Development and Production
The first 152 mm divisional mortar for the RKKA was developed in by Kirov Plant in 1930. The gun weighed about 1,500 kg. It utilized a breechblock and other elements of the 152 mm fortress howitzer M1909. It is not clear whether the piece was ever completed.
From late 1920s, USSR looked for foreign assistance in modernizing its artillery. Germany could and was willing to offer such assistance. The cooperation with USSR allowed Germany, constrained by the Treaty of Versailles, an opportunity to proceed with arms development. In 1929, German arms manufacturer 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 undertook to help USSR with production of six artillery systems:
- 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
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.
Among other pieces, Rheinmetall brought to USSR eight 152 mm mortars. The guns went through ground trials in June 1931 and were tested by the army in August 1932. The weapon was adopted as 152 mm mortar M1931. In the contemporary documents it is often referred to as N or NM.
The gun was in production from 1932 to 1935 at Plant no. 172 (MZM - Motovilikha Machinery Plant; Russian: МЗМ - Мотовилихинский завод машиностроения). The production continuously lagged behind the schedule. In 1932, 5 mortars were manufactured; in 1933 - 50, in 1934 – 59, and in 1935 – 15 pieces. During the production period the gun was repeatedly modified; for example, the barrel of was lengthened by 65 mm.
In 1937 a modernized variant was developed. This variant, designated ML-21, reached factory trials on 27 March 1937 and ground and army trials in 1938. The trials revealed some minor defects. The ML-21 was never adopted.
Meanwhile, in Germany a modified variant of the original Rheinmetall design was adopted as 15 cm sIG 33.
Read more about this topic: 152 Mm Mortar M1931 (NM)
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