Served as coxswain on board the U.S. Sloop John Adams, Sullvan’s Island Channel, 28 November 1864. Taking part in the boarding of the blockade runner Beatrice while under heavy enemy fire from Fort Moultrie, O’Brien, who was in charge of one of the boarding launches, carried out his duties with prompt and energetic conduct. This action resulted in the firing of the Beatrice and the capture of a quantity of supplies from her.