Hinnegan served on board the U.S.S. Agawam, as one of a volunteer crew of powder boat which was exploded near Fort Fisher, 23 December 1864. The powder boat, towed in by the Wilderness to prevent detection by the enemy, cast off and slowly steamed to within 300 yards of the beach. After fuses and fires had been lit and a second anchor with short scope let go to assure the boat's tailing inshore, the crew again boarded the Wilderness and proceeded a distance of 12 miles from shore. Less than 2 hours later the explosion took place, and the following day fires were observed still burning at the forts.