AgustaWestland AW101

Origins In 1977, the UK Ministry of Defence issued a requirement for an anti-submarine warfare (ASW) helicopter to replace the Royal Navy's Westland Sea Kings, which were becoming inadequate in the face of advances in Soviet submarine technology. Westland Helicopters put together a proposal, designated WG.34, for a three-engined helicopter of similar dimensions to the Sea King; the WG.34 was to feature more autonomy and a greater range than its predecessor. At the same time, the Italian Navy (Marina Militare) was also considering the replacement of its fleet of Sea Kings, which had been built by the Italian company Agusta; Westland and Agusta soon began talks regarding the joint development of a successor helicopter. Agusta and Westland finalised an agreement to work on the project together, and formed a jointly owned new company, EH Industries Limited (EHI), to pursue the development and marketing of the new helicopter to potential operators. On 12 June 1981, the UK government confirmed its participation in the project, allocated an initial budget of £20 million to develop nine pre-series examples. A major agreement, which secured funding for the majority of the EH101's development program, was signed by both the British and Italian governments in 1984. At the 1985 Paris Air Show, Agusta showed a mock-up of a utility version of the new helicopter, leading to a more generalised design that could be customised to meet the needs of various civilian or military customers. The first prototype flew on 9 October 1987. In 1987, Canada selected the EH101 to replace its Sea Kings in the anti-submarine warfare and search and rescue roles. The EH101's third engine and increased range compared favourably with rival aircraft, such as the Sikorsky Seahawk. The range and de-icing capability were also seen as vital for North Atlantic operations. The fledgling EH101, of which up to 50 were on order to replace the Canadian Armed Forces's (CAF) Sea Kings, found itself subject to a wider political battle between the country's Conservative and Liberal parties, the latter viewing the aircraft as too costly. Critics attacked the EH101 purchase as excessive and unnecessary after the Cold War's end in the early 1990s. Wide-ranging cost estimates were presented by both proponents and opponents of the EH101 procurement, with opponents backing life extensions of Sikorsky CH-124 Sea King and Boeing Vertol CH-113 Labrador helicopter fleets. The EH101 controversy was seen as a factor in the 1993 Canadian federal election. The order was cancelled by the new Liberal government in 1993 resulting in a $470 million cancellation fee. Into production Several pre-production aircraft were assembled during the late 1980s and early 1990s. The first pre-production aircraft had its first flight powered by General Electric CT7-2A engines on 9 October 1987. Flight tests were suspended for six months following the crash of the second pre-production aircraft on 21 January 1993. On 6 June 1993, the first EH101 took its maiden flight with the Rolls-Royce Turbomeca RTM322 turboshaft engine. Nine prototypes were built to explore military and civil applications, including a "heliliner" configuration. In February 1995, Britain formally placed its first order for a total of 22 EH101s; this was quickly followed by Italy's order for 16 EH101s in October 1995. The EH101 order was not without controversy, the RAF had declared its preference for an all-Chinook fleet; also, Boeing allegedly offered cheaper terms for the Chinook. RAF deliveries began in 1997; RN deliveries started the following year. Following the merger of Westland and Agusta to form AgustaWestland in 2000, there was no need for the separate EHI entity; the EH101 was formally re-branded as the AW101 in 2007. By April 2009, more than 180 AW101s had been sold worldwide; the combined operational fleet had also accumulated a total of 170,000 flying hours. Further developments In November 2007, Algeria signed a contract for six AW101 helicopters. In August 2012, it was reported that Algeria had signed an agreement with AgustaWestland for the provision of up to 80 helicopters, 42 of which were to be AW101s. Under the terms of this arrangement, early aircraft were to be manufactured by AgustaWestland, while Algeria was to commence the assembly of some AW101s later on. By September 2013 AgustaWestland was in the