ShVAK cannon

ShVAK 20 mm
Type
Place of origin	USSR
Service history
In service	From 1936
Used by	Soviet armed forces
Wars	From World War II
Production history
Designer	Boris Shpitalniy and Semyon Vladimirov
Designed	1935–1936
Produced	1936–1946
Variants	three 20 mm variants for aircraft mounts plus, one tank variant (TNSh) also, 12.7 mm predecessor
Specifications
Weight	39.92 kg (88 lb)
Length	1,679 mm (66.1 in) for the wing-mounted version
Cartridge	20×99mmR
Cartridge weight	(OZ) 96.0
Caliber	20 mm (0.787 in)
Barrels	One
Action	gas-operated
Rate of fire	700–800 rounds/min
Muzzle velocity	750–790 metres per second (2,500–2,600 ft/s)
Feed system	belt-fed
Filling weight	(OZ) 2.8 g HE + 3.3 g incendiary
Detonation mechanism	(OZ) Nose fuze

The ShVAK (Russian: ШВАК: Шпитальный-Владимиров Авиационный Крупнокалиберный, Shpitalnyi-Vladimirov Aviatsionnyi Krupnokalibernyi, "Shpitalny-Vladimirov large-calibre for aircraft") was a 20 mm used by the Soviet Union during World War II. It was designed by Boris Shpitalniy and Semyon Vladimirov and entered production in 1936. ShVAK were installed in many models of Soviet aircraft. The TNSh was a version of the gun produced for light tanks (Russian: ТНШ: Tankovyi Nudel’man-Shpitalnyi).

The development of the 12.7 mm ShVAK was in response to a Soviet government decree passed on 9 February 1931, directing domestic manufacturers to produce an aircraft machine gun for the 12.7×108mm cartridge that had been introduced a couple of years before for the DK machine gun. Tula designer S.V. Vladimirov answered the call by producing basically an enlarged version of the ShKAS, with a 1246 mm long barrel and a total length of 1726 mm. The first prototype was ready for trials on May 28, 1932. The testing process was fairly drawn out, but the 12.7 mm ShVAK was nominally adopted into service in 1934.

Series production officially started in 1935 at the INZ-2 factory in Kovrov, but production soon fell well behind schedule because the ShVAK receiver was fairly complex to manufacture. According to Soviet records, out of the 410 12.7 mm ShVAKs planned for aircraft in 1935, only 86 were completed; for the tank version, 40 had been planned but only 6 were delivered that same year. A 1952 Western intelligence report indicates that only "a few" ShVAKs were produced in the 12.7 mm caliber.

A further problem complicating the adoption of the gun was that the 12.7 mm ShVAK ended up not using the 12.7×108mm rimless cartridge used by the DK machine gun, but rather—because it was an adaptation of the ShKAS mechanism—it required its own rimmed 12.7 mm cases. Production of the rimmed 12.7 mm ammunition ceased in 1939, when it was decided that the Berezin UB was preferable because it could share ammunition with the DShK.