In the past, Fort George used to defend Grand Cayman from attacks by Spanish marauders from Cuba; though piracy on the high seas was over by this time, there was still frequent lawless activity.
The fort was also used as a coastal lookout for enemy ships as recently as World War II. Despite its small size, Grand Cayman was said to have had both German and British spies present during World War II, and a US Naval base was set up in the area behind the George Town Public Library. Caymanians did much to aid the allied efforts and several also enlisted in Trinidad to support the British during the war.
https://nationaltrust.org.ky/our-work/historic/fort-george/