Landing craft, mortar

As the combat period approached, Colonel Unmacht and his stafiF turned their attention from numerous projects in gas warfare defense and decontamination to the nontoxic chemical weapons and munitions. Their work on the flame thrower tank, and later on stabilized flame thrower fuels, was the outstanding overseas development work of the worldwide CWS. Unmacht was a strong proponent of the use of the 4.2-inch chemical mortar with high-explosive shell, and the development, testing, and combat supply of a landing craft mortar mounting for Pacific amphibious operations represented one of his achievements in the field of combat support. The mortar gun boat development was also a noteworthy example of Army-Navy co-operation. 

In a remarkable case of CWS-Navy co-operation, the kind which typified the activities of Colonel Unmacht on Oahu, there emerged a new type of craft, one armed with 4.2-inch chemical mortars. It was not born without difficulty. The Navy provided three LCT s for the project and later several LCI s. The latter, dubbed LCI (M) (the M for mortar), were to become the standard mortar-landing craft combination. ... 

The CWS in 1942 experimented with mortars mounted on landing craft, including the LCI s and the LCT s. It took the view that mortars... 

Robert W. Elton and Lt Donald W. Gerlitz, 4.2-Inch Emplacement for Landing Craft, Vehicular. TDMR 640, 7 May 43. (2) TB 3-320-1, 4.2-Inch Chemical Mortar Mount LC, E2R2, 27 Jan 44. 

Technicians rigged an oblong wooden frame, filled with a mixture of sand and sawdust, on the floor of the craft. A thick slab of wood, grooved to take the bottom of the baseplate, sat on top of the sand-sawdust filling. This served as an artificial land emplacement for the mortar. The Amphibious Training Command, Carrabelle, Fla., to which the CWS sent the firing platform, saw the utility of the device and asked the service to design a standard model. 

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