Robert Wiley Milligan was born on April 8, 1843, in Philadelphia, Pennsylvania. He was the son of James and Mary (Thornton) Milligan and a grandson of Robert Milligan who emigrated from County Down, Ireland, to Pennsylvania, sometime before 1840.
After attending Philadelphia grammar and high schools, Milligan entered the navy as a third assistant engineer, March 3, 1863, and served through the remainder of the Civil War in the Mackinaw, participating in both attacks on Fort Fisher, the fall of Wilmington, and the subsequent campaign on the James River. Engineering duty on many ships and stations in the ensuing thirty years was broken by two assignments as Naval Academy instructor, 1879-82 and 1885-89, and service on the Board of Inspection and Survey, 1893-96.
Milligan went to Oregon as chief engineer in January 1897 and was in this ship during her famous cruise around South America and her outstanding work at Santiago in the Spanish-American War. Both were essentially feats of engineering, justifying in a measure Admiral C. F. Pond's statement, made on "The Battleship Oregon Day" at the Panama-Pacific Exposition, that to Milligan, "more than to any other one man, was due the wonderful success of this ship". Leaving San Francisco on March 19, 1898, Oregon, with a trial speed of 16. 7 knots, averaged 11. 16 on the fourteen-thousand-mile cruise, making Florida in sixty-eight days, fifty-four underway. That no machinery accidents or delays occurred was due primarily to the chief engineer and his devoted assistants, who both at sea and during the brief overhauls worked under great strain. On the Santiago blockade, Milligan "ran a sweat-shop". As during the cruise, he insisted on fresh water only for the boilers, and his was the only ship to keep all four boilers constantly under steam. As a result, Oregon in the battle shot "like an express train, " in Capt. Robley D. Evans' words, past all her consorts but the Brooklyn, averaging 12. 9 knots, whereas the 21-knot Brooklyn averaged only 13. 2. The last spurt, which brought her in range of the Cristobal Colon, was made with superior coal which Milligan brought from San Francisco and kept under lock and key. Milligan was advanced five numbers and after a year as fleet, an engineer was stationed at the Norfolk Navy Yard from July 1899 until his retirement as a rear admiral on April 8, 1905. He had been made captain in 1902 after the amalgamation of engineers with the line. His death occurred at Annapolis, where he had made his home after retirement, and he was buried there in the naval cemetery.
During the Civil War, Milligan served on the U. S. S. Mackinaw, and participated in the attack on Fort Fisher, the fall of Wilmington and the fall of Richmond and Petersburg. With the outbreak of the Spanish America War he was serving as Chief Engineer on the U. S. S. Oregon, on the Pacific Coast, and he continued service on that ship until the end of the war. After the close of the Spanish American war, he was advanced five numbers in his grade for eminent an conspicuous conduct in battle.
Milligan was a well-built man above medium height, slow-spoken, thoughtful, and whole-hearted in his work.
Milligan was married on February 17, 1870, to Sarah Ann Du Bois of Annapolis, Maryland, and was survived by two daughters.
