United States Navy Rear Admiral. Entering the United States Navy as a Midshipman in 1838, he was promoted to Passed Midshipman in 1844 and in 1851 accompanied Commodore Matthew C. Perry on the Japanese expedition to establish a base for steamships in Japan and the diplomatic assignment for opening of trade discussions between the two countries. During the next several years Nicholson stayed under the command of Commodore Perry, serving around the globe on numerous stations. In 1861 he was assigned to the steamer "USS Pocahontas", which went to the relief of Fort Sumter in Charleston Harbor, but by the time his command arrived the fort had already been surrendered. His next assignment was aboard the steamer "USS Isaac Smith" on the Potomac River engaging the Confederates at the Battle of Port Royal. After Port Royal his command assisted in the capture of St. Augustine, Fernandina and Jacksonville, Florida. On July 16, 1862 he was commissioned a Commander and in 1863 was transferred to ordnance duty in New York and later that year took command of the monitor "USS Manhattan". He participated in the August 1864 Battle of Mobile Bay and the capture of the rebel ironclad ran "USS Tennessee", and was instrumental in the capture of Fort Morgan during the engagement. He was promoted to Captain on July 25, 1866 and was assigned as Commandant of the New York Navy Yard. On November 8, 1873 he was commissioned Commodore and by 1875 he was appointed the Commandant of the Brooklyn Navy Yard, remaining in that position until the following year. He was promoted to Rear Admiral on October 1, 1881 and commanded the European Squadron from September 16, 1881 to February 1883. He was credited with the rescue of records from the American Consulate when the British bombarded Alexandria, Egypt in 1882 taking the records and refugees aboard his flagship "USS Lancaster". He retired on March 10, 1883 after over forty years of service to the Navy.