 During the Second Seminole War Trenchard cruised in the West Indies, and on the coast of Florida, and had a tour of duty in the Mediterranean Sea aboard the sloop under the command of Hiram Paulding.Promoted to passed midshipman on July 16, 1840, he attended the Philadelphia Naval School, then returned to the Mediterranean in 1841 to serve aboard the sloops and .During the winter of 1845-46 he was aboard the schooner engaged in surveying the coast of Georgia and Florida, and received his commission as lieutenant on February 27, 1847.