The Iron Brigade became one of the most celebrated units of the Civil War from 1861 to 1865. Of its five regiments, three came from Wisconsin: the Second, Sixth, and Seventh Wisconsin Volunteer Infantry, while the other two were the Nineteenth Indiana and the Twenty-fourth Michigan. Together, these units ranked among the most gallant and effective of the 3,559 regiments of the Union army. The brigade earned its nickname during its first campaign at South Mountain in northern Virginia in the fall of 1862, and afterward fought in all major campaigns of the Army of the Potomac, the Union's principal force in the eastern theater of war. Second Manassas, Antietam, Gettysburg, and Spotsylvania were recorded on its colors. Its casualties ranked among the highest of the war: the Twenty-fourth Michigan sustained casualties of 80 percent at Gettysburg, higher than any other Union regiment in that battle; the Second Wisconsin suffered the greatest percentage of loss in the entire Union army; and during the course of the war, the Seventh Wisconsin had more men killed in battle than any other Union regiment.