process of acquiring civil certification for the AW101; prospective customers include offshore oil platform operators and VIP clients. As of February 2014, AgustaWestland was considering adapting the AW101 as a heavyweight unmanned aerial vehicle, it is proposed that in this configuration an AW101 could be optionally crewed. On 7 June 2010, it was announced that Boeing had acquired a manufacturing licence and the rights from AgustaWestland for US production of a localised AW101 variant, designated as the Boeing 101. In October 2012, the aircraft was submitted in a U.S. Air Force competition to replace the HH-60 Pave Hawk; however, the bid was dropped three months later. ==Design==

Overview The AW101 follows a conventional design layout, but makes use of advanced technologies, such as the design of the rotor blades, avionics systems, and extensive use of composite materials. The fuselage structure is modular and comprises an aluminium–lithium alloy, designed to be both light and damage-resistant. The AW101 is designed for operating in extreme weather conditions; it is fitted with a de-icing system and rated to operate in temperatures ranging between −45 and +50 °C. The aircraft's control systems allow the AW101 to maintain a stable hover in crosswinds. The cockpit is fitted with armoured seats for the crew, and can withstand an impact velocity of over 10 m/s. Dual flight controls are provided, though the AW101 can be flown by a single person. Powerplant The AW101 is powered by three turboshaft engines. Initially the Rolls-Royce Turbomeca RTM322 producing and the General Electric CT7 producing were the two available engine types, but by 2020 new aircraft were only being sold with the CT7-8E. The RTM322 powerplant was specifically developed for the AW101; it was subsequently adopted on the AgustaWestland WAH-64 Apache and the NHIndustries NH90 helicopters. According to Rolls-Royce, about 80% of AW101s use the RTM322 The engines power an diameter five-bladed main rotor. The rotor blades are constructed from carbon/glass with nomex honeycomb and rohacell foam, edged with titanium alloy in a sandwich construction. The shaping of the main rotor blades is derived from the BERP rotor blades first used on the Westland Lynx. This blade design improves aerodynamic efficiency at the blade tip and reduces the acoustic signature. Improved BERP IV rotors have since been developed; when installed this increases the AW101's maximum take-off weight. The AW101 can also be fitted with a probe for aerial refuelling. An inlet particle separator system can be installed, protecting the engine when operating in sandy environments. Armament and defensive systems Most variants of the AW101 are equipped with self-defence systems, such as chaff and flare dispensers, directed infrared countermeasures (infrared jammers), ESM (electronic support measures in the form of RF heads), and a laser detection and warning system. British Merlins have been outfitted with protective armour against small-arms fire. Two hardpoints are present in the underside of the airframe on which the HM1 model can carry four Sting Ray torpedoes or Mk 11 Mod 3 depth charges. Some customers have chosen to deploy the Marte anti-ship missile on the AW101; as of 2011, the Royal Navy is considering equipping their Merlin fleet with an anti-surface missile. The Mk1, Mk3 and Mk3A variants can mount general purpose machine guns in up to five locations in the main cabin, aimed out of both door and window apertures. AgustaWestland has examined the integration of rockets and additional ground-attack weapons. The AW101 features a network of helicopter management and mission systems designed to reduce pilot workload and enable the helicopter to undertake a wide variety of missions. A digital automatic flight control system (AFCS) is employed by the AW101. The AFCS allows the operation of a four-axis (pitch, roll, yaw and collective) autopilot and the automatic stabilisation system, and is linked in with the aircraft's flight management systems. The AFCS, manufactured by Smiths Aerospace, is a dual-duplex system using two flight computers to provide redundancy and fault-tolerance. The AW101's navigation system includes a GPS receiver and inertial navigation system, VHF omnidirectional radio range (VOR), instrument landing system (ILS), TACAN, and automatic direction finding. The Mk1 and Mk3 are equipped