Thatcher, Henry Knox was born on May 26, 1806 in Thomaston, Maine, United States. Son of Ebenezer and Lucy Flucker (Knox) Thatcher.
Attended United States Military Academy.
Appointed midshipman United States Navy, 1823. Served in ship United States, 1824-1827. Made cruise in west Indies as acting master in Erie, 1831.
Commissioned Lieutenant, 1833. Commanded storeship Relief of Brazil Squadron, 1851-1852. Executive officer Naval Asylum, Philadelphia, 1854-1855.
Commander, 1855; commanded Decatur in Pacific, 1857-1859. Executive officer Boston Navy Yard, 1861. In command corvette Constellation for special duty in Mediterranean, November 1861.
Commodore, 1862; assigned in Colorado of North Atlantic Squadron, 1863. Commanded 1st division of Admiral Porter’s fleet and served with distinction at attack on Fort Fisher, North Carolina, December 1864-January 1865. Appointed acting rear admiral, ordered to take command of West Gulf blockading squadron, 1865.