by the Leningrad Optical Mechanical Association (LOMO). However, development was slowed between 1975 and 1977 after the introduction of the 9K33 Osa missile system, which seemed to fill the same requirement but with greater missile performance. After some considerable debate, it was felt that a purely missile-based system would not be as effective at dealing with very low flying attack helicopters attacking at short range with no warning as had been proven so successful in the 1973 Arab-Israeli War. Since the reaction time of a gun system is around 8–10 seconds, compared to approximately 30 seconds for a missile-based system, development was restarted. The initial designs were completed in 1973, with pilot production completed in 1976 at the Ulyanovsk Mechanical Factory. System testing and trials were conducted between September 1980 and December 1981 on the Donguzskiy range. It was officially accepted into service on 8 September 1982 and the initial version, which was designated 2K22/2S6, had four missiles in the ready to fire position (two on each side) and two 2A38 autocannons. The Tunguska entered into limited service from 1984, when the first batteries were delivered to the army. After a limited production run of the original 2K22, an improved version designated 2K22M/2S6M entered service in 1990. The 2K22M featured several improvements with eight ready-to-fire missiles (four on each side) as well as modifications to the fire control programs, missiles and the general reliability of the system, and improved autocannons, 2A38M. Tunguska underwent further improvement when, in 2003, the Russian armed forces accepted the Tunguska-M1 or 2K22M1 into service. The M1 introduced the new 9M311-M1 missile, which made a number of changes allowing the 2K22M1 to engage small targets like cruise missiles by replacing the eight-beam laser proximity fuze with a radio fuse. An additional modification afforded greater resistance to infrared countermeasures by replacing the missile tracking flare with a pulsed IR beacon. Other improvements included an increased missile range from , improved optical tracking and accuracy, improved fire control co-ordination between components of a battery and the command post. Overall, the Tunguska-M1 has a combat efficiency 1.3–1.5 times greater than the Tunguska-M. Description The GRAU index lists the "Tunguska" system as 2K22. A complete system or battery consists of six 2S6 combat vehicles armed with the 9M311 "Treugol'nik" (triangle) surface-to-air missile and two 2A38 30 mm cannons. These are accompanied by up to three 2F77 transloader trucks. The 2K22