with a Doppler velocity system (DVS) which provides relative ground velocities; the DVS is also linked into the AFCS as part of the autostabilisation system. For safety, the aircraft is equipped with obstacle and terrain avoidance warning systems, traffic collision avoidance system (TCAS), and both voice and flight data recorders. As part of the Royal Navy's Merlin HM2 upgrade program, Lockheed Martin implemented a series of improvements to the radar, notably allowing it to track 40 times the number of targets previously capable. Danish EH101s are fitted with the RDR-1600 search and weather radar. Crew and cargo The AW101 is typically operated by a crew of three: a pilot, an observer, and a crewman/operator. The pilot is able to fly for the majority of a mission in a hands-off mode, enabled by the sophisticated autopilot. All crew members have individual access to management computers and tactical information. The fuselage has a volume of and the cargo compartment is in length, wide and high. The military version of the AW101 can accommodate up to 24 seated or 45 standing combat troops and their equipment. Alternative loads include a medical team and 16 stretchers, and cargo pallets. The ramp, , can take a load, allowing it to carry vehicles such as Land Rovers. The ramp and cabin floor are fitted with flush tie-down points. A cargo hook under the fuselage can carry external loads of via the use of a semi-automatic cargo release unit (SACRU). A rescue hoist and a hover trim controller are fitted at the cargo door. An optional cargo winch can be installed near to the rear ramp. ==Operational history==

Royal Navy The British Royal Navy's final order was for 44 ASW aircraft, originally designated Merlin HAS.1 (Helicopter, Anti-Submarine Mark 1) but soon changed to Merlin HM1 (Helicopter, Maritime Mark 1). The first fully operational Merlin was delivered on 17 May 1997, entering service on 2 June 2000. All aircraft were delivered by the end of 2002, and are operated by 3 Fleet Air Arm squadrons: 814 NAS, 820 NAS, 824 NAS and 829 NAS (now disbanded and merged with 814 NAS), all based at RNAS Culdrose in Cornwall. 700 NAS was the Merlin Operational Evaluation Unit from 2000 to 2008. In March 2004, Navy Merlins were temporarily grounded following an incident at RNAS Culdrose in which a tail rotor failed due to a manufacturing defect. An improved tail rotor was designed and adopted on most AW101s which significantly reduced associated maintenance. In 1995, it was announced that the Navy's Westland Lynx helicopters would be retired in favour of an all-Merlin fleet. However, the subsequent Strategic Defence and Security Review 2010 stated that the future naval helicopters would be the Merlin and the Wildcat, a derivative of the Lynx. Royal Navy Merlins have seen action in the Caribbean, on counter-narcotics and hurricane support duties, as well as maritime security duties in the Persian Gulf. Merlins have also seen active duty in Iraq, providing support to British and coalition forces based in the region. The Merlin HM1 has been cleared to operate from the Royal Navy's aircraft carriers, amphibious assault ships, Type 23 frigates, Type 45 destroyer and several Royal Fleet Auxiliary (RFA) vessels including the . 30 aircraft have been upgraded to Merlin HM2 standard under the £750m Merlin Capability Sustainment Programme; Lockheed Martin UK delivered the final HM2 on 11 July 2016. The HM2 has a new mission system, digital cockpit, electro-optical camera and multi-static sonar processing. The HM2 achieved IOC on 30 June 2014 after flying 480 hours from Illustrious during Exercise Deep Blue earlier that month. It was also reported that some of the eight airframes not scheduled to be upgraded for financial reasons may be updated. Five HM2s are in maintenance at a time, leaving 25 available, of which 14 were theoretically to be assigned to the . During the 2021 carrier strike group deployment to the Pacific, for instance, seven Merlins were embarked with the task group. In addition to its ASW role, the HM2 will be able to carry an airborne early warning (AEW) pod known as the Crowsnest, replacing the Sea King ASaC7. In September 2011, Thales UK proposed re-using Sea King ASaC7 equipment, such as the Searchwater 2000, on the Merlin; Lockheed Martin has proposed developing a new multi-functional sensor for both the AW101 and other aircraft. Lockheed