In the Book of Genesis, Nimrod is the name of a King of Babalonia regarded in ancient times as being a mighty hunter. It was therefore highly appropriate that Nimrod was the name adopted for a new anti-submarine warfare (ASW) and maritime patrol (MP) aircraft developed by Hawker Siddeley. The first Nimrod entered service in 1969 and since then the aircraft has become widely acknowledged as one of the finest ASW/MP designs ever produced. Modernised over the years to maintain its effectiveness, Nimrod has also spawned an electronic intelligence (Elint) platform and an ill-fated airborne early warning (AEW) variant, as well as having proven its basic capabilities in combat operations.
however, but the idea of modifying an existing airliner had proved sound and so when Hawker Siddeley responded to ASR.381, it again opted to use an existing airliner airframe as the basis for its proposal. This time the company decided to use the de Havilland Comet 4C, which had been adopted by the RAF as a strategic transport back in 1955 and had also been widely used by commercial airlines. By using an already proven aircraft, Hawker Siddeley was saving itself considerable time and expense as much of the design work had been done. Additionally, the company’s factory at Woodford in Cheshire was fully geared up for building Comets, allowing more money to be saved by eliminating the need for retooling and workforce retraining.
By May 1965, the Type Specifications for the Shackleton replacement had been formalised and a month later the Government granted Hawker Siddeley the go-ahead for its HS.801 design (as the MP Comet was initially known). A £100-million fund was allocated for the development of two prototypes and the production of 38 aircraft for the RAF. Although the Government relaxed its
Nimrod MR. Mk 2 XV232 is shown here in its current configuration. The Nimrod has the ability to cover large areas of ocean on a range of missions, making it a valuable and versatile element in the RAF’s inventory. (BAE Systems via David James)
In June 1964, the British government issued a requirement for a replacement to supersede the RAF’s Avro Shackleton, which was in service as a land-based, long-range ASW and MP aircraft. Air Staff Requirement No.381 (ASR.381) called for a new aircraft to be in service by late 1966, which meant that the winning design team would have only a short time in which to develop the project.
Hawker Siddeley responded to the challenge, having studied an MP variant of its Trident airliner a few years earlier. This aircraft failed to attract support, original in-service target date of 1966, it insisted that Hawker Siddeley have the new aircraft (which was soon named Nimrod) in service within 48 months of the contract being signed.
Above: The first Nimrod prototype, XV148, undergoes a test flight in May 1967. Of two prototypes, XV148 was the only one fitted with Spey engines. It was used to examine the Nimrod’s flight and aerodynamic characteristics.
Left: XV147 was the second Nimrod prototype. Its use of Avon 524 turbojets meant that electrical generators had to be fitted in under slung pods below its engine nacelles, as can be seen here, (both BAE Systems via David James)
Nimrod airplane, design and development
Aware of the strict timetable, Hawker Siddeley opted to use two redundant Comet 4C airframes as the basis of the Nimrod prototypes, eliminating the need to build airframes from scratch. The Comets, actually the final pair to be assembled before production of the airliner ceased, were serialled XV147 and XV148 and were moved to Hawker Siddeley’s Chester facility for immediate conversion.
Although the two prototypes were based on Comet 4Cs, the Nimrod featured a reduction in its fuselage length by 6 ft 6 in (1.98 m) which made it more akin to the earlier Comet 4. An unpressurised underfuselage section was to be added, protruding forward of the aircraft’s nose and running back approximately three quarters of the length of its fuselage. This pannier gave the Nimrod its distinctive ‘double bubble’ appearance and is used to store the aircraft’s operational equipment, together with a large-capacity, 48-ft 6-in (14.78-m) long weapons bay.
Initially the pannier was to incorporate a forward lookout’s position that could only be manned when the aircraft was operating at lower, unpressurised
Left: The Nimrod MR. Mk 1 flight deck was a mass of switches, levers, dials and gauges. The Nimrod’s cockpit windows were enlarged compared to those of the Comet, giving its pilots improved visibility.
Below left: An early shot of the Nimrod MR. Mk 1’s radar display screen. The ASV. Mk 21 system was based on the Shackleton’s radar and although effective for its time, was replaced by the far superior EMI Searchwater in the later Nimrod MR. Mk 2.
Below right: The internal sonobuoy storage racks of the Nimrod MR. Mk 1 allowed it to carry a wide variety of buoys, markers and other target indicators for use in ASW or locating a stricken vessel. Such devices are normally dropped into the water via rear underfuselage tube dispensers, or a rotary sonobuoy launcher, (all BAE Systems via David James) altitudes. This, it was swiftly realised, would be impractical and so Hawker Siddeley decided to abandon it. The pannier also led to an increased keel, which in turn created a large reduction in the aircraft’s directional stability. To counter this, an enlarged dorsal fin was devised, at the top of which was mounted an elliptical fairing for some of the aircraft’s planned electronic surveillance measures (ESM) equipment.
XV148 is shown here minus MAD, although it has been fitted with the tail fin ESM fairing. The Nimrod was the world’s first jet-powered maritime patrol aircraft to enter operational service. (BAE Systems via David James)
All but 11 of the original Comet fuselage windows were removed, while large observation windows were added forward. The flight deck windows were altered to provide far greater visibility for the pilots, this being considered essential if the Nimrod was to fly effectively at low levels in poor weather conditions.
The first of the two prototypes, XV148, was fitted with four 12,140-lb (53.99-kN) thrust Rolls-Royce RB.168 Spey Mk 250 turbofan engines. This was the powerplant that Hawker Siddeley intended using on the production aircraft. As in the Comet, the new engines were wing mounted, but since the Speys were considerably larger than the Avons used on the Comet, Hawker Siddeley had to redesign the Nimrod’s wing centre section to accommodate them. The Speys also required more air, so XV148’s intakes had to be enlarged, as did its jet exhausts.
The Nimrod retained the bullet-shaped leading-edge auxiliary fuel tanks of the Comet 4C. On the production aircraft the starboard tank was fitted with a powerful searchlight at its forward end, to aid the aircraft’s surface-search capabilities in bad weather or at night. To protect against the salt laden environment in which the Nimrod was to operate, the whole airframe and engines were given a coating of anti-corrosion protection.
As the primary combat duty of the Nimrod was ASW, Hawker Siddeley incorporated a magnetic anomaly detector (MAD) unit to help the aircraft search for submerged submarines. This device is housed in a fuselage tail cone which extends aft, well beyond the aircraft’s fin and rudder. In the rear fuselage section ample storage space is provided for a wide variety of sonobuoys, marine markers and other maritime sensors. These can be dropped through tube launchers and once in the water the information they provide was relayed to a pair of acoustic data processors onboard the Nimrod. These processors were to capable of accurately monitoring and interpreting the sonobuoy data and then transferring it to the aircraft’s Marconi computer-based integrated navigational and weapons control system. Making use of four onboard computers, this system managed the Nimrod’s various sensors and sent the appropriate information to the relevant operator’s console in the aircraft’s Tactical Crew Compartment in the forward fuselage.
The system also managed the Nimrod’s surface surveillance radar. This was an EMI ASV. Mk 21D unit, similar to those carried by the Shackleton and was mounted in the Nimrod’s nose. To provide accurate, long-range navigation, the aircraft was equipped with a new Tactical Navigation (TacNav) system, while a comprehensive communications suite, including various frequency radios and transmitters, provided a range of links with shore bases, aircraft and warships. To supply adequate electrical power, a new electrical generating system was developed using feed-off from the Speys.
