Served as coxswain on board the U.S.S. Monticello during the reconnaissance of the harbor and water defenses of Wilmington, N.C., 23 to 25 June 1864. Taking part in a reconnaissance of the enemy defenses which lasted two days and nights, Warren courageously carried out his duties during this action which resulted in the capture of a mail carrier and mail, the cutting of the telegraph wire, and the capture of a large group of prisoners. Although in immediate danger from the enemy, Warren showed gallantry and coolness throughout this action which resulted in the gaining of much vital information of the rebel defenses.