In this article, we examine the layout, equipment and initial trials programme for RFA Stirling Castle, the first of the vessels recently purchased by the RN for use as a mothership.
Background
Early in 2023 the former walk-to-work and subsea support vessel, MV Island Crown was purchased from Norwegian owners (Island Offshore) for £40M, primarily as a platform for operating autonomous mine hunting systems. The acquisition of this vessel is positive news and demonstrates visible progress as the Naval Service embraces new ways to deliver capabilities. The generation process has been rapid and she will begin operations within 6 months of concluding the purchase. (It took the RN 9 months for the much smaller XV Patrick Blackett bought off the shelf from the Netherlands to achieve the necessary certifications to go to sea.)
She arrived in Devonport on 29th January still under the Norwegian flag and the MoD purchased her shortly after midday on 30th January. Very little conversion work was done during her time in the dockyard and the focus was on completion of paperwork relevant to the transfer to the MoD as well crew familiarisation and safety aspects. The ship was formally re-named Stirling Castle and registered in London. New nameplates were fitted and the vessel was assigned a pennant number of M01, although this has yet to be marked on the ship’s side. Taking a vessel built and operated entirely to commercial standards and then working out how she will be run using RN and RFA procedures inevitably takes some negotiation and compromises.
By RFA standards she is a relatively compact vessel, 96.8 metres long (including the crane overhang) with a displacement of 5,800 tonnes. She was refitted by the Norwegian owners shortly before sale to the MoD and was handed over in excellent condition, having also been well-maintained in service since she was constructed in 2013. The large tower and compensated gangway used to provide access to and from offshore installations that had been fitted on the port quarter was removed sometime before the ship was handed to the RFA but the long-reach crane has been retained.
In order to save time and expense, Stirling Castle will not be painted grey until the next refit in about 4 years’ time. She has not yet received a military communications fit which enables the handling of secret-grade material although equipment may be embarked later as the RN develops its concept of operations. Force protection weapons have not been fitted yet but mounts for 50cal Heavy machine guns may be added in the future.
At work
The main working deck that runs nearly half the length of the ship will be used to store, prepare and deploy boats and UUVs on mine warfare and hydrographic survey tasks. The boats, accompanying support equipment and C3 systems are mostly designed for transportation in TEU containers and much of the kit will be embarked this way. At least for now, it is envisaged the crane will be used to launch and recover boats over the side. A door in the stern transom and a removable panel in the starboard bulwark also offer alternative routes that craft might be deployed if suitable Launch and Recovery Systems (LARS) were added.
A pontoon could be secured alongside to facilitate personnel transfer on and off the boats. (Despite being fully capable of autonomous or remotely piloted operation, they often have crew on board for safety purposes in busy waters). The Dynamic Positioning (DP) system allows the ship to remain stationary despite wind, tide or currents. The ship can be manoeuvred so that the boats are protected in the vessel’s lee for launch and recovery. Like any small craft, operations will inevitably be subject to safe weather operating limits.
The working deck is well served with adjacent workshops and store rooms for the RN teams to maintain kit. Compared to her sister ships, Island Crown was built with an additional accommodation block aft of the main superstructure. This section will be occupied by the embarked RN personnel numbering up to 43 sailors. There is also a conference room, offices and recreational spaces.
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The working deck is protected by wooden planking and has plenty of securing points for TEU containers. The full-height bulwarks around the deck will provide excellent shelter to for personnel and mine warfare boats. -
Looking aft on the working deck, there is a door in the port half of the transom that can be lowered for access to the water. -
The large crane has a considerable reach with a safe working load of 10 tonnes at a 34m radius and 5 tonnes at a 40m radius. -
There is a removable section in the starboard bulwark that would allow loads to be lowered directly over the side. -
A long way down… the view from the flight deck. -
A storage area with workshops on either side opens onto the work deck. -
Workshop space for use by the RN team.
The lightweight aluminium flight deck is not rated for naval helicopter operations and is unlikely to be used except maybe in CASEVAC emergency. Its only role might be as a launch point for small uncrewed air systems. As the flight deck generates considerable windage on the vessel and is slightly surplus to requirements it could be removed in future.
