Searching for the enemy below - 814 NAS

Often operating in the harsh conditions of the north Atlantic, Royal Navy Merlin HM.2 helicopter crews describe the tactics and technology they use in the ‘cat and mouse game’ of hunting submarines, using dipping sonar and sonobuoys to locate and track the subs. The experts in anti-submarine warfare are the sailors of 814 Naval Air Squadron (NAS) – nicknamed ‘The Flying Tigers’ with their aircraft adorned with a fierce tiger motif.

814 NAS ‘The Flying Tigers’

Royal Naval Air Station Culdrose is home to the Royal Navy’s Leonardo Merlin HM.2 force where initial training on the type is completed at 824 Naval Air Squadron, before aircrew and engineers move onto the operational squadrons of 814 and 820.

Commander Ed Holland leads the front line 814 Naval Air Squadron (NAS), which is maintained in a constant state of high readiness. The squadron comprises deployable flights of aircrew, engineers and support staff. Lieutenant James ‘Waggy’ Wagstaff said ‘We have a 7 flight construct at 814, so that includes flights that are on board the type-23 frigates in the north Atlantic, as well as DSO1 (defence strategic number objective 1) flights, which are embarked on a duty tanker and ready to escort any vessels that are coming through British waters, that need shadowing and intelligence collection.’

He continued ‘at this time we have two maritime task group flights which go away with the CSG (Carrier Strike Group). We have one embarked with the frigate HMS Richmond and one on the Royal Fleet Auxiliary support ship RFA Tidespring. This is a new thing we have started to delve back into as of 2025. Those flights are composite, so when they are generating these flights, they always train and deploy as a crew and have a specific aircraft that they will be taking. But when we operate here at RNAS Culdrose, it is a mix and match of crews as to what is needed in relation to training and day to day flying.’

Aircrew use the Merlin HM.2 anti-submarine warfare (ASW) helicopter, which is equipped with dipping sonar, sonobuoys and torpedoes, to locate, track and, if required, eliminate submarines. In addition to ASW, the aircraft is called upon to complete other vital tasks whilst deployed on board the ship including, search and rescue (SAR), troop delivery from ship to ship and to land, casualty and medical evacuation, surface warfare and replenishment from shore and ship to ship.

For these various roles Lieutenant James Ramsey stated ‘The role fit can be changed internally and externally, for example, in ASW role the observer and aircrewman have their own consoles, there is a dipping sonar in the cab, and a carousel of deployable sonobuoys, which can all be removed to provide the extra room for whatever role is needed. There is also a winch hoist and an external underslung load hook that can be fitted quite quickly’. Petty Officer aircrewman Sam Baker ‘we normally fly with the hoist fitted, so the change from the primary ASW role to the SAR role is usually quick.’

A ’normal’ day

Waggy, James and Sam gave an insight into the day-to-day training cycle for crews in 814 NAS, ‘a standard 2hr staff training sortie, continued currency, will include about 45 minutes of core roles regarding ASW, then switch to using the aircraft’s radar to avoid surface contacts on land. Waggy continued ‘the observer has a competent radar qualification, which means we can deconflict between aircraft and surface contacts, if the weather is poor then we can drive the aircraft around the sky. Lt. Ramsey ‘we’ll be on just instruments in the front trusting the observer in the back to point us in the right direction.’ After 30 minutes ‘we move straight into winch transfers to simulate getting someone on or off a deck.’ On completion of the various roles on the sortie it’s time to return to the airfield. Lt. Ramsey continued ‘We need a certain number of instrument approaches to the airfield within a certain time period. We train for several hours simulated and an actual number of hours flying with instruments only. Approaches can be completed at various airfields but invariably we stay local at RNAS Culdrose.’

With the Merlin being largely a ship-based asset there is a need to train with vessels in the various roles, although Waggy stated that we don’t train with ships ’as often as we would like but this is due to the availability of the vessels. If you’re one of the duty crews, when you are generating to embark on one of the flights, you spend more time working with the ship that you are going away with. They probably get about 6 months working with the ship. These crews are then on a four-month rotation.’ PO. Baker added ‘If a ship is deploying soon, they have their own currencies to keep up so they may request that a cab (aircraft) can complete some deck landing practices rather than it just being our own currencies. It’s great in the fleet to be able to support each other’s needs.’

The standard crew for the Merlin is 2 pilots, one aircrewman (in charge of sonar) and 1 observer (weapons officer and mission commander). The division of labour is the handling pilot in the right seat and left seat is the co-pilot who manages communications and monitors systems. Crew co-ordination is explained by Lt. Ramsey ‘Some of the switches cannot be reached from the right seat, so we need the co-pilot to support, and this is really important when completing some manoeuvres including coming into the hover for ASW, where there are a series of checks that need to be completed between the handling pilot and co-pilot. The pilots’ role is to keep the aircraft safe and, in the configuration to how the observer needs it to complete the mission. You can pre-empt the situation through listening in to communications, but you don’t want to get sucked into it too far as you still need to be aware of the weather and fuel and if you are in a safe place.’

