During its heyday, the MiG-21 was in service in more than 60 countries. The practicality of the MiG-21 comes from its very physical appearance. The aerodynamic design and fuselage structure is almost the successor and upgrade from the MiG-15, MiG-17, and MiG-19. The MiG-21 can do well in both a fighter and interceptor role. It was the first Soviet military aircraft capable of both.