At the end of 1931, the designers of Factory #8 installed a new 45mm barrel on the gun-carriage of the 37mm Anti-tank Gun Model 1930 and slightly strengthened it. The new gun was accepted for service in March 1932, under the designation of «45-mm Anti-tank Gun Model 1932»; the gun's factory designation was — 19K. Afterwards, the designers of Factory #8 redesigned the 19K field gun to allow a tank installation; it received the designation of «45-mm Tank Gun Model 1932» and, correspondingly, the factory designation of 20K.

Compared to the B-3 gun, the 20K Tank Gun had a number of advantages. The armour penetration of the AP rounds was somewhat improved. The weight of the fragmentation projectile was significantly increased from 0.645 kg to 2.15 kg, and the weight of the explosive charge in this projectile was increased from 22 grams to 118 grams. Lastly, the rate of fire was increased after introducing a vertical wedge semi-automatic breech block, though the refining of the semi-automatic operation took around four years. The first batches of 20K guns were manufactured with the ¼ automatic operation. Later versions were fitted with semi-automatic operation for armour-piercing rounds and ½ automatic operation for high explosive fragmentation rounds. The first deliveries of the guns with the properly refined semi-automatic operation for all the kinds of ammunition began in 1935. The 20K gun had a disadvantage: it did not fit into the small turrets of the T-26 and BT-2. Theoretically, it could be «crammed» into the turret, but that required the introduction of a balancing mechanism, a new elevation mechanism, and thus left only enough room for one crewmember. There was no space for a second crewmember. The RKKA High Command did not approve of this, and the T-26 and BT tanks begun to be manufactured with a new large turret — correspondingly the single turret T-26. This version of the T-26 tank with the 45-mm Tank Gun Model 1932 was delivered to NIAP on 31 May 1933.

Since 1932, the 20K gun had been in production at Factory #8. Ten guns were produced in 1932; 2099 in 1933; 2005 in 1934; 2443 in 1935 and so on. Altogether, 21564 20K guns had been produced by January 1, 1941.

Factory #8 received an order to produce 2664 45mm 20K Tank Guns in 1941. There were no plans to cancel production of the 20K in the near future, because they were to become the armament for the new main tank (T-50 or T-126SP). Actually, 2759 guns were produced in 1941.

Since 1942, production of the 20K was transferred to Factory #235 where 5090 guns were manufactured in 1942, and 3040 were produced in 1943. Production of the 20K was then finally stopped. From the beginning of the 1930's to mid-1943, a 45mm gun system remained practically the only anti-tank gun. This was a result of these guns being able to penetrate the armour of any German tank, prior to 1942, from up to 500 metres. Theoretically, they were superior to the German 37mm Pak 36, as they had a more effective HE capability. However, on practice it was doubful due to some flaws with AP ammunition issued in 1941; firing tests indicated certified penetration was about 18-20mm at 500 metres while all sources of that time claimed 35-40mm. Flaws occured due to over-heat the AP projectle so it's nose tended to brake up in piecese during impact.

The 20K had undergone several modifications. For instance, the Model 1934 gun differed from the standard prototype (Model 1932) in design of the semi-automatic mechanism, recoil systems, elevation mechanism etc. The Model 1938 gun featured the introduction of an electric firing mechanism. Our website lists all these artillery systems under the common designation of «45mm Tank Gun Mod.1932/38», to avoid repeating insignificant details.

In 1938, the TOS gun-sight with stabilisation of the line of fire in the vertical plane was developed for the 45mm Gun Mod.1938 with the electric firing mechanism. Stabilisation was achieved by way of a gyroscope hung in the front section of the sight's housing. Some T-26 and BT-7 tanks were equipped with the TOS, but this system was taken out of service at the beginning of the war. This was done because it was not properly mastered by combat units; and also due to some shortcomings in design and operational service for which there was no time to address in that difficult period.

Several years before, in 1936, an experimental prototype of the automatic loading mechanism for 45mm tank guns was designed by engineer Rozhdestvenskiy. It was manufactured at the Military Electro-technical Academy of RKKA. Factory #8 was assigned to refine this mechanism and start its mass production, although it had not begun this assignment after two years, and later it rejected the assignment altogether.

In 1938, the 45mm Automatic Tank Gun VETOG, with an automatic belt fed ammunition mechanism patterned after the 37mm Maxim Gun, was created in NITI on the basis of the 20K. In the same year, the Artillery Directorate decided to cancel all work on the «VETOG» gun for the following reasons:

«Factory #8 works on 45mm and 37mm automatic guns. Only the one that is finished earlier will be recommended for use in teletanks (remotely controlled tanks)»

The work to create the 45mm armour-piercing chemical (APCh) projectiles for the 19K (field) and 20K (tank) guns is also quite interesting. Such a projectile would explode behind the tank's armour (i.e. inside the fighting compartment) and would produce poison gas to kill the crew. In 1934, the trials of the 45mm APCh projectile by «Blueprint #180» were commenced in NIAP. Unfortunately, the trials results still remain top secret to this day.

* Turned from 47 mm Hochkiss naval round;
** Developed and accepted for service on 1.04.42;
*** Canister with 137 bullets of total weight of 1,48 kg

Translation: Rodion Podorozhny
Proof-read: Chris Amundson
Sources: «Artillerijskoye Vooruzhevie Sovetskikh Tankov 1940-1945» Armada-Vertical, #4, 1999
A. Shirokorad «Entsiklopediya Otechestvennoi Artillerii», 2000
M. Svirin, A. Beskurnikov «Pervie Sovetskie Tanki», Armada #1