Hawker Siddeley MR.2 [Kinross Maritime Wing @ RAF Waddington]
In July 1963 the RAF set about replacing the Avro Shackleton as the standard long-range maritime patrol aircraft. Proposals included the HS.800, a tri-jet design based on the Hawker Siddeley Trident, but the estimated costs involved in developing such an aircraft proved much too high. In an attempt to prevent the French Breguet Atlantic aircraft from winning the contract, engineers at Hawker Siddeley (formerly Avro) came up with the idea of mating the proven Comet Mk.4 airframe with an under fuselage pannier similar to the one developed for the HS.800 proposal. In a very short space of time, the designers developed an un-pressurised lower fuselage fairing which snugly fitted over the lower portion of the Comet fuselage, giving it a distinctive 'double-bubble' shape. Extending from the nose to the rear fuselage the pannier brought a dramatic increase in useable space for operational equipment and weapons while minimising additional drag. By replacing the existing Rolls Royce Avon engines with the Spey turbofan engines a very acceptable endurance could be achieved. To keep costs down, much of the mission avionics would be similar to that already used in the Shackleton. Designated HS.801, the Comet 4C derivative was offered in July 1964 and agreed in January 1966.
The Nimrod remains the only jet powered long range maritime patrol aircraft in military service. Offering the advantages of speed and height during transit, while still capable of long patrol periods and, in particular, stealth in the anti-submarine mission as propeller-engine aircraft make a distinct resonance that can be detected by submerged submarines whereas the jet noise of the Nimrod is virtually undetectable. The Nimrod carries out three main roles; anti-submarine warfare, anti-surface unit warfare and search and rescue. Its endurance, without refuelling, is around ten hours and is capable of carrying up to twenty-five crew members. The Nimrod bomb bay carries the Stingray torpedo and the Harpoon missile for the anti-surface unit mission while for search and rescue duties the aircraft has a selection of air deliverable multi-seat dinghies, survival packs and other stores. Internally the aircraft can carry around one-hundred-fifty sonobuoys of several different types. During the Falklands War the Nimrod became technically the largest fighter in the world, when it was fitted with Sidewinder air-to-air missiles to allow for opportunist attacks on opposing surveillance aircraft.
Two Comet 4Cs were converted to act as Nimrod (HS.801) prototypes. The first prototype, the aerodynamic test-bed, flew for the first time on 23rd May 1967 and was fitted with RB.163-20 Spey engines, while the second prototype, the electronic test-bed, was fitted with Avon engines. Deliveries of the production Nimrod MR.1 (Maritime Reconnaissance) aircraft began in October 1969, the first thirty-eight Nimrods were delivered between 1969 and 1972, equipping five squadrons and No 236 OCU; another eight were delivered in 1975. The MR.1 was fitted with ASV-21D search radar and a Marconi Elliott 920B central computer. The MR.2 variant was the designation given to the last eight production MR.1 aircraft which had, amongst other things, an updated communications system and a strengthened structure. MR.2's were offered to the Air Forces of Canada and Australia but the offer was taken up. Three MR.1s, designated R.1, were converted to the electronic intelligence role. Basically new avionics were fitted and with the tail-boom and searchlight removed, radar domes and antenna above and below the fuselage were fitted instead together with auxiliary fuel tanks in the weapons bay. Later on wingtip ESM pods were fitted and some cabin windows deleted to allow for the installation of additional equipment. From 1979 the MR.1 fleet was upgraded to MR.2 standard. The flight deck and general systems remained the same while the main underwater and search systems were given a significant upgrade. New avionics fit together with Thorn EMI Searchwater radar, a GEC central tactical system, an AQS-901 acoustics system and a new communications suite. An air scoop on the port rear fuselage close to dorsal fin was also fitted for the avionics cooling system. Flight refuelling equipment was added at the time of the 1982 Falklands war.
A much less successful variant due to poor management by the MoD, was the AEW.3 (Airborne Early Warning). In 1973 the RAF had begun to examine the options for replacing the AEW variant of the Shackleton operated by No.8 Squadron. Boeing offered a variant of the successful E-3A but its radar was judged to be poor so in March 1977 the Nimrod AEW.3 was accepted. Basically an MR.1 conversion it had bulbous radar domes in the nose and the tail-cone, weather radar in starboard external fuel tank and ESM pods on the wing tips. Successive significant changes to the radar specification by the RAF led to significant changes to the electronics, the hardware and the software which in turn led to significant timescale extensions. The first interim standard AEW aircraft was delivered to No.8 Squadron in 1984 to allow crew training to commence but in September 1986 the AEW requirement was reopened and in December 1986 a deal for the Boeing E-3 Sentry was signed. The Nimrod AEW was immediately cancelled and AEW airframes were stored at RAF Abingdon until they were scrapped in the 1990s.
The entire Nimrod fleet is scheduled to be rebuilt by 2012 (?), retaining only the fuselage shell of existing aircraft. The new aircraft, designated Nimrod MRA.4 (Maritime Reconnaissance Attack), will have new wings, undercarriage, BMW/Rolls Royce fuel-efficient engines and a completely new mission system.