The 7th Wisconsin was raised at Madison, Wisconsin, and mustered into Federal service September 2, 1861. The regiment was initially equipped with smoothbore .69 caliber muskets converted from flintlock to percussion; in early 1862, they were replaced with Austrian Lorenz rifles. Unlike their sister regiment the 2nd Wisconsin, which had Lorenz rifles in the unmodified .54 caliber, the 7th's were bored out to .58 caliber to fit a standard Minie ball. The regiment saw its first action at Second Bull Run, followed by the Maryland Campaign which produced severe casualties.