The Type 89 "Grenade Discharger" was another of Imperial Japan's "light mortar" systems utilized throughout World War 2. Hardly a true mortar system by any standard, the Imperial Japanese Army nonetheless found use for the weapon throughout the Pacific Theater and in the Second Sino-Japanese War against China. The Type 89 was developed in an attempt to improve upon the inherent limitations of the Type 10 of 1921 and ended up replacing this earlier model in whole by 1941. The Type 89 saw service from 1929 to 1945 and proved a more accurate weapon with substantially greater range - and thusly a more tactically useful implement.
The Type 89 weighed in at a manageable 10lbs and sported a 24-inch length, 10 inches of this made up by the firing tube itself. The Type 89 operated with 50mm modified grenade projectiles and was ranged between a 131 yard minimum and a 732 yard maximum. When compared to the Type 10, the Type 89 differed mainly in its use of a rifled barrel as opposed to the smoothbore one. Additionally, the Type 89 did away with the gas vent-based ranging system of the Type 10, replacing this instead with an adjustable firing pin for ranging. The lower the firing pin was set inside the barrel, the longer the expected range of the projectile would be. Conversely, the higher the firing pin was set in the barrel, the shorter the range. Aiming was utilitarian to the extreme as there was nothing more than an aiming line marked on the barrel - no optical sights were provided for. This proved manageable enough, especially for the trained Japanese soldier. The small cost in weight for the return of firepower was enough to offset the basic nature of the weapon. The array of ammunition was also a bonus.
A trained Type 89 crew could let off about 25 rounds-per-minute, comparable in number to the light mortar systems utilized by her enemies. The relatively lightweight of the Type 89 also meant that transport could be accomplished individually and via a handy leather case all the while maintaining a soldiers basic equipment and weapons load. The Type 89 maintained a psychological hold against the American Marine operating in the Pacific, now trained to hit the dirt at the sound of a launching Type 89.
Like the Type 10, the Type 89 was nothing more than the firing tube, an attached baseplate and the projectile itself. The soldier need only to set the baseplate down and angle the firing tube away from himself (fixed at a 45-degree angle). The projectile was then dropped (bottom-down) into the firing tube and activated by the firing pin at a predetermined range set by the operator. Type 89 operation formally required three personnel for optimal effectiveness but a single user could still operate the weapon if need be. The spade baseplate was designed so that the operator could pin the launcher base against a fixed object such as a fallen tree for recoil support when firing.
The Americans mistakenly translated the accompanying Japanese mortar manuals incorrectly and thought the Type 89 (and the Type 10) were designed to fire from the thigh, giving the weapons the collective nickname of "knee mortars". This was, of course, wholly wrong for firing a weapon with such recoil would (and did) lead to self-inflicted operator injuries if attempted.
A slightly new type of grenade was designed for the new Type 89. Like the Type 10 and other mortar systems, the Type 89 was made to fire a variety of projectile types to suit battlefield needs. The primary round became the Type 89 50mm HE "High-Explosive" projectile and operated with an impact-type detonator, able to cause a good amount of damage while adding a psychological effect. The Type 91 was a fragmentation-based round with a 7-second delayed time fuse useful in cutting through the thick foliage and canopies inherent in jungle warfare. The fuse was activated automatically in-flight after the grenade had been launched free of the firing tube. There was also an incendiary shell that could be used for both illumination (flare/signaling) and against personnel as well as the Type 94 practice shell for target training.