Following the outbreak of hostilities between the north and south in April 1861, thousands of Maine men rushed to answer President Lincoln's call for troops. The Fifth Regiment Maine Volunteer Infantry was one of the first Maine regiments to be mustered in. The regiment consisted of 1046 men (another 500 joined later) from southern and central Maine. Three of the ten companies in the regiment were composed of men from Portland, thus earning the regiment the nickname the Forest City Regiment. (Portland was known as the Forest City). The men left Portland by train in July 1861, stopping briefly in New York where they were presented with a silk flag by Portlanders living in that area.

Upon arriving in Washington, the regiment was assigned to the Sixth Corps of the Army of the Potomac. The Fifth fought in 22 battles from First Bull Run (Manassas) to Petersburg. During the battle of Rappahannock Station the regiment is credited with capturing 4 Confederate battle flags and 1200 prisoners (several of them officers). The Fifth was known as one of Maine's fighting regiments. It captured more prisoners than the number of men who served in the regiment and three times the number of battle flags than any other Maine regiment captured. After three long years only 193 men were mustered out in July 1864. The rest had been killed in action, died from disease, wounded, deserted, or transferred to other regiments.