On 3 August 2001, the first flight of the aerodynamically modified Global Express prototype occurred, which validated the modifications required for the ASTOR system. During 2007, service trials of the Sentinel were conducted. By January 2009, the type had entered regular service with
5 Squadron of the
Royal Air Force (RAF), based at RAF Waddington. In addition to its presence in the Afghan theatre, the Sentinel routinely performed surveillance flights over the
Baltic Sea, monitoring military forces stationed in the
Kaliningrad Oblast and
Belarus; during such missions the type was frequently intercepted by Russian
Sukhoi Su-27s. In 2010, the UK government's
Strategic Defence and Security Review announced its intention to "withdraw the Sentinel airborne ground surveillance aircraft once it is no longer required to support operations in Afghanistan." The Sentinel's role above
Libya in 2011 was described as "pivotal" by the head of the RAF. On 30 March 2011, the longest Sentinel flight, of 12 hours and 30 minutes was flown during
Operation Ellamy over
Libya. While operating along the Libyan coast, it was observed that the Sentinel's dual-mode radar was capable of tracking vessel movements around Libyan harbours, providing viable battlefield intelligence. In February 2014, it was reported that the Sentinel had been used to map the scale of flooding in Southern England. On 18 May 2014, the
MoD announced that a Sentinel had departed to
Ghana as part of
Operation Turus to assist in the search for the 223 schoolgirls abducted by the Islamic militant group
Boko Haram in
Nigeria on 14 April 2014. In 2014, Prime Minister David Cameron announced the retention of the aircraft, even after operations end in Afghanistan in Autumn 2018. This reprieve fuelled speculation that not only would the Sentinel be retained but that upgrades of the fleet, particularly for use in a maritime surveillance capacity, might occur. In the absence of UK government backing, Raytheon self-financed development work for over five years on a mid-life upgrade of the Sentinel's mission systems, referred to as
Overseer, but this was not applied. However, due to a combination of its operational commitments and constrained budgets, neither the Sentinel or its missions systems received any upgrades for an extended period, which led to some of its onboard systems becoming increasingly obsolescent by the end of the decade. In addition to the Sentinel, the RAF also deployed other surveillance assets, including the
Boeing Rivet Joint,
General Atomics Reaper,
Beechcraft Shadow and
Boeing Sentry, for surveillance missions over Iraq and Syria around this time. Despite the RAF reportedly hoping to retain the entire five-strong fleet, Accordingly, in July 2017, one of the five aircraft was permanently withdrawn. During the following month, the type was formally withdrawn from RAF service. years, the five aircraft flew approximately 32,300 hours roughly distributed across 4,870 sorties. On 16 November 2021, according to
UK Defence Journal, the MoD accepted a proposal from Raytheon/Bombardier to purchase and refurbish the airframes for ultimate use by the
United States Army." ==Former operators==