Type 91 grenade
The Type 91 grenade was a fragmentation hand grenade developed by the Imperial Japanese Army in 1931 as an improvement over the earlier Type 10 grenade, featuring a versatile design that allowed it to be thrown by hand, launched from a rifle using the Type 100 grenade cup discharger, or fired from the Type 89 50 mm grenade discharger (commonly known as the "knee mortar").[1] It consisted of a cylindrical, serrated cast-iron body weighing approximately 530 grams, filled with 65 grams of TNT explosive, and equipped with a distinctive two-stage arming mechanism: a safety pin was first removed, followed by striking a percussion cap on a hard surface (such as a helmet or tree) to initiate the 7- to 8-second delay fuse, which produced a characteristic metallic "ping" sound often recognized by Allied troops as a warning to take cover.[2] This design made the Type 91 a standard-issue weapon for Japanese infantry throughout World War II, seeing widespread use by both Army and Special Naval Landing Forces from 1932 until 1945 in conflicts including the Second Sino-Japanese War and the Pacific Theater.[3] Production of the Type 91 began in 1932 and continued in large quantities by Japanese state factories, with over a million units manufactured by the war's end, though quality issues arose later due to material shortages, leading to some unreliable fuses if stored improperly.[1] In 1937, it was partially supplemented for hand-thrown roles by the Type 97 grenade, which featured a shorter 4- to 5-second delay and a friction igniter for simpler arming, but the Type 91 remained in service across all its multi-role configurations due to its adaptability and existing stockpiles.[2] Despite its innovative versatility, the grenade's fragmentation pattern produced relatively small and less lethal shards compared to Allied equivalents like the U.S. Mk 2, limiting its effectiveness in open combat, though it proved dangerous in close-quarters jungle fighting and booby-trap applications.[3] Post-war, captured Type 91 grenades were repurposed by Chinese and North Korean forces during the First Indochina War and Korean War.[1]History
Development
The Type 91 grenade originated as an enhanced iteration of the Type 10 fragmentation hand and rifle grenade, introduced by the Imperial Japanese Army in 1921, which had demonstrated shortcomings in fragmentation effectiveness and operational reliability during early field evaluations.[1] To remedy these issues, development commenced in 1931 under the oversight of the Imperial Japanese Army's Technical Arsenal (ordnance department), aiming to produce a more robust and adaptable explosive device suitable for diverse infantry applications.[2] The design process emphasized versatility, enabling the grenade to function not only as a hand-thrown weapon but also when launched from rifles via adapters or from the Type 89 grenade discharger (a light mortar-like device), thereby standardizing equipment across infantry units and enhancing tactical flexibility in close-quarters and suppressive fire scenarios.[1] Initial testing focused on improving safety mechanisms, such as a percussion-activated delay fuze initiated by striking the fuze head against a hard surface after removing the safety pin, with inertia activation for launched use, and optimizing the cast-iron body for better shrapnel distribution, addressing the Type 10's inconsistent performance.[2] Following successful trials, the grenade was officially adopted and entered production in 1932, designated "Type 91" to reflect the corresponding year in the Japanese imperial calendar (year 2591).[2] This multi-role capability was rationalized as a means to equip infantry with a single ordnance item capable of multiple delivery methods, reducing logistical burdens and promoting unit versatility in evolving combat doctrines.[1]Production
The Type 91 grenade was manufactured at Imperial Japanese Army state arsenals during the 1930s and 1940s.[1] Markings on the grenade body and fuze typically indicated production dates using the Showa era calendar, such as Showa 12 (corresponding to 1937) or Showa 16.12 (December 1941), along with arsenal symbols like circular stamps for inspection or origin.[4] Production volumes for the Type 91 are estimated at approximately 998,791 units between 1932 and 1936, based on aggregated data from arsenal records, with output peaking in the late 1930s and early 1940s as demand surged for infantry weapons ahead of and during World War II; total production exceeded one million units by the war's end, though comprehensive figures remain unavailable due to the destruction or loss of wartime documentation.[5][1] Manufacturing processes were plagued by inherent quality issues, including inconsistent fuze timing from the standard 7-second delay element, which proved unreliable for hand-thrown applications and often resulted in duds or premature detonations.[4][6] The cast iron body, externally serrated into 50 segments to promote fragmentation, frequently yielded poor and irregular shrapnel patterns due to material inconsistencies and casting variations.[6] Assembly errors, such as loose fuze seating or incomplete explosive packing of the 65 grams of powdered TNT filling, further contributed to high dud rates.[6][5] Wartime efforts to address these defects involved substituting scarcer materials with alternatives amid resource shortages, such as lower-grade explosives or simplified components, but such measures largely failed to resolve the persistent reliability problems.[5][4]Design
Specifications
The Type 91 grenade, a versatile fragmentation device employed by the Imperial Japanese Army, featured a compact design optimized for hand-throwing, rifle projection, or mortar discharge. Its specifications emphasized reliability in multi-role applications while prioritizing fragmentation lethality through a serrated body construction. Key parameters included a total weight of 530 grams, enabling effective throwing distances up to 30-40 meters by trained soldiers.[1] The grenade's body consisted of cast iron with external serrations forming 50 grooves to promote uniform fragmentation upon detonation, enhancing its anti-personnel effectiveness. This material choice provided durability for projection while containing 65 grams of TNT as the high-explosive filling, sufficient to generate lethal fragments. Dimensions measured approximately 95 mm in length and 50 mm in diameter, with the cylindrical form facilitating attachment to launchers.[7][1][8] The standard fuze incorporated a delay mechanism of 7-8 seconds, allowing safe arming and projection before explosion; this timing was calibrated for the grenade's primary roles beyond mere hand use. The fragmentation pattern produced relatively small shards with limited lethality compared to Allied equivalents.[1][3]| Specification | Value | Notes/Source |
|---|---|---|
| Overall Weight | 530 grams | Total loaded weight.[1] |
| Explosive Filling | 65 grams TNT | Powdered trinitrotoluene for burst effect.[8] |
| Body Material | Cast iron | Serrated with 50 grooves for fragmentation.[7] |
| Length | ~95 mm | Approximate body length excluding attachments.[8] |
| Diameter | ~50 mm | Cylindrical body profile.[8] |
| Fuze Delay | 7-8 seconds | Standard time fuze for activation.[1] |
| Effective Casualty Radius | N/A | Small fragments limited lethality in open terrain.[3] |