Nimrod


The early 1960s saw the RAF flying the lumbering and aging Lancaster derived Avro Shackleton in the maritime reconnaissance and anti-submarine warfare roles. The Nimrod evolved from a Hawker Siddeley feasibility study, in October 1963, of a number of aircraft to meet the requirement raised by the Air Staff Target No 357 (AST 357), after an abortive attempt at finding a NATO standard Maritime Patrol Aircraft failed in 1959.

Shortly afterwards, the Ministry of Aviation asked the company to advise the possibility of producing an aircraft to meet an in-service date of 1968. Although no written requirement was issued for this earlier aircraft, it was suggested by the Ministry that the main design aim should be to approach the AST 357 requirement as far as possible within the new time scale, and to take the fullest possible account of subsequent development potential.
In April 1964, Hawker Siddeley (HS) submitted its response to the request. Its proposal was the HS 800; a development of the successful Trident airliner to be fitted with the most advanced navigation, search and attack system that could be developed by 1968.

However, on 17th June 1964 HS received details of a new requirement, Air Staff Requirement 381 (ASR 381), dated 4th June 1964. ASR 381 called for an interim aircraft to enter services in late 1966. The overall capability required of this aircraft was not in the same class as that defined in AST 357, in fact substantially less in all respects.

In July 1964, HS produced a report offering the HS 801 as a possibility to meet the demands of ASR 381. The HS 801 was to be a Comet 4C conversion. As Treasury purse-strings gradually tightened, it made sound economic sense to use a tried and tested airframe. The Comet had gained an excellent record as both a military and civilian passenger transport, accumulating around 1.5 million flying hours. Much of the structural design work, therefore, had already been proven, and existing jigs and a workforce familiar with production methods, could be quickly utilised.

The Preliminary Type Specification was issued in October, followed by the completed Type Specification a couple of months later in December 1964. Issue Two of the Type Specification was made in May 1965 and in June 1965, approval was given for the initial work to commence. In January 1966 the Government decision was finally made to go ahead with the production of the aircraft, by now designated 'Nimrod'.

The contract for most of the programme was negotiated on a fixed-price basis, totaling around £100 million. This included design, research and development, the supply of two prototypes and the subsequent production of 38 aircraft.

The Preliminary Type Specification outlined a production timetable for two prototypes and 38 production aircraft based upon the Invitation To Progress (ITP). The programme was to utilise two Comet 4C airframes which were already available; the first of these was to have its fuselage shortened and was to be equipped with a full maritime reconnaissance weapon system, similar to those already used in the Shackelton. The military version of the Rolls Royce Spey engine, the RB168-1, were to be fitted and the intakes modified accordingly. This prototype was to be used as a systems development aircraft with the weapons pannier fitted but without operating doors. The initial flight of the systems development aircraft was to be 23 months after ITP.

The second existing Comet 4C airframe was to be modified to the same basic standard as the first, with the entire weapons system installed prior to the first flight and a completely operational pannier with associated weapons carriers. The initial flight of this aircraft was to be 30 months after ITP.

The initial flight of the first production airframe was originally planned for 33 months after ITP, then to be followed by one aircraft every two months up to the fourth, and thereafter two aircraft per month. The complete build programme of 38 aircraft was scheduled to take 59 months from ITP.


The Birth and into Service

 

Nimrod Prototype XV148 (grey/white)

Nimrod Prototype XV148 (grey/white/red)

The last two Comet 4C airframes to leave the production line, fitted with Avon engines, were available and offered an early opportunity to commence prototype flying. The airframes were converted and the first aerodynamic prototype, XV148, flew on 23rd May 1967-23 months from ITP. Spey engines were installed and the electrical generation, fuel and hydraulic systems were all made representative of the final design. By April 1968, XV148 had averaged 25 flying hours per month as the handling and performance aircraft.

XV147, the second prototype, was externally configured to Nimrod standard, although the original Avon engines were retained for reasons of economy and time. Underslung pods were fitted to the engine nacelles to permit adaptation of the generators to ensure the supply of electrical power, as XV147 was to be used for the development of the tactical systems; it first flew on 31st July 1967, some 25 months from ITP.