As the Nimrod was considerably heavier than the Comet, Hawker Siddeley had to revise the existing undercarriage assembly. Additional modification work involved fitting a weapons pylon below each wing, so that air-to-surface missiles such as the Martel or AS12 could be employed, revising the existing hydraulic systems, updating the fuel supply to the new engines and a general strengthening of the aircraft’s framework.
Finally, in May 1967, XV148 took to the air on its initial test flight. It was extensively employed in researching the performance of the Speys, in aerodynamic trials and for assessing the Nimrod’s flight systems. By April 1968, it was averaging 25 flying hours a month as the test programme intensified and weapons trials commenced.
By this time the aircraft had been joined by the second prototype, XV147. This aircraft retained its original Avon 524 turbojets for reasons of economy and because of the tight deadline imposed on Hawker Siddeley. Taking to the air for the first time during July 1967, XV147 was fitted with underslung pods below its engine nacelles to allow its onboard electrical generators to supply power for the Nimrod’s avionics, which this aircraft was intended to prove.
While the two prototypes continued testing, Hawker Siddeley began constructing the first of the 38 production aircraft at its Woodford site. The first completed example, XV226, flew in June 1968 and the new aircraft received the RAF designation Nimrod MR. Mk 1. It was sent to the Aeroplane and Armament Experimental Establishment (A&AEE) at Boscombe Down for engineering trials, where it was soon joined by XV148. The second and third Nimrods to leave Woodford (XV227 and XV228) were handed over in February and March 1969, respectively, and they too joined the programme at the A&AEE, where they were employed in weapons, navigation and tactical systems research.
By November 1969, another trio of MR. Mk Is had been delivered and the RAF was able to form a Maritime Operational Training Unit (MOTU) at St Mawgan in Cornwall. The MOTU’s task was to train personnel for the first frontline Nimrod squadron. The first aircraft to join the MOTU was XV230 and like all the Nimrods being delivered, it wore a colour scheme of White upper surfaces and Light Aircraft Grey undersides, with ‘D’-Class red/white/blue roundels and Black serial codes. With more Nimrods arriving, the MOTU was redesignated as No.236 Operational Conversion Unit (OCU).
The honour of becoming the first front-line Nimrod unit fell to No. 201 Sqn, based at RAF Kinloss in Moray. Scotland. The squadron began to convert from its Shackleton MR. Mk 3s during 1970. By July of that year it had 10 Nimrods on strength and was declared operational.
Next to convert from Shackletons was No. 42 (ТВ) Squadron at St Mawgan. By August 1972, all 38 Nimrods ordered had entered service and the aircraft had also re-equipped Nos 120 and 206 Sqns at Kinloss. together with No. 203 Sqn at Luqa in Malta, allowing the remaining Shackletons to be retired. With this initial order completed, the British government placed a follow-up contract with Hawker Siddeley for eight more aircraft, to be delivered between 1975 and 1977.
In service the Nimrod normally carried a crew of 12 and apart from ASW duties it could also be used for routine MP, search and rescue (SAR) and anti-shipping strikes. Its large weapons bay could accommodate a range of torpedoes, depth charges, mines, bombs and additional sonobuoys. Although rarely used, the undenting hardpoints could also mount a selection of bombs, mines, gun pods or rocket launchers.
Performance wise, the Nimrod soon impressed. It could achieve a maximum speed of 575 mph (925 km/h), with a cruising speed of 547 mph (880 km/h) and a low-level patrol speed of 230 mph (370 km/h). With an operational ceiling of 42,000 ft (12802 m), the aircraft had a typical ferry range of 5,755 miles (9262 km) and an endurance of 12 hours. An on-station patrol time of 6 hours could be achieved at a range of 1,150 miles (1851 km) from base, by cruising on just two engines, with the other pair shut down. In an emergency, the Nimrod could even climb and cruise on just one Spey. To extend its range even further, the Nimrod could be fitted with up to six auxiliary fuel tanks in its weapons
Nimrod MR. Mk 1 XV.228, shows off the clean lines of the design and the original fuselage window arrangement. This aircraft was the third production Nimrod and entered service during March 1969, whereupon it was allocated to the A&AEE for service trials. (BAE Systems via David James) bay and if necessary it could also fill in as troop transport, with seating for up to 45 soldiers in its fuselage.
The aircraft’s crews were quick to praise its smooth flying characteristics and airliner-style comfort – a major bonus on long-range patrols and far superior to anything experienced on the Shackleton. The Nimrod’s submarine detection qualities were also favourably commented upon and demonstrated during numerous NATO training exercises, while many a submerged Soviet submarine was tracked as it headed for the North Atlantic. Indeed, submariners soon remarked how difficult it was to spot the turbofan-powered Nimrod using air detection equipment, when compared to its noisier turboprop-engined rivals such as the American P-3 Orion.
Soon the Nimrod began to achieve a number of firsts. As early as November 1971, aircraft from No. 201 Sqn were engaged in real SAR missions, activities which became important for all Nimrod units. Aircraft were frequently called upon to undertake long-range sorties in atrocious weather conditions to locate vessels in distress. During 1973, Nimrods won the prestigious Finecastle Trophy competition for maritime aircraft for the first time, beating crews from Australia, New Zealand and Canada. It was an event the Nimrod won another four times during the 1970s and it continues to dominate it to this day.Operational surveillance missions were undertaken for the first time from 1973, during the Cod War fishing dispute between Iceland and the UK. These patrols lasted until 1976, when a political settlement was reached, but the duty established the Nimrod as an excellent fishery protection aircraft. It was therefore no surprise when, in 1977, the aircraft embarked upon Operation Tapestry. Lasting until 1986, this mission involved Nimrods flying fishery protection flights over the North Sea and other UK territorial waters, as well as the monitoring of the newly developed offshore oil industry. At its height, Operation Tapestry involved three Nimrod sorties a week.
Electronic Reconnaissance (ER) is composed of four sub-disciplines: Electronic Intelligence (Elint), Communications/Signals Intelligence (Comint/Sigint), Radar Intelligence (Radint) and Telemetry Intelligence (Telint). No. 192 Sqn, RAF was formed for the ER role as an ‘operational signals research’ unit in 1951. In August 1958 it became No. 51 Sqn. equipped with Canberras and, eventually, Comet R. Mk 2s. During the early 1970s, the RAF began to consider a replacement for No. 51 Sqn’s ageing Comets and soon settled on a variant of the Nimrod, as suggested by Marshalls of Cambridge, which had originally worked on the Comet R. Mk 2. It was decided that three Nimrod MR. Mk Is would be converted to Nimrod R. Mk 1 specification for the ER mission.
In July 1971 the first of these Nimrods, XW664, was handed over for conversion. The work took two years to complete and it was late 1973 before XW664 commenced flight trials in its new configuration. It was followed by XW665 and XW666.
During May 1974, the Nimrod R. Mk 1 was officially commissioned into service with No. 51 Sqn. By February 1975 the three aircraft were in place, allowing the last Comet to be retired. For training, an MR. Mk 1 (XZ283) was borrowed between 1976 and 1978.
