MiG-21SMT (1971; Izdeliye 50; NATO "Fishbed-K")
S = Sapfir (referring to the Sapfir-21/RP-22 radar).
M = Modernizirovannyy ("Modernised")
T = Toplivo ("Fuel," referring to increased fuel capacity)
A development of the MiG-21SM with increased fuel capacity. This variant is easily spotted thanks to its larger spine