Type 98 320 mm mortar (Japanese 32-cm spigot mortar)

A heavy Japanese spigot mortar adopted in 1938, the Type 98 320 mm was a short-range, high-angle siege weapon used by the Imperial Japanese Army during conflicts of the late 1930s and World War II.

Type 98 320 mm mortar (九八式臼砲, Kyūhachi-shiki-kyūhō) was a heavy, high-caliber mortar fielded by the Imperial Japanese Army. Often described in English as a "32-cm" or 320 mm weapon, it belongs to a family of unconventional launchers known as spigot mortars, which differ in construction from tube-fired pieces.

Design and mechanism

Unlike conventional tube mortars, a spigot mortar fires a projectile that slips over a central rod or spigot. The explosive charge is located in the tail of the bomb and is detonated when the propellant driving it leaves the spigot. This arrangement allows a relatively lightweight launcher for the caliber, but requires specially designed ammunition and a reinforced spigot to withstand stresses.

Characteristics and ammunition

The Type 98 was notable for its very large bore and short barrel length, optimized for high-angle, plunging fire rather than long-range precision. Its shells were fin-stabilized and designed to deliver large explosive or demolition payloads against fortifications, bunkers, and entrenched positions. Rate of fire and mobility were limited compared with lighter infantry mortars.

History and service

The "Type 98" designation indicates adoption in 1938 under the imperial calendar. The mortar saw service in the later 1930s and during World War II in operations where heavy, short-range bombardment was needed—for example in siege actions and island defenses. As with other heavy siege weapons, its use tended to be specialized rather than widespread across all formations.

Role and notable aspects

Primary role: destruction of fortifications and bunkers through steep-angle fire.
Advantages: large explosive effect for its launcher weight compared with a conventional tube of the same calibre.
Limitations: complex ammunition logistics, slow rate of fire, and limited range.

As part of Japan's heavy artillery inventory, the Type 98 illustrates trade-offs in weapon design between destructive power and tactical flexibility. After the war such specialized siege systems largely disappeared from frontline inventories as air power and more mobile artillery took precedence.