Stirling entered the Royal Navy at age 12 and as a midshipman saw action in the Napoleonic Wars. Rapid promotion followed and when he was 21 he received his first command, the 28-gun sloop , and, in the War of 1812 between the US and the UK, seized two prizes. The "Brazen" carried the news of the end of that war to Fort Bowyer and took part in carrying to England the British troops that had captured the fort. On return to the West Indies, Stirling made two surveys of the Venezuelan coast and reported on the strengths, attitudes and dispositions of the Spanish government and various revolutionary factions, later playing a role in the British negotiations with these groups.