http://www.nps.gov/archive/wapa/indepth ... 0/sec5.htm
One of the unique Japanese weapons that Marines encountered on Iwo Jima was the 320mm spigot mortar. These enormous defensive weapons were emplaced and operated by the Japanese Army's 20th Independent Mortar Battalion.
The mortar tube, which had a small cavity at the muzzle, rested on a steel baseplate which, in turn, was supported by a wooden platform. Unlike a conventional mortar, the five-foot long projectile was placed over the tube instead of being dropped down the barrel. The mortar shell had a diameter of nearly 13 inches, while the mortar tube was little more than 10 inches wide. The weapon could hurl a 675-pound shell a maximum of 1,440 yards. The range was adjusted by varying the powder charge, while changes in deflection were accomplished by brute force: shoving and pushing the base platform.
Although the tubes only held out for five or six rounds, enough shells were lobbed onto Marine positions to make a lasting impression on those who suffered through that campaign. According to a platoon leader who served with the 28th Marines, the spigot mortar (referred to as "the screaming Jesus" in his unit) was always afforded a healthy respect and, along with the eight-inch Japanese naval rocket, remains one of his most vivid memories of Iwo Jima. General Robert E. Cushman, Jr., who commanded the 2d battalion, 9th Marines, at Iwo Jima and went on to become the 25th Commandant of the Marine Corps, recalled that the tumbling projectile's inaccuracy made it that much more terrifying. "You could see it coming," he said, "but you never knew where the hell it was going to come down."
