The Antonov An-124 Ruslan is a large, strategic airlift, four-engined aircraft that was designed in the 1980s by the Antonov design bureau in the Ukrainian SSR of the Soviet Union (USSR). The An-124 is the world's second heaviest gross weight production cargo airplane and heaviest operating cargo aircraft, behind the destroyed one-off Antonov An-225 Mriya. The An-124 remains the largest military transport aircraft in service.