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320 mm Type 98 mortar
Captured 320mm Mortar during Battle of Iwo Jima
Type Mortar
Place of origin Japan
Service history
Used by Japan
Wars World War II
Weight 675 lbs (projectile)

The 320 mm Type 98 mortar (Kyūhachi-shiki-kyūhō = Type98 mortar ), was an artillery weapon used the Japanese Military during World War II, especially on Iwo Jima;[1];. The weapon was also used on Okinawa to frighten American soldiers.[2]



During World War Two, the Japanase Imperial Army deployed somewhere between 12 and 24 320 mm spigot mortars on Iwo Jima, as well as 24 on Bataan.[3][4]

Iwo Jima

Japanese officers believed the 320 mm spigot mortar's most effective method of employment was as a psychological weapon, intended to scare American soldiers more than inflict casualties.[2] The 675 pounds (306 kg) shells left craters 8 feet (2.4 m) deep and 15 feet (4.6 m) wide, but caused relatively few casualties due to minimal fragmentation.[2] The mortars were mainly operated by the 20th Independent Mortar Battalion.[1]

During the Iwo Jima campaign, many of the 12-24 launchers were placed inside the mouths of caves to protect them from American artillery bombardment, requiring the gun crews to live in the caves that housed their guns, like the infantry.[2] Due to the relative difficulty[5] involved in moving such a massive weapon system, their locations usually remained fixed during battles. During the campaign, the object of the gun crews seemed to be mainly to inflict psychological damage on the American troops instead of killing them, since many rounds were shot over the heads of the US troops.[6] It is unclear why such massive rounds would be intentionally wasted when a similar effect likely could have been achieved by landing the rounds among the troops.



The launchers themselves were essentially steel tubes closed at one end by a steel baseplate, resting on a wooden platform. The 675 pound, five foot long, thirteen inch wide shells were placed over the barrel, instead of being dropped straight down, as is usually done with mortar tubes. The range of each shot was adjusted by adding different size powder charges at the base of the round. Though the barrels could only handle five or six shots apiece, when used in large groups, as was often done, it produced a fearsome effect known as "the screaming Jesus" to American Marines.[1] To absorb the massive recoil caused by firing their projectiles, the mortar tubes were almost always placed up against a mound of dirt.[5]


  1. ^ a b c CLOSING IN: Marines in the Seizure of Iwo Jima
  2. ^ a b c d Japanese Antitank Tactics
  3. ^ The High Cost of Faulty Intel
  4. ^ Chapter IV: Where Is The Enemy
  5. ^ a b Journal of the United States Artillery (1919:148)
  6. ^ HyperWar: Iwo Jima: Amphibious Epic [Chapter 4]



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