The first production aircraft XV226 first flew on 28th June 1968, 36 months after ITP. Initially used for development work, XV226 accumulated some 479 flying hours before entering operational service on 15th January 1973.

Following a remarkably trouble free flight test programme, on 2nd October 1969 the RAF took delivery of its first aircraft, when XV230 was delivered to the Maritime Operational Conversion Unit (MOCU - later 236 OCU) at St Mawgan in Cornwall. Production aircraft were soon being delivered to operational units at Kinloss and St. Mawgan with the last unit to re-equip being 203 Sqn at Luqa, Malta, receiving its first aircraft during October 1971.


Nimrod MR.1, MR.2 & MRA.4

Nimrod MR.1 XV266

Recognising the need to remain at the forefront of Cold War maritime warfare technology, in 1975 the RAF started the Nimrod update programme, so it could remain a viable weapons platform until the end of the century. On 23rd August 1979, XV236, the first of 32 converted MR.1 (now known as the Nimrod MR.2) was transferred to RAF Kinloss following work by British Aerospace at Woodford. The vast majority of the conversion from MR.1 to MR.2 involved a major refit of the navigational and attack systems. The ASV Mk.21 radar was replaced by the Searchwater radar representing a quantum leap in surface search and surveillance technology. Even today, the Searchwater remains one of, if not the most, capable maritime search radar available. The underwater detection capability if the Nimrod was also significantly enhanced with the introduction of a completely new acoustic monitoring system. Major modifications to the Tactical Navigation systems were also undertaken and overall, the upgrade of the four main computers employed to manage the sensors resulted in a fifty fold increase in the computing power of the MR.2 over the MR.1.

Nimrod MR.2 XV232

To provide adequate cooling for the large increase in electronic equipment fitted within the aircraft, it was necessary to supplement the existing duplicated cabin conditioning systems. A third conditioning system was installed in the rear fuselage, aft of the pressure hull. This gave rise to probably the most external feature of the Nimrod MR.2; a large pitot style air intake fitted to the port fuselage slightly forward of the fin.

Nimrod MR.2 XV231

In 1992 the RAF started the Replacement Maritime Patrol Aircraft (RMPA) procurement programme to replace the Nimrod MR.2 aircraft. To meet the requirement BAe proposed re-building each Nimrod MR.2 with new engines and electronics, which it called 'Nimrod 2000'. The RAF considered bids from Lockheed with its P-3 Orion, the Loral Corp with rebuilt ex-US Navy Orion's and Dassault with the Atlantique 3, but in December 1996 awarded the contract to BAe for the Nimrod 2000 - subsequently renamed the Nimrod MRA.4.

The MRA.4 is essentially a new aircraft, with Rolls-Royce BR710 turbofan engines, a new larger wing and fully refurbished fuselage. Much larger air intakes are required, because the airflow of the BR710 engine is significantly higher than that of the original Spey 250/251. The rebuilt aircraft borrows heavily from Airbus technology; the wings are designed and manufactured by BAe Systems (the UK Airbus partner) and the glass cockpit is derived from that of the Airbus A340.

Nimrod MRA.4 ZJ517

Development has taken longer than anticipated and the first of 18 MRA.4s have not yet entered service although the flying test programme is well underway. The contract was initially for the supply of 21 rebuilt Nimrod's, but due to technical problems the project was brought to a halt following the discovery that none of the Nimrod airframes supplied by the RAF for refurbishment were to a common standard. During 2004 it was announced that the programme would only see 16 aircraft upgraded, this was further reduced to twelve aircraft during July 2006 when the £1.1 billion production contract was signed. Entry into front line service is now expected during 2009.


