Radio Caroline is a British radio station founded in 1964 by Ronan O'Rahilly and Alan Crawford initially to circumvent the record companies' control of popular music broadcasting in the United Kingdom and the BBC's radio broadcasting monopoly. Unlicensed by any government for most of its early life, it was a pirate radio station that never became illegal as such due to operating outside any national jurisdiction, although after the Marine, &c., Broadcasting (Offences) Act 1967 it became illegal for a British subject to associate with it.

Mi Amigo was originally a three-masted cargo schooner, that later gained international recognition as an offshore radio station. She was built as the schooner Margarethe for German owners. A sale in 1927 saw her renamed Olga and she was lengthened in 1936. During the Second World War, she was requisitioned by the Kriegsmarine and served as an auxiliary ship between 1941 and 1943. In 1953, the ship was again lengthened to 133 feet 9 inches (40.77 m). In 1959, she was sold for conversion to a floating radio station and was renamed Bon Jour. Subsequently, she was renamed Magda Maria in 1961 and Mi Amigo in 1962. She served, intermittently, as a radio ship, until 1980, when she sank in a gale.