helo sonar to half of the centre circle, and a buoy equivalent to perhaps the D on the penalty area. The lack of detection range is one of the reasons that MPAs drop at least 4+ buoys in any string, not including the ‘bathy’ buoy.
Prior to dropping buoys, the receiver depth needs setting, something you can’t alter once it’s ejected. Not can they reposition themselves, once gone. The buoy has a squib/explosive charge which goes of to activate the inflation collar which keeps the antenna above the water, the sound of which travels further then the detection range of the buoy on any given day. It is reasonably easy for a SM to avoid a string of buoys if the squib is detected, rendering them somewhat redundant as they drift away on the current. Depending on the prevailing sea conditions, active buoys can have a range advantage over their passive counterparts.
An issue with using a dipping sonar on a UAV is that the wire also contains the power and data cable. So said UAV would need some form of data transmission unit to send the info to the control aircraft, adding both weight and power requirements.
Using UAVs isn’t an easy fix, but is probably the way forward to supplement crewed systems in the future given the costs of manned air assets.
From reading some accounts of ASW work during the cold war, I understand that another limitation for sonobuoys is the distance that they can transmit their data to a receiver for processing- whether that’s a helo or fixed wing aircraft. Given the large ranges that ASW can cover, even if they have a contact on their sonar, a sonobuoy could be “unheard” and therefore useless in the hunt.
As the article says, having the UAVs as relays for these sonobuoys builds the real-time picture of the total area.
Autonomous systems may help, but in addition to data processing electronics and multiple systems each Drone would need employ, you need to find space on the Helicopter platform to control the entire operation, which is likely (and in facts needs to be) over the horizon from the warship/battle group/convoy.
There is then the issue of weather (especially in the Atlantic or Artic winter), seven before you consider the question of failure rates, redundancy, minimum number needed to cover a specified area etc etc. Then is there enough space in the warship (storage, repairs, additional crew, fuel, weapons etc ) ?
I have often wondered just how effective the protection of a Carrier group with just two ASW frigates plus helicopters from the carrier) would actually be in a real war time environment with air, sea and submarine submarine threat spheres operating at once.
I also wonder about electronic noise as a possible method of detection let alone the question of submarine and airborne ECM/EW issues.
Very true, one of the benefits of Merlin is its size for equipment and people for managing the data throughput. That’s one of the reasons also why I was seeing the UAVs first used as data relays rather than processors- much easier to manage as a staged development of capability.
Size and space is always a tricky one, and your question about sufficient resource to protect a CSG is a valid one. I suppose, given the reduced size of the Russian sub fleet, it’d be OK (as long as we keep developing stuff like the UAVs). But with China’s fleet, I’m not so sure. Yes, they’re not as good, but there’s an awful lot of them…
how much space and weight do you really need to handle the compute and memory to process all this. A single desktop has tremonous memory and compute power, especially with some the custom silicon that leverages the process parallelization of GPUs. When the merlin was first envisioned in prototyped in the 1980s extra space for compute power might of been a greater issue. In the 90s performance was usually measured in mbs and now its gbs.
I don’t think cable would be that heavy, what would it be a strengthened weight baring USB C cable. Also recon drones with payloads of only a few kgs already transmit video data over many 10s of km. Should be able to handle audio data transmission.
and outside of Medium Rotary-Wing there is MQ-9B.
Sea Guardian would certainly be a huge force multiplier for our small Posiden force.
If you increased the Posiden force to 12 and added another 10 airframes to our Protector fleet of 16, (with 8/10 Sea Guardian kits), then you would have a really capable and sustainable Maritime patrol force.
For when bigger is best.
Anti-Submarine Warfare System | General Atomics Aeronautical Systems Inc. (ga-asi.com)
It seems we are looking at three possible rotary classes: 200kg MTOW, 700kg MTOW and 3 ton MTOW.
The 200kg class, exemplified by the RN Peregrine is just too small to be useful for ASW. I had thought perhaps at least as a relay carrier, until I saw the relay size in the photo. To dismantle a useful (and expensive) ISR to let it carry a few sonobuoys or a relay is a waste of effort and money.
