The Royal Air Force’s Raytheon Sentinel surveillance fleet completed its final operation on February 25, 2021. The last aircraft flew a mission from its base at RAF Waddington in southern England, monitoring Russia’s Kaliningrad enclave, and Belarus, from Polish and Lithuanian airspace. The RAF Sentinels have been frequent visitors to the Baltic airspace, often provoking a reaction from Russian Su-27 Flanker interceptors based in Kaliningrad.
The Sentinel R.Mk 1 is a radar reconnaissance version of the Bombardier Global Express business aircraft, and was tasked with providing long-range, wide-area battlefield surveillance, and with delivering critical intelligence and target-tracking. The platform was the end result of a long-running program by the UK to deploy what was originally known as a Corps Airborne Stand-off Radar (CASTOR) for detecting and tracking Warsaw Pact tank and vehicle movements for the British Army of the Rhine. This eventually evolved into the ASTOR requirement, for which Raytheon offered a Global Express, equipped with a derivative of the U-2’s ASARS-2 radar.
Though the end of the Cold War removed the original justification for the aircraft and made funding difficult, the 1991 Gulf War confirmed the need for such an aircraft. A production contract was finally signed in December 1999. Raytheon flew an aerodynamic prototype (the original Global Express prototype) on 3 August 2001, and flew the first of five production Sentinel R.Mk 1s on 26 May 2004. Subsequent aircraft were converted at Broughton in the UK. Service trials began in 2007 and No. V (AC) Sqn flew the first operational Sentinel mission over Afghanistan in November 2008.
The 2010 Strategic Defence and Security Review suggested that the Sentinel would be withdrawn as soon as the Operation Herrick commitment in Afghanistan ended, but the system proved so valuable to British and allied commanders that it was given a reprieve. Additonal roles and equipment were discussed, but in the event they were not funded.
Since then, the Sentinel has participated in Operation Ellamy over Libya in 2011, becoming a vital link in the chain of target identification and prosecution, especially against fleeting targets. The Chief of the Air Staff described its role in Libya as “pivotal”. In January 2013, the RAF deployed a Sentinel to Dakar-Ouakam Air Base in Senegal, in support of Operation Newcombe in Mali, while 2014 saw the aircraft used to map the scale of flooding in southern England under Operation Pitchpole. In May 2014, a Sentinel operating from Ghana assisted in the search for the 223 schoolgirls abducted by Boko Haram in Nigeria.
In March 2015 two Sentinel aircraft were deployed in support of Operation Shader, providing surveillance to coalition forces fighting as part of the military intervention against Daesh (ISIL) forces in Syria and Iraq. It was announced that the fleet would be cut to four aircraft with effect from 2017 and the out-of-service date was pushed back to 2021. One aircraft was withdrawn from use in July 2017.
The aircraft’s operational commitments (together with budgetary constraints) meant that the aircraft and its mission systems did not receive the upgrades that were required and, as a result, the radar and mission system became increasingly obsolescent. Retaining the aircraft would have required significant upgrade expenditure and the decision was taken to retire and scrap the aircraft in March 2021. During their 12.5-year service life, the five aircraft flew approximately 32,300 hours, in about 4,870 sorties.
The official view is that the new P-8A Poseidon aircraft and the forthcoming Protector will carry out the surveillance role previously conducted by the Sentinel, though neither type has suitable sensors or datalinks to allow them to achieve the same results.