Here are 10 things to know about the MiG-21 Bison:
At least 110 MiG-21 jets were upgraded in 2006 to MiG-21 Bison. The upgrades include equipping it with powerful multi-mode radar, better avionics and communications systems.
From carrying 'dumb bombs', the MiG-21 Bison also got the ability to carry a wide range of guided munitions. Its air-to-air combat effectiveness also improved considerably after it was fitted with the R-73 Archer short range and R-77 medium range anti-aircraft missiles.
MiG-21 Bison pilots also get helmet-mounted sight, worn by pilots of other advanced jets like the Mirage 2000, the aircraft that dropped laser-guided bombs on a camp of the terror group Jaish-e-Mohammed in Balakot inside Pakistan on Tuesday morning.
With the upgrades, the MiG-21 Bison turned into a capable modern fighter jet that can stand up to challenges thrown in by the Pakistani F-16s. The Bison's beyond visual range missiles can lock on to Pakistani F-16s from a safe distance.
The MiG-21 is not a very large aircraft. In high speed, it has good chances of sneaking up to enemy planes from low altitude. It has a delta wing, similar to the Mirage 2000 and LCA Tejas, that makes it highly manoeuvrable in dogfights.
With the Indian Air Force, the MiG-21 saw action in the war with Pakistan in 1971 and in Kargil in 1999, flying strike missions and combat air patrols. A MiG-21 piloted by Squadron Leader PK Bundela took down a Pakistani Breguet Atlantic maritime patrol aircraft using a heat-seeking air-to-air missile over the Rann of Kutch in 1999, just after the Kargil conflict.
MiG-21s used by the vastly outnumbered air force of North Vietnam scored several kills against the more advanced US Air Force during the Vietnam War in the 1960s, with many MiG-21 pilots emerging as "flying ace", pilots who have shot down several enemy aircraft during dogfights.
India signed an agreement with the Soviet Union in 1962 to buy the MiG-21 and deliveries began the next year. In 1967, Hindustan Aeronautics Ltd (HAL) started making the first MiG-21 under a licence obtained from the Soviet Union. The country celebrated 50 years of the MiG-21 in 2013.
Air Chief Marshal BS Dhanoa has flown in the MiG-21. In May 2017, he led a four-aircraft 'Missing Man' formation in honour of the servicemen killed during the Kargil conflict.
The MiG-21 has seen several crashes over the years and has had its share of bad press. The MiG-21 Bison, which is the definitive variant of the legacy fighter, will start being phased out of the IAF from 2019 onwards.