In 1762 Crillon moved to Spain, where he served as a lieutenant-general – the highest rank in the Bourbon armies – and was made a Knight of the Order of Charles III in 1780. During the Anglo-Spanish War, when Spain and France allied with the Americans to fight Britain, he was given command of a Spanish army tasked with capturing Minorca from the British. The army landed on the island on 19 August 1781 and laid siege to the British garrison in Fort St. Philip at Mahon. The siege was concluded successfully on 5 February 1782 when the British surrendered, for which Crillon was made a grandee of Spain and took the title of Duke of Crillon-Mahon. He was subsequently put in charge of the joint French and Spanish force that had been besieging Gibraltar since 1779. Despite his efforts, Gibraltar proved impregnable and peace was restored in 1783.