The Hawker Siddeley Nimrod maritime patrol aircraft was an extensive modification of the de Havilland 106 Comet 4. On 4 June 1964, the British Government issued Air Staff Requirement 381, which sought a replacement for the aging Avro Shackleton maritime patrol aircraft which was fast approaching its fatigue life limit.
Hawker Siddeley 801
The first two prototypes, designated Hawker Siddeley HS801, were modifications of unsold de Havilland 106 Comet 4C airframes, retained at the Hawker Siddeley factory in Chester. These aircraft (serial numbers XV147 and XV148) can generally be distinguished by their retention of the original airliner passenger windows. The first Hawker Siddeley HS801 prototype flew on 23rd May 1967.
Compared with the de Havilland Comet, the HS801 Nimrod was fitted with Rolls-Royce Spey engines, and featured a new lower fuselage containing a forward-looking search radar and a lengthy sonobuoy and weapons bay. A magnetic anomaly detector (MAD) sting was mounted in the extreme tail, with electronic surveillance sensors mounted in a fairing at the top of the tail fin, all of which aided the aircraft in its primary roles of maritime patrol and anti-submarine operations, with secondary roles including anti-ship operations and long-range search and rescue support.
HS801 Nimrod MR1
The initial service variant was the HS801 Nimrod MR.1, of which 46 were ordered during 1967, with the first service aircraft (XV230) being delivered in October 1969. Compared with the prototypes, this production aircraft featured a reduced number of cabin windows.
HS801 Nimrod R1
Three HS801 Nimrod MR1 aircraft were adapted for the signals intelligence (SIGINT) role and designated HS801 Nimrod R1. The HS801 R1 was visually distinguished from the HS801 Nimrod MR2 by the lack of the rear MAD boom, together with the introduction of a number of additional external aerials, mounted on the upper and lower fuselage. Additional internal rotating dish aerials were fitted in the weapons bay, within the rear fuselage and in the front of the wing-mounted pinion tanks. It had a flight crew of four (two pilots, a flight engineer and one navigator) and up to 25 crew operating the mission equipment. The last flight of the type was on 28th June 2011 and the aircraft (XV 249) is now preserved at the RAF Museum Cosford, West Midlands.
HS801 Nimrod MR2
From 1975, 35 HS801 Nimrod MR1 aircraft were upgraded to HS801 Nimrod MR2 standard. This upgrade included extensive modernisation of the aircraft's electronic mission equipment. It also added the new EMI Searchwater radar, a new acoustic processor (GEC-Marconi AQS-901), a new mission data recorder and new Electronic Support Measures equipment (Yellow Gate). The Nimrod MR2 carried a flight crew of two pilots, one flight engineer and two navigators (one tactical navigator and a routine navigator), with a mission crew comprising of one Air Electronics Officer (AEO), the sonobuoy sensor team of two Weapon System Operators and finally four EW System Operators to manage passive and active electronic warfare systems.
The Nimrod MR2 fleet was based at RAF Kinloss in Scotland (with 120, 201 and 206 Squadrons), and RAF St Mawgan in Cornwall (with 42 and 38(R) Squadrons). The aircraft were withdrawn at the end of March 2010 and with it 42 Squadron was disbanded and amalgamated with 38(R) Squadron. The last official flight of a Nimrod MR2 (XV229) took place on 26th May 2010, flying from RAF Kinloss to Kent International Airport at Manston whereafter it was used as an evacuation training airframe at the Ministry of Defence Fire Training and Development Centre.
British Aerospace Nimrod AEW3
In the mid-1970s, a modified HS801 Nimrod was proposed for the Airborne Early Warning (AEW) mission, as a replacement for the long-serving Avro Shackleton AEW.2. Eleven existing HS801 Nimrod airframes were to be converted by British Aerospace at Woodford, predominately to house the GEC Marconi radars, accommodated in bulbous nose and tail radomes. The British Aerospace Nimrod AEW3 project suffered numerous delays, many due to technical problems with the integration of the mission equipment, which resulted in the cancellation of the programme in December 1986.
BAE Systems Nimrod MRA4
The BAE Systems Nimrod MRA4 was intended to replace the capability provided by the HS801 MR2. Essentially it was a new aircraft, with the more efficient Rolls-Royce BR710 turbofan engines, installed in a new larger wing, with a fully refurbished fuselage. The first prototype (ZJ516) flew for the first time on 26th August 2004. However, significant delays and cost overruns were encountered and the Nimrod MRA4 programme was dramatically reduced in scope. Following a Strategic Defence and Security Review (SDSR) in 2010, the 9 aircraft program was cancelled on 19th October 2010. At the time of the cancellation of the program, three development aircraft and two production aircraft had been flown.
Despite its abrupt ending, the Nimrod was considered one of the best maritime aircraft of its generation and was in service with the RAF for over 40 years.