The spacious bridge has a 360º view around the ship and is typical of modern highly automated commercial vessels. When using the DP system, the operator is seated at the rear of the bridge looking aft over the working deck. The RFA currently has very few personnel currently qualified on DP systems and training up more operators will be a priority.
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The command and helm positions on the bridge. -
The bridge is spacious and includes a comfortable seating area. -
When using the Dynamic Positioning system it is controlled from this seat facing aft on the bridge – the controller has a commanding view. -
Looking forward from the flight deck -at the mainmast and diesel exhausts – there is no funnel as such.
Machinery
Stirling Castle has diesel-electric propulsion designed for simplicity, redundancy and manoeuvrability. Four diesel generators provide power for the ship’s hotel load as well as the two azimuth thrusters at the stern that can rotate 360º. There are also twin bow thrusters and a retractable azimuth thruster at the bow. In DP mode, the forward and aft thrusters may be set to gently push against each other so that a decrease in power on one will provide an instant response to a change in conditions such as gusting wind.
The two DGs and the stern thruster on each side of the ship are completely independent of the other to provide backup in case of failure. With just 5 marine engineers on board, the machinery spaces are usually unmanned except during routine maintenance. The engine exhaust uptakes that run through the accommodation areas are well shielded the ship is very quiet when underway.
The centre section of the vessel under the working deck is occupied by cargo tanks for semi-liquid products such as minerals used in oil drilling or cement, a legacy of her former employment in support of offshore energy projects. These tanks are not relevant to her new role but remain in place. In-service support will be provided by Cammell Laird as part of their cluster contract with the RFA. CL will conduct maintenance in their shipyard or, if needed, send engineering teams to repair the ship wherever she may be deployed.
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The small Machinery Control Room – engine monitoring on the left and ship controls duplicating those on the bridge on the right. The space is not always manned and if the IPMS detects a problem, duty engineers are alerted by a paging system. -
Four diesel generators provide the power for the propulsion motors and the ship’s hotel load. -
One of the four diesel generator sets. -
The motor on the left drives the azimuth thruster below through the gearbox on the right. -
The well-equipped marine engineer’s workshop.
Accomodation
Living spaces on board are in line with the usual high standards of RFA vessels. Most of the crew and embarked personnel have comfortable two-berth cabins with en-suite toilet and shower. Many cabins and living spaces have large scuttles and there is plenty of natural light. Officers and crew dine together in a cafeteria and there are several recreation spaces. In common with HMS Protector, Stirling Castle has a sauna, a feature of many Scandinavian-built ships.
Stirling Castle has two crews that rotate every 2 months, (reducing to 36 days once she is operational) in a change from the manning model used by the majority of the RFA where everyone serves at sea for around 4 months, followed by 3 months off before being assigned to another vessel. The ‘one ship – two crews’ model has several advantages as that crew will be on that ship for around two years. This ensures familiarity with the platform and helps build a greater sense of ownership. It also allows a small measure of flexibility for sailors as they can negotiate the timing of when they are relieved by their opposite number on the other crew.
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The dining hall. -
The food servery area. -
2-berth cabin – the ensuite toilet and shower is through the door on the right. -
Day room for off-duty relaxation. -
Mess
Into service
In late June, the RN’s Maritime Autonomous Systems Trials Team (MASTT) and Defence Equipment & Support (DE&S) teams embarked on Stirling Castle to oversee a week of initial trials operating autonomous boats from the new vessel. RNMB (Royal Navy Motor Boats) Apollo, Hydra and Hazard were deployed successfully from the ship in the sheltered waters of Portland Harbour. Stirling Castle has now arrived in Devonport to undergo a specially tailored FOST package to certify the ship and crew are safe before beginning more demanding trials with the MCM systems.
