37 mm anti-tank gun M1930 (1-K)

37 mm anti-tank gun model 1930 (1-K) was a Soviet light anti-tank gun used in the first stage of the German-Soviet War.

Description
1-K was a Soviet anti-tank gun initially developed by the German company Rheinmetall. The gun was closely related to the German PaK 35/36. It lacked some improvements eventually introduced in PaK 35/36, but it was basically the same design; each gun could use ammunition of the other. 1-K had split trail carriage with unsprung wooden wheels (while PaK 35/36 received suspension and new wheels). It was equipped with horizontal sliding block breechblock, hydraulic recoil buffer and spring recuperator.

Development and production
Soviet Union started to develop anti-tank guns in late 1920s. These attempts failed to advance beyond early stages, as Soviet engineers lacked experience with this kind of weapons. It was clear that USSR needed technical assistance in modernizing its arsenal.

Germany could offer such assistance; its first anti-tank gun–37 mm gun model 18–was introduced before the end of World War I. Treaty of Versailles forbade Germany to have anti-tank artillery, but Rheinmetall secretly continued to work on anti-tank guns and in 1926 built a pre-production sample of a new 3.7 cm gun model 26. From their part, Germans were interested in any opportunity to proceed with development of this and other types of weapons.

In 1929, Rheinmetall created a dummy company Butast for contacts with USSR. In accordance with the Sovnarkom decision from 8 August 1930, on 28 August in Berlin a secret agreement was signed. Germans obliged to help USSR with production of six artillery systems: For $1,125 mil. Rheinmetall supplied pre-production samples, documentation and parts from which in USSR a few pieces of each type could be assembled. All involved weapons were modern, many of the same designs were eventually used by Wehrmacht in World War II. In USSR these weapons were adopted; however even with German help Soviet industry still was not ready for mass production of some types, such as anti-aircraft autocannons.
 * 37 mm anti-tank gun
 * 76 mm anti-aircraft gun
 * 152 mm mortar
 * 152 mm howitzer
 * 20 mm anti-aircraft autocannon
 * 37 mm anti-aircraft autocannon

Among other pieces, Rheinmetall brought to USSR 12 37 mm anti-tank guns, which can be seen as early variant of PaK 35/36 - the most numerous anti-tank gun of Wehrmacht until 1942. In USSR the gun was designated 37 mm anti-tank gun model 1930 (1-K) (37-мм противотанковая пушка образца 1930 года (1-К)).

Production
The gun was produced at the Plant no. 8 (named after Kalinin), where it received index 1-K. The production rate was slow as manufacturing process included handicraft operations. In 1931 the plant built 255 pieces, but none passed quality control. In 1932 404 pieces were accepted (and in 1933 105 more followed, still from the 1932 bunch), but then the production was stopped due to adoption of more powerful 45 mm anti-tank gun M1932 (19-K).

1-K was also a base for the 37 mm tank gun B-3 (5-K), the main armament of the BT-2 light tank.

Service
1-K was the first dedicated anti-tank gun of the Red Army (RKKA) and as such was actively used for training of anti-tank units. On 1 January 1936 RKKA possessed 506 guns of the type, of them 422 operational, 53 waiting for repair, 28 used for training, 3 unfit. When RKKA received large numbers of more powerful 45 mm guns, many 1-Ks were apparently relegated to training facilities and depots. The exact number of 1-Ks in service in June 1941 has not been determined. It is known that the gun was present in some units, e.g. 8th Mechanized Corps and it is likely that pieces stored in army depots were also rushed into active service. However there are no certain reports of their combat use. Apparently most of the guns were lost in combat at the early stage of the German-Soviet War.

Summary
The significance of the 1-K lies in the fact that it was the first Soviet anti-tank gun. As such, it gave some valuable experience. It also became the base for a series of Soviet 45 mm anti-tank guns.

It was a light and compact gun which could be easily moved by its crew. The drawbacks were a lack of suspension, weak fragmentation shell (because of small caliber) and poor manufacturing quality. RKKA wanted a larger-caliber gun that could be used as a battalion gun as well as in an anti-tank role, so the 1-K was quickly replaced in production by its 45 mm descendants.

By 1941 the gun was adequate only against lightly armoured vehicles. Modern tanks could only be penetrated from their side and only at short (less than 300 metres) range. The situation was aggravated by low ammunition quality, which explains smaller penetration figures compared to the PaK 35/36. As noted above, the 1-K could fire German shells, improving its anti-armor performance roughly to the level of early Soviet 45 mm guns, as those also suffered from problems with ammunition quality. This was due primarily to the use of gunpowder with a nitrocelluose primer as propellant in all Soviet small arms, artillery and anti-tank artillery up until well into 1942, when British convoy shipments of Cordite and more advanced propellant technology became available. Also the continued use of obsolete APHE technology ammunition, which most nations had long abandoned for considerably improved penetration performance of solid shot AP, APC and APCBC ammunition technology.

The APHE shell itself was of the 1890s Hotchkiss naval type consisting of a hard-nosed forged-steel projectile with a base-mounted inertial deceleration shock-delay fuse with a stable explosive filler, most likely Picric Acid. APHE shells are more effective against battlefield sandbag, earthwork or log improvised fortifications and domestic buildings than equivalent-calibre impact detonating HE or fragmentation shells. APHE can be regarded as a useful dual-purpose round in many respects.

German Rheinmetall-Borstig evaluation tests on a captured 1-K, during 1941, gave a maximum penetration of up to 42 mm of perpendicular rolled homogenous armour plate at 100 metres with APHE and up to 61 mm of perpendicular hardened carbon steel armour plate at 100 metres with APHE. (Note that all tank-building nations had abandoned the use of carburized hardened carbon steel in favour of the increased protection offered by rolled nickel-chromium homogeneous steel armour plate, cast nickel-chromium steel and cast ferro-nickel based armoured alloys by the mid-1920s onwards).

By comparison the German 37 mm PaK 35/36 could penetrate up to 44 mm of perpendicular rolled homogenous armour plate at 100 metres with PzGr.18. APHE, up to 64 mm of perpendicular hardened carbon steel at 100 metres with PzGr.18. APHE, up to 65 mm of perpendicular rolled homogenous armour plate at 100 metres with PzGr.39. APCBC and up to 79 mm of perpendicular rolled homogenous armour plate at 100 metres with PzGr.40. APCR.

The PaK 35/36 used Binatol as a propellant.