105 mm Improvised artillery mortar

Accession Number RELAWM36878
Collection type Technology
Object type Artillery
Maker Japanese Armed Forces
Place made Pacific Islands: Bismarck Archipelago, New Britain, Gazelle Peninsula, Rabaul Area, Rabaul
Date made pre March 1945
Conflict Second World War, 1939-1945

Japanese improvised mortar. The weapon consists of a base, a spigot mounting and a ground peg (missing). The spigot is a 17 inch long, 4 inch external diameter tube, welded to a 4" x 4" angle iron, which is secured at an angle of 45 degrees to a further angle iron on the base by means of two bolts and improvised wing nuts. Both pieces of angle iron are very roughly gas torch-cut, with little attempt made to fettle the ends. Two sled-like steel tubes form the main ground base. The spigot tube is sealed by a metal disc welded 3 1/2 inches from the forward end, forming the charge chamber. Threaded through the centre of the metal disc is the primer holder, which is shaped to accommodate a rimmed cartridge used as a primer. Up to two propellant gags made of lightweight silk could be placed in the charge chamber.

The primer is fired by a firing pin which is set into the cocked position by a cocking handle operating against a spring. The cocking handle is held in the cocked position by a latch to which is attached a 20 foot long lanyard (missing). On releasing the cocking handle, the firing pin strikes the primer which in turn detonates the propellant charge, thus discharging the projectile. The fuze was a modified instantaneous action Type 88 DA percussion fuze for field and mountain guns.

The ground peg (not available) is driven through the forward loop of the base, preventing any backward movement on firing. The rod through which the ground peg is attached is formed from round bar, with threaded ends, which penetrate through the two sled-like base supports. It was thought by the Master General of the Ordnance (who inspected the weapon after its capture) that the ground peg might also act as a pivot, enabling the mortar to be directed onto previously ranged target areas. There is no provision for elevating the mortar and the only sighting device is a white line painted on the spigot.

The projectile was also an improvised one. It consisted of a 105 mm shell from a Type 91 Howitzer, below the driving band of which is riveted a portion of a cartridge case used in a 105 mm Type 88 gun. The cartridge case was emptied of its charge, the base cut off, and four brass fins attached. The cartridge case losely fitted over the spigot unil the base of the shell rested on the forward end of the spigot.

History / Summary

This was an improvised weapon used by the Japanese Army during the Second World War. This particular weapon was captured by 14/32 Battalion AIF at Waitavalo, Wide Bay, New Britain, at 1235 hours on 18 March 1945. The map reference was given in the Battalion's war diary (Folio 19 AWM 52 8.5.53) as 632521. Its exact capture position, near Lamshed's Hill, is shown in the map at folio 70.

The weapon is described in Section 3, 'Jap. Equipment' in Australian Military forces; M.G. O. Military Equipment; No 19 1945; p 66. (The date of capture was incorrectly given in that document as 13 March 1945)