The Type 97 81 mm infantry mortar was a Japanese 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 beginning in 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. The mortar and its calibre had its origin as almost all 81.4 mm, 82 mm or "8 cm" mortars in the French Brandt mle 27 81.4 mm mortar. The improved version Brandt Mle 27/31 had become the basis for copies, near-copies and license-built mortars all over the world. The Brandt mortars themselves were evolved from the British Stokes Mortar of different calibre. 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