The Nimrod R. Mk 1 is immediately recognisable by its lack of a MAD tail boom and the addition of radomes for various sensors on the noses of the external wing fuel tanks. It initially retained the MR. Mk l’s fuselage window arrangement, tail-fin mounted ESM pod, 12-strong crew and flight performance, including the ability to loiter for long periods which made it ideal for intelligence gathering purposes.
The R. Mk 1 was packed with a host of highly classified electronics equipment, housed in its fuselage and within the erstwhile weapons bay. In addition, collection of new antennae sprouted from the aircraft’s underbelly.
Although the exact nature of the R. Mk l’s mission remains top secret, it is widely believed that the aircraft regularly operate on behalf of GCHQ and so they are thought to be both Elint and Comint capable.
The Nimrod R. Mk 1 was been employed over the Baltic Sea during the Cold War to monitor the air defence networks of several Warsaw Pact nations, including the Soviet Union’s defences around what was then Leningrad. The aircraft have also scanned areas around the White Sea and are known to have been deployed to Malta and Cyprus to record the activities of the Soviet Black Sea Fleet, as well as the electronic transmissions originating from a host of Middle Eastern states.
The Nimrod has a maximum ceiling of 42,000 ft (12802 m), although it rarely operates at such altitudes. After the addition of inflight-refuelling probes, the type’s normal endurance of 12 hours can be exceeded. On-station time is also increased by shutting down two engines in cruising flight. (BAE Systems via David James)
During the 1982 Falklands Conflict it is widely accepted that an element of No. 51 Sqn participated in Operation Corporate. One R. Mk 1 (XW664) is thought to have operated from Ascension Island on sorties to intercept and monitor Argentine signals traffic. Shortly after the conflict ended, XW664 was seen with a newly added inflight-refuelling probe. Similar modifications were carried out to MP Nimrods assigned to Operation Corporate.
At some point during the 1980s, the RAF’s trio of R. Mk Is received a classified updating that altered their external appearance. Among these alterations was the addition of an array of nine inverted ‘L’-shaped antennas above the aircraft’s forward fuselage, on both wing fuel tanks and also over the tailplanes. New, tubular ESM pods were added to the wingtips, while signs of improved communications equipment included a collection of UHF/VHF aerials along the top of the fuselage. The existing window arrangement was also revised, with a reduction in number.
Whilst XW664 had already received it’s inflight refuelling gear, the other two machines were similarly equipped during the course of their upgrading.
During the 1991 Gulf War with Iraq, No. 51 Sqn deployed to RAF Akrotiri, Cyprus, and from there to an unspecified location somewhere in the Gulf region.
From 1992 to 1993, the Nimrod R. Mk 1 found itself over the Adriatic Sea monitoring air defence systems in the disintegrating Yugoslavia. In May 1995, the small force suffered its first loss when XW666 crashed over the Moray Firth, following an engine fire.
The loss of this aircraft placed a huge burden on the two remaining aircraft. Therefore, a month after XW666 was lost, the Ministry of Defence (MoD) awarded British Aerospace (BAe) a contract to supply a replacement using a surplus MP Nimrod. XV249 was duly converted to R. Mk 1 standard and joined No. 51 Sqn in December 1996. In January 1997. it was passed on to E-Systems for installation of the new SRIM-6113 Starwindow avionics system. This comprised a pair of high-speed search receivers, a wide-band digital directionfinder, a network of 22 digital intercept receivers supported by an interception unit for use against frequency-agile radar transmitters and an inflight technical analysis device. The system also incorporated a digital recording and playback suite, a multi-channel digital data demodulator and an enhanced pulsed signal processing capacity.
Suitably equipped, XV249 was finally declared fit for service in April 1997. It was considerably more capable and versatile than the other two R. Mk Is some pundits suggested a redesignation to R. Mk 3. It is likely that both XW664 and XW665 now have Starwindow.
Most recently the R. Mk 1 variant has participated in NATO’s Operation Allied Force against Serbia during 1999 and Operations Enduring Freedom against the Taliban regime in Afghanistan and Telic against Iraq.
The RAF’s Nimrod force underwent its first changes during 1975, when it was announced that 32 aircraft were to be upgraded to a new MR. Mk 2 standard. With submarine technology ever changing, the RAF had recognised the fact that no matter how good the Nimrod MR. Mk 1 was, if it was to remain effective to the end of the 20th century, then a measure of modernisation would have to be undertaken.
The MR. Mk 2 programme did not affect the Nimrod’s airframe, but concentrated on improving its avionics. The work was to be carried out by Hawker Siddeley at Woodford, but in 1977 the company was absorbed into the newly created, nationalised, BAe group. It was under this new company’s authority that the upgrading scheme was implemented.
BAe employed the original Nimrod prototype, XV147, to research the upgrade, while the MoD decided that one of the additional eight MR. Mk Is ordered in 1972 but not yet completed, would be delivered as a brand new MR. Mk 2.
One of the cornerstones of the whole MR. Mk 2 upgrade was the replacement of the existing ASV. Mk 21 radar with a new, more advanced and highly capable EMI Searchwater system. This offered far greater surface search and surveillance capacity and even today is regarded as being one of the best maritime radars around.
With newer-generation submarines able to dive to greater depths and run with far less noise, it was necessary to update the Nimrod’s detection equipment. The MR. Mk 2 would feature a completely new Marconi AQS.901 acoustic monitoring device, which could also employ the Anglo-Australian produced Barra long-range sonobuoy and sonics system. The four original 1600D tactical computers of the MR. Mk 1 were retained, but their capacity was increased by 50 percent.
Attention was also given to the Nimrod’s TacNav equipment which was improved through the addition of an INS. Communications were boosted through the fitting of online encryption and revised radio teletype sets.
To provide adequate cooling for the increased amount of avionics installed, the Nimrod’s existing duplicated Cabin Conditioning System (CCS) was supplemented by a third unit. This was fitted in the rear fuselage section, beyond the pressurised hull compartment andmeant that a large ram-air intake had to be added to the port side of the fuselage, just forward of the tail fin. This immediately created a recognisable feature unique to the MR. Mk 2 variant. The first modernised MR. Mk 2 was returned to RAF Kinloss in 1979, wearing a new paint scheme of Hemp upper surfaces with Light Aircraft Grey undersides. Lower visibility red/blue roundels were carried, except below the wings, where the original ‘D’-Class markings were retained. This new scheme was borne by all MR. Mk 2s and was slowly adopted by the remaining MR. Mk Is. While the programme of conversions continued, No. 206 Sqn became the first unit to begin MR. Mk 2 operations. By this time there was one less Nimrod formation, since No. 203 Sqn had disbanded in December 1977. The aircraft formally flown by No. 203 were either stored, or distributed among the remaining Nimrod units. In November 1980, the first Nimrod to write off occurred, when XV256 crashed in the Roseisle Forest after suffering a bird strike while taking off from Kinloss. The aircraft’s pilots were killed, but their brave actions in trying to control the Nimrod’s impact enabled the remaining 18 personnel onboard to survive. Only three months earlier, XV256 had undergone conversion to MR. Mk 2 standard.
