In early 1863, the 6th Missouri was transferred to Grand Gulf, Mississippi, where the regiment help construct fortifications. The regiment was present at the Battle of Grand Gulf on April 29. Along with many of the other men of the First Missouri Brigade, the 6th Missouri was shifted to Port Gibson, Mississippi on May 1 to counter a Union landing. At the Battle of Port Gibson, which took place on May 1, the 6th Missouri was used to support the right wing of the Confederate line. When Union troops threatened to cut off the Confederate route of retreat, the 6th Missouri counterattacked. The charge drove deep into the Union line, but was forced to retreat some distance when it encountered Union reinforcements. The 6th Missouri became isolated from the rest of the Confederate force, began to run out of ammunition, and was forced to make a fighting retreat to rejoin the main Confederate force as it retreated.