A carte-de-visite group portrait photograph of (presumably) Company B of the 18th Wisconsin Infantry Regiment, at ease. The soldiers are in various states of dress, some wearing frock coats, five-button sack coats, or other civilian clothes. Their arms - Springfield rifles - are stacked.
http://wisvetsmuseum.pastperfectonline.com/photo/54254425-EC87-4CC8-A287-034310291640
A carte-de-visite group portrait photograph of (presumably) Company B of the 18th Wisconsin Infantry Regiment. All are in full uniform, wearing frock coats, sack coats, and Hardee hats. The company commander with officer's sash on the left and the drummer in shell jacket on the right. One line of soldiers are posed charge bayonet, while another line is kneeling in a similar pose. Charles O. Hansen, a Decator, WI resident who served in the 17th (also known as the "Irish Brigade" [not in association with actual Irish Brigade in the AoP]) and 18th Wisconsin Infantry Regiments during the Civil War, is second from the bottom right, marked with an "x."
http://wisvetsmuseum.pastperfectonline.com/photo/4C8D4437-CD39-4666-8D0E-775474932320
Summary of the 18th Wisconsin's service:
http://www.civilwarindex.com/armywi/18th_wi_infantry.html
Battles in which the 18th Wisconsin was engaged:
Shiloh
Corinth
Jackson
Champion Hill
Siege of Vicksburg
Missionary Ridge
Allatoona Pass