Following the collapse of the Soviet Union, a number of prolific weapons programs developed to provide the superpower with a qualitative edge over its Western adversaries were terminated as the Cold War came to an end and the largest Soviet successor state Russia faced a severe economic crisis. Cancelled programs ranged from the Ulyanovsk Class nuclear powered supercarrier to plans for an upgraded T-80 battle tank with a massive 152mm cannon, among dozens of others. In the field of military aviation, the Yak-41 vertical takeoff and landing capable fighter and the MiG 1.44 and Su-47 fifth generation stealth fighters were all cancelled, while plans for an upgraded Su-27 fighter designated Su-27M would be delayed by over 15 years before finally entering service in 2014. One of the less well known but most critical weapons program which was terminated was that for a heavily enhanced new variant of the MiG-31 Foxhound heavy interceptor - the MiG-31M. This program had the potential to provide Russia with the world’s most capable aircraft for air to air combat - one which despite its lack of fifth generation capabilities could have posed a serious threat to the supremacy of fifth generation aircraft in the air when they began to enter service following the turn of the century. The original MiG-31 Foxhound was the Soviet Union’s first combat aircraft with fourth generation capabilities, and remains until this day the largest aircraft in service anywhere in the world that was designed for air to air combat. The Foxhound was the only aircraft of its kind equipped with a phased array radar for over 20 years, until the introduction of the Japanese F-2 in 2002 and the American F-22 in 2005. It was also the first aircraft in the world with an electronically scanned array radar - the Zaslon - which had a performance wholly unrivalled for its time. In terms of long range air to air capabilities the Foxhound was only seriously challenged by the U.S. Navy’s F-14D Tomcat, an extremely costly design which entered service in small numbers from 1991 and was retired just 15 years later due to its excessive operational costs. The Soviet interceptor not only the fastest modern combat aircraft in the world - a title it still holds today - but it was also considered the most capable combat jet fielded by any air force worldwide in terms of air to air capabilities during the Cold War.The MiG-31M expanded the Foxhound’s capabilities considerably, although the full details of its capabilities remain unknown. Where the original MiG-31 weighed approximately 41,000kg, the MiG-31M was heavier with a take off weight of around 50,000kg depending on how much fuel and armaments it carried. The new Foxhound variant made its first flight in 1985, and made use of a new Zaslon-M radar which had a larger antenna and significantly greater detection range. The new radar also increased relative target speed detection to over Mach 6, which was particularly useful since the aircraft was one of the few aircraft in the world designed to intercept missiles in flight. The MiG-31-M also integrated a new more powerful and more fuel efficient engine - the enhanced D-30F-6M - as well as a larger middle fuselage fairing cross section and a caseless windshield on its cockpit canopy. The aircraft could also be more heavily armed with fuselage weapon stations increased from four to six. The new Foxhound could be distinguished from the original by large leading edge extensions on its wings and a non-retractable infra red direction finder under the forward fuselage. The aircraft also benefitted from new avionics, controls and electronic warfare countermeasures, with ECM and individual defence systems united into the integral defence system. An increased internal fuel tank capacity and an in flight refuelling capability further improved the aircraft’s endurance, while deployment of new R-37 air to air missies which were much longer ranged, faster and more reliable than the older R-33 all served to make the MiG-31M a significant improvement over the original design. The MiG-31M was cancelled in 1995 after multiple successful flight tests due to a serious economic crisis in Russia - which saw the country’s economy contract in size by 45% in just four years. This prevented Russia from pursuing more ambitious upgrades to its very heavy weight MiG-31 or its medium weight MiG-29 fighter, with the country instead focusing on modernising the heavyweight Su-27 Flanker fighter jet both for its own use and for export. The Su-27 was far inferior to the MiG-31 in terms of the power of its sensors or its performance at long ranges, but was a more versatile design which could engage almost any enemy aircraft on favourable terms at all ranges including visual range combat. It was also much cheaper to operate than the MiG-31 as well as to produce, and could be more easily adapted to roles other than air to air combat such as that of a maritime strike fighter. Although China reportedly considered acquiring MiG-31 interceptors in considerable numbers, its choice of the cheaper Su-27 for a large scale license production deal meant the MiG-31M could not support itself with foreign sales as the Flanker was doing. One prototype and six pre production units of the MiG-31M were produced before the program was cancelled.Research and development efforts for the MiG-31M were not entirely wasted, with many of the standard MiG-31B airframes upgraded to the MiG-31BM and later the MiG-31BSM standards. This saw the aircraft integrate the same Zaslon-M radar and R-37 missiles intended for the MiG-31M, as well as many of the same avionics and electronic warfare technologies. Other than perhaps the Su-57 fighter which only entered service in the Russian Air Force in December 2020, the MiG-31BSM is considered the country’s most capable combat jet in terms of air to air capabilities today. The MiG-31 has also been modernised to fulfil a number of other roles, including delivery of hypersonic ballistic missiles as the MiG-31K as well as anti satellite warfare. Russia is set to induct an entirely new class of interceptor into service around 2030, approximately 50 years after the original Foxhound first joined the Soviet Air Force, with the upcoming sixth generation MiG-41 jet expected to focus on space warfare and be able to fly at hypersonic speeds close to double those of the MiG-31.