Port Royal is on a spit of land, the Palisadoes, which covers the entrance to Kingston Harbour in Jamaica. The Island was taken by the British in 1655 from the Spanish who had been there since about 1509. The British encouraged continuing attacks on the Spanish in the Caribbean, and to facilitate this they issued letter of marque to privateers who mounted attacks for financial reward.
The Royal Navy established a naval base at Port Royal from as early as 1692. By the start of the Napoleonic Wars the British had established a hospital and victualling yard at Port Royal, similar to that at English Harbour, Antigua.
The British coastal defences were sited not just to protect Port Royal but the anchorage around Kingston.