Hawker Siddeley HS801 Nimrod
In July 1963, MOD Air Staff Target (AST) 357 called for a sophisticated, medium-sized, jet-powered, long-range aircraft to replace the piston-engined Avro Shackleton, which entered service in 1951, becoming the United Kingdom’s principal Maritime Patrol Aircraft (MPA). Hawker Siddeley Aviation (formerly De Havilland) formally proposed converting the Comet 4C turbo-jet powered airliner into a military aircraft (HS801). The redesigned underside of the Comet fuselage housed a large bomb bay and extra fuel tanks to increase range and endurance, and Spey 250 engines replaced the Rolls-Royce Avon engines. In February 1965, the Parliament announced the selection of the HS801 to replace the Shackleton.
The HS801 became the first Nimrod, the Nimrod MR1. The type was designed for anti-submarine and anti-surface unit warfare, surface surveillance, and search and rescue operations, i.e., the traditional roles of the MPA. The Nimrod MR1 was equipped with a wide range of radar and acoustic equipment and could drop sonobuoys, detect and track submarines, and carry weapons such as torpedoes and Search and Rescue (SAR) equipment. The first flight of a prototype Nimrod MR1 was on 23 May 1967. The first flight of a new-build production Nimrod MR1 was on 28 June 1968.
As stated above, the RAF took delivery of its first Nimrod MR1 on 2 October 1969, at RAF St. Mawgan, when the No. 236 Operational Conversion Unit put XV230 into service. The 43 Nimrod MR1s were operated primarily from RAF Kinloss, Morayshire, and RAF St. Mawgan, Cornwall. No. 203 Squadron at Luqa, Malta, was also equipped with Nimrods, but following the 1974 Defence Review, this Squadron was disbanded, and its Nimrod MR1s were flown back to the UK and placed in storage.
Three additional airframes were also ordered from Hawker Siddeley to replace the aging Comet R2s still used by the RAF for Electronic Intelligence (ELINT) duties. These three extra airframes were first delivered to RAF Wyton in July 1971. They were each fitted with sophisticated and sensitive electronic intelligence-gathering equipment and antennae and were designated Nimrod Reconnaissance Mk 1 (Nimrod R1). The principal external difference from the maritime Nimrod was that they did not have the Magnetic Anomaly Detector probe fitted in the tail. As stated above, the three original Nimrod R1s were built by Hawker Siddeley at Woodford and delivered to the RAF between 1970 and 1973. They were operated by the No. 51 Squadron from RAF Waddington. In 1995, a Nimrod R1 (XW666) was lost following an engine fire (see below). It was replaced in December 1996 by converting a Nimrod MR2 (XV249), then in storage at RAF Kinloss, into a Nimrod R1. The Nimrod R1 played a crucial role in the Falklands Conflict of 1982. Since then, its increasingly important electronic intelligence (ELINT) capabilities have been employed in almost every conflict involving UK forces.
In 1975, a comprehensive program of upgrading the avionics on the MR1 began, including fitting the new Thorn EMI Searchwater radar, a new GEC Central Tactical System, and the AQS-901 acoustics system compatible with the latest generation of sonobuoys, and the Loral Electronic Support Measures System located in two new wingtip pods. The upgraded aircraft became the Nimrod MR2. A total of 35 Nimrod MR1s were upgraded to the Nimrod MR2 standard by BAE Systems between 1975 and 1984. The first Nimrod MR2 was delivered to 201 Squadron at RAF Kinloss on 23 August 1979. The decision by the Argentinean junta to invade the Falkland Islands in April 1982 gave rise to an Urgent Operational Requirement (UOR) to equip the Nimrod MR2 with an Air-to-Air Refuelling (AAR) capability as part of Operation Corporate. In just 18 days, eight Nimrod MR2s were fitted with in-flight refueling probes, taken from Vulcans, and stabilizing winglets on the tailplane.
The probes were linked to ordinary ground refueling hoses running through the cockpit, down the center aisle of the aircraft, and exiting the cabin in the galley area to join the refuel gallery in the wings. The fitting of the AAR capability extended the Nimrod's endurance to 20 hours in the air. Hawker Siddeley enhanced the Nimrod MR2s' self-defense capability by modifying their under-wing hard points to take AIM-9L Sidewinder air-to-air missiles. They flew numerous patrols over the South Atlantic from Ascension Island in support of British operations during the Falklands War. In recent years, the MR2s were with an electro-optical camera for imagery intelligence (IMINT) tasks.
In August 1972, the RAF issued an AST to replace its Airborne Early Warning (AEW) variant of the Shackleton operated by No. 8 Squadron. In March 1977, the procurement was announced of a specialized version of the Nimrod. This variant would have a sizeable bulbous radome in the nose and tail to house Marconi scanners providing 360º radar coverage. Three AEW3 development aircraft were manufactured, and the first flew on 16 July 1980. A production batch of eight Nimrod AEW3 aircraft was laid down using eight redundant Nimrod MR1 airframes. The first AEW3 took to the air on 9 March 1982, and by late 1984 the first ‘interim standard’ Nimrod AEW3 aircraft was delivered by British Aerospace to No. 8 Squadron to allow crew training to commence. In September 1986, however, technical problems with the AEW3 system led to the program being re-opened to competing bidders. In December 1986, the Boeing E-3 Sentry AWAC won the contract, leading to the Nimrod AEW3 program cancellation. The Nimrod AEW3 airframes were stored at RAF Abingdon until they were scrapped in the 1990s.
n 1993, Air Staff Requirement (ASR) 420 called for a replacement for the MR2. On 25 July 1996, the contract was awarded to BAE Systems, who proposed using the existing MR2 airframes, fitting larger wings (127 feet), Rolls-Royce BMW BR.710 engines, new radar and sensor systems, and a new tactical computer system. February 1997 saw the first three stripped-down Nimrod fuselages delivered to FR Aviation in Bournemouth for refurbishing. By 1999, however, the program was three years behind schedule, and the prototype Nimrod MRA4 flight did not take place until 26 August 2004. September 2004 saw the reduction of the planned order for the Nimrod MRA4 from 18 to "about 12" aircraft. The original in-service date for the MRA4 was April 2003, but it was delayed five times and planned in 2010.
As a result of the Strategic Defence and Security Review, at which point it was £789 million over budget and nine years late, the UK Government canceled MRA4 in 2010, including the scrapping of the development airframes. The cancellation of the MRA4 marked an abortive end of the Nimrod's era; other assets rook over its functions, including using unmanned aerial vehicles (UAVs) to conduct maritime surveillance.