In its definitive form the ultimate extrapolation of the basic MiG-19 design, the SM-12 evolved, by a process of incremental modification, as a mixed-power point defence interceptor. As the MiG-19S was phased into service with the VVS mid-1956, the MiG OKB was continuing the refinement of the Izdeliye SM twin-engined fighter initiated in 1951 with the SM-1 (I-340). The SM-12 first saw life as an exercise in drag reduction by means of new air intake configurations, and the first of three prototypes, the SM-12/1, was essentially a MiG-19S with an extended and straight-tapered nose with sharp-lipped orifice and a pointed, two-position shock cone on the intake splitter.
The third prototype, the SM-12/3, differed from its two predecessors primarily in discarding the paired AM-9B (RD-9B) engines for two R3-26 turbojets developed from the earlier power plant by V N Sorokin. These each offered an afterburning thrust of 3600kg, enabling the SM-12/3 to attain speeds ranging between 1430km/h at sea level, or Mach=1.16, and 1930km/h at 12000m, or Mach=1.8, and an altitude of between 17500 and 18000m during its test programme. This outstanding performance prompted further development with a view to production as a point defence interceptor.
Similarly powered by RS-26 engines and embodying major nose redesign with a larger orifice permitting introduction of a substantial two-position conical centrebody for a TsD-30 radar, a further prototype was completed as the SM-12PM. Discarding the wing root NR-30 cannon of preceding prototypes, the SM-12PM was armed with two K-5M (RS-2U) beam-riding missiles and entered flight test in 1957. The SM-12PM was tested with a search/track radar mounted in a conical housing in the centre of the intake, and an enlarged dorsal spine, carried two AAA Alkali air-to-air missiles and is claimed to have reached a speed of Mach 1.6 and an altitude of 17400 m (57100 ft), taking only four minutes to attain a height of 10000 m (32800 ft).
This was joined at the end of 1958 by yet another prototype, the SM-12PMU. This had R3M-26 turbojets uprated to 3800kg with afterburning and augmented by a Duch-kin U-19D liquid rocket boost motor which took the form of a permanent ventral pack containing an RU-013 rocket motor and its propellant tanks. Developed by D D Sevruk, the RU-013 delivered 3000kg of thrust. With the aid of this rocket motor, the SM-12PMU attained an altitude of 24000m (78,740 ft) in 1958 and a speed of Mach=1.69, but the decision had been taken meanwhile to manufacture the Ye-7 in series as the MiG-21P and further development of the SM-12 series was therefore discontinued.
Max. speed: 1720 km/h / 1069 mph
Ceiling: 17400 m / 57100 ft
Range: 1700 km / 1056 miles