William Kennon Mayo was born on May 29, 1829 at Drummondtown (or Accomac), Virginia. He was the son of Peter Poythress and Leah Custis (Upshur) Mayo, and a descendant of William Mayo, an English civil engineer who came to Virginia about 1723. His mother was a sister of Abel P. Upshur, secretary of the navy and secretary of state under Tyler.
Appointed midshipman from Virginia October 18, 1841, Mayo made his first cruise in the frigate United States of the PacificSquadron, and was in charge of the boats of the landing party at the temporary occupation of Monterey, Cal. , October 1842. The following year he was transferred to the Cyane. In the sloop St. Mary's he saw active duty throughout the Mexican War, including the blockades of Tampico and Vera Cruz and service of the naval battery during the attack on the latter port. He attained the grade of passed midshipman, August 10, 1847, and after study at the newly established Naval Academy, 1847-48, he was for several years engaged in survey and scientific work, returning to Annapolis in 1854 as instructor in seamanship and gunnery. While on this duty he prepared a manuscript, "System of Naval Tactics and Fleet Sailing, " used for the instruction of midshipmen. Promoted to lieutenant September 15, 1855, he was on the Asiatic station in the Minnesota, 1857-59; instructor in ethics and English at the Naval Academy, 1859-60; and in the St. Mary's, Pacific Squadron, from December 1860 to January 1862. Service on this remote station doubtless facilitated his decision to remain loyal to the Union in the Civil War. He was the only member of his family to do so; his younger half-brother Wyndham Mayo joined the Confederate navy. Early in 1862 he was transferred to the East Coast and became executive of the Housatonic off Charleston. After promotion to lieutenant commander, July 16, 1862, he commanded the Kanawha of the West Gulf Squadron from November 1862 to November 1863, capturing six blockade-runners and receiving commendation from Commodore H. K. Thatcher for gallantry in a sharp action, October 12, 1863, with Fort Morgan. He commanded the monitor Nahant off Charleston from July 1864 until the evacuation of Charleston in February 1865, and then until the close of the war was ordnance officer of the South Atlantic Blockading Squadron, retaining his command of the Bay Point Depot until May 1866. Commissioned commander July 25, 1866, he was engaged during the next three years in technical navigation work at Boston, during which time he designed a new type of navy binnacle. Subsequently, he commanded the Tuscarora and the Congress of the North Atlantic Squadron, 1870-71; the Omaha in the Pacific, 1872-74; and the Hartford in the South Atlantic, 1877-79; and was commandant of the Norfolk Navy Yard, 1882-85. He was promoted to captain December 12, 1873, and to commodore July 2, 1882, but failed of promotion to rear admiral owing, it is said, to "infirmity of temper, " and retired voluntarily May 18, 1886. His home thereafter was in Washington, D. C. , where his death occurred after a brief illness.
Mayo was twice married, first to Virginia Kendall of Hartford, Connecticut, and second to Nannie Glover, who survived him. There were no children by either marriage.