At the start of Operation Corporate to retake the Falkland Islands, it was appreciated by the British commanders that the Argentine navy’s small force of diesel-electric patrol submarines posed a potentially serious threat to the Task Force and it’s crucial supply lines back to Ascension. Although the Royal Navy’s warships and ASW helicopters could guard against this risk, they would be stretched to the limit by other demands and could not be spared to guard ships heading back and forth between the Task Force and Ascension. The RAF’s Nimrod force was the ideal solution to this problem.
The first Nimrods involved in Corporate were the MR. Mk Is of No.42 (ТВ) Sqn. On
4 April 1982, the unit received orders to prepare two aircraft, three flight crews and the necessary ground support staff for imminent deployment to Ascension Island.
XV244 and XV258 arrived at Ascension’s Wideawake airfield on
5 April, after an overnight stop over in the Azores. Two days later, the first operational sortie was flown when XV258 undertook a 6-hour 10-minute surface surveillance and submarine support sortie. The same aircraft repeated the mission two days later, this time staying in the air for 6 hours and 45 minutes.
Over the following days, both Nimrods flew long-distance missions, with XV244 logging the longest flight for the squadron on 11 April, when it completed a 9-hour 50-minute sortie. Meanwhile, back at RAF Kinloss, there were 13 MR. Mk 2s cleared for operations and it was decided that because of their more advanced radar and avionics they would be better suited for deployment to Ascension.
On 13 April, the first Nimrod MR. Mk 2 (XV230) arrived at Wideawake followed by XV255 four days later. Both of No.42 (ТВ) Sqn’s aircraft then returned to St Mawgan, where the unit was put on standby to provide SAR cover for Harrier reinforcement flights heading to Ascension. One MR. Mk 1 was assigned to this duty at St Mawgan, while a second aircraft flew out to Freetown in Sierra Leone to provide cover from there. Other MR. Mk Is assumed much of the KLW’s SAR and fishery protection duties, thus allowing Kinloss to concentrate on supporting Operation Corporate.
As the Task Force continued to edge closer to the Falklands, the MoD began to consider ways of extending the range of the Nimrod so that it could continue to provide ASW cover far down in to the South Atlantic. On 14 April, the MoD instructed BAe at Woodford to proceed with equipping a number of Nimrods with inflight refuelling equipment, using surplus probes from the RAF’s recently retired Vulcan bombers. A test aircraft (XV229) was quickly modified with the refuelling probe being mounted above its flight deck. This created a stability problem so the engineers at Woodford added a small ventral fin beneath the aircraft’s rear fuselage and finlets above and below the tailplane. Thus modified, XV229 was employed in aerodynamic tests before moving back to Kinloss at the end of the month to commence inflight refuelling training.
Next to undergo this modification work was XV238, which went to the A&AEE for a series of intensive clearance trials. This resulted in the probe-equipped Nimrod being given the all-clear on 5 May. Aircraft that received inflight-refuelling capability were redesignated as Nimrod MR. Mk 2Ps by the RAF.
The inflight-refuelling system received its operational baptism on XV227, which flew to Wideawake unaided during 7 May. Two days later, this aircraft conducted a 2,750-mile (4426-km) flight south west of Ascension to provide ASW screening to elements of the Task Force. It was airborne for 12 hours 45 minutes, successfully refuelling several times along the way from Victor K. Mk 2 tankers.
By this point the MoD had begun to express concerns that such long range sorties, gradually moving ever nearer to the Falklands and the Argentine mainland, might leave the Nimrod vulnerable to airborne interception. The Sea Harriers and Harriers of the Task Force were achieving air-to-air kills, but could not completely establish air supremacy in the area and so there remained a possibility that Argentine fighters could engage a patrolling Nimrod, which would be unable to defend itself against attack.
Just some of the Nimrod MR. Mk 2P’s sensor displays are depicted here. The MR. Mk 2 upgrade gave the Nimrod an enhanced detection capability to deal with advances in submarine technology. The Nimrod MRA. Mk 4 will ensure that the aircraft remains at te forefront of maritime aircraft design. (BAE Systems via David James)
Fortunately, a team at Woodford quickly devised a way of adding a pair of launcher rails for AIM-9G Sidewinder AAMs to the Nimrod’s undenting hardpoints. Trails of this new fit commenced on 26 May, again using XV229, and the necessary acceptance tests were hurriedly rushed through two days later. On 31 May, XV232, which had returned from Ascension, flew for the first time as a fully Sidewinder-capable Nimrod. It returned to Wideawake airfield five days later.
During the conflict, the Nimrod also had its offensive weapons carrying ability improved. Some aircraft received cockpit-mounted bomb sights to enable them to use 1,000-lb HE or BL.755 cluster bombs against surface targets or land positions. An important new addition to the Nimrod’s arsenal was the American AGM-84A Harpoon anti-shipping missile (AShM). The Nimrod’s weapons bay had to be modified for Harpoon and it was not until 10 June 10 that the first MR. Mk 2P cleared to fire Harpoons (XV234) took to the air on test flights. This aircraft subsequently deployed to Ascension on 2 July, long after Argentina had surrendered.
During the course of Operation Corporate, 111 Nimrod sorties were launched from Ascension. Most were long-range ASW patrols or surface surveillance flights, of increasing duration and risk as the conflict intensified. For example, on 15 May, XV232 undertook a 19-hour 5-minute sortie, covering about 8,300 miles (13357 km) and at one stage reaching a point just 60 miles (97 km) off the Argentine mainland. There it conducted a survey of the coastline with its radar, covering a strip of land 400 miles (644 km) wide by 1,000 miles (1609 km) long. The purpose of this extraordinary mission was to confirm that the Argentine navy was still blockaded in its home ports by the threat of attack from lurking British nuclear-powered submarines. Although extremely vulnerable to radar detection and air interception as it flew parallel to the Argentine shore at altitudes of between 7.000 and 12,000 ft (2134 and 3658 m), the Nimrod went unchallenged.
A total of two MR. Mk Is, three MR. Mk 2s and five MR. Mk 2Ps deployed to Ascension at some point during the conflict and by mid-June 1982 the number of Nimrods with inflight refuelling gear stood at 13. After the war there was still a need for vigilance and SAR cover, so Nimrods continued to fly from Wideawake until August 1982, when XV234 undertook the final sortie prior to returning to Kinloss.
After the Falklands conflict, the remaining MR. Mk 1 aircraft were converted to
MR. Mk 2 standard and eventually the whole force was brought up to a common MR. Mk 2P standard complete with Sidewinder and Harpoon capabilities.
During the 1980s, the aircraft also began to receive enhanced ESM equipment in the shape of Loral ARI. 18240 Yellowgate wingtip pods. This allowed the Nimrod to detect and classify hostile radar emissions, as well as other electromagnetic signals. The first aircraft to receive the new system was XV241 and by the mid-1980s the whole fleet had been updated.
In June 1984, XV257 became the second Nimrod to be lost when it suffered a fire in its weapons bay. Severely damaged, the aircraft was withdrawn and later scrapped. However, it was more or less replaced by XZ284, which entered service that year (after having been originally ordered in 1972 and finished as an MR. Mk 2P) and represented the last new-build Nimrod to join the RAF.
In the wake of Iraq’s August 1990 invasion of Kuwait, part of the RAF’s contribution to Operation Granby was the deployment of three No. 120 Sqn Nimrods to Seeb, Oman, where they were to assist Coalition naval forces in blockading Iraqi seaborne traffic. Additional crews were provided by Nos 42 (ТВ) and 206 Sqns.
