As with other participants of World War 2 (1939-1945), the Imperial Japanese Army (IJA) adopted several different types of infantry-level field mortars. In 1939 came about a new design of 81mm caliber designated the "Type 99" (after the Japanese calendar year of "2599"). The Type 99 was a short-tube weapon and classified as a compact "trench mortar" during a time when it was believed that wars would still be fought through "Trench Warfare" as it was in World War 1 (1914-1918).
The Type 99, as a complete weapon system, showcased a weight of 53lb and a length of over two feet. Its launch tube measured just over a foot long. A bipod assembly, hinged to affect elevation, was affixed under the muzzle and a basic rectangular plate was fitted at the tail end of the unit. The baseplate measured over two feet wide.
The Type 99 fired 81mm shells of 7lb weight out to an effective range of 710 yards (650 meters). Absolute range was near 2,200 yards (2,000 meters). The loading system was entirely manual as most weapons of this class were. The integral mounting hardware allowed for an elevation span of +45 to +85 degrees and the projectiles exited the muzzle at 270 feet per second.
Available ammunition types included the standard explosive type, a smoke round (parachute), signal round (green smoke), mine dispenser round and a chemical round. The projectile was a self-contained munition featuring the primer cartridge, propellant charge, percussion fuze and spring-loaded fins for stabilization during the flight path. Projectiles detonated upon impact or - with some operator interference - through delayed action.
Type 99 mortars were in use until the end of the war in 1945.