Haydon served through some of the most important engagements of the period. He began as a third sergeant and ended as a lieutenant colonel. In the East he witnessed the rush to the colors, the first Bull Run, the building of the Army of the Potomac, the Peninsula campaign, and the fighting at second Bull Run and Fredericksburg. Early in 1863 his regiment was transferred to the western theater, where it served in Kentucky and under Grant at Vicksburg. Haydon was severely wounded in Mississippi. During the winter of 1863-64 he was in Tennessee and engaged in the campaigning around Knoxville. In March 1864 - ironically, on his way home on furlough - Haydon contracted pneumonia and died.
Charles Haydon had considerably more education than the average soldier, and his journal reflects the fact. A good half-dozen years older than most of his fellow recruits, he had studied for four years at the University of Michigan, read law, and was in practice when he volunteered. His journal, which was meant to be read, was a deliberate and conscientious attempt to record his experiences and thoughts of the war.