originally planned to use a derivative of the F-35's APG-81 radar; however, a rival Elta system and the Thales system both commenced flight trials in 2014. On 22 May 2015, the MOD and prime contractor Lockheed Martin UK selected Thales to provide the radar and mission system for the Crowsnest. Initial operating capability of the system was significantly delayed. While Crowsnest was deployed with the U.K. carrier strike group in 2021, it experienced operating challenges and revised plans meant that Crowsnest achieved initial operating capability in July 2023. Full operating capability had been expected in 2024/25. It was reported that initially only five Merlins will be equipped with Crowsnest, three of these being normally assigned to the "high readiness" aircraft carrier. In 2025, nine Merlin HM2s from 820 Naval Air Squadron were specifically assigned to embark on HMS Prince of Wales as part of the Royal Navy's carrier strike group deployment to the Indo-Pacific region. Six of the Merlins were in the ASW role and three in the AEW role, with the Crowsnest system having formally reached full operating capability. Problems with Merlin/Crowsnest have caused the Royal Navy to look for a replacement. As of 2023 the system had a planned retirement date of 2029. In 2021, the UK's Defence and Security Accelerator (DASA) announced that options would be examined and might draw on the already existing Project Vixen, researching the utility of a naval unmanned system that could encompass strike, AEW, and air-to-air refuelling components. If implemented, the replacement of Merlin/Crowsnest by another system would permit all Merlin helicopters to focus on ASW operations for the remainder of their service lives. On 15 December 2009, plans were announced to transfer RAF Merlin HC3s and HC3As to the Royal Navy's Commando Helicopter Force to replace retiring Sea King HC4 helicopters. 846 NAS reformed with ex-RAF Merlin HC3s on 30 September 2014; 845 NAS followed on 9 July 2015. On 25 May 2018, the first of 25 converted Royal Marines Commando Merlin Mk4/4A were delivered to Royal Naval Air Station (RNAS) Yeovilton. In July 2020, the Merlin HM2 and HC4/4A helicopters were planned to be in service until 2029 and 2030, respectively. On 11 June 2021, it was confirmed that their Out of Service Date (OSD) had been moved to 2040. By the end of 2022, all HC helicopters were upgraded to the HC4/4A Commando Merlin standard. Royal Air Force Afghanistan, 2012 The RAF ordered 22 Merlin HC3 for transport missions, the first of which entered service in January 2001 with No. 28 Squadron RAF based at RAF Benson. The type is equipped with extended-range fuel tanks and is capable of air-to-air refuelling. The Merlin is frequently utilised for troop transport duties and for the transport of bulky objects, either internally or underslung, including vehicles and artillery. The Merlin Depth Maintenance Facility at RNAS Culdrose performed most tasks upon the Merlin HC3. The Merlin's first operational deployment was to the Balkans region in 2003. RAF Merlins were first deployed to Iraq as part of Operation Telic in 2004, supporting coalition forces and were operated as the main medevac asset in southern Iraq; both Flight Lieutenant Kev Harris and Flight Lieutenant Michelle Goodman were awarded the DFC during this period. Merlins routinely operated around Basra until Britain's withdrawal in June 2009. In 2002, Westland made an unsuccessful unsolicited offer to the British Ministry of Defence, proposing an enhanced Merlin variant intended to satisfy the demand for additional lift capacity. An alternative measure was the acquisition of six AW101s from Denmark in 2007; designated Merlin HC3A, these were assigned to the RAF, allowing Merlins to be deployed in Afghanistan. The HC3A is used for training and not for frontline operations due to various configuration differences. In 2009, five Merlin Mk3s were operating in Afghanistan, transporting troops and supplies. The deployment to Afghanistan was criticised as the aircraft reportedly lacked protective Kevlar armour. By July 2010, the Merlin fleet was fully fitted with ballistic armour. The deployment of Merlins to Afghanistan allowed the detachment of Sea Kings to be withdrawn from the region in October 2011. As part of the UK drawdown in Afghanistan, Merlins were withdrawn from theatre in June 2013. In 2012, the RAF's Merlin HC3/3A