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RNMB Apollo on its cradle embarked on the working deck. -
Lifting -
RNMB passing ‘mother’ -
Crane extended
The future
Stirling Castle will ultimately be based in Faslane, co-located with the First Mine Countermeasures Squadron (MCM1) which already operates autonomous boats under Project Wilton. For the foreseeable future, she will predominantly operate around the south coast, from Portsmouth, Portland or Devonport. Thales UK at Turnchapel in Plymouth is working on development of the Anglo-French/UK Maritime Mine Countermeasures (MMCM) programme and French work on the system is being undertaken not far away at Brest in Brittany. Besides MMCM, Block 1 of the RN’s Mine Hunting Capability (MHC) programme includes the Combined Influence Sweep system developed by AEUK based in Dorset as well as a suite of UUVs. Stirling Castle will play an important part in the evaluation of these new systems as well as increasing the range at which they can be deployed.
This vessel adds another capability to the RFA, a service that should be noted as offering careers with plenty of varied and interesting opportunities supporting the RN. RFA Stirling Castle (and RFA Proteus) will provide the navy with useful operating experience of very modern commercial vessels designed for lean manning and efficient operation that may help inform the design of future auxiliaries and warships built around smaller crews. She may also be just the first of the ‘Castle class’ as the RN wants eventually to acquire up to three more motherships to host globally deployable autonomous systems.
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Moody. -
Making her first entry into Portsmouth on 1st June (Photo: Gary Davies, Maritime Photographic). -
(Photo: CNPics) -
The pair of yellow tubes fitted at the stern and on the starboard side are designed so the fast rescue boat can hold position by pushing its bow in between them. Personnel can then climb off and ascend the ladder between the tubes or if incapacitated, can be winched up using a pulley mounted in the A-frame at the top (Photo: Jake Corben).
Could a crane that big be used to resupply Mark 41 VLS tubes? As long as you can get the two ships to bob up and down against each other out at sea.
No.
They can be reloaded at sea but the work takes a lot longer.
A full reload can be done in port with dock cranes in a day.
https://www.youtube.com/watch?v=EwWMuLj8wXU
It has been attempted at sea.
indeed, “attempted” !
And given up as a bad job. Too many variables on a suspended pendulating load. That’s before you get to handling the empties and putting them somewhere before you load a new canister.
One of my previous jobs helicopters ( Squirrel type) lowering 5m heavy poles into previously drilled holes in the ground for foundations did occur.
Amazing downdraft underneath!
The risk assessment for VERTREP of a VLS store would mean that it will never happen unless its in extemis during war time. Imagine hovering above a loaded silo, lose an engine, cut the load to keep power available, the ammo falls onto the silo because if you dont do that the helo will spoof in onto the silo.
I don’t think anyone is mental enough to try VERTREPing VLS for the reasons GB states above. The issue for ship to ship VLS reload are that :
It would make a good video game.
Thats the very largest size of canister so is the extreme situation and a long range strike mission might be shifted to another means if the ship has none left. Im thinking of the smaller self defence missiles where defence of the ship itself is essential. Also theres obviously wind and sea state conditions that are more ideal than others.
Remember the missile is always loaded vertically by a crane or similar at dock and that needs ideal conditions too
Having done some work into the feasibility (or otherwise) of this – and witnessed some of the shenanigans involved in loading VLSW at a munitions quay – I’m well aware of the limitations thanks.
I’ve also seen what the Navsea came up with at Port Hueneme in the early noughties to try and crack the problem. Sadly, no open source footage of it, because the comedy value is immense.
You have never craned something over the side of a ship have you?
This sort of thing is sci-fi……..
tell me how they unload the existing canister and load a new one for any warship ( or submarine)
Harry Potter ?
It must be dangling at the end of a wire.
I wouldnt have thought a small helicopter could lift these large construction poles, hanging vertically and slot them in either. of course they are guided at the end. And military helicopters are normally much much more powerful than those built for civilian use.
Is 2 -3 days in port the only choice ?
https://www.usni.org/magazines/proceedings/2018/july/reload-missile-shooters-sea
This pic is from along aside a stores ship
You are conflating replenishment alongside the wall with replenishment at sea.
The RFA is moving three ways. The warship is moving three ways.
The missile on the end of the cable is moving three ways. Too much movement to do this with ease at sea. It is not trivial.
Honest friend we are not trying to be awkward. 🙂
Well, then don’t give up your pole dancing job yet may come in handy, ho ho ho.
