Modern airforces have become dependent on airborne radars typically carried by converted airliners and transport aircraft such as the E-3 Sentry and A-50 'Mainstay'. They also depend on similar aircraft for inflight refuelling (e.g. Vickers VC10), maritime patrol (e.g. CP-140 Aurora), reconnaissance and electronic warfare (e.g. Tu-16 'Badger' E & J) and C4ISTAR (e.g. VC-25 "Air Force One"). The loss of just one of these aircraft can have a significant effect on fighting capability, and they are usually heavily defended by fighter escorts. A long-range air-to-air missile offers the prospect of bringing down the target without having to fight a way through the fighter screen. Given the potential importance of "blinding" Western AWACS, Russia has devoted considerable resources to this area. The R-37 (missile) (AA-13 'Arrow') is an evolution of their R-33 (AA-9 'Amos') with a range of up to , and there have been persistent rumours – if little hard evidence – of an air-to-air missile with a range of based on Zvezda's Kh-31 anti-radar/anti-shipping missile or its Chinese derivative, the YJ-91.