The 700kg class (such as the Schiebel S-300) seems far more promising. With 5 times the payload of the S-100 on which Peregrine is based, it could already carry the weight of a lightweight dipping sonar such as the L3 Harris Firefly (<220kg) for 4 hours, long enough to be useful. Whether it has the space to carry this inside or underslung is unknown, and power may also be an issue, but we may be close to a working system. Furthermore the S-300 fits in a 20ft container or a Navy POD and could be worked on alongside a Merlin in a T26 hangar. The larger VSR-700, for all its heavier payload and longer duration, might be a less easy fit.
3 ton Proteus (payload >1ton) should be able do it all, if not necessarily at once: sonobuoys, dipping sonar, multistatic sensor fusion, lightweight torpedo. It should have the power, the range and the useful duration, although we’ll have to wait until 2025 for flight testing to be sure. It won’t be able to fit in a hangar alongside a Merlin and would have to be kept in the T26 mission bay, although no problem to put it alongside a Wildcat in a T31 or a T45 hangar.
With P8s and MQ-9Bs the UK local airspace out to a few hundred miles should have good coverage, but efforts further afield will need to be ship based. The right combination of ASW drones would need to be figured out as information comes in and may ultimately depend on cost: perhaps something like Proteus for dipping sonar and overall coordination, a couple of S-300s for sonobuoy distribution, with Wildcat for the torpedoes. Working towards getting a 700kg class rotary seems worthwhile, but I wonder if USVs or UUVs with a tail would be the better complement to Proteus for second-tier sub hunting from a T31.
As T31 and T45 don’t have onboard ASW capabilities why would you carry an ASW drone?
So that you have some way to detect Submarines/UUV’s at a lower cost than fitting the whole ship with ASW sensors and quietened hull form + insulation etc
We don’t really know the current state of play.
My *suspicion* of PiP was also to quieten the T45 machinery. It is an EP system so is fundamentally suited to ASW – OK wrong hull form etc.
As for T31 it is know that an upgrade package was agreed with Babcock – what is in it is unannounced. Its parent IH is an acceptable ASW asset.
So I’d be surprised if nothing was the answer to capability.
The thought process appears to be ATM – how can capability be added fast and relatively cheaply into existing programs without stalling them…..
I’m wondering if the addition of ASW features to the T31 might not be to deal with traditional submarine threats, but rather UUVs? We’ve seen, both in Ukraine and the Red Sea, the havoc that UAVs can cause. The development of UAVs is more advanced currently, but UUVs have the potential to carry larger warheads and hit ships below the waterline.
Imagine a swarm attack, not of UAVs but UUVs, and any current warship would be in trouble. Outrunning the UUVs at full speed would be one option, but in doing so, would expose any ships they were escorting.
That also assumes that the drones cannot be retargeted onto the ships being escorted?
Shame there is a war on: information is therefore somewhat limited.
I’d assume they can be retargeted which is why the escorted ships would be exposed if the warships did a high-speed runner.
As for war, one thing is known. HMG has drastically ramped up spending in industry on research and development projects since the start of the war.
HMG has drastically ramped up spending in industry on research and development projects since the start of the war
Do you have any sources that you could quote? Where does the finance come from?
The instigation of PIP on the T45s addresses many issues that the T45 propulsion system had, but turning the T45 into a stealthy ASW capable unit isnt one of them.
Yes is does address some of the noise issues the T45 has\had. Newer DE will run quieter then those they replaced thereby decreasing your radiated noise signature (which they needed as they were always v noisy ships), which is always a bonus.
Don’t believe that the first two T32s will have an active sonar fit yet, as the hull doesn’t have the cut outs to incorporate one. It is possible to do that further down the line at their first major docking period should the RN so desire. FFBNW for a TA system, different ball game entirely. I can see all the plumbing going into that effort more readily then a hull mounted active set up. That just leaves the issue of finding enough sonar operators to man the system…….
Thing was that T45 had to have a GT running in order to be under way under the old setup. The two DGs were not man enough.
Now a T45 can run at lower speeds solely on the three new DG sets. As they are bound to be in acoustic enclosures and the published specs were for rafted I think we can assume a big noise reduction.
I agree that it doesn’t make T45 an ASW optimised hull but it does mean that it isn’t a CSG’s prime noisemaker!
To supplement the manned ASW helicopter
lol.
You don’t say and I thought that it was for pizza delivery. lol
“As T31 and T45 don’t have onboard ASW capabilities why would you carry an ASW drone”
Often the main feature of this story escapes some
You could add the BAE Strix….
That has sonobuoy dropping AND dipping sonar configurations….plus light attack with Brimstone, Razer, Sea Venom etc…plus the usual ISTAR stuff…
The question is how small and light can you make a dipping sonar. The smaller it is, the smaller the drone, the more you can pack in a ship, the more you can afford, the more ocean you can search. Does anyone know what are the constraints to making these sensors smaller or lighter? Alot of these sensors are routed in the 80s and 90s. Alot of tech has become much smaller and more powerfull since then. Is it possible to use any tech we have today which wasn’t available before to make these things more compact and light?
Do you have to put the drones on a dedicated warship like a type 26 or 31. Could you just put them on a cargo ship deck in a convoy.
Just wonder at the cost of expendable sonobuoys, how you deny the enemy obtaining a buoy or maybe the tech is not valuable.
That is built into the calculus of using them.
We have been using them for years……
The secret sauce is really in the signal aggregation and processing which isn’t done in the buoy itself.
Thank you
Nowadays state-of-the-art signal processing is done by software and the buoys are just essential underwater microphones array collecting data and forwarding them to somewhere else for processing. After the battery runs out on the buoy then it normally sinks to the bottom.
Back in the 70s, there was an incident where the US managed to get hold of a Soviet buoy and discovered that inside it was some Texas Instrument chips from the US. Most probably more buoys were retrieved by other countries, friend and foe.
Remember the incident of the USN EP-3E being forced to land in Chinese territory in 2001?
During the journey to landing, the crews onboard were busy destroying the hardware with fire axes, pouring coffee inside the PC/laptop, and throwing paper documentation overboard.
What was critically important was to destroy the hard disks with the software stored on them. The hard disks contained the collected data, signal processing algorithms, documentation, and encryption keys that can give away what the USN was interested in and its capability.
Throwing the hard disks overboard and hoping sea water could damage the magnetic medium enough so that not much data could be retrieved should they ever be recovered is a quick way.
There are better methods to destroy hard disk data but takes a long time.
How much sensitivity information the Chinese managed to recover from the EP-3A is unknown.
https://sgp.fas.org/crs/row/RL30946.pdf
Diversity of options for ASW is there.
What is clear is, all idea needs thorough evaluation. So, why not try and verify? Just “thinking” of “super good idea”, waiting for some “final good option” is not the way to go.
History says,
reality is much more important than assumption. Many “brilliant idea” dies after just a short trial. Then just do it.Simple and robust wins.New technology rapidly evolves = increase its weights and powerAs such, “cheap and numerous” is attractive but I cannot believe it is easy. In ASW, “cheap and numerous” example is only sonobuoys to date. Helicopter carried dipping sonar has evolved so large to keep it effective, that even Wildcat faces big endurance cut when equipped with. For any RWUAS, “good dipping sonar” will be deadly heavy.
With this simple thinking, “UAV deployed and relayed sonobuoy” shall be the first choice, and “re-usable sonobuoy type technology” will be the second promising.
Just one opinion.
“good dipping sonar” -may be or may not be deadly heavy. It depends of RW UAV payload and requirement for actually “good enough” dipping sonar. Currently manufactured active sonobuoys (considered as basis) offer couple options for weight and performance
I think the trend will be more towards optionally manned aircraft.
I was expecting some mention of LUSVs, such as an autonomous XV Patrick Blackett, carrying a containerised towed array as here, TRAPS – Towed Reelable Active/Passive Sonar – GeoSpectrum Technologies Inc . This adds persistence beyond anything UAVs can provide and there is still the prospect of adding UAVs to them. Maybe this will be a topic for a later edition of your eminent organ.
I think, the topic is focused on unmanned aerial assets so why would we expect mention of USV? No argument about TRAPS, its performance elipse anything what UAV may have be equipped today, but one does not exclude another. Surface-borne sonar systems are more porwerful -nothing new here. But even having such beast like S2087 LFAS on frigate, aerial assets provide advantage in manouver and short reaction (beyond USVs capabilities). I agree with prospect about USV with towed array in group with UAVs