When "At Quarters" (stations/duties during battle), EVERY crewman -- from the commanding officer, down to the ships Boys -- had specific duty assignments such as passing powder and ammunition, fire/damage control parties, assisting the wounded, or simply relaying orders and reports between the captain and other officers.

Clerks and Stewards were often assigned as messengers and there are several reports in which the Captain mentions those so assigned for the bravery and coolness with which they performed during an engagement and Ahern seems to fall into this category.

At least the Army site lists him together with his "citation" at http://www.army.mil/cmh/mohciv.htm