tail. The Nimrod AEW3 project was plagued by cost over-runs and problems with the GEC 4080M computer used. Eventually, the MoD recognised that the cost of developing the radar system to achieve the required level of performance was prohibitive and the probability of success very uncertain, and in December 1986 the project was cancelled. The RAF eventually received seven Boeing E-3 Sentry aircraft instead. MRA4 The Nimrod MRA4 was intended to replace the capability provided by the MR2. It was essentially a new aircraft, with current-generation Rolls-Royce BR710 turbofan engines, a new larger wing, and fully refurbished fuselage. The project was subject to delays, cost over-runs, and contract re-negotiations. The type had been originally intended to enter service in 2003 but was cancelled in 2010 as a result of the Strategic Defence and Security Review, at which point it was £789 million over-budget; the development airframes were also scrapped. Some functions were allocated to other assets, with Hercules transport aircraft and Sentry Airborne Early Warning aircraft given some tasks, but the cancellation of the MRA4 resulted in a significant gap in long-range maritime patrol and search-and rescue capability. In July 2016, the Ministry of Defence announced the purchase of nine Boeing P-8A Poseidon aircraft for the RAF. The RAF declared the P-8 had reached initial operating capability (IOC) on 1 April 2020, by which time two of the planes had been delivered. The nine aircraft will be based at RAF Lossiemouth. Design Overview The Nimrod was the first jet-powered maritime patrol aircraft (MPA) to enter service, being powered by the Rolls-Royce Spey turbofan engine. Aircraft in this role had been commonly propelled by piston or turboprop powerplants instead to maximise fuel economy and enable maximum patrol time on station. Advantages of the Nimrod's turbofan engines included greater speed and altitude capabilities, and it was more capable of evading detection by submarines, as propeller-driven aircraft are more detectable underwater by standard acoustic sensors. The Nimrods had a flight endurance of ten hours without aerial refuelling. The MR2s were later fitted to receive mid-air refuelling in response to demands of the Falklands War. At the start of a patrol mission all four engines would normally be running; as the aircraft's weight was reduced by fuel consumption, up to two engines could be shut down, allowing the remaining engines to be operated more efficiently. Instead of relying on ram air to restart an