fleet began to be transferred to the Royal Navy for use by the Commando Helicopter Force. Royal Navy personnel worked alongside RAF crew at Benson to build experience during the transition. The £454m Merlin Life Sustainment Programme resulted in 25 HC3/3A airframes being fitted with the cockpit electronics of the HM2, folding tails and main rotor heads, strengthened landing gear, deck lashing mounting points, obsolescence updates, fast-roping points and a common emergency egress system. The first HC4 began flight trials in September 2017, with an IOC in mid-2018; The RAF's 28(AC) continued to operate as part of the Commando Helicopter Force until July 2015, when 28(AC) Sqn stood down and 845 Naval Air Squadron stood-up. 846 NAS relocated from RAF Benson to RNAS Yeovilton in March 2015, with 845 NAS following in June 2016. Italian Navy In 1997, the Italian government ordered 16 AW101 helicopters for the Italian Navy, with options for four more. These AW101 included eight of the anti-surface/submarine (ASuW/ASW) version, four airborne early warning (AEW), four amphibious support helicopters (ASH). The government then exercised its option for four additional ASH helicopters, which were delivered by 2006. In total 22 AW101 helicopters have been delivered to the Italian Navy. In 2011, it was reported that the Italian contingent in Afghanistan, consisting of AW101s, had been providing coverage of a wide area of the country. Italian Air Force In June 2011 the AW101 was chosen by the Italian Air Force to replace its ageing Sea King HH-3F helicopters in the combat search and rescue role. A total of 15 helicopters in the HH-101A variant were ordered and delivered between 2016 and 2020. Royal Canadian Air Force In 1997, in light of the declining condition of its helicopter fleet, Canada launched the Canadian Search and Rescue Helicopter competition. It was won by the EH101, which was designated CH-149 Cormorant in Canadian service. In 2004, the EH101 was entered into a Canadian competition to replace the shipboard Sea King fleet, but the Sikorsky CH-148 Cyclone was selected. In 2013, following difficulties with the CH-148 procurement, the Royal Canadian Air Force (RCAF) was reported to be seriously considering cancelling the contract with Sikorsky and was investigating the possibility of procuring the AW101 instead. However, an initial batch of six Cyclones was delivered to the RCAF in June 2015. In December 2022, Canada's Department of National Defence announced a C$1.24-billion contract for procurement of three additional aircraft and upgrades to the existing fleet to current configuration of the helicopter; this will increase the fleet to 16 aircraft. The RCAF also acquired its own advanced training simulator configured to the new modernized cockpit. Royal Danish Air Force In 2001, the Royal Danish Air Force (RDAF) announced the purchase of eight EH101s for SAR duties and six tactical troop transports for 722 Squadron. The last of the 14 AW101s was delivered in March 2007 and the first SAR AW101s became operational out of Karup Airport in April 2007. In 2007, the six troop transport AW101s were transferred to the British MOD; in exchange, the British government ordered six new-build AW101s as replacements for the RDAF. Danish AW101s have a higher gross weight capacity of 15,600 kg and were, as delivered, coated in a paint designed to reduce the aircraft's infrared signature. In the SAR role, RDAF AW101s have a crew of six and were initially painted yellow to distinguish themselves from AW101 allocated to military duties, On 28 January 2008, the drive shaft of a Danish AW101 broke, leading to an emergency landing at Billund Airport. Following the incident, the Danish fleet was grounded as a precaution and the AW101's future was publicly debated. In the first six months of 2008, the RDAF reported an operational availability of roughly 50%, well below the target of 80%, partly due to an inadequate maintenance organisation and staff shortages. In January 2011, the Danish Ministry of Defence reportedly could not afford the retrofitting of the AW101 fleet for Afghanistan operations, against earlier reports of a deployment in 2012. In February 2013, Aviation Week reported that earlier reliability problems had been resolved and that a full upgrade package would be applied to Danish AW101s; these included the addition of electronic warfare pods and