Located off the coast of Suffolk, England, the Principality of Sealand is an unrecognised micronation established on HM Fort Roughs, a decommissioned World War II seafort. In 1978, Alexander Achenbach, a German lawyer who claimed to be Sealand's prime minister, staged an armed takeover of the platform using German and Dutch mercenaries while founder Paddy Roy Bates was away. Bates and his son Michael launched a daring helicopter counter-strike, successfully retaking the fort and capturing the invaders.
While the mercenaries were quickly released, Achenbach held Sealand citizenship and was charged with high treason against the platform nation. He was sentenced to a hefty fine or life imprisonment on the fort. Faced with a captured national, the West German government requested assistance from the United Kingdom, but British authorities declared they had no jurisdiction over events taking place on the international waters platform.
Left with no alternative, West Germany sent a senior diplomatic envoy from its London embassy directly to Sealand to negotiate Achenbach's release with Roy Bates. After weeks of negotiation, Bates freed Achenbach. Following the ordeal, Sealand's leadership argued that the direct diplomatic intervention of West Germany constituted de facto sovereign recognition under international law, as sovereign states typically do not send official diplomatic envoys to treat with private citizens on pirate radio platforms.