The lightweight Type 10 operated from a trigger action and suffered from limited range.
Authored By: Martin Foray | Last Edited:
Credit: Views of the Type 10 50mm grenade discharger and its 50mm grenade
The 50mm Type 10 was the first of two primary "light mortars" to serve with the Imperial Japanese Army during World War 2. Introduced as early as 1921, the Type 10 was hardly anything but a light mortar design when compared to its contemporaries. The weapon essentially fired what was nothing more than the highly-adaptable Type 91 hand grenade (fitted with stabilization fins) and thusly became regarded as a "grenade discharger" or grenade launcher than a true light mortar. To add to its inherent limitations, the Type 10 was severely restricted in terms of effective range - essentially ranged out to about 175 yards - making the system an extremely-local, fire-support weapon. The limitations of the Type 10 eventually spurred the development of a better solution, this inevitably becoming the heavier, rifled-barrel Type 89 - though also termed a "grenade discharger". The Type 10 was also fielded in the Second Sino-Japanese War between China and Japan.
The Type 10 design centered around a smooth-bore firing tube attached to a simple baseplate. The weapon was loaded from the muzzle like most any other mortar system and fired by way of a trigger-type mechanism. Range was controlled via an adjustable gas vent. As a smooth-bore weapon, the Type 10 relied on the fins on its projectiles to maintain a flight trajectory. The typical projectile round became the Type 91 High-Explosive (HE) grenade though smoke (Type 11) and illumination rounds (Type 10 Flare/Signal, Type 91 Pyrotechnic) were part of the Type 10's forte. Therefore, the greatest strengths of the Type 10 lay not only in its lightweight design but also in its ammunition variety. The operator need only to set the launcher down to the ground and angle the tube away from him in preparation to fire. A live projectile could then be dropped down the muzzle, the vent gas system adjusted for range and the trigger mechanism activated to complete the firing operation.
With the arrival of the Type 89 in 1929, the Type 10 was relegated to target illumination duty and the like. Nevertheless, the weapon remained in service from 1921 to 1945 alongside the Type 89 and saw heavy use in the Pacific Theater.
An American translation error erroneously referred to the Type 10 and Type 89 grenade launchers as "knee launchers". This came from the Japanese manual which instructed soldiers to carry the launcher with the baseplate clipped at the belt, leaving the firing tube dangling out over the thigh. For a time, American GIs mistook this to mean that the mortar could be fired from the thigh, leading to a few accidents via experimentation as the weapon still packed quite a recoil when fired despite its small size and light weight. Such firing almost assured the operator a broken leg.
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