A number of urgent improvements were introduced to provide the Nimrods with greater operational flexibility and better combat
effectiveness. A new self-defence suite (similar to the type installed on the RAF’s fighters that were sent to the Gulf) comprising chaff/flare launchers and radar-jamming devices was added, as was a GEC-Marconi Ariel airborne towed decoy system which was mounted in the aircraft’s tail fin housing in place of the ESM antennae normally situated there. A forward-looking infra-red (FLIR) sensor in an underfuselage turret was also incorporated, giving the Nimrod an improved night/poor weather surveillance capability. The onboard tactical control systems were revised and newer communications links allowed for greater inter-service co-operation.
The Nimrod performed well and assisted in the sinking of a number of Iraqi gunboats. Working closely with other Coalition aircraft and warships, the Nimrods flew a total of 396 missions, amassing 2,367 flying hours during the blockade and subsequent liberation of Kuwait, before Iraq agreed to a ceasefire in February 1991. Even after the fighting had died down, the Nimrods continued to fly regular patrols over the Persian Gulf and racked up a further 169 hours spread over 25 sorties before they returned to the UK in April 1991.
No sooner had the Gulf War ended, than the RAF’s Nimrods were again being called upon to assist the United Nations. This time te action was in the Balkans and from 1992 to 1993, MR. Mk 2Ps deployed to Sigonella, Italy, to help enforce a UN-sponsored maritime blockade of Serbia in a mission that was known as Operation Sharp Guard.
At this time, over 20 years of continuous and demanding service in some of the harshest maritime weather had begun to affect the Nimrod fleet. Corrosion and fatigue problems began to show up and in September 1991 XV238 and XV253 had to be withdrawn from use. Exactly a year later, XV242, XV247 and XV249 were taken out of service and placed in storage. Other aircraft also suffered varying degrees of wear and tear, which meant they were beyond economical repair at a time when Britain’s defence budget was being cut yet again. They too were retired. By the end of 1992, only 26 Nimrods remained operational.
This number was further reduced during September 1995, when XV239 crashed into Lake Ontario, Canada, during an air display. All onboard were killed.
During 1992, the Nimrod OCU moved to Kinloss and in September of the same year No. 42 (ТВ) Sqn was disbanded. It later reformed as No. 42 (Reserve) Sqn in a shadow capacity for the OCU, whose role the squadron took over.
Modernisation of the remaining MR. Mk 2Ps continued and in September 1998 it was announced that 10 aircraft were to receive Link-11 digital data buses, with the remainder of the force to undergo similar upgrading at a later point. At the 2001 Paris Air Show it was publicly acknowledged that the Nimrods had also received a Replacement Acoustic Processor (RAP), made by Ultra Electronics. Known officially as the AN/UYS-503, this new data processor provided the Nimrod with a vastly improved ability to detect, identify and track underwater sound sources. It is also thought that some aircraft have been given Missile Alert Warning System (MAWS) devices. Linked to the Nimrod’s chaff/flare launchers, MAWS provides advanced warning of incoming surface-to-air missiles (SAMs) and directs the appropriate countermeasures.
Design studies for an aircraft to replace the RAFs Shackleton AEW. Mk 2 began in 1973 and a Nimrod based proposal was soon put forward. The large fuselage capacity, excellent range and ample power reserves of the Nimrod made it an ideal candidate as an AEW platform. At the same time as the Nimrod was being suggested, the Americans were strongly promoting their new Boeing E-3A Sentry. This had been undergoing tests since 1970 and was due to enter service with the USAF during 1977. It was also on order for NATO, where a consortium of European member states was buying a force of 18.
While the RAF favoured the E-3A, the British government was unsure whether to develop the Nimrod variant or join the NATO programme. The drawback with the latter option was that by sharing a relatively small fleet of E-3As with other NATO nations, the aircraft would not be wholly available to serve the UK’s national interests. In March 1977 therefore, the MoD announced that it was prepared to fund the development of the Nimrod AEW
BAe was awarded the contract and it was planned to produce a force of 11 aircraft by converting surplus Nimrod MR. Mk 1 airframes (redundant since the disbanding of No. 203 Sqn) together with completing two of the MR. Mk Is ordered in 1972 as AEW aircraft.
BAe opted to go for a fore-and-aft radar antenna arrangement on the Nimrod, with scanners mounted at each end of the aircraft’s fuselage in large, swollen radomes. It was believed that this layout would not hinder radar performance, since the radar would not be screened by any part of the airframe.
The heart of the Nimrod AEW was its Mission System Avionics (MSA) which was comprised of three main sensors – radar, signal processors and IFF devices. The Marconi radar was a multi-mode, pulse-Doppler unit. As well as detecting airborne targets, the radar could also provide surface surveillance and weather monitoring.
From the radar, information concerning target range, azimuth, radial velocity and altitude was passed to a Marconi 920ATC signal processing computer. This would then correlate the data with a ground control station if necessary, before relaying it to a GEC 4080M data-processing computer.
The 4080M would digest the information before passing it on to one of six appropriate Multi Function Display and Control Consoles (MFDCC) located in the Nimrod’s forward-fuselage Tactical Area. Each MFDCC was operated by one technician who would deal directly with the appropriate command staff, warship or airborne interceptor via an Automatic Management of Radio and Intercom System (AMRICS) communication link.
In addition the 4080M would receive data from two wingtip Loral ARI-18240/1 ESM pods (a modified version of the type carried by the Nimrod MR. Mk 2). Extra support would be given by a Cossor Jubilee Guardsman IFF device, plus a pair of Ferranti FIN-1012 INS units.
To provide extensive communications support, the Nimrod AEW was to carry a range of UHF, VHF and HF transmitter-receivers, a radio teletype and a NATO-standard Link-11 datalink.
BAe envisaged giving the Nimrod AEW a flight crew of four, plus a six-strong tactical crew. Although part of the flight crew, the aircraft’s navigator was also tasked with supporting the tactical crew and so occupied a station alongside them.
Within the Tactical Area all the MFDCCs were arranged in a row along the port side, while the opposite side was used for housing the various avionics and communications modules. The main radar installations and spare avionics were positioned in the rear fuselage compartment.
Apart from its forward and aft radomes, the Nimrod AEW required very little structural modification. BAe anticipated that this would save time on flight development and allow for lower operating costs, since the RAF already held a large stock of basic Nimrod spares. Even the existing Rolls-Royce RB.168 Spey Mk 250 turbofans were retained as were the two wing leading-edge fuel tanks. However, as it was planned to operate the Nimrod AEW at higher altitudes than the maritime patrol variant, the aircraft’s ability to patrol on just two of its four engines was deleted. Since additional electrical power would be required to support the aircraft’s new avionics, BAe decided to supplement the existing engine-mounted electrical generators with new 48-kW alternators.
The RAF specified an in-service date of 1982 for the new aircraft and allocated it the designation Nimrod AEW. Mk 3.
