McNabs Island played an increasingly important role in the defence of Halifax Harbor through much of the 1800s and into the 1900s with several fortifications constructed on the island, including a Martello Tower, Fort Ives, Fort McNab and Fort Hugonin. Prior to the arrival of the British in 1749, the 980 acre island was seasonally occupied by the Mi’kmaq and used by French and other fishermen to dry their catch. It was acquired and settled by merchant Peter McNab in the 1780s.
Work on Fort Ives at the northern end of the island began in the 1860s. During the First World War an anti-submarine net was installed between the fort and Point Pleasant Park as well as a protected minefield and searchlights. During the Second World War the fort served as a barracks for soldiers. Fort McNab was built in the late 1890s closer to seaward to defend the outer harbor entrance and closer to York Redoubt across the harbor. During the Second World War a coastal battery protected the harbor entrance supported by a plotting centre and radar base. Fort Hugonin was built on the western shore of the island in the 1890s with a battery to cover the harbor minefield. The RCN took over the fort from the Army in 1942 to use as an instrument centre to degauss ships.