a new electro-optical system, in advance of a deployment in Afghanistan in 2014. In September 2013, Danish AW101s were to receive L-3 Wescam MX-15 electro-optical/infrared (EO/IR) sensors; SAR aircraft already carry the FLIR Systems Star Safire II EO/IR sensor. Royal Norwegian Air Force On 25 October 2007, a project started that had the intent to replace all Westland Sea King search and rescue helicopters with new rescue helicopters by 2020. On 19 December 2013, a contract was signed between AgustaWestland and the government, for the purchase of 16 AW101 helicopters. The agreement came about after fierce competition between different manufacturers to satisfy the Norwegian requirements. Participants were AgustaWestland, Eurocopter, NHIndustries, Sikorsky Aircraft Corporation and Boeing. The government considered that AgustaWestland AW101 met the requirements and specifications in the best possible way. On 12 June 2017, Per-Willy Amundsen, Minister of Justice and Public Security, announced the opening of Leonardo's AW101 Norway Training Centre at Stavanger Sola Air Station. The training centre includes an AW101 Full Flight Simulator (FFS), jointly developed by Leonardo and CAE to Level D, which is a CAE Series 3000 device, along with an AW101 SAR console training system linked to the FFS to provide rear crew training. The first training course at the centre started prior to delivery of the first rotorcraft. The training centre will be used by both Norwegian and foreign AW101 customers. The first AW101 was delivered in November 2017. The Norwegian AW101s officially started operating in the rescue role on 1 September 2020. The Sea King was phased out in December 2023, after 47 years of service as rescue helicopter in the Royal Norwegian Air force, and replaced with the AW101. The AW101 is named SAR Queen in Norwegian service, and performed the flight from Mainland Bodø to Jan Mayensfield using two engines, and then back, in 2025. Portuguese Air Force Portuguese Air Force The Portuguese Air Force had purchased 12 Merlins under a €446 million contract, the first of which was delivered on 22 December 2004. The type has been used to conduct transport, search and rescue, and maritime surveillance missions, progressively replacing the Aérospatiale Puma previously tasked with these missions. The main role of Portuguese AW101s is to perform search and rescue missions within Portugal's maritime zone. They are operated by 751 Squadron and are kept on constant alert at three bases: Montijo near Lisbon, Lajes Field on the Azores, and Porto Santo Island. Japan Maritime Self-Defense Force The Japan Maritime Self-Defense Force (JMSDF) ordered 14 aircraft in 2003 to use in both the airborne mine countermeasures (AMCM) and transport roles. The AW101 was modified by Kawasaki Heavy Industries, and the Japan Defense Agency designated the model MCH-101. Special features include the automated folding of the rotor and tail. For the mine-hunting role, the MCH-101 has been outfitted with Northrop Grumman's AQS-24A airborne mine-hunting system and AN/AES-1 Airborne Laser Mine Detection System (ALMDS) for a complete surface-to-bottom mine detection capability, as well as Mk-104 acoustic mine sweeping gear. In 2002, AgustaWestland, Kawasaki and Marubeni entered a general agreement for cooperation; Kawasaki began the assembly of both the CH-101 and the MCH-101 in 2003. Kawasaki also began licensed production of the RTM322 engines in 2005. In a separate agreement between Marubeni and AgustaWestland, a supply depot was established in Japan to support the MCH-101 and CH-101 fleets. The first MCH-101 was delivered to the JMSDF on 3 March 2006. After a whistle-blower alleged that the MSDF's preference had been improperly changed an investigation was launched. On 16 December 2016 the Japanese Ministry of Defense (the Defense Agency having been upgraded to a ministry in 2007) stated that it had not confirmed lobbying efforts but the ministry admonished Tomohisa Takei, the JMSDF chief of staff, for mentioning the MCH-101 by name during the procurement process to his subordinates. This had come after MSDF officials had reported that the Mitsubishi-built SH helicopters may be best. VIP and other usage AgustaWestland developed a specialised luxury variant, the AW101 VVIP (Very Very Important Person, i.e. a head of state), aimed at business and VIP customers. As of April 2009, 