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Soviet World War Two 50mm Light Mortars (RM-39 & RM-40)

Forgotten Weapons
Published on August 25, 2025
Category: Tactical & Gear
Duration: 13:01

This entry details the Soviet 50mm light mortars, specifically the RM-39 and RM-40, highlighting their rapid development and eventual obsolescence. It covers their unique gas-venting range adjustment system, mechanical features, and wartime simplification efforts. The history of these captured weapons, particularly their journey through Finland to the US, is also explored.

Tags

Soviet RM-39
Soviet RM-40
50mm Light Mortar
World War Two
Artillery
Military History
Forgotten Weapons
Ian McCollum
Finnish Capture
NFA Destructive Device

Quick Summary

Soviet 50mm light mortars, such as the RM-39 and RM-40, utilized a unique gas-venting system for range adjustment at a fixed firing angle. The RM-39 was complex and high-quality, while the RM-40 simplified design for wartime production. These mortars were eventually replaced by 82mm versions due to limited effectiveness and many captured units were later imported into the US.

Chapters

  1. 00:00Introduction: Soviet 50mm Mortar Evolution
  2. 01:10Comparison to German Mortars & Range Adjustment System
  3. 03:16The RM-39: Quality and Complexity
  4. 04:53RM-39 Mechanical Features: Sight and Recoil Buffer
  5. 07:06The RM-40: Wartime Simplification
  6. 09:21RM-40 Internals and Baseplate Design
  7. 10:58Surplus, Capture, and US Import History

Frequently Asked Questions

What was unique about the Soviet 50mm light mortar's range adjustment system?

The Soviet 50mm mortars, like the RM-39 and RM-40, featured a distinctive range adjustment system that used vent holes at the bottom of the tube. These holes released propellant gases, allowing the operator to control the range while maintaining a fixed firing angle.

How did the RM-40 differ from the earlier RM-39?

The RM-40 was designed for wartime simplification. While it retained the gas-venting range adjustment and recoil buffer, its bipod legs were made from stamped sheet metal, and complex screw adjustments of the RM-39 were replaced with simpler mechanisms to speed up production.

What is the history of Soviet 50mm mortars in the United States?

Many Soviet 50mm mortars were captured by Finland and later imported into the US by Interarms in the 1960s. Today, they are typically registered as NFA Destructive Devices or deactivated for display purposes.

Why were Soviet 50mm mortars eventually replaced?

By 1943, the 50mm mortars were largely superseded by 82mm versions. This shift occurred because the 50mm shell's limited effectiveness made it less practical for battlefield support compared to the larger caliber rounds.

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