BAe produced the first development aircraft by converting Comet 4C XW626. On 28 June 1977 this aircraft, equipped only with the nose radome, took to the air on its maiden flight. The first aerodynamically representative aircraft, XZ286, undertook its initial flight two years later. Surprisingly only marginal changes in directional stability resulted from the airframe modifications and to correct these BAe increased the height of the Nimrod AEW’s tail fin by 3 ft (0.91 m). Vortex generators were added around the rear fuselage to eliminate slight buffeting that had been noticed. Suitably revised, XZ286 was sent to the A&AEE for trials.
The next aircraft to undergo conversion was XZ287 which flew in January 1981, followed by XZ281 in July. All three aircraft were to be extensively employed for research, before joining the eight other machines in front-line service with No. 8 Sqn. Some of the aircraft were to be equipped with inflight-refuelling gear and these were redesignated as AEW. Mk 3Ps by the RAF, which intended to retrofit the whole force to this standard once it was operational.
However, it was not long before the Nimrod AEW programme began to encounter serious problems. Independently, the aircraft’s systems worked fine, but once they were integrated a mass of faults appeared.
One of the most significant problems concerned the 4080M computer. Its memory was simply incapable of handling the large amounts of data it was supposed to receive and adding additional memory failed to solve the problem. Marconi believed that in time the system’s capabilities could be improved by 500 per cent, by changing its software. Initially it was thought that 300,000 man hours would be needed to improve the software but this estimate soon proved grossly inadequate and by tinkering with the existing programming, Marconi was creating extra problems.
Nimrod AEW. Mk 3 prototype X2286, flies alongside the Tornado ADV development aircraft for a publicity shot. This combination was intended to be the core of Britain’s air defences for the latter part of the 20th century and beyond. Nimrod AEW failed to overcome a catalogue of defects, however, and was eventually cancelled in 1986. (BAE Systems via David James)
The 4080M’s lack of storage capacity had caused it to act slowly when providing a full multi-target tracking operation and numerous false contacts ended up being displayed as the computer became overloaded. As an interim solution to this particular problem, new software was introduced which allowed the individual MFDCC operators to focus their attention on certain sectors by ‘blanking out’ others thus letting the computer concentrate solely on just a handful of targets in one area at a time. This clearly limited the Nimrod AEW’s operational effectiveness, since by devoting attention solely to one zone, incoming hostile aircraft in other areas were being ignored.
In the longer term, Marconi had hopes of replacing the 4080M altogether with a new 4190 Series 32-bit computer. This offered a 300 per cent improvement in operating speed and capacity. Two 4190s could be carried, thus boosting the aircraft’s operational effectiveness even more, but the system was expensive and would not be available for some time.
The radar also failed to live up to expectations and quickly proved susceptible to high clutter returns which confused the signal processing computer, causing it to overload. Modification work to this computer managed to reduce the amount of clutter to an acceptable level, but it was still far above what had originally been forecast.
Further difficulties arose concerning the radar transmission levels and frequency stabilisation, which caused reliability to became a serious issue. Target tracking was erratic, with numerous false returns being reported, while it soon became clear that BAe’s fore-and-aft antenna arrangement actually failed to give the promised full 360 coverage.
During 1984 GEC-Avionics (as GEO and Marconi had now become) announced a Radar Performance Growth Programme (RPGP), aimed at resolving the numerous radar faults. By this time the whole project was already two years behind schedule and development costs were continually rising.
Tested on XZ281 and XZ287, the RPGP refinements showed a 200 per cent improvement in radar performance, as well as a considerable increase in reliability, especially in terms of target detection and maritime surveillance. RPGP was, however, horrendously expensive.
By 1984/85, Nimrod AEW was costing £5^6 million a month and the total bill for the project had soared to £816 million. This was already £300 million above the original budget forecasts and a final price tag of £1.05 billion was now being predicted. The Government was rightly concerned. It began to demand financial restraint from the MoD, while ministers were concerned over the public’s reaction to a programme that was soaking up taxpayers’ money like a sponge when other public spending schemes were being slashed. BAe was still unable to provide a definite date for when the Nimrod AEW would be fully operational.
From 1985 the RAF stopped publicly supporting the Nimrod AEW and once again began to grumble that all along it had wanted the Boeing E-3A. The RAF realised that if the Nimrod AEW was rushed in to service with its main faults still unresolved or with interim solutions adopted, it would be of little value. It had therefore had to persevere with its ‘stopgap’ Shackletons. What was particularly galling for the RAF was that the E-3A had been in service with the USAF since 1977 and NATO from 1982, with outstanding success.
It soon became obvious that Nimrod AEW would not be ready before 1987 at the earliest and the government’s patience began to wear thin. Three options were now open to the politicians in Whitehall. The first was to abandon the whole project. The second was to carry on with the project and spend an extra £1 million updating the Shackletons. The final option was to cancel Nimrod AEW and buy the Boeing E-3A Sentry.
The first of these options was politically and militarily totally unacceptable. The second idea was like signing a blank cheque and it was doubtful whether the Shackleton force could be successfully updated. The Government therefore began to seriously consider buying the E-3A. However, the Sentry was not cheap – it looked likely to cost between £600 million and £800 million to buy a small force of E-3s, on top of the £1 billion that would have been wasted on Nimrod AEW.
Finally, during 1986, the MoD issued GEC-Avionics with a six month deadline to bring the Nimrod AEW up to a specification acceptable to the RAF or the entire programme would be terminated. Working closely with BAe, GEC-Avionics tried hard to resolve the problems, but in September 1986 the MoD’s deadline expired and the Government announced that the project was cancelled. A handful of updated E-3s was ordered in October 1986 and the RAF finally got the aircraft it had always wanted.
All eleven Nimrods that had been marked out for conversion had by this point been aerodynamically reconfigured. However, only the three development aircraft had actually received any of the planned systems or radar. The whole force was withdrawn upon termination of the programme and placed in to immediate storage, despite the airframes being in excellent condition. Some were held at RAF Abingdon, while others were located at various bases and robbed of spares before being cut up for scrap.
Nimrod MRA. Mk 4
In January 1995, the MoD issued its Staff Requirement (Air) No.420 (SRA.420) specification for a Nimrod MR. Mk 2 replacement (the MR. Mk 2P designation having reverted to MR. Mk 2 by this stage). Under this specification the new aircraft would have long-range, high-endurance, large load-carrying capability, excellent operational availability and low running costs, over an anticipated service career of 25 years. Envisaged world wide operations in a post-Cold War era dictated that the aircraft should be capable of wide-ranging autonomous missions from remote bases, with the minimum of logistical and personnel support.
SRA.420 attracted a number of interested contenders including the Dassault Atlantique 3 from France, refurbished P-3C Orions from the United States and Lockheed’s proposed Orion replacement, the P-7. In Britain, BAe suggested an upgraded Nimrod variant known to the company as Nimrod 2000. After much consultation the MoD finally announced in July 1996 that BAe’s Nimrod 2000 had been selected to fulfil SRA.420.
Although based upon the existing MR. Mk 2, the Nimrod 2000 upgrade involved an extensive reconstruction of 80 per cent of the airframe components, with sixty per cent of this work involving the replacement of certain structures with brand new parts. A whole new wing assembly was to be built, increasing span by 12 ft 2 in (3.71 m).