The R.1

Whilst initial MR.1 production was getting underway, the Nimrod was seen as the ideal replacement for the ageing Comet 4Cs then used by the RAF for Electronic Intelligence (ELINT) duties. Offering ample internal space for electronic equipment and excellent cruise performance, three additional airframes were ordered under the designation Nimrod R.1. The first of the variant was delivered to 51 Sqn at Wyton (as virtually an empty shell) in July 1971. Over the next three years a complex array of sophisticated electronic eavesdropping equipment was fitted to the three aircraft, resulting in a large number of antennae appearing on the fuselage. The aircraft initially only differed externally in having the MAD probe in the tail deleted and dieletric radomes in the nose of each external wing tank and in the tailcone. Over the years, the R.1 has undergone numerous equipment upgrades as electronic surveillance becomes ever more sophisticated. Some of the cabin windows have been blocked up to allow installation of more equipment, and the fuselage antennae have exhibited several changes. Around 1982 the three R.1s gained wing tip ESM (Electronic Sensing Measures) pods of a design later fitted to the AEW.3 and MR.2 variants.

Nimrod R.1 XV249 51 Sqn

In 1995 R.1 XW666 was lost during a post servicing test flight when the engines caught fire and the aircraft was ditched in the Moray Firth. To replace it, MR.1 XV249 was converted to R.1 standard. The R.1 and 51 Sqn keep a low profile but perform a key role in many conflicts, from the Falklands War to the current anti-terror operations, identifying and classifying enemy air defence systems and gathering information on enemy activities.


The Falklands and AEW.3

The 1982 invasion of the Falkland Islands, and the subsequent aerial shadowing of the Royal Navy Task Force by Argentine aircraft in the south Atlantic, saw a hasty requirement to fit Eight MR.2s with ex Vulcan in-flight refuelling probes on the fuselage, above the cockpit. Given the designation MR.2P, the unused underwing hardpoints were also adapted to carry AIM-9 Sidewinder missiles, allowing the MR.2P to be described in the popular press as the world's largest fighter! Patrols were flown over the south Atlantic looking for Argentine submarines and surface vessels, and also in support of British operations from Ascension Island.

In the late 1980s, all MR.2s were fitted with new BAe designed in-flight refuelling probes and from 1985 all MR.2s began to be fitted with wingtip ESM pods, as developed for the R.1, to enhance their surveillance capability. Late 1990 saw several MR.2s fitted with an underwing FLIR turret under the starboard wing, BOZ pod under the port wing and a Towed Radar Decoy, under the unofficial designation MR.2(Gulf Mod) for service over the Arabian Gulf sea lanes during the 1991 Gulf War. The Nimrod returned in 2003 to take part in the liberation of Iraq.

A much less successful variant of the Nimrod was the AEW.3 - in 1973 the RAF had begun to examine the options for replacing the Airborne Early Warning (AEW) variant of the Shackleton, operated by 8 Sqn from Lossiemouth. Boeing offered a variant of the successful E-3A, but the over water performance of its radar was judged to be poor and in March 1977 it was announced that a specialised version of the Nimrod, the AEW.3 would be procured instead. This would be based on the Nimrod airframe but featured a large bulbous radome in the nose and a similar radome in the tail, providing 360 degree radar coverage. A weather radar was located in the starboard external fuel tank and ESM pods fitted on the wing tips.

Nimrod AEW.3 XZ286

On 28th June 1977, XW626, a suitably converted Comet 4C made the first of a series of flight trials. Initial results were promising, and so 3 AEW.3 development aircraft were produced by converting redundant MR.1 airframes to carry the prototype radar equipment. The first of these flew on 16th July 1980.

While development of the radar electronics, (and the software that controlled it), was proceeding, the Ministry of Defence (MoD) chose to impose a new and more stringent specification on the radar system. Meeting the new requirement meant a lot of re-design and re-testing for British Aerospace and GEC, which inevitably delayed the planned in-service date for the aircraft. Nevertheless, a production batch of eight aircraft was laid down down, using further redundant MR.1 airframes. The first example flew on 9th March 1982 but by now the MoD had changed the technical specification several more times and the increased workload of trying to meet a constantly changing requirement, with an extremely advanced electronics system which depended on sophisticated hardware and software was now proving to be an extremely difficult task. The first interim standard AEW aircraft was delivered to 8 Sqn in 1984 to allow the start of crew training. At the same time a thorough review of the whole AEW programme was launched to determine whether a reliable and effective system could be produced and put into service. In September 1986 the AEW requirement was re-opened to competing bidders and in December of that year the Boeing E-3 Sentry was declared the winner. The Nimrod AEW was immediately cancelled and 11 unusable AEW airframes were later scrapped.


