The TNSh was a version of the gun produced for tanks (Russian: ТНШ: Tankovyi Nudel’man-Shpitalnyi).
The ShVAK 20 mm autocannon is a large-caliber version of the ShVAK heavy machine gun, which was in turn based on the widely used ShKAS machine gun. The INZ-2 manufacturing plant began production of these ShVAK machine guns in 1935. They were chambered in a 12.7 mm rimmed cartridge. Between 1935 and 1936 the 12.7x108mm ShVAK was converted to 20 mm and serial production started. Some months later production of the 12.7 mm version ceased.
The autocannon version differed only in caliber. It was a gas-operated disintegrating link ammunition belt fed weapon, with either cable or pneumatic charging in remote applications. ShVAK ammunition consisted of a mix of fragmentation-incendiary and armor piercing-incendiary rounds. By 1944 the ShVAK was supplanted by a 20 mm development of the Berezin UB 12.7 mm machine gun (UBS), the Berezin B-20, which offered the same performance as the ShVAK but with an advantage of being significantly lighter.