- March 1, 2021, 6:30 AM End of the road: Sentinel R.Mk 1 ZJ694 lands at Waddington on February 25 to bring the type’s operational career to a close. (Photo: RAF Waddington) 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.