Gustavus was mustered into the Company A, Iowa 14th Infantry Regiment on 02 Oct 1861.

He then transferred to Company A, Iowa 41st Infantry Regiment on 23 Oct 1861 as a Wagoner.

According to Guy LaFrance of the Eastern National in Manassas, Virginia (Battlefield of the Civil War – Bull Run), "he role of a wagoner was to transport the supplies needed by the army. He was responsible for driving the wagon and maintaining it, feeding and caring for the mule team that pulled it, ensuring that it was loaded properly, and seeing that its cargo reached its destination safely. The cargo could be anything that an army of that time required; food, medicines, weapons, ammunition, clothing, shelter tents, tools, the soldier’s knacksacks, officer’s luggage, and anything else the Quartermaster Corps, the branch of the U.S. Army that was responsible for obtaining and distributing supplies felt was needed. It was, and still is an essential job, one that is too often overlooked when studying military history.”

Gustavus Emerson