15% of all AW101s sold were for VIP purposes. However the programme encountered significant cost overruns and political opposition, which led to the procurement being scrapped in June 2009. After the cancellation, the delivered helicopters were sold to Canada for $164 million, where they were used as source of spare parts for its fleet of AgustaWestland CH-149 Cormorant search-and-rescue helicopters. Separately, the Marine Corps had also conducted studies into the adoption of the EH101 as a fall-back option to the Bell-Boeing V-22 Osprey tiltrotor during the 1990s. The selection followed field trial assessments between the AW101 and the Sikorsky S-92 held in 2008. However, the procurement was put on hold and subsequently cancelled due to the 2013 Indian helicopter bribery scandal, in which Finmeccanica, AgustaWestland's parent company, was accused of using bribery to win the contract. The three helicopters delivered as part of the contract may be returned to the manufacturer as part of the arbitration process. Potential operators The Royal Norwegian Air Force is considering ordering the AW101 Merlins for anti-submarine use. ==Variants==

;Pre-production • PP1 – Westland-built basic air vehicle prototype, first flown 9 October 1987. • PP2 – Agusta-built Italian basic air vehicle prototype first flown on 26 November 1987 and used for deck trials but was destroyed on 21 January 1993 following a rotor brake malfunction. • PP3 – Westland-built and the first civil configured Heliliner, used for engine vibration tests and icing trials in Canada. • PP5 – Westland-built Merlin development aircraft eventually equipped with Merlin avionics. • PP6 – Agusta-built development aircraft for Italian Navy variant first flown 26 April 1989. ;Model 112 : Italian Navy early warning variant with same airframe as Model 110 but with Eliradar HEW-784 radar in large underfuselage radome. Four built. ;Series 200 : Proposed military utility version with no rear-loading ramp. In 2000, British International Helicopters conducted service trials using PP8; these did not lead to a commercial service. ;Model 410 : Italian Navy transport variant with folding rotors and tail boom. Four built. ;Model 413 : Italian Navy special forces and amphibious assault transport with more advanced avionics. ;Model 500 : Proposed civil utility variant with rear-ramp. ;Model 512 : Merlin Joint Supporter for Royal Danish Air Force. Eight acquired for search and rescue (512 SAR) and six for tactical troop transport (512 TTT). The six transports were sold to RAF (as Merlin HC3As) and replaced by six new-build Merlins. ;Model 514 : Portuguese Air Force search and rescue variant, six built. ;Model 515 : Portuguese Air Force fisheries protection variant, two built. 15 on order. ;Model 612 (SAR Queen) : Norwegian search and rescue variant, operated by the Air Force. 16 ordered with option for 6 more. ;Model 614 : Polish ASW/CSAR "convertible" variant, operated by the Polish Navy, 4 delivered. ;Model 615 : Canadian military search and rescue variant, upgraded -511 variant, again designated the CH-149 Cormorant. 16 to be delivered. ;Model 640 : Saudi Arabian VVIP variant, operated by the Air Force. 2 delivered. ;Model 641 : Indian VVIP variant. (See 2013 Indian helicopter bribery scandal). Latterly delivered to Nigerian and Azerbaijani Air Forces. ;Model 642 : Algerian VVIP variant, 2 delivered. ;Model 643 : Turkmenistani VVIP variant, operated by the Air Force. 2 delivered. ;Merlin HM1 : Royal Navy designation for the Model 111. HM2 cockpit, folding tail/blades and other adaptations for naval use. ;EH-101A :Italian Navy designation for the AEW variant. ;Kawasaki Heavy Industries MCH-101 :Japan Defense Agency designation of Model 518 ==Operators==

; • Algerian Air Force • Algerian Navy ; • Royal Canadian Air Force (see CH-149 Cormorant) ; • Royal Danish Air Force • Italian Navy ; • Japan Maritime Self-Defense Force - 10 ; • Nigerian Air Force ; • Royal Norwegian Air Force ; • Portuguese Air Force ; • Turkmen Air Force ; • Tokyo Metropolitan Police Department ; • Royal Air Force ==Notable accidents==

On 4 September 2024, a member of Royal Navy personnel died after a Royal Navy Merlin Mk. 4 helicopter ditched in the English Channel near Dorset while conducting night flying exercises with HMS Queen Elizabeth. The two other crew on board were taken to a hospital. ==Specifications (Merlin HM1)==