ALQ-164). ZEUS was one of the main systems in the British design, being a modern and costly apparatus, with an estimated cost of $1.7 million per set. The Harrier II's cockpit has day and night operability and is equipped with head-up display (HUD), two head-down displays known as multi-purpose colour displays (MPCD), a digital moving map, an inertial navigation system (INS), and a hands-on-throttle-and-stick system (HOTAS). Like the British Aerospace Sea Harrier, the Harrier II used an elevated bubble canopy to provide a significantly improved all-round view. A combination of the new design of the control system and the greater lateral stability of the aircraft made the Harrier II fundamentally easier to fly than the first generation Harrier GR1/GR3 models. The RAF used Harriers in the ground attack and reconnaissance roles, so they relied on the short-range AIM-9 Sidewinder missile for air combat. The Sidewinder had proven effective for Royal Navy's Sea Harriers against Argentinian Mirages in the Falklands War; however, from 1993 the Sea Harrier FA2 could also carry the much longer-range AIM-120 AMRAAM, a radar-guided missile. The Sea Harrier had a radar since its introduction and the USMC later equipped their AV-8B Harriers with a radar as part of the AV-8B+ upgrade; however Britain's Harrier IIs never carried a radar. When the Sea Harrier was retired, it was suggested that its Blue Vixen radar could be transferred to the Harrier IIs. However, the Ministry of Defence rejected this as risky and too expensive; the Armed Forces Minister Adam Ingram estimated that the cost would be in excess of £600 million. Further developments Even prior to the Harrier GR5 entering service, it was clear that alterations were required for the aircraft to be more capable in the interdictor role. A more advanced model, designated as the Harrier GR7, was developed primarily to add a night-time operational capability and avionics improvements. The GR7 development programme operated in conjunction with a similar USMC initiative upon its AV-8B Harrier fleet. Additional avionics include a nose-mounted forward-looking infrared (FLIR) and night vision goggles, an electronic countermeasures suite, new cockpit displays and a replacement moving map system. The GR7 conducted its maiden flight in May 1990 and entered service in August 1990. Following the full delivery of 34 Harrier GR7s in 1991, all of the GR5s underwent avionics upgrades to become GR7s as well. Some GR7s were equipped with uprated Rolls-Royce Pegasus engines, correspondingly