Type 97 81 mm infantry mortar The Type 97 81 mm infantry mortar was a Japan ese mortar used primary by Imperial Japanese Army during World War II . The Type 97 designation was given to this gun as it was accepted in the year 2597 of the Japanese calendar ( 1937 ) . It entered service in 1937 . Japanese infantry units often are equipped with 81 - mm mortars . The Type 97 81 mm mortar is very commonly used and is referred to by the Japanese as an " Infantry Gun " . which breaks down into 3 sections for transport . The markings which appear on the base of the barrel read " 97 model small trench mortar . " The modified version used by Imperial Japanese Navy with designation Type 3 mortar was used by naval land forces and as anti - submarine weapon on escort ships since 1943 . Design . The Type 97 is a smooth bore , muzzle - loading weapon . It has a fixed firing pin in the breech assembly , and the percussion of the propelling cartridge of the mortar shell against the firing pin propels the shell from the mortar . As many as six propellant increments can be attached to the fins of the mortar shell for the purpose of increasing the range . A captured Type 97 mortar , which has been studied in detail , was marked " Type 97 High - Angle Infantry Gun " . The weapon was manufactured in 1942 in the Osaka Army Arsenal . Although the Japanese weapon closely resembles the US 81 - mm mortar , M1 , there are several identifying features by which the two can be distinguished . The adjusting nut of the Japanese mortar is on the right bipod leg , while the sight is on the left . Other differences are the buttress - type threads on the traversing and elevating screws of the Japanese weapon , as well as the use of welding to fasten bipod legs to the clevis joint and grease fittings dissimilar to those used by the US model . The collimator sight for the Type 97 Japanese mortar is heavier and more complicated than that utilized on the US 81 - mm mortar Ml . The Japanese sight examined was made entirely of steel , except for the brass bushings used for the elevating and cross - leveling screws . A US M4 sight may be fitted to the Japanese weapon by shimming the sight bracket slightly . The Type 97 mortar examined had an extension fitted to the sight , raising the latter to the level of the muzzle of the mortar . This extension probably was added to permit sighting of the weapon when it was deeply dug in or slightly in defilade . Elevation scale of the sight is graduated in 50 - mil intervals from 700 to 1 , 600 mils , and a micrometer drum enables elevation readings to be made to the nearest mil . The collimator can be traversed in a full circle , and the azimuth scale is calibrated in 100 - mil graduations in two sections of 3 , 200 mils each . As in the case of elevation , a micrometer drum permits azimuth readings to be made to the nearest mil . There is a throw - out lever for rapid traverse of the collimator , which may be placed at an angle of elevation and locked in position by a series of meshing notches . There are no open sights for rough laying of the piece . Ammunition . Ammunition recovered for the Type 97 thus far is usually the Type 00 ( 1940 ) HE shell . This shell is 12 . 87 inches long and weighs 6 . 93 pounds , 1 pound of which is the weight of the TNT filler . The fuze is of the instantaneous type , which can be set for delay action , however , by the insertion of a delay pellet in the fuze nose prior to firing . The shell can be fired in the US 81 - mm mortar M1 , but the range will be about 10 per cent shorter than achieved with the US M43 and M43A shells . A firing test of Japanese shells in the US 81 - mm M1 weapon gave the following results that cannot be regarded as wholly conclusive in view of deterioration of the shells . The 81mm mortar was also used to launch an unusual AA Mine Discharger shell . Specifications . Specifications of the weapon are as follows :