Co-ordination and communication is essential between the pilots and the observer during an intense mission and ‘It’s great to have somebody in the front to suggest ideas when you’re maxed out and really focused on one task, there is the potential to become tunnel visioned and it’s good to have someone with capacity to say ‘have you thought about this.’ , says Waggy.

Keeping them flying

Keeping the Merlins in the sky at 814 NAS are around 120 hard-working maintenance personnel who are being tested currently to work on the 7-flight construct.

‘Post sortie, the aircrew will sign the aircraft back in and they will have a conversation with the watch chief, and avionics and mechanical supervisors. If there are any issues with the aircraft, these will get recorded in the aircraft documentation. From that we will do fault diagnosis and change components to rectify the fault along with servicing the aircraft.’ stated air engineer Chief Petty Officer Michael Hay.

For the post flight service CPO Hay said ‘you’ll have 2 -3 Air Engineering Technicians (AETs) who will service the aircraft, which involves a raft of inspections to the various systems and physical airframe, plus the replenishment of oils and lubricants. The Merlin is very advanced, and it tells you what the issues are, but we do have faults that come up that involve diagnosis from the mechanical and avionic supervisors. That can be driven by the CIETP (Compound Interactive Electronic Technical Publication), which is like a Haynes manual but for the Merlin. In addition to that we have calendar-based maintenance and every component on the aircraft will have a service life that will be dictated either hourly or number of operations the part has completed. All this information is captured in our asset management system and the maintenance personnel can search the programme and see what’s due, see what’s coming up and plan out maintenance.’

There are major maintenance jobs that are completed on the Merlins less frequently and the biggest is the replacement of engines and gearboxes. CPO Hay continued ‘There is an aircraft on the squadron that has had the main gearbox and engines replaced. An engine removal is generally a shift evolution, so around 8 hours, for 3 people of which one will be a supervisor. It generally takes about a week to remove the gearbox from the aircraft, another week to dress across components onto the new gearbox, and then another week to reinstall. After this you have to functionally test and return the aircraft to a flying condition.’

Post replacement, before the aircraft is allowed back into the sky, there is a need for a ground run.

Chief Petty Officer Hay added: ‘The ground run was for over an hour and because it has had a gearbox change, we have to flat track the head, so that involves changing the pitch on the blades. The ideal is that we get a flat track on the blades and from that we can see how we can make the flight as smooth as possible with the changes to the pitch, this in turn reduces the fatigue on the aircraft.’

After the post ground-run checks, the aircraft can be air tested and once back on the ground the analysis by the engineers begins to ensure that any issues raised by the on-board system or the crew can be rectified and the aircraft can be put back into service.

After 730 hours the aircraft is brought into the hanger and placed in a dedicated maintenance bay and a team of personnel will complete a full service of all the components, including the main rotor head, tail rotor, gear box and flight control systems. At this time any minor faults that had been deferred will be remedied.

For each of the 7-flight construct there is ‘one chief petty officer, a petty officer of each trade (avionics and mechanical) who complete independent inspections, a leading air engineering technician of each trade and then 4 AETs,’ said Chief Petty Officer Hay.

Away for the base at RNAS Culdrose, when the Merlin is embarked on one of the type-23 frigates, the deployed maintenance personnel are made up of two chief petty officers, two petty officers (one from each trade), two leading hands and four AETs, with deployments lasting from one week up to four months. This is a challenging environment to work in especially in the confines of the hangar space.

UK Interoperability

The Merlin isn’t the only maritime aircraft available to the British forces. The Poseidon MRA.1 is the Royal Air Forces modern Maritime Patrol Aircraft and can work with the Merlin to complete the mission. There were some teething issues initially as to the interoperability between these two airframes which Waggy and PO Baker explained, ‘Whomever arrives first to the scene and makes initial contact with the submarine becomes the commander at the scene of actions. Initially we were in competition with the Poseidon. We were confused about how each asset was to be tasked when the commander at the scene of action was the other aircraft type. At times the Poseidons were trying to use the Merlin as a wide area search platform but that doesn’t work, as they can lay a massive field of sonobuoys to then work out roughly where the submarine is located and then task the Merlin to move into the area and localise the target. We would then be utilised for weapon delivery as we can get that much closer to the target.’ Stated Waggy. PO Baker added that ‘the comms are really important as the Merlin needs to stay away from where they are laying buoys, as they fly at a greater height and we don’t need one through the cab creating a major incident.’

Lt. Baker continued ‘Some crew men from 814 NAS have been on exchange to RAF Lossiemouth with the frontline Poseidon squadrons 120 and 201, to inform them of how we operate and gain invaluable knowledge from them too, which has been great, because it now gives us that flow of communication and point of contact if we need anything quickly.’ In addition, ‘They have started a monthly table top tactics meeting where we dial in, running through scenarios, discussing tactics for a couple of hours and how to employ both assets.’

