Here's What You Need to Know: Heavy mortar proved successful for the Soviet Union.

The mortar as an infantry support weapon has been in use for centuries, but it was during the Second World War that its role on the battlefield proved rather decisive. It was used by all of the six main armies of the war including those of Germany, Japan, Italy, the United States, Great Britain, and the Soviet Union.

It was the Soviet’s Red Army that was, without a doubt, the greatest proponent of the use of mortars during the so-called “Great Patriotic War,” which began with the German invasion of the Soviet Union in late June 1941. During the retreat and throughout the resurgence of the Red Army batteries of mortars were successfully mixed with conventional tubed artillery.

Early on in the war when the Red Army was fighting for its very existence, Soviet military planners realized the usefulness of the rapidity with which the mortar could be brought into action and deployed, along with the level of firepower that it would deliver on a target in that short span of time.

Soviet strategy for mortars actually predated the Russian Revolution and went back to the Russian military reforms of 1904, which included a deeply flawed doctrine for the use of artillery. At the turn of the twentieth century Russian artillery doctrine was based on the concept of fortresses with massive guns. Even in the years leading up to the First World War, the Russians spent more money on fortress guns than on field artillery—which is ironic given that Russian war plans called for an invasion of Germany rather than that of defense.

Following the Russian Revolution, which transformed the nation into the Soviet Union, the Red Army adopted a series of tactical and operational doctrines that led to a complete reorganization. A greater emphasis was placed on heavy artillery to break through an enemy’s fortified position, while automatic weapons and supporting artillery would allow the infantry to penetrate the enemy’s defenses and destroy rear support.

Although Stalin severely undermined these improvements as a result of the Great Purge of 1936-38, these new tactics proved successful in the Soviet-Japanese clashes on the Manchurian border. While the Red Army didn’t fare as well in the 1939-40 Winter War with Finland and was caught off guard by the German invasion in 1941, these were a result of the purges as well.

However in 1941 the Soviet Red Army was nearly twice the size it had been in 1939 and while unprepared for war, the mortar was actually part of the “Deep Battle“ concept. As the Soviets looked to increase the number of artillery units the mortar was actually used as well, and it offered advantages over traditional artillery—notably the aforementioned mobility and rapid deployment.

Following the Winter War, a Soviet rifle division was comprised of three rifle regiments, each with three battalions; and each of those, in turn, had three rifle companies along with a support company that was equipped with machine guns and mortars.

During the 1930s the Soviets had relied on a large number of mortar designs, but during World War II these were standardized to four main calibers including the 50mm RM40 and RM41 mortars; the 82mm BM37, BM40, and BM41; the 107mm BPHM38, which was used by mountain troops; and finally the 120mm HM38.

The 50mm mortars were thus allocated two per rifle company that served as part of a mortar section under the company HQ. The sections were used through 1943 when they were eliminated.

A rifle battalion’s sixty-one-man mortar company included three platoons with three 82mm mortars each; while each of the rifle regiments also possessed a seventy-man mortar battery with two platoons. These platoons further included two sections of two 120mm mortars, thus bringing a total of eight mortars in the battery. In addition, there were also specialized brigades that were formed within divisions, and these were equipped with at least 100 120mm mortars.

The M1938 120mm heavy mortar was in fact an update to the French-designed Mortier Brandt de 120mm mle 1935, which had been imported to France prior to its fall to the Germans in June of 1940. The Soviets produced some 12,000 of these 12cm mortars by the end of the war, and this weapon was in fact utilized very much like traditional artillery.

This particular weapon did require a team to deploy and fire. It weighed 622 pounds and had a range of 6,500 yards. While it was mounted on wheels it could be separated into three parts for transport. Its one notable feature was the large circular baseplate that allowed rapid changes in traverse without the need to dig it out to realign the direction. Large stocks of this heavy mortar were captured by the Germans as well as Finnish and Romanian armies—and copies were produced by Germany as the Granatwerfer 42. Rounds were apparently compatible between the German and Soviet-made versions.

This heavy mortar proved so successful that it remained in production after the war and was used by various Soviet allies. Its last use in combat was in the Vietnam War when it was used by the Communist forces of the Viet Cong.

The Light Infantry Mortars

The first model of the 50mm mortar to enter service in the Soviet Red Army was the RM-38 in 1938. It was in fact developed as a variant of the far larger 120mm mortar. The RM-38 was based on the British trench mortar invented by Sir Wilfred Stokes KBE. This concept was based around a smooth-bore, muzzle-loading system that allowed for high angles of fire. The original Stokes mortar was called a “3-inch mortar,” but was in face 3.2 inches or 81mm.

The barrel consists of a drawn-steel tube necked down at the breech or base end, where it is fitted with a base cap, within which is secured the firing pin that protrudes into the barrel. The range was determined by the amount of the propellant in the charge along with the angle of the barrel. The significant downside to this firing method is that the recoil would be severe because the barrel only weighs about three times that of the projectile as opposed to the one hundred or more times the weight of traditional artillery.

The RM-38 mortar’s barrel was actually clamped at two elevation angles including 45 and 75 degrees and range variations were made by altering the sleeve around the base of the barrel. This in turn opened a series of gas ports, which bled off exhaust gases and determined the range. With only two fixed elevations, which required the adjustments to be made by gas escape, the RM-38 was far from accurate. It also proved to be dangerous to the mortar team as well, while the minimum shooting range of 200 meters was further considered impractical in frontline situations. The mortar’s complexity, along with high production costs, were factors that were quickly addressed. Thus the RM-38 was actually only produced for a short time before being replaced.

The RM-38 was approved for use in 1938 but only entered production in 1939. It was replaced in quick succession by the RM-39, RM-40, and RM-41. The RM-41 remained in production until 1943 when the Red Army opted not to produce further 50mm mortars.

The RM-40, which saw minor improvements over the previous models, fired a very light HE (high explosives) bomb of just 1.875 pounds, while its rate of first was about 30 rounds per minute. It had a maximum range of 800 meters. This line of mortars weighed 21.3 pounds and had a barrel length of 21 inches.

The RM-41, which was essentially a new design and influenced by the German 50mm mortars, featured a modified bipod as well as having the barrel hinged to the baseplate, where it was fitted with a venting system to exhaust excessive propelling gases at the base of the barrel. The RM-41 weighed 22 pounds and had a barrel length of 22 inches. It could fire the same ammunition as the prior models.

While these mortars were light enough to be carried by a single soldier, none of the 50mm light mortars proved to be widely popular with the Soviet Army. Despite the increased weight soldiers of the Red Army preferred mortars with greater hitting power. At the time of the German invasion of the Soviet Union in June 1941, the Soviets had 84 50mm mortars in each infantry division, but by the end of 1944, these mortars were completely removed from service.

Medium Mortars

The 50mm mortar, as noted, had its advantages in size but it lacked hitting power and was replaced by a series of 82mm mortars. The Soviets actually had a number of 82mm mortars in use prior to the German invasion, and these included the 82-PM-36 (sometimes also written as 82-BM-36), which was first introduced in 1936. It was essentially a direct copy of the French Brandt mle 27/31 mortar. Soviet arms designer B.I. Szayrin revised the mortar by adding recoil springs to reduce the firing loads on the bipod, and this became the 82-PM-37 or M-37 mortar.