At the height of the Cold War, a Soviet response was necessary to avoid the possibility of a new American fighter gaining a serious technological advantage over existing Soviet fighters. Thus the development of a new air superiority fighter became a priority. In 1969, the Soviet General Staff issued a requirement for a "Perspektivnyy Frontovoy Istrebitel" ("PFI", roughly "Advanced Frontline Fighter"). Specifications were extremely ambitious, calling for long range, good short-field performance (including the ability to use austere runways), excellent agility, Mach 2+ speed, and heavy armament. The Russian aerodynamics institute TsAGI worked in collaboration with the Sukhoi design bureau on the aircraft's aerodynamics.