Safety Record

Since their introduction into service the 'MR' Nimrod's have maintained an excellent safety record, with only five major incidents recorded, although two past tragic accidents do regrettably stand out. In 1980 two pilots were sadly killed when XV256 struck birds during take off and crashed in woods to the east of Kinloss airfield, the remainder of the crew survived. In 1995, during a display at the Canadian International Airshow, Toronto, XV239 and its entire crew of seven were tragically lost when the aircraft crashed into Lake Ontario whilst performing its display routine.

The 2nd September 2006 saw the loss of XV230 and 14 crew, whilst supporting anti-terror operations in Afghanistan. Although officially reported to be the result of an explosion following a fuel leak, the incident serves as a reminder that Nimrod crews, as indeed many other RAF crews, face risks on a daily basis whilst supporting anti-terror operations around the world.


Development History

HS.801 prototypes

Two Comet 4Cs converted to act as Nimrod prototypes. Ventral weapons pannier under cabin, search radar in nose, MAD stinger in tail, fin-tip radome, dorsal fin added. First prototype (aerodynamic test bed) with RB.163-20 Spey engines, second prototype (electronic test bed) with Avon engines.
Nimrod MR.1
Initial production version (38 aircraft). ASV-21D search radar, Marconi Elliott 920B central computer.
  Last eight production aircraft (second batch) delivered with updated communications system - as later used on MR.2. Strengthened structure for gross weights of 192,000 lb (87090 kg).
Nimrod R.1
Specialised ELINT version of MR.1 with completely new avionics fit. No MAD tailboom, no searchlight. Dielectric radomes in each external wing tank nose, numerous antenna above and below fuselage. Auxiliary fuel tanks in weapons bay. Later fitted with wingtip ESM pods and some cabin windows deleted as additional equipment fitted.
Nimrod R.1P
Designation applied to R.1 when fitted with in-flight refuelling probe in 1982. Small swept finlets added to tailplane. 'P' suffix later dropped.
Nimrod MR.2
Upgraded Maritime Reconnaissance version. New avionics fit with Thorn EMI Searchwater radar, new GEC central tactical system, new AQS-901 acoustics system, new communications suite. Air scoop on port rear fuselage close to dorsal fin, for avionics cooling system.
Export Nimrod
Version of MR.2 offered to Canada and Australia. Strengthened structure for gross weights of 192,000 lb (87090 kg). Additional fuel tanks in weapons bay. New APU. Provision for Flight Refuelling drogue pod under each wing. Not built.
Nimrod MR.2P
Designation applied to MR.2 when fitted with in-flight refuelling probe in 1982. Small swept finlets added to tailplane. Wingtip ESM pods subsequently fitted and tailplane finlets enlarged. 'P' suffix dropped in late 1990s.
Nimrod MR.2P(GM)
'Gulf Mod' version tailored for use in 1991 Gulf War. Underwing FLIR turret on starboard wing, BOZ pods, Towed Radar Decoy.
Nimrod AEW.3
Specialised Airborne Early Warning (AEW) version. Conversion of MR.1 with bulbous radome in nose and tailcone. Weather radar in starboard external fuel tank. ESM pods on wing tips.
Nimrod AEW.3P
Designation applied to AEW.3 XV263 when fitted with in-flight refuelling probe.
Nimrod MRA.4

Significantly upgraded Maritime Reconnaissance Attack version with new larger wing, larger engine air intakes, BR710 engines, new stronger wider-track undercarriage, large tailplane finlets. Completely new mission system: Searchwater 2000MR radar, UXS503/AQS970 acoustic processor, Nighthunter IR/TV electro-optical turret under nose, EL/L-8300UK ESM suite, DASS self-protection system, advanced communication system. 2-man Airbus-style 'glass' cockpit.


