The Buk missile system is a family of self-propelled, medium-range surface-to-air missile systems developed by the former Soviet Union and Russian Federation and designed to engage cruise missiles, smart bombs, fixed- and rotary-wing aircraft, and unmanned aerial vehicles. The Buk missile system is the successor to the NIIP/Vympel 2K12 Kub (NATO reporting name SA-6 "Gainful"). The first version of Buk adopted into service carried the GRAU designation 9K37 and was identified in the west with the NATO reporting name "Gadfly" as well as the US Department of Defense designation SA-11. Since its initial introduction into service the Buk missile system has been continually upgraded and refined with the latest incarnation carrying the designation 9K37M2 "Buk-M2".