The Red Army put much faith into mortar strength to augment their infantry capabilities leading into World War 2 (1939-1945). There proved several types in circulation by then, ranging from limited small caliber offerings in the 50mm range to the larger siege-type 160mm variants. Like other national powers the Soviets would adopt the popular French Brandt series of 1927 and took an interest in the qualities of the British Stokes 3-inch. In 1937, a new indigenous design was being developed as a 50mm light infantry mortar and adopted in 1938 as the 50-RM 38 ("50mm caliber, company level mortar, Model 1938"), also designated the RM-38 in some sources. This design was influenced on the original British Stokes design of 1915, a weapon debuting decades prior during World War 1. Success of the Stokes system lay in its simplicity, reliability and - perhaps above all else - its portability in the field, supplying a field commander with on-call, indirect artillery fire as needed. Soviet production of the RM-38 began in 1939.
The Soviet 50-RM 38 utilized the classic mortar arrangement that included a launch tube, baseplate and bipod assembly. The unit could, therefore, be relatively easily hauled by crew or pack animals into action. The overall unit weighed 27lbs and featured a near-two foot length launch tube. As with other mortar-type implements, the 50-PM 38 was loaded from the muzzle, each 0.85kg High-Explosive (HE) shell dropped into the tube and its propellant ignited by an awaiting firing pin at the base. The resulting forces would propel the projectile out of the tube and along its path, guided at this point by pure physics. The elevation on these models was fixed at either 45- and 75-degrees though a few were given a third 82-degree level. Variable ranges was achievable, however, through a cumbersome management of vents at the sides of the tube that could dictate the launch pressures and, thusly, allow the mortar team to achieve the desired range results. The weapon held a maximum engagement range of up to 870 yards when at 45-degrees and could achieve a target area down to 110 yards when elevated at the 82-degree angle. Traversal of the unit was limited to six degrees to either side utilizing hand wheels while a sighting device was included along the bipod. Muzzle velocity was 310 feet per second.
In practice, the 50-PM 38 models were not a complete solution for then-current Red Army needs. The gas management system proved the series relatively inaccurate when compared to contemporaries. Additionally, self-management of the pressures could injure the mortar team itself through a simple mistake or an ill-trained team. The 50mm projectile also proved limiting in its reach and overall shock value to the point that the RM-38 line was consistently evolved throughout the early war years in the 50-RM 39, 50-RM 40 and 50-RM 41 models. While minor improvements were witnessed in the RM-39 and RM-40, it was only the RM-41 model that was a true departure from the original offering of 1938 and this was mainly due to careful study of captured German 50mm types. The Germans had invaded the Soviet Union in June of 1941 to begin the Eastern Front, so many weapons fell to either side in the fighting.
Regardless, 50-PM 38 series mortars were used as stocks allowed for the Red Army need for any weapon proved dire - particularly during the German invasion and subsequent Soviet offensives. Some stocks also fell into use by the equally desperate Germans. By and large, the 50mm light mortar was eventually given up by the Soviet Army as thought now shifted to larger, more destructive mortar designs that included 82mm and 120mm types.
RM-38 - Original Model of 1938; 780mm barrel length; 12 kilogram weight.
RM-39 - Improved Model 1938; 775mm barrel length; 14- to 17kg weight.
RM-40 - Improved Model 1939; 630mm barrel length; 12 kilogram weight.
RM-41 - Based on the German 50mm offering through captured examples.
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Finland; Nazi Germany; Soviet Union
