During World War II, the UK deployed several military platforms around its coast, including Rough’s Tower, which happened to sit outside the 3-mile range that the UK considered part of its territory. After the war, all the platforms were abandoned, and Rough’s Tower sat empty until the days of pirate radio. A broadcaster named Roy Bates ran off some other broadcasters to take control of the platform in 1967. The UK outlawed broadcasting from even outside the 3-mile zone, so Bates never used Rough’s Tower for radio. Instead, he renamed it Sealand and declared it a sovereign country.
In 1968, Roy’s son Michael shot at some British workers, and Roy was brought up on arms charges. The court decided the case couldn’t proceed because Sealand was not in British waters, and Roy took this to mean his micronation’s sovereignty had been fully recognized. He made a Sealand flag, a national anthem, and a currency.
At some point, Roy made Alexander Achenbach Prime Minister of Sealand, which was probably a mistake because Achenbach took over the place while Bates was away in 1978. Bates flew in with a helicopter and some mercenaries and captured Achenbach and his men. Germany sent a diplomat to negotiate Achenbach’s release, as Bates was holding him prisoner for treason. Bates gave his prisoner up and took the visit as another country’s acknowledgement of his sovereignty.
In the last ten years, Sealand was home to data haven HavenCo. After that, Pirate Bay was interested in the platform, but Michael Bates decided against selling because he had written a book and “Hollywood [was] making a movie out of it”. Meanwhile, the government-in-exile is busy hawking a free energy device.
Also here you can find a midi file of Sealand’s anthem.