MiG-31

The Mikoyan MiG-31 (Russian: МиГ-31) (NATO reporting name "Foxhound") is a supersonic interceptor aircraft developed to replace the MiG-25 'Foxbat'. The MiG-31 was

designed by the Mikoyan design bureau based on the MiG-25.[2] The MiG-31 was the most recent interceptor fielded by the Soviet Union before its dissolution.
The MiG-25 'Foxbat', despite Western panic about its tremendous performance, made substantial design sacrifices in capability for the sake of achieving high speed, altitude,

and rate of climb. It lacked manoeuverability at interception speeds, was difficult to fly at low altitudes, and its inefficient turbojet engines resulted in a very short combat range

at supersonic speeds. The MiG-25's speed gauge was redlined at Mach 2.8, and pilots were instructed not to top Mach 2.5 in order to preserve the engines. Achieving the

MiG-25's maximum speed of Mach 3.2 would result in the destruction of the engines.
Development of the MiG-25's replacement began with the Ye-155MP (Russian: Е-155МП) prototype which first flew on 16 September 1975. Although it bore a superficial

resemblance to a stretched MiG-25 (with a longer fuselage for the radar operator cockpit), it was in many respects a totally new design. Soviet manufacturing limitations forced

the MiG-25 to use nickel steel for 80% of its structure. The Ye-155MP doubled the use of titanium to 16% and tripled the aluminum content to 33% to reduce structural mass.

More importantly, supersonic speed was now possible at low-level altitudes. Fuel capacity was also increased, and new, more efficient low-bypass-ratio turbofan engines were

fitted.