Ambrosio O'Higgins, 1st Marquis of Osorno - in Chile

In Chile

About 1760, O'Higgins enrolled in the Spanish Imperial Service as draughtsman and then engineer. He was directly responsible for the establishment of a reliable postal service between La Plata colony and the General Captaincy of Chile. On his first harrowing journey over the Andes mountains separating Argentina and Chile during the winter of 1763-64, O'Higgins conceived the idea of a chain of weatherproof shelters. By 1766, thanks to O'Higgins' efficient execution of this plan, Chile enjoyed all-year overland postal service with Argentina, which had previously been cut off for several months each winter.

In 1764, John Garland, another Irish engineer at the service of Spain who was military governor of Valdivia, convinced him to move to the neighbouring, and less established, colony of Chile as his assistant. He was initially commissioned as a junior subaltern in the Spanish army. In 1770, now in his late forties, the president of Chile appointed him captain of a column of cavalry to resist the attacks of the Araucanian Indians, whom he defeated, founding the fort of San Carlos in the south of the province of Arauco. He gained the good-will of the Indians by his humanity and benevolence, and recovered big swathes of territory that had been lost by the Spaniards.

He rose quickly in the ranks. As a consequence of his services viceroy Manuel de Amat appointed him, on 7 September 1777, a colonel in the army. He soon rose to be brigadier, and viceroy Teodoro de Croix appointed him Intendant of Concepción in 1786. In 1788, in return for his efforts in South America, King Charles III of Spain created O'Higgins as 1st Barón de Ballinar (a title of the Spanish Crown not to be confused with the family's existing Gaelic title), and promoted him to major-general. Soon afterward he became Captain General and Governor of Chile.