Type 98 50 mm Mortar

The Type 98 50 mm mortar is a smooth-bore, muzzle-loading weapon. The Type 98 designation was given to this gun as it was accepted in the year 2598 of the Japanese calendar (1938)

Design
The Type 98 50 mm mortar may be identified by the rectangular, sectionalized base plate, the fixed position of the bipod, the V slots painted white and located at 12 o'clock on both the barrel collar and the projection of the muzzle hoop and the marking which is on the outside of the container in which the weapon is packed. (This marking, which is read "Kyuhachi Shiki Totekiki" from right to left, means "98 Type discharger.")

The propelling charge consists of black-powder increments packed in small silk bags. Each increment is approximately 3.75 inches long and 1.25 inches in diameter. A pull-type friction primer, 0.88 inch in length, equipped with a loop lanyard, is designed to fit into the primer seat, or touch hole.

The mortar consists of three main parts the base plate, the bipod, and the barrel. It has a fixed elevation of about 40 degrees. Provision is made for a limited traverse. At the base of the tube is an offset primer seat. Two links, one on each side, extend from the barrel collar. A range slide, graduated from 0 to 60, may be clamped to the muzzle of the mortar.

The Type 98 50 mm mortar fires a formidable stick bomb weighing nearly 10 pounds and containing an explosive charge of approximately 7 pounds of picric acid in rectangular blocks. The body of the bomb, made of sheet metal (three-sixteenths of an inch thick), is rectangular in shape 4 1/2 by 4 1/2 by 6 1/2 inches) and is painted black. A hardwood stick 21 inches long and 1.91 inches in diameter fits into a socket in the base of the body, and is held in place by nails or screws. The bottom end of the stick is covered with a metal cap. Two friction-type pull igniters, with black-powder delay trains giving a delay interval of approximately 7 seconds, fit into holes in the base of the charge.

Firing system
To load, insert one or more powder increments in the muzzle. Place the stick of the stick bomb in the tube. Then, to aim, adjust the graduated range slide to the desired distance. This regulates the length of the stick extending into the barrel of the mortar. The greater the distance the stick extends into the barrel, the greater the range. The principle involved is similar to that employed in adjusting the range of the Type 89 50 mm grenade discharger. To traverse, loosen the two wing nuts that secure the bipod, and swing the bipod feet around the are in front of the base plate. Finally, to arm explosive charge, insert the two friction-type pull igniters in the holes provided in the base.

Adjusting graduated range slide on Type 98 50 mm mortar of the charge. Connect each igniter by cord to one of the two links extending from the barrel collar of the mortar on each side. Insert a pull-type friction primer in the primer seat, which is on the side of the barrel near the base.

To fire, pull the loop lanyard attached to the friction primer.

Ammunition
The stick bomb described above, is the only ammunition for this weapon that has been recovered to date. A recent report states, however, that a finned Bangalore torpedo may also be used.

Maintenance
The Type 98 50-mm mortar may be given the same care as would be given to US mortars. There is a cleaning brush which comes attached to the underside of the carrying box cover. The mortar is easy to disassemble. Unscrew the thumb screws and remove the bipod feet from the traversing plate; then remove the barrel assembly ball out of the socket in the base plate. Remove the collar which attaches the bipod to the barrel. To assemble the weapon, proceed in the reverse order.