 

Version
Quantity 
 Assembly Location
Time Period
HS.801 prototypes
(2 conversions)
Chester
1964-July 1967
Nimrod MR.1
38
Woodford
1967-Aug 1972
Nimrod R.1
3
Woodford
1970-1973
Nimrod MR.1
8
Woodford
1973-1975
Nimrod MR.2
(35 conversions)
Woodford
1978-mid 1984
Nimrod AEW.3
(11 conversions)
Woodford
1979-1984
Nimrod R.1
(1 conversions)
Woodford
Oct 1995-Dec 1996
Nimrod MRA.4
(12 conversions)
Woodford
Feb 1997-2012
Total:
49 (all variants)
   

 

Nimrod Fleet Quick Guide

XV147
HS.801 
f/f 31/07/1967; scrapped 2003
XV148
HS.801 MR.1
f/f 23/05/1967
XV226
Nimrod MR.2
f/f 28/06/1968
XV227
Nimrod MR.2
To MRA.4 as PA-8/ZJ521
XV228
Nimrod MR.2
To MRA.4 as PA-10/ZJ523
XV229
Nimrod MR.2
Kinloss Wing, grey paint scheme
XV230
Nimrod MR.2
Written off 02/09/2006; In flight fire and explosion following fuel leak during operations over Afghanistan 
XV231
Nimrod MR.2
Kinloss Wing, grey paint scheme
XV232
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV233
Nimrod MR.2
To MRA.4 as PA-7/ZJ520
XV234
Nimrod MR.2
To MRA.4 as PA-2/ZJ518
XV235
Nimrod MR.2
Kinloss Wing, grey paint scheme
XV236
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV237
Nimrod MR.2P
Scrapped 1994
XV238
Nimrod MR.2P
Scrapped 1991
XV239
Nimrod MR.2
Written off 02/09/1995; Crashed during air display, Toronto, Canada
XV240
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV241
Nimrod MR.2
Kinloss Wing, grey paint scheme
XV242
Nimrod MR.2
To MRA.4 as PA-3/ZJ517
XV243
Nimrod MR.2
To BAE Woodford 04/2006 for MRA4 conversion, to MRA.4 PA-11/ZJ524
XV244
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV245
Nimrod MR.2
To MRA.4 as PA-9/ZJ522
XV246
Nimrod MR.2
Ex 51 Sqn Waddington; to BAe Warton 12/2007
XV247
Nimrod MR.2
To MRA.4 as PA-1/ZJ516
XV248
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV249
Nimrod R.1
51 Sqn Waddington
XV250
Nimrod MR.2
Kinloss Wing
XV251
Nimrod MR.2
To MRA.4 as PA-4/ZJ514
XV252
Nimrod MR.2
Kinloss Wing, grey paint scheme
XV253
Nimrod MR.2
To MRA.4 as PA-12/ZJ525
XV254
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV255
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV256
Nimrod MR.2
Written off 17/11/1980; Bird strikes to three engines, crashed during take off, near Forres, Kinloss.
XV257
Nimrod MR.2P
Written off 03/06/1984; Suspected bomb bay fire near Lands End
XV258
Nimrod MR.2
To MRA.4 as PA-5/ZJ515
XV259
Nimrod AEW.3
Scrapped 1998
XV260
Nimrod MR.2
Kinloss Wing, hemp paint scheme
XV261
Nimrod AEW.3
Scrapped 1995
XV262
Nimrod AEW.3
Scrapped 1992
XV263
Nimrod AEW.3
Scrapped 2002, fuselage to Woodford
XW664
Nimrod R.1
51 Sqn RAF Waddington
XW665
Nimrod R.1
51 Sqn RAF Waddington
XW666
Nimrod R.1
Written off 16/05/1995; Emergency ditching in sea after engine fire, Moray Firth 

 

 

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