Complex sentence: There were also ad-hoc units, such as the Michigan Fencibles and the Missippi Volunteer Artillerym which served in a specific theater, such as the west around Prairie du Chien and Credit Island.
Split into simpler sentences: There were also ad-hoc units, such as the Michigan Fencibles and the Missippi Volunteer Artillery. These units served in a specific theater, such as the west around Prairie du Chien and Credit Island.