In 2019, then-Defence Secretary Gavin Williamson signed a £1.5bn deal to purchase five E-7 Wedgetail aircraft.
The fleet of E-7s is set to replace the E-3D Sentry aircraft as the UK's Airborne Early Warning and Control capability.
The Royal Air Force is expected to receive its first E-7 Airborne Early Warning and Control aircraft in 2023.
Responding to a written parliamentary question in early June, Minister for Defence Procurement Jeremy Quin said the fifth and final E-7 is set to arrive in 2026.
The RAF previously said the aircraft, known as the 'Wedgetail', was expected to begin service in the early 2020s.
Unconfirmed reports suggest the Ministry of Defence may have plans to reduce the order from five to three aircraft to save money.
What is an E-7 'Wedgetail'?
The E-7 is based on a standard Boeing 737 airliner aircraft.
However, the Wedgetail is modified and it carries a Northrop Grumman Multi-Role Electronically Scanned Array (MESA) surveillance radar and a sophisticated mission computer system.
The radar is operationally ready minutes after takeoff and it can cover four million square kilometres over a 10-hour period, meaning it can track multiple targets simultaneously.
Information gathered by E-7s would be used by the Armed Forces to provide situational awareness and direct other assets such as fighter jets or warships.
What are the aircraft's specifications?
- Length: 110ft 4in (33.6m)
- Height: 41ft 2in (12.5m)
- Powerplant: two CFM56-7B Turbofan
- Service ceiling: 41,000ft (12,500m)
- Cruise speed: 530 mph (853km/h)
- Crew: 12 (two pilots, 10 mission crew)
Who uses E-7 aircraft?
The Boeing 'Wedgetail' platform is currently in service with the Royal Australian Air Force (RAAF), the Republic of Korea Air Force and the Turkish Air Force.
In Australia, the RAAF has six E-7A 'Wedgetail' aircraft and they have been used on operations in the battle against so-called Islamic State in Iraq and Syria.
The Republic of Korea Air Force also use E-7 aircraft, where it is known as 'Peace Eye'.
A total of four aircraft were delivered by Boeing to Gimhae Air Base in Busan between August 2011 and October 2012 and they are currently in use.
The Turkish Air Force also has four E-7 aircraft, known there as 'Peace Eagles', in use.
Cover image: An artist's impression of E-7 Wedgetail aircraft (Picture: RAF).