Final answer:
The specific number of days the 83rd Chemical Mortar Battalion spent in combat during WWII is not provided in the given information and would require additional research to determine.
Step-by-step explanation:
The provided information does not directly specify the number of days the 83rd Chemical Mortar Battalion (83D CM BN) spent in combat during World War II. Research specific to this unit's wartime activity would be required to determine the exact duration of their combat experience. However, in the context of World War II, units often faced varying lengths of combat involvement, with some such as the 369th Infantry Regiment, known as the Hellfighters, being noted for their significant and valorous service under French command, and others like the 101st Airborne Division enduring the harsh conditions of the Battle of the Bulge. Units across different battles and campaigns would have faced combat for differing periods based on strategic needs and the flow of war.