The aircraft’s flight deck area was to be stripped out and replaced by a new two-crew cockpit, complete with fully digital instrumentation. The Tactical Compartment was also to be fully updated. A new powerplant, new undercarriage, new fin fillets, rudder, auxiliary fins, weapons bay doors, avionics and improved self protection devices were all to be included as part of the programme. Any original MR. Mk 2 components retained were to be zero-rated so that the new aircraft could remain operational until 2025.
After announcing that Nimrod 2000 had been chosen, the MoD issued BAe with
Contract MAR-21a/100 in January 1997. Worth £2.5 billion, this deal authorised BAe to produce a trio of development aircraft using stored MR. Mk 2s, followed by the conversion of 21 of the RAF’s remaining Nimrods to the new specification. It was planned to have the development aircraft delivered between January and February 2000, with the first updated Nimrods being handed back to the RAF from 2001. All 21 were expected to be operational by 2003.
In February 1997 the three stored MR. Mk 2s highlighted for conversion (XV234, XV242 and XV247) were airlifted, in a HeavyLift Antonov An-124 transport, from Kinloss to FR Aviation at Hum, Bournemouth. This company had been subcontracted by BAe to undertake much of the airframe refitting work, while BAe concentrated on engineering and ground testing of the Nimrod 2000 design at its Warton, Lancashire, factory using the MR. Mk 1 prototype. XV147. for the purpose. Once updated at Hum, the Nimrods were to be flown to Warton for fitting out with avionics.
Nimrod 2000 included replacement of the Spey engines with four new BMW Rolls-Royce BR710 turbofans, each capable of 14,900 lb (66.26 kN) thrust. These provided a 23 per cent increase in power over the Speys, but were far more fuel efficient.
The BR.710 already powered the Gulfstream V executive jet, but for the Nimrod the engine required a certain degree of modification work. This centred on improved corrosion resistance, the adding of a new mixer unit to match the engine’s combustion characteristics with the aerodynamic constraints imposed by retaining the original Nimrod wing root engine positions, and a new electrical network, including full-authority digital engine control (FADEC), to interface the powerplants with the Nimrod 2000’s flight control systems.
Engine ground tests commenced during September 1998, followed by a four-week-long altitude performance research programme at the Defence Establishment Research Agency (DERA). In May 1999, the first 150 hour endurance tests were being conducted in Germany, with the BR.710 demonstrating its superior thrust levels, greater reliability and far lower maintenance requirements when compared to the Spey. Service certification for the new engine was achieved in 2000, with production commencing the following year.
The new wings were to be of all-metal, twin-spar construction and comprised a centre section, two stub wings and a pair of outer panels. The centre and stub sections accommodated the increase in span necessary to allow the new powerplants and undercarriage assembly to be fitted. Also, greater capacity fuel tanks were incorporated, boosting the aircraft’s fuel load by 15-17 per cent. The wing design work was allocated to BAe’s Filton plant, with assembly being carried out at BAe Chadderton. Originally the company had planned to retain the existing outer wing panels of the MR. Mk 2 but, at the request of the RAF, these too were redesigned by Filton and built at Prestwick, Ayrshire, Scotland.
Nimrod 2000’s fuselage had all-metal, semi-monocoque construction, with a fully pressurised upper component and unpressurised lower pannier, as in the MR. Mk 2. Fuselage rebuilding was widely dispersed throughout BAe’s factories, with Prestwick handling the design of the central section, while the pannier and forward fuselage was drafted at Farnborough, Hampshire. The rear component was designed in France by Dassault, while the fuselage assembly was carried out at Brough, Humberside.
A cantilever, all-metal tail unit, surmounted by a glassfibre fin-tip pod, was drawn up by Farnborough and Prestwick, with the latter carrying out the construction in conjunction with FR Aviation. BAe’s Farnborough centre also undertook the design work for the Nimrod 2000’s weapons bay doors, elevators and rudder.
A brand new flap actuation mechanism was produced by Dowty, which was also responsible for the redesigned landing gear. Other new items included revised wingtip ESM pods and fin fillet, and enlarged finlets.
Retained from the MR. Mk 2 was the fuselage pressure hull and most of the empennage, both of these sections receiving new protective treatments.
The flight deck was fitted with a seven-screen Electronic Flight Instrumentation System (EFIS), made by Sextant. Each of the displays was a full-colour, liquid-crystal multi-functional display (MFD), able to supply both pilots with a variety of information. Full Night Vision Goggle (NVG) compatibility was also added.
The Tactical Compartment was revised with a new seven-station Tactical Team Position, plus two optional locations for visual observers and one for a sonobuoy loader. Thirteen additional seats were provided for support personnel or a relief crew. To improve crew comfort, the Nimrod 2000 employed an environmental control system (ECS) and new oxygen supply facility, both produced by Normalair-Garrett.
A major updating of the Nimrod’s avionics was a key feature of the programme. At the heart of the new aircraft’s systems was the Racal Searchwater 2000MR surveillance radar. This state-of-the-art unit offered high performance and better detection rates in all weather conditions, with much reduced clutter feedback. It could undertake automatic tracking of over a hundred surface targets simultaneously and could also be employed to localise aircraft when operating in its pulse-Doppler mode. A specialised SAR and weather monitoring programme was also included in the radar’s options.
For submarine hunting a new set of AQS.970 acoustic processors, linked to the AN/UYS.503 data processor of the RAP-modified MR. Mk 2, was employed. Also carried over from the earlier Nimrods, though in an improved form, was the ASQ.504(V) MAD device, which became fully integrated into the aircraft’s tactical system for the first time. An Electro-Optical Surveillance and Detection System (EOSDS), supplied by Northrop-Grumman, boosted the Nimrod 2000’s sensory capabilities through the use of an underfuselage turret-mounted Nighthunter FLIR.
BAE Systems has released a number of artists impressions of the Nimrod MRA. Mk 4 as it might appear in service. At left it is shown flying the anti-ship mission with AGM-84 missiles, while at right it is shown on an ASW sortie. The type will take over the anti-ship mission of the RAF’s Tornado GR. Mk 1B fleet when it enters service, hence the addition of ‘A’ for attack into the type’s core designation. The first MRA. Mk 4 is not likely to be delivered to the RAF until 2005. (BAE Systems via Paul E. Eden)
In a deal announced during July 1998 and worth $US30 million, Boeing was contracted to equip the Nimrod 2000 with a brand new Tactical Command System (TCS). This combined highspeed, data-processing Raytheon Model 960 computers, with fully reconfigurable software controls at each of the Tactical Team Positions, allowing full processing and data display from the aircraft’s sensors. The TCS also integrated, controlled and displayed information from the self-defence, communications and weapons-control systems. From the outset, the TCS was designed to reduce crew workloads, thereby enhancing mission success rates and promoting team co-ordination between the operator stations.
The flight systems were thoroughly revised with the fitting of a Smiths Industries Navigation and Flight Management System (NFMS). This interlinked, via a Mil Std 1553B databus, various avionics, such as the Rockwell Collins TCAS-2 Traffic Alert and Collision Avoidance System, a Sextant Automatic Right Control System (AFCS) and a pair of Litton LN-100G GPS devices to provide automatic control of the Nimrod 2000’s flight performance, route planning, navigation and way-point steering. Also linked in to this was a TACAN unit, a Triplex air data system, a radar altimeter and a microwave landing guidance suite. The net result of this was a new aircraft with an optimum level of navigation and flight performance.
