China-Burma-India WWII

Independent artillery mortar battalions (Dokunitsu Kyoho Daitai) in Burma were issued with a ponderous 320mm Type 98 (M1938) spigot mortar which could throw a 675 lb bomb over 1,000yd. This weapon was clearly akin to the 320mm spigot mortar designed specifically for demolition work. (Few of them were made and they were little used).

In both cases the spigot mortar itself comprised a steel spigot, a domed steel mounting plate — supported by a dome-shaped wooden block, and a steel baseplate; these were all bolted to a heavy wood block base. The spigot was a steel cylinder with a cavity at the upper end for the propellant. The wooden base consisted of three sections of rectangular baulks of timber, the top section, the middle and the bottom sections — alternate sections being laid at right angles to one another.

Provision was made for a limited amount of traverse and the spigot-seating bolts were so constructed as to permit setting up for line. Changes in range were obtained by varying the propellant charge.

Bombs were in three parts which screwed together; an HE warhead fitted with a nose-fuse, a cylindrical central portion with an internal cavity for a secondary filling, and a cylindrical finned tail unit. The primary and augmenting charges were contained in a brass case which fitted into the spigot cavity; ignition was by means of an electric ignitor through a flash channel in the side of the spigot and the bomb tail.