The Spanish fishing trawler Sonia sank off the Cornish coast of England on 20 October 1984. On 19 October, in Irish territorial waters off the coast of County Wexford, the Sonia had been spotted by the Irish Naval Service patrol vessel Aisling and was suspected to be fishing illegally. The Sonia was ordered to halt and prepare to receive a boarding party, but did not comply.
The Aisling pursued the Sonia for five hours, during a force 8 gale. The crew of the Aisling fired almost 600 rifle, machine-gun and autocannon rounds during the pursuit, initially as warning shots, but soon targeting the trawler itself. The pursuit was called off after both vessels entered the British exclusive economic zone (EEZ). Some seven hours later, just after midnight on the morning of 20 October, the Sonia broadcast a distress signal stating that she was taking on water. An RAF Search and Rescue Force helicopter was mobilised and picked up thirteen of her crew; the remaining three were rescued by the West German cargo vessel Achat. The Sonia sank soon afterwards.
The Aisling's actions in carrying out the pursuit were legal under the 1958 Convention on the High Seas, as the Sonia had been ordered to stop in Irish territorial waters. Although it was not clearly defined in the law of the time, maritime law writer Clive Ralph Symmons considers that the amount of force used by the Aisling's crew was proportionate and legal. Symmons considered that the right of the Aisling to continue the pursuit into the British EEZ was not clear in international law, but Robin Churchill and Alan Lowe writing in The Law of the Sea (1999) state that it is legal to do so.
The sinking happened during negotiations for Spain to join the European Economic Community, while Ireland held the presidency of the bloc, with disagreements over access to fisheries being a key sticking point in the negotiations.