Promoted to lieutenant on 22 December 1842, Key was posted to the fifth-rate HMS "Curacoa" on the South America Station. In February 1844 he transferred to the steam frigate HMS "Gorgon" and was in acting command of the schooner HMS "Fanny" at the Battle of Vuelta de Obligado in November 1845 during the Anglo-French blockade of the Río de la Plata. Promoted to commander on 18 November 1845, he was given command of the paddle sloop HMS "Bulldog" in the Mediterranean Fleet in May 1847. Promoted to captain on 11 October 1850, he then took command of the steam frigate HMS "Amphion" in November 1853 and saw service in the Crimean War. In May 1854, HMS "Amphion" and the steam screw frigate HMS "Conflict" captured the town of Liepāja, a town of some 10,000 inhabitants, in Latvia without a shot being fired. He also took part at the Battle of Bomarsund in August 1854 and the Bombardment of Sveaborg in August 1855. He was appointed a Companion of the Order of the Bath on 5 July 1855.