 In 1824, at the age of 18, Coe joined the Chilean fleet, then commanded by Lord Cochrane, and served on board the brig "Protector" during the Peruvian War of Independence.Serving as an officer in the Argentine fleet under Admiral William Brown, he achieved distinction in the battles of Juncal and Monte Santiago in the Cisplatine War that led to the Uruguayan independence in 1828.After the war with Brazil, he moved to Montevideo and became a partisan of Fructuoso Rivera and the Colorado Party.