Fort Mitchel was one of four forts constructed to protect Cork Harbour. Construction of the fort began in 1790. By virtue of Cork Harbour being a Treaty Port, it remained occupied by British Forces until July 1938 when control was handed over to the Irish Defence Forces.
Fort Westmoreland was named after the then Lord Lieutenant, the Earl of Westmoreland. When handed over to the Irish Defence Forces it was renamed Fort Mitchel after John Mitchel who was an Irish nationalist activist and political journalist interred on the island prior to deportation to Van Diemen’s Land in 1848.
Fort Westmoreland occupies the high ground on Spike Island. It is a regular six bastioned work surrounded by a ditch. Originally, there were two entrances on the northern side with the main armament mounted on the southern side, in bastions 2,3 and 4. On the northern side there were two sets of casemates. They linked bastions 5, 6 and 1 and it was these that the Royal Commission recommended be completed when they incorporated the fort into the defences. The casemates are now the cells of the prison establishment that occupies the fort. The entrance gateway is in a plain classical style without ornament or decoration.
Two barrack blocks on the western side of the fort remain as shells, but the old military detention block and the main magazine remain intact in No 6 Bastion. Other internal buildings survive and these are used by the prison administration. It was No 3 Bastion that contained the main armament of the fort. This was originally three 12-inch RML guns which were later replaced by two 6-inch mark VII guns. Due to the alterations made by the Irish Army during the war and security arrangements by the prison authorities, nothing remains of these positions. On Bastions 2 and 4 can be seen the casemates for a 6-inch mark VII gun constructed by the Irish Army during the war with the added bonus of a 6-inch gun in each casemate. Underneath, the old magazines and stores were adapted to serve the guns