Sir Alexander Armstrong, KCB (1818 – 4 July 1899), born in County Donegal, Ireland, was a naval , explorer, and author who from 1850 to 1854 sailed the Arctic on HMS Investigator under the command of Robert McClure in search of the lost expedition of explorer Sir John Franklin. Armstrong's account of the voyage, Personal narrative of the discovery of the north-west passage, was published in London in 1857.