Type 3 81 mm Mortar The Type 3 81 mm mortar is a smooth bore , muzzle loading infantry weapon used by the Imperial Japanese Army during World War II . The Type 3 designation was given to this gun as it was accepted in the 3rd year of Emperor Taishō ' s reign ( 1914 ) . Design . Two specimens of the Type 3 81 mm mortar were captured in the Marshall Islands during the Gilbert and Marshall Islands campaign which occurred between late 1943 and early 1944 . They are marked " Type 3 81 mm Trench mortar made in 1943 , Yokosuka Navy Arsenal " . Despite the Type designation , the mortar was believed to be a forerunner of the Type 97 81 mm infantry mortar , the base plate of which can be used with the Type 3 . The general appearance of the Type 3 is identical with that of the Type 97 90 mm Infantry Mortar which was accepted by the Imperial Japanese Army in 1937 , ( year 2597 on the Japanese calendar ) . The tube of the Type 3 has the same length as that of the Type 97 , but on the former there are two collars machined on the forward portion of the barrel for securing the bipod clamp . The bipod of the Type 3 is constructed of light - weight tubing , and there is no cross - leveling device . Rough cross - leveling adjustment could be made , however , by breaking the bipod support and moving the leg on the low side inward . The threads of the traversing and elevating mechanisms are of the square type , rather than of the efficient buttress type utilized in the Type 97 . No sight has been reported for the Type 3 , and the sight for the Type 97 will not fit . The sight mount of the Type 3 is considered unstable . The total weight of the Type 3 is . The tube weighs , the bipod , and the base plate . Ammunition . The Type 3 8 cm ( 80 mm ) shell recently has been identified for use in the 81 mm mortars . Shaped like the usual types of mortar ammunition , this shell has three features which are new in Japanese mortar shells . The fuse is set for a predetermined time by rotation of a time ring in the lower part of the fuze . On firing , set - back causes the time - train firing pin to function . This initiates the powder in the time - train ring and ignites the safety powder pellet , freeing the impact firing pin . Thus the fuze will function on impact if impact occurs before expiration of the set time . The time - setting can be eliminated altogether by turning the setting ring off the scale . It should be noted that the fuze is not interchangeable with fuzes used in other 8 cm mortar ammunition . Ammunition for the Type 3 mortar is issued disassembled , but with all components packed in the same box . To prepare a round for firing , the shipping plug is pulled from the booster cavity , and the fuze locked in place by screwing in the set screw located in the nose of the projectile . An ignition cartridge then is pushed firmly into place in the base , and the desired number of small powder bags called " increments " are placed between the fins . The fuze is covered with metal foil and has a projecting wire loop which operates as a tear - wire to aid in removing the foil . Misfires may occur with some frequency as a result of the base of the ignition cartridge remaining in the tube , preventing the next round from seating . A Type 100 ( 1940 ) fuze for 81 mm mortar shells recently has been identified . The fuze has three main parts ; It is made of brass with the exception of the striker - detonator assembly . The nose , which screws into the body , is held by a set screw and contains the arming - firing device . A cavity behind the nose is covered with a perforated brass disk to distribute the flash from the detonator . In the bottom of the cavity is a cylindrical brass plug . This plug is pierced in the middle by a diametrical hole , while another hole , corresponding to the radius , enters at right angles . This second hole is filled with black powder which acts as a delay train . For instantaneous action the plug is turned so that the flash travels directly from the detonator to the booster without passing through the delay train . Turning the plug clockwise 90 degrees makes the flash travel through the delay - train hole prior to reaching the booster .