The MiG-21 - that redoubtable warhorse of the Indian Air Force - will be phased out of active service by September, to be replaced by the newer and nimbler Tejas Mk1A fighter jets. The IAF has 36 MiG-21 planes left in its arsenal, a far cry from the nearly 900 - of which around 660 were built in India - that so successfully protected the nation's skies and territories. The MiG-21 first entered service in 1963, on a trial basis. The Russian-made jet went on to form the backbone of the Air Force till the mid-2000s, when the Sukhoi Su-30MKIs were brought in.