The first recorded sighting of Nanumea by Europeans was by Spanish naval officer Francisco Mourelle de la Rúa who sailed past it on 5 May 1781 as captain of the frigate ''La Princesa'', when attempting a southern crossing of the Pacific from the Philippines to New Spain. He charted Nanumea as ''San Augustin''. Keith S. Chambers and Doug Munro (1980) identified Niutao as the island that Mourelle also sailed past on 5 May 1781, thus solving what Europeans had called ''The Mystery of Gran Cocal''. Mourelle's map and journal named the island ''El Gran Cocal'' ('The Great Coconut Plantation'); however, the latitude and longitude was uncertain. Longitude could be reckoned only crudely at the time, as accurate chronometers did not become available until the late 18th century.