François Étienne de Rosily-Mesros was born to the sea. The son of a naval officer, he entered the same profession at age fourteen, serving on Atlantic voyages as a garde de la marine. By 1772, he was an ensign and assigned to Yves-Joseph de Kerguelen-Trémarec’s expedition to find Terra Australis Incognita. While they did not locate the southern continent, they did find and name the Kerguelen Islands in the Indian Ocean.
His first command came in 1777 and he was promoted to lieutenant the next year. In the same year, he was part of a skirmish between French and English ships, resulting in his capture. He remained in England for twenty months, only gaining release in February 1780. Rosily shuffled between European and Indian Ocean waters. As captain, in 1784, Rosily took on the hydrographic work that would define the rest of his career. In the Vénus, Rosily surveyed coasts of Africa, the Red Sea, the Persian Gulf, and India. By 1790, he was named commander of the French naval division in India.
With the coming of the Revolution, Rosily was promoted rear admiral and given command of the navy at Rochefort. In 1795, he became director and inspector general of the Dépôt de la Marine. A year later he was promoted to vice admiral. As one of the highest-ranked officers in the fleet, Napoleon finally called on him in 1805, when Rosily was supposed to replace Admiral Villeneuve. Villeneuve instead sailed out of Cadiz, ultimately losing the famed Battle of Trafalgar. Now in command of the shattered remains of the French fleet, Rosily was blockaded in Cadiz. By 1808, he was surrounded by land and sea; Rosily had to surrender and return to France and the dépôt.
In his later years, Rosily was named a Count of the Empire and a member of the nation’s Bureau of Longitude. He also served as the President of the Council of Naval Constructions. In addition to his official charts, he was a prolific author and a free associate of the Académie des sciences. He died in 1832.