Having been involved in construction where things get done, oh how it compares with the box tickers who have no hands on experience and say ..cant be done. lets go back to port and spend 2-3 days and do it that way.
Here. Just for you.
https://www.youtube.com/watch?v=EwWMuLj8wXU&ab_channel=DefenseUpdates
“This sort of thing is sci-fi”
Yet the image I provided is a submarine tender ( Emory Land) replenishing missile cannister for a ship along side
Something else that was considered impossible at the time.(1912)
Reconstruction (2021)of the RN first seaplane the Waterbird
They too were lifted on and off the water by crane from its mother ship…surely cant be done as well ?
Not the same.
Something else thats impossible
But with the right equipment and the proper training two large ships can travel very close together ( crazy impossible) and also transfer solid stores and fuel from one to the other- horizontally ( impossible)
Again replenishment of a missile cannister between moving ships at sea
‘HMS Manchester receives Sea Dart via Replenishment At Sea, April 1988. The bulky missile canister is transferred horizontally from the RFA stores ship via jackstay. It is then attached to a hydraulic arm on the launcher and raised to the vertical position. The missile is then withdrawn from the bottom of the canister by another hydraulic ram that lowers it down to the magazine below. The empty canister is returned to the RFA. (Photos: Kev Slade)
https://www.navylookout.com/from-sea-dart-to-sea-viper-area-air-defence-for-the-royal-navy/
Not the same.
And what happened to the nuclear flying Aircraft Carriers?
No RAS-ing isn’t impossible. It is difficult.
of course , ‘peace’ came along and the easy way was preferred as it always is. Look how complicated the Sea Dart reloading was with a special container which needed to be re used the ram to extract the missile from the container etc. Now each missile has its own box which stays with it from ‘farm to plate’- to reuse a phrase.
I can think of aviation aerial refuelling where in order to have the process available ‘when needed’ its done plenty of times when not needed to make sure the skills arent lost
It fails to mention how many tins of beans and Sausages (snorkas) she can carry,
Belgium is spending £1 billion on six of those. And they’re considerably smaller with significantly less accommodation than RFA SC.
Yes. I note Stirling Castle has a 2.20 metre greater draft. Nice deep hull always useful for when working in coastal waters and channels, not.
80% of the solution at 25% of the price, and we get it now rather than four years from now. Bargain. If some aspects aren’t perfect, well nothing is.
Bargain and cheap aren’t synonyms for each other.
I wonder how happy they and the Dutch are happy about their decision now.
Probably very happy. The Koninklijke Marine hasn’t a bad track with procurement.
1) I assume those tanks are filled for ballast.
2) What a lot of wasted volume.
At the moment. As the concepts of use develop over the next few years I’m sure uses will be found for the space.
1) It helps at times when others go out of their way to state the obvious. Thank you.
Just looking at those tanks and wondering if they were removed them and you put in a lift to the working deck, just how many RNMBs or other autonomous vehicles you could fit in that garage. Now that has me thinking of a smaller version of the carrier’s weapon handling system.
I was always a bit doubtful about retiring our MCM fleet without replacement. All the official comment suggested autonomous systems could be deployed from frigates or operated from shore. At the same time, Belgium ad Netherlands were ordering new bespoke platforms.
But if we can buy an effective platform like this for £40m, and get it into service so quickly, then the RN has got it right.Now we need a few more.
I wouldn’t buy any more till the RN/RFA have had a few years to properly evaluate what things are and aren’t needed on the sort of ship.
That kind of thinking is the enemy of getting the service sorted.
If there’s a need, budget and available crew, putting together a working group to advise the committee to report to the steering group to advise the Minister to wait a few years until the requirements sub-committee has had chance to properly evaluate and work up the business case, isn’t the way I would go.
If it’s reasonably good and it’s cheap, buy it. Then if it isn’t perfect and you can’t upgrade it, sell it later. At least the Navy will have had a few years of working capability while someone whips up their perfect gold-plated requirements list back in the office.
And rushing in to something new without proper testing and evaluation is how lots of money is wasted. Money the MoD doesn’t have much of now or likely in the next few years.
