Background In the mid 1960s, following the development of the
Grumman E-2 Hawkeye carrier-borne AEW aircraft and its associated systems, the British government began looking for a radar system that could provide
airborne early warning for the United Kingdom. At the time, the only recognised AEW aircraft in British service was the
Fairey Gannet aircraft used by the
Fleet Air Arm on board
Royal Navy aircraft carriers. These were fitted with the AN/APS-20 Radar, which had been developed during World War II and was rapidly becoming obsolete. Work had been started in the early 1960s on a brand new AEW platform for the Royal Navy to replace the Gannet that would encompass both a new type of radar system mounted on a new aircraft, the
P.139. While the defence cuts of the mid-1960s led to the cancellation of the P.139, work continued on a British designed radar system. Meanwhile, it was decided that the RAF needed an AEW aircraft to operate as part of the national air defence strategy. To fulfill the planned requirements for a new AEW aircraft, the government had a number of factors to consider: • The
Frequency Modulated Interrupted Continuous Wave (FMICW) radar initially proposed for the P.139 and intended for the RAF's new aircraft would not operate effectively near
propellers, meaning a jet aircraft would be needed. • The size of antennas needed for the required scanning range, together with the fairly large mission crew, meant that a large aircraft was required. Designers at
Hawker Siddeley Aviation came up with a proposal that would see the FMICW radar system installed using a Fore Aft Scanner System in the new
Nimrod aircraft. This proposal was rejected as being too expensive, with instead a proposal to convert surplus
Andover transport aircraft. This was also rejected due to the potential cost of development. Around the same time, it was decided not to proceed with FMICW technology as the basis of an AEW system, as research from the
United States Air Force (USAF) had shown that
pulse-Doppler radar was superior and would be used in the
Boeing E-3 Sentry then under development. As a consequence, the idea of a new land-based AEW aircraft for the RAF was re-examined, and again it was decided that the Nimrod met the requirements. However, the complex multi-lateral negotiations eventually led the United Kingdom to pursue the all-British development. The first of these was rolled out in March 1980 and flew for the first time in July, and was intended to test the flight characteristics, with the second airframe planned to carry out trials of the
Mission Systems Avionics (MSA) package. To provide some degree of cover, several Nimrod MR.2 were quickly modified to undertake the airborne surveillance role for the task force however.
Aircraft The choice of the Nimrod airframe proved to be the wrong one, as it was too small to accommodate the radar, electronics, power generation and cooling systems needed for a system as complex as the one required – at just over , the Nimrod was close to shorter than the
Boeing 707 aircraft that formed the basis of the E-3 Sentry, with the planned all-up weight around half that of the American aircraft, but was expected to accommodate sufficient crew and equipment to perform a similar function. This was in contrast to the Nimrod's "
heat sink" design that dispersed the heat through the fuel system, and which needed the fuel tanks to be at least half-full to work efficiently when the aircraft's system operated at full power. However, getting the two scanners to synchronise proved difficult, resulting in poor all-round surveillance capability. In spite of the project's difficulties, India expressed interest in procuring the Nimrod AEW3; these investigations continued even after the British government's eventual cancellation of the project. The Nimrod programme had cost in the region of
£1 billion up to its cancellation, contrasting with manufacturer claims in 1977 that the total cost of the project would be between £200–300 million. The unused airframes were eventually stored and used as a source of spares for the
Nimrod R1 and MR2 fleets, while the elderly Shackleton aircraft that had been commissioned in 1971 as a "stop-gap" measure for AEW cover until the planned entry of the Nimrod were forced to soldier on until 1991 when they were replaced by the Sentry. The scandal over the collapse of the Nimrod AEW project was a major factor in Prime Minister
Margaret Thatcher's stance to open up the UK defence market to competition. Following the cancellation of the Nimrod AEW programme, BAe began looking at ways that the now redundant airframes could be re-used, and commenced studies looking at the potential use of the Nimrod as a missile carrying strike aircraft. This would have seen the AEW modifications, primarily the FASS scanners, and the fuel and cooling systems installed in the weapons bay, removed. The
Searchwater radar, at the time fitted to the Nimrod MR.2, would have been installed in a nose installation, and the weapons bay outfitted to accommodate up to six
Sea Eagle anti-ship missiles. However, this did not go beyond the study phase, and the airframes were eventually scrapped during the 1990s. ==Operators==