The communications equipment of the Nimrod 2000 featured an enhanced digital arrangement made by Telephonies supported by HF, VHF and UHF radio sets. Secure, long-range satellite communications links were provided by Raytheon for UHF and by MATRA/BAe for VHF transmissions. The Link-11 datalink was carried over from the MR. Mk 2.
To boost its self-protection capabilities, Nimrod 2000 was equipped with an integrated Defensive Aids Sub-System (DASS) made by Lockheed-Martin. This utilised a Raytheon AN/ALE-50 towed decoy device mounted in the tail fin housing, Vinten combined chaff/flare dispensers, an improved Sanders MAWS sensor and an AN/ALR-56M radar warning receiver. One key advantage of the DASS is that it allows for future upgrading, thus enabling the aircraft’s self – protection devices to be thoroughly modernised as time goes by.
For offensive operations, a Smiths Industries Armament Control System (ACS), conforming to Mil Std 1760, handled all aspects of the Nimrod 2000’s weapons direction. The ACS automatically checks through the aircraft’s inventory as well as undertaking test and fault diagnosis. Unlike the earlier Nimrod versions, the 2000 was fitted from new with four under wing pylons, each of which is able to carry a pair of Sidewinders or a single AGM-84 Harpoon. The internal weapons bay was capable of holding up to nine ASW torpedoes, such as Stingray or the newer Tigerfish, as well as a variety of depth charges, bombs, mines, additional sonobuoys or auxiliary fuel cells. Alternatively, for surface-attack missions, the bay could accommodate two Harpoons.
Inside the fuselage, a pair of Normalair-Garrett rotary sonobuoy launchers were fitted in the rear compartment, each one capable of handling up to 10 Size ‘A’ buoys, while supplementary racks provide storage for another 150. A new Sonobuoy Positioning System (SPS) provided the aircraft with improved dropping accuracy and location finding. The wingtip ESM pods incorporated the Elta EL/L-8300UK device in place of the previous Yellowgate system.
The Nimrod MR. Mk 2s allocated as development aircraft received new identity codes upon their arrival at Hum, with XV247 becoming PA-1, XV234 becoming PA-2 and XV242 becoming PA-3. A fourth Nimrod (XV251) flew to Hum in November 1998 to become PA-4. The aircraft undergoing conversion would receive similar identities from PA-1 to PA-21.
In March 1999 BAe announced that the new aircraft, which had already received its RAF designation of Nimrod MRA. Mk 4 by this stage, would not be ready for service before 2005. The company was not specific about the reasons for the delay and would only admit to ‘resource and technical difficulties’. Privately it was believed that
BAe was less than satisfied with FR Aviation’s handling of the subcontracted airframe work.
Meanwhile, the RAF had decided to allocate the MRA. Mk 4s new serial numbers, owing to the extensive rebuilding work involved. Originally it had intended to keep the MR. Mk 2 identities, but now a new ZJ514 to ZJ534 serial range was introduced. Hence PA-1 would become ZJ516, while PA-2, PA-3 and PA-4 would become ZJ518, ZJ517 and ZJ514, respectively, and so on.
In November 1999, BAE Systems (as BAe had become following its merger with Marconi Electronic Systems) cancelled FR Aviation’s contract and transferred the MRA. Mk 4 airframe work to its Woodford factory. As conversion work had already commenced on PA-1, this aircraft remained with FR Aviation while the other three Nimrods were airlifted to Woodford at the end of 1999, again by An-124. There they were joined by XV258, which was delivered direct from the RAF to become PA-5 (ZJ515).
By September 2000, final assembly work had commenced on PA-1 and it was predicted that the first Nimrod MRA. Mk 4 test flights would commence during June 2002. Although it is behind schedule, the RAF is prepared to wait for the new Nimrod in the light of the enhanced capabilities it offers over the MR. Mk 2, and the fact that the MR. Mk 2 fleet is running out of airframe life. Indeed, BAE Systems is so confident of the new aircraft that it has begun offering it for export, although a bid to replace the US Navy’s P-3 Orions has failed. Should any overseas orders be placed for the Nimrod MRA. Mk 4, then production would have to be relaunched.
For more than 30 years the Nimrod has faithfully and efficiently served the RAF as a long-range ASW and MP aircraft, with its Elint derivative, the R. Mk 1, performing equally well. With the new MRA. Mk 4 variant breathing new life into the design, the Nimrod will remain the mightiest of hunters for many years to come.
Nimrod MR. Mk 1 XV257/57
This aircraft carries the white over Light Aircraft Grey scheme that was worn across the Nimrod fleet until the arrival of Hemp with the MR. Mk 2.
Nimrod MR. Mk 1 XV263/63. No. 208 Sqn White over Light Aircraft Grey.
Nimrod MR. Mk 2 XV242/42
Shown in early MR. Mk 2 configuration, this aircraft was withdrawn from use in September 1992. Note the high-visibility, two-tone roundels and fin flash.
Nimrod MR. Mk 2P XV250. No. 201 Sqn
Hemp over Light Aircraft Grey, with standard national markings and No 201 Sqn badge on the fin.
Nimrod MR. Mk 2P XV240/40
Hemp over Light Aircraft Grey, with standard national markings and last two of serial number in white on fin.
Nimrod MR. Mk 2P XV228. No. 42 (Reserve) Sqn
For display work in the mid to late 1990s, No. 42 Sqn finished this aircraft with a blue fin. The squadron number was carried in yellow on the blue background, along with the unit badge.
Nimrod MR. Mk 2 XV236/36
In recent years the RAF has abandoned the Hemp/Light Aircraft Grey scheme in favour of this rather anonymous overall grey finish. Nimrod MRA. Mk 4 is likely to enter service in this finish.
Nimrod AEW. MK 3 XV263/63
The RAF would have finished its Nimrod AEW. Mk 3 fleet in the standard Hemp/Light Aircraft Grey scheme. Indeed, a handful of the aircraft built were so finished.
Nimrod AEW. Mk 3 XV265/65
Had the AEW. Mk 3 entered service. No. 8 Sqn unit markings might well have been added to the basic Hemp/Light Aircraft Grey scheme.
Nimrod R. Mk 1P XV249. No. 51 Sqn
Finished in the standard Hemp over Light Aircraft Grey of the maritime aircraft, this R Mk 1P replaced XV666. Note the No. 51 Sqn goose applied directly to the fin.
Nimrod R. Mk 1 XV664/64. No. 51 Sqn
Finished in the standard Hemp over Lighl Aircraft Grey, but with the high-visibility fuselage roundels and fin flash No. 51 Sqn badge is presented on a white disc. Aircraft number and serial are in black.
Nimrod MR. Mk 2P XV234/34, No. 201 Sqn
Depicted following full conversion to MR. Mk 2P standard. XV234 is shown in the Hemp over Light Aircraft Grey scheme. Low-visibility roundels are carried on the fuselage, with standard D -Class markings under the wings.
Nimrod MR. Mk 2P XV235/35
With the pooling of aircraft during the Hemp/Light Aircraft Grey era. squadron marking became less often used.
Nimrod R Mk 1 XV665. No. 51 Sqn
Finished in the standard Hemp over Light Aircraft Grey, but with the low-visibility fuselage roundels and fin flash No. 51 Sqn badge is presented in a ring.
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