Chemical mortar battalions were United States Army non-divisional units that were attached to infantry divisions during World War II. They were armed with 4.2-inch (107 mm) chemical mortars. For this reason they were also called the "Four-deucers".[1]
In 1943, General Mark Clark's Fifth Army established a policy that no infantry division would be committed to combat without a chemical mortar battalion attached. As a result, when infantry units were rotated out of combat, the mortar battalions often stayed in the line and were attached to fresh units. Chemical mortars were in such high demand that often the companies of a battalion would be split up and assigned to different divisions. On the first day that General George S. Patton's Third Army became operational, in the summer of 1944, he issued a standing order to his staff that no infantry division would be committed to combat without a chemical mortar battalion attached, and no infantry regiment would be committed without a mortar company attached.[2]