Exercises

Training with NATO and other nations is essential and 814 NAS participate in ‘about 6 exercises a year with NATO, for example we headed to Norway to participate in EX Green Eel, which is a big ASW EX but before that we are doing EX Dynamic Mongoose, which is another ASW EX in the north Atlantic,’ Waggy stated. More regularly, ‘every Thursday we have the ‘Thursday war’ which involves FOST (Fleet Operational Sea Training), and NATO partners, that send their ships to come and participate in FOST, so we’ll go out and work with NATO frigates.’

As well as these exercises Lt. Ramsey stipulated that ‘Within NATO and British forces have the ability to facilitate and support each other’s training. For example, we have accomplished some ASW work with Norwegian and Dutch Submarines, completing their submarine commanders’ course, so they need to be hunted to practice their evasion techniques whilst we can train being the hunter.’

HIGHMAST exercise

The large force multinational Exercise HIGHMAST is taking place in the Indo Pacific region throughout 2025 and the Merlin’s from 814 NAS have been participating, embarked on the carrier strike group escort ships and lead ship, HMS Prince of Wales.

Lt. Ramsey said ‘HIGHMAST is a good opportunity to develop an understanding of the various platforms and the ships.’ ASW is one aspect of the exercise that is the bread and butter of the Merlin. The unseen battle between the submarine and the helicopter is a challenging scenario and relies on the skills of the Merlin crews to be able to detect and prosecute the target. Whilst trying to locate the submarine the Merlin needs to try to stay undetected by ‘having a passive posture, we have different sonobuoys which we can deployed just to listen, or ones which are command activated, sending out a transmission and then listening for the return. We can wait for the target to pass by a HIDARs (High Instantaneous Dynamic Range Analysis and Recording) sonobuoy, as this buoy detects sounds rather than emitting its own.’ stated Po Baker. As well as ‘keeping the radar off and transmissions to a minimum and staying at a standoff range as the aircraft transmits a sound into the water and the subs can hear both the tail and main rotors.’ Said Waggy, ‘It’s a cat and mouse game trying to stay undetected whilst being proactive in trying to find the target and balancing that risk as to when to push further and when to stay passive. As soon as the submariners receive the transmission of the merlin’s radar, they know immediately what it is and its then mast straight down into deep water to get away from us.’

Although this can be a positive as ‘You can still be delivering an effect even if you do not know where the submarine is, just by your presence and being in the search phase the submarine may have to put itself in a challenging situation where it could be discovered by other forces either surface or aerial assets,’ said Waggy.

Lt. Ramsey added, ‘post exercise the debrief is with all participants who can then give the feedback in relation to the different assets used. They put up on the screens a replay of the missions showing, in real time, where and when contacts were made or where a target was that you hadn’t found.’

Copyright UK MoD

EX. Green Eel 2025

100 personnel from 814 and 824 NAS made the journey north to Norway for EX. Green Eel. The detachment was based near Bergen in the west of Norway. The Haakonsvern Helikopterbase is on top of a steep rocky hill above the naval base. Two Merlin HM.2 helicopters took part in a series of exercises against Norwegian and German submarines.

The Merlin’s objective was to locate and aggressively track the submarines in a new and challenging underwater environment with unfamiliar terrain, the targets being the Norwegian submarine HNoMS Utvaer and the German U-boat U34. Using sonobuoy listening devices dropped into the fjords and the Merlin’s in-built dipping sonar to locate ‘the enemy below’, the helicopter crews flew anti-submarine warfare sorties every day, amassing around 50 hours of high-quality training.

Captain James Hall, the commanding officer of RNAS Culdrose, said ‘My thanks go to our allies, the Norwegians and the Germans, for participating in this important exercise, which has allowed us to practice our warfighting skills in a challenging, live environment.

‘As well as presenting our crews with an unfamiliar area of seabed, what is particularly special about Haakonsvern is that you have all the different elements together in one place. The base accommodates the aircraft, the surface ships and the submarines.’

‘It means everyone involved can learn from each other to improve and evolve the exercise as it progresses, as well as understanding and countering their adversaries’ tactics. This strengthens the bond between our countries and supports our ability to work in unison within the wider NATO context.’

For the frontline crews like Lt. Ramsey, PO Baker and Waggy, EX. Green Eel offers them invaluable experience against live opponents in a different environment than they train in day to day in the UK. It also allowed the engineers and support personnel to build on their experience, working with the UK’s allies at distance from their main base in Cornwall.

Thanks to 814 Naval Air Squadron for the opportunity to speak with the aircrew and maintenance personnel. Also thanks to G. Wilkinson, PRO at RNAS Culdrose.