Lots of money? Absent a crisis, the decisions that are rushed are the decisions to cancel, not the decisions to buy.
Nevertherless, overlong evaluation times are no protection against failure and extended decision making typically leads to budget overruns. (Remind me how many years and how much money was spent evaluating Crowsnest?) What kind of requirements might we fail to discover over a year of MCM operations from Stirling Castle that the extra years you are asking for will uncover? The longer you leave it, the more nice-to-haves accrete, masquerading as requirements and pushing up prices.
I would argue the absence of timely decision making has cost the Navy far far more than rushing into things, certainly over the last twenty five years. Overall, I’d rather chance wasting money to have capability than chance wasting money to lack it.
I agree. So often we hear the refrain ” buy ready made off the shelf equipment”. In many cases, there is no such kit available. But for MCM motherships, there is obviously a commercial off the shelf option that avoids the seemingly unavoidable delays and cost overruns in major procurements.
Last I heard they were looking for up-to 4 additional mother-ships, now it’s up-to 3!
Still think it’s a massive shame we didn’t pursue a common OPV sized platform to replace the Hunt’s/Sandown’s/Echo’s and Rivers.
But i guess a clutch of RFA’s is better than nothing at all, and with an additional ability to deploy the autonomous kit from other vessels it’ll be a pretty versatile capability.
Penny pinching indeed. Lets say that Stirling Castle is a great purchase as a trails ship to work out the kinks in the deployment of remote systems. Do we think that 3 more mother ships can replace the final 13 Hunts and Sandown’s?
Have we seen any figures on how one mother ship with its remote systems is as “useful” or “efficient” as a given number of Hunts or Sandowns? You know the usual “we only need one third as many hulls because the off board systems are so much more efficient” ???
By the way, even if one mothership is equivalent to 3 or 4 Hunt’s or Sandown’s in pure MCMV work, if you loose 1 MCMV to battle damage, the other 3 keep working….. how does that work for the mothership?
To your point Challenger, does the other recent commercial purchase of a “Seabed operations” capability plus the MCM motherships replace the hydrographic capabilities of Echo and Enterprise – once again, platforms are great, but one platform can only be in one place at a time.
Wouldn’t it be forward looking if we got in now with our Danish allies who have signed for the design phase of a multi-purpose vessel (MPV), which could replace the MCMV’s, Enterprise and Echo and both B1 and B2 Rivers…. eventually…..
All that commonality on the platform, while the modularity of the “Navy PODS” system provides the kit for a given capability. Of course while these MPV’s will be low crew, if they are RN ships, rather than RFA’s that leads to a whole other discussion of recruiting and retaining!
1) We had what 28 MCM hulls with Sandown and Hunts?
2) The Dutch have 5 Tripartite class in service and are buying 6 City class.
3) You would think ‘defence’ of Faslane would be best mounted from a hull built to naval standards. Or perhaps I am wrong?
4) Buying commercial hulls is all very well and good until the need comes to clear a field off a shore you don’t ‘own’.
RFA Stirling Castle is a large auxiliary ship and a great platform to test various autonomous systems.
I wonder if the R1´s and R2´s could be used as motherships in the future for some autonomous systems or are they to small for that?
The R1’s are too old to consider.
It’s not just space for launch and recovery systems that’s needed but also space to maintain the equipment. I suspect the R2’s would struggle for maintenance space. Plus the R2’s have jobs to do already which HMG considers important.
Lovely boats.
As we know the Hunts and Sandowns are armed as they were/are asked to enter contested areas. Stirling Castle is not to be armed, certainly in the short term, is it the plan that she just operates in UK waters and or purely a test ship at present? Or is she likely to rely on other vessels for security? I’m interested not just wanting to start an argument.
1) It isn’t so much being armed. It is serviceability of the hull. Those Dutch and Belgian hulls I mention above are designed to take damage. Commercial hulls not so much; saying that ships do have a lot of redundancy but not to warship standards.
1a) I remember Endurance was not very warship like.
2) It is an obvious issue to me. But many here don’t seem to think about it.
I presume the crane is weather compensated and the ship has DP