When it sought a replacement for the veteran Avro Shackleton in the airborne early warning role, the RAF turned to the proven Boeing E-3 Sentry AWACS (airborne warning and control system) aircraft, based on the Boeing 707. It procured seven examples of the E-3D model, powered by CFM56 turbofan engines; the type is known as the Sentry AEW1 in RAF service. Six remain on strength with No 8 Squadron at RAF Waddington, Lincolnshire, the UK's contribution to the multi-national NATO Airborne Early Warning Force. On board is a crew of 18: four on the flight deck, three technicians and an 11-man mission crew. From a cruising altitude of 30,000ft, the Sentry's AN/APY-2 look-down radar, mounted in the aircraft's distinctive 'rotodome' atop the fuselage, can detect aerial or surface targets up to 300 miles away, providing vital battlespace intelligence in any air or land campaign.