Jackman resigned on September 25 to return to Missouri to continue recruiting; Jackman was replaced as commander of the regiment by Josiah H. Caldwell. On December 7, the regiment fought in the Battle of Prairie Grove as part of Brigadier General Mosby M. Parsons' brigade. Early in the fighting at Prairie Grove, Parsons' Brigade was aligned to support the Confederate left flank; the regiment (now known as Caldwell's Missouri Regiment) was on the left flank of Parsons' line. Later in the battle, Parsons' Brigade attacked a portion of Major General James G. Blunt's division. Parsons outflanked Blunt, and the Union troops were forced back. However, when a further attack was pressed against the Union line, Caldwell's Regiment was squeezed out by Parsons' advancing regiments and could not participate in the second charge. The regiment suffered 48 casualties at Prairie Grove. The Confederate army then fell back from Prairie